# Forum More Stuff Debate & Technical Discussion  Electrical DIY Questions - Part 2.

## elkangorito

Well, I got bored so I worked up the 2nd batch of questions.
Again, this quiz is for non-qualified people. 
I'll respond with my suggested answers in about 2 weeks.
Have fun.  :Biggrin:    
Part 2 of Electrical Questions for DIYers.
A little more difficult than the 1st quiz.   
1]
In your back shed, you have a "home made" metal bench with metal legs...100% metal. It sits on the concrete floor (not bolted down). On this bench, there is a "plug in" bench grinder. Ocassionally, when using the grinder, you get a small "tingle" from the bench.
What can be done to remedy the situation.   
2]
You have a computer. The tower is metal. Occasionally, you get a "tingle" when you touch the metal tower.
What is the problem & what can be done to correct the problem?   
3]
You are an "experienced" electrical DIYer & you wish to install 2 x 150 watt driving lights onto your motor vehicle. You already have two other 100 watt driving lights on your motor vehicle. 
a]
Before you procced with the work, what must you do? 
b]
When you are satisfied that the work can be done, how will you do it?   
4]
How should a good quality, fully charged car battery be "safely" stored?   
5]
Your existing meter box is old. It only has rewirable fuses in it. You now wish to add a new power circuit to your home. You have contacted an electrician for a quote. The electrician visited your home & after inspection, has given you a "good" price to install the following; 
a]
New wiring from the meter box to the new GPO's. 
b]
The cost of the GPO's (parts). 
c]
The cost of a rewirable fuse. 
Should you engage the electrician to do this work?   
6]
You have noticed that the soil around your solid copper 13mm earth stake is rather parched, cracked & dry.
Do you; 
a]
Pour water over the earth stake. 
b]
Make a solution of salt & water, & then pour it over the earth stake. 
c]
Buy special & expensive chemicals, which are designed to decrease earth impedance, & then pour over the earth stake. 
d] Do nothing. Your earth stake can fend for itself.   
7]
You have just built a new shed down the back yard & you wish to save a few bucks. You've decided that you wish to have a couple of fluorescent lights & a couple of GPO's in the shed. You also think that you may like to add some woodworking/metalworking equipment in the future. Your future ideas consist of a woodworking/metalworking lathe, an extraction fan & extra fixed lighting. You've also decided that you wish to run the cable underground, buy the conduit, dig the trench & pull in the cable from the meter box to the shed. You will then hire an electrician to connect everything.
You have 3 phase connected to your house for the purpose of supplying your 3 phase instantaneous hot water heater. All of your future shed equipment will be 3 phase. 
a]
What must be done before you even think about proceeding with this work? 
b]
How deep will you dig the trench? 
c]
What size conduit will you buy? 
d]
How will you determine the size cable you will need/buy? 
e]
What else should you buy?    
8]
You live "way out in the sticks" in a caravan (temporarily, while you are building your new house) & your power supply is not all that good. Sometimes, the power can be off for as long as 1 day (24 hours). As a consequence, you wish to install a generator to supply the caravan in times of supply failure. You have a computer, a sound system, a fax machine, a fridge & an airconditioner in your caravan. 
a]
How will you calculate the size of generator you need? 
b]
What kind of generator will you buy? 
c]
How will you isolate the "normal" supply from your generator supply?    
9]
You are about to perform a major electrical "upgrade" to your home. A friend has offered you an assortment of RCD's, circuit breakers & main switches for free. These items were previously used in his home but were not required after he had a major electrical upgrade done to his home. He tells you that the items are about 5 years old. He is not an electrician.
Would you accept the items & use them in your upgrade?
If yes, explain why.
If no, explain why not.  
10]
You are having a shower & when you turn off the metal shower taps with your wet hands, you sense a very small "tingle". 
a]
What could the problem be? 
b]
What steps need to be taken to ensure that this problem doesn't occur again?

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## Ashore

> Well, I got bored so I worked up the 2nd batch of questions.
> Again, this quiz is for non-qualified people. 
> I'll respond with my suggested answers in about 2 weeks.
> Have fun.    
> Part 2 of Electrical Questions for DIYers.
> A little more difficult than the 1st quiz.   
> 1]
> In your back shed, you have a "home made" metal bench with metal legs...100% metal. It sits on the concrete floor (not bolted down). On this bench, there is a "plug in" bench grinder. Ocassionally, when using the grinder, you get a small "tingle" from the bench.
> What can be done to remedy the situation. Make a decent wooden bench  
> ...

  Pretty obvious, get the wife to turn off the taps

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## rrobor

1/ Check the earth on the grinder, check the earth stake.
2/This is static. Computer uses a switch mode supply sealed in a tin box. If you violate that by say earthing the computer box you may send 240V up  a telephone line and cause untold damage in an exchange.
3/ I dont drive at night, too many hoons about.
 A/ Have a short nap
 B/ In an armchair with my feet up
4/ In a good quality car
5/ No he is a mean begger, the fuse should be a give. Anyways I wanted trips not fuses and its his issue as to cost, I just wanted a quote.
6/ Non of those, I would treat it like the lemon tree but taking care to do it in short squirts.
7A/  Have a short nap. 
 B/ did all this when we dug the foundations of the shed, the Phone b4 you dig stuff
C/D/E Sparky supplied all that stuff.
8 Council refuse permission to live on building site 
 A/B/C ditto
9 Id ask a sparky
10/  Id divert the shower water to the earth stake, truth be told in this instance the earth stake is crap, Id dig a trench to it one meter deep and as long as I was fit enough to dig chuck a piece of copper pipe in it and hitch it to the stake.

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## elkangorito

Both of you (rrobor & Ashore) failed dismally. Try to be a little more serious, if possible. :Rolleyes:

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## chrisp

1] and 10] are to do with equi-potential bonding.  The electrical earth is "bonded" to the plumbing services to prevent small earth elevations causing tingles. 
In the case of the shower, I'd be checking the bond between the plumbing and the electrical earth, and the earth connection itself and the MEN point. 
With the metal bench, I'd initially check the wiring is okay - especially the earth connections (pre- and post-GPO).  If all is good, I'd electrically connect the bench ("bond") to the mains earth, by sitting/screwing/bolting the earthed body of the grinder to the metal frame.

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## elkangorito

Thanks for your "sensible" reply chrisp.  :2thumbsup:  Do the other questions interest you?

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## rrobor

Perhaps we got bored with the second lot of questions after all didnt you say you made em up out of boredom.

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## elkangorito

> Perhaps we got bored with the second lot of questions after all didnt you say you made em up out of boredom.

  I hereby award you my "Tosser Of The Week" award, which involves the colour red. I like red...I hope you do too. 
Have a fantastic day :Biggrin: .

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## watson

:Toot:

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## chrisp

> Thanks for your "sensible" reply chrisp.  Do the other questions interest you?

  Other questions interest me, but I thought I'd hold back and let a few others have a go first.

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## Wildman

1]
In your back shed, you have a "home made" metal bench with metal legs...100% metal. It sits on the concrete floor (not bolted down). On this bench, there is a "plug in" bench grinder. Ocassionally, when using the grinder, you get a small "tingle" from the bench.
What can be done to remedy the situation.  I would earth the bench and get the grinder checked or a new grinder.   
2]
You have a computer. The tower is metal. Occasionally, you get a "tingle" when you touch the metal tower.
What is the problem & what can be done to correct the problem?  If it is not just static build up (more likely from my woollen pants on a nylon seat) and it happens more than once, I would blow out the entire PC and power supply with compressed air to ensure it is clean, if it continued I would replace the power supply.  
3]
You are an "experienced" electrical DIYer & you wish to install 2 x 150 watt driving lights onto your motor vehicle. You already have two other 100 watt driving lights on your motor vehicle. 
a]
Before you procced with the work, what must you do? Make sure your alternator can supply an extra 25 amps then make sure the wiring can handle it. 
b]
When you are satisfied that the work can be done, how will you do it? Personally I would run a new suitable power wire with a fusable link and a relay which is activated from the same circuit as the existing driving lights.  
4]
How should a good quality, fully charged car battery be "safely" stored?  Up the right way with the positive terminal protected from accidental contact with any metal items and protected from accidental impacts which may damage the casing   
5]
Your existing meter box is old. It only has rewirable fuses in it. You now wish to add a new power circuit to your home. You have contacted an electrician for a quote. The electrician visited your home & after inspection, has given you a "good" price to install the following; 
a]
New wiring from the meter box to the new GPO's. 
b]
The cost of the GPO's (parts). 
c]
The cost of a rewirable fuse. 
Should you engage the electrician to do this work?  No. Rewirable fuses??  
6]
You have noticed that the soil around your solid copper 13mm earth stake is rather parched, cracked & dry.
Do you; 
a]
Pour water over the earth stake. 
b]
Make a solution of salt & water, & then pour it over the earth stake. 
c]
Buy special & expensive chemicals, which are designed to decrease earth impedance, & then pour over the earth stake. 
d] Do nothing. Your earth stake can fend for itself.  I would put something near the earth stake to slowly drip water into the ground to ensure adequate moisture. If this happened again, I would put a second earth stake in another location that had a higher likelihood of retaining ground moisture, eg near external tap.  
7]
You have just built a new shed down the back yard & you wish to save a few bucks. You've decided that you wish to have a couple of fluorescent lights & a couple of GPO's in the shed. You also think that you may like to add some woodworking/metalworking equipment in the future. Your future ideas consist of a woodworking/metalworking lathe, an extraction fan & extra fixed lighting. You've also decided that you wish to run the cable underground, buy the conduit, dig the trench & pull in the cable from the meter box to the shed. You will then hire an electrician to connect everything.
You have 3 phase connected to your house for the purpose of supplying your 3 phase instantaneous hot water heater. All of your future shed equipment will be 3 phase. 
a]
What must be done before you even think about proceeding with this work?  Call a sparky, I know my own limitations. 
b]
How deep will you dig the trench? 
c]
What size conduit will you buy? 
d]
How will you determine the size cable you will need/buy? 
e]
What else should you buy?    
8]
You live "way out in the sticks" in a caravan (temporarily, while you are building your new house) & your power supply is not all that good. Sometimes, the power can be off for as long as 1 day (24 hours). As a consequence, you wish to install a generator to supply the caravan in times of supply failure. You have a computer, a sound system, a fax machine, a fridge & an airconditioner in your caravan. 
a]
How will you calculate the size of generator you need?  Add up the maximum load of all appliances and add about 50% and get a generator for this. Bigger if I can afford it. 
b]
What kind of generator will you buy?  A diesel one compatible with my UPS 
c]
How will you isolate the "normal" supply from your generator supply?  With a big two way switch, either normal power or generator power and no way to select both. THe internal delicate electronics will be behind an online UPS to ensure stable power during the changeover.    
9]
You are about to perform a major electrical "upgrade" to your home. A friend has offered you an assortment of RCD's, circuit breakers & main switches for free. These items were previously used in his home but were not required after he had a major electrical upgrade done to his home. He tells you that the items are about 5 years old. He is not an electrician.
Would you accept the items & use them in your upgrade?
If yes, explain why.
If no, explain why not.  No. They are probably fine but with no simple way to test and check them offline it is not worth the risk.  
10]
You are having a shower & when you turn off the metal shower taps with your wet hands, you sense a very small "tingle". 
a]
What could the problem be?  Faulty earth 
b]
What steps need to be taken to ensure that this problem doesn't occur again?   Make sure the wiring is not old and using the plumbing as the main earth, make sure the plumbing is earthed and make sure the earth spike is properly connected and in moist soil.

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## journeyman Mick

> Well, I got bored so I worked up the 2nd batch of questions.
> Again, this quiz is for non-qualified people. 
> I'll respond with my suggested answers in about 2 weeks.
> Have fun.    
> Part 2 of Electrical Questions for DIYers.
> A little more difficult than the 1st quiz.   
> 1]
> In your back shed, you have a "home made" metal bench with metal legs...100% metal. It sits on the concrete floor (not bolted down). On this bench, there is a "plug in" bench grinder. Ocassionally, when using the grinder, you get a small "tingle" from the bench.
> What can be done to remedy the situation. Wear rubber soled boots 
> ...

  Check tio seeif this is the case, hammer in an earth stake and reconnect earth wire and metal pipes to it 
Mick

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## Terrian

> 1]  Make sure the wiring is not old and using the plumbing as the main earth, make sure the plumbing is earthed and make sure the earth spike is properly connected and in moist soil.

  ya know, the one thing I have yet to find around here is an earth stake

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## watson

We've got one!
1/2" copper belted into the ground. Watched the apprentice do it.
No metal plumbing around here ....all black Poly. 
2 Cents please.

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## Terrian

> We've got one!
> 1/2" copper belted into the ground. Watched the apprentice do it.
> No metal plumbing around here ....all black Poly. 
> 2 Cents please.

  we use to have gal pipe for the water, that was replaced a few years ago with poly 
do I get any change from that 2 cents ?

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## watson

Kaching!!...1 Cent change sir.

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## rrobor

My house doesnt have one, theres a copper braid wire laid down in the trench they dug for the storm water. How far it goes, no one knows.

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## Pulse

1]
In your back shed, you have a "home made" metal bench with metal legs...100% metal. It sits on the concrete floor (not bolted down). On this bench, there is a "plug in" bench grinder. Ocassionally, when using the grinder, you get a small "tingle" from the bench.
What can be done to remedy the situation. 
The grinder needs an insulation resistance test (?deteriorated winding insulation)   
2]
You have a computer. The tower is metal. Occasionally, you get a "tingle" when you touch the metal tower.
What is the problem & what can be done to correct the problem?  The tower case is at greater than 0V, probably fault in switch mode power supply or one of the components. Replace the power supply or check the individual components with Megger.  
3]
You are an "experienced" electrical DIYer & you wish to install 2 x 150 watt driving lights onto your motor vehicle. You already have two other 100 watt driving lights on your motor vehicle. 
a]
Before you procced with the work, what must you do? check the current rating of the alternator is adequate 
b]
When you are satisfied that the work can be done, how will you do it? New cable direct from battery with fuse close to battery. Use a relay using the existing lights you want it to switch with. Earth reliably to chassis near fitting.  
4]
How should a good quality, fully charged car battery be "safely" stored? Stored in dry, well ventilated area. Charged every few months (will make hydrogen when charged) Protection from accidental shorting by covering terminals also.  
5]
Your existing meter box is old. It only has rewirable fuses in it. You now wish to add a new power circuit to your home. You have contacted an electrician for a quote. The electrician visited your home & after inspection, has given you a "good" price to install the following; 
a]
New wiring from the meter box to the new GPO's. 
b]
The cost of the GPO's (parts). 
c]
The cost of a rewirable fuse. 
Should you engage the electrician to do this work? No, supply line may need to be enlarged. Maximum demand calculation needs to be done. RCD needs to be fitted also. Rewirable fuses are not permitted either (don't know where in AS3000 though)  
6]
You have noticed that the soil around your solid copper 13mm earth stake is rather parched, cracked & dry.
Do you; 
a]
Pour water over the earth stake. 
b]
Make a solution of salt & water, & then pour it over the earth stake. 
c]
Buy special & expensive chemicals, which are designed to decrease earth impedance, & then pour over the earth stake. 
d] Do nothing. Your earth stake can fend for itself. The earth stake needs a permanently damp location. I'd start with the water and look for a new location.  
7]
You have just built a new shed down the back yard & you wish to save a few bucks. You've decided that you wish to have a couple of fluorescent lights & a couple of GPO's in the shed. You also think that you may like to add some woodworking/metalworking equipment in the future. Your future ideas consist of a woodworking/metalworking lathe, an extraction fan & extra fixed lighting. You've also decided that you wish to run the cable underground, buy the conduit, dig the trench & pull in the cable from the meter box to the shed. You will then hire an electrician to connect everything.
You have 3 phase connected to your house for the purpose of supplying your 3 phase instantaneous hot water heater. All of your future shed equipment will be 3 phase. 
a]
What must be done before you even think about proceeding with this work? Assess maximum demand of dwelling and supply line. But first speak to the electrician you will get to connect
b]
How deep will you dig the trench? 600mm to allow 500mm cover
c]
What size conduit will you buy? 50mm HD orange conduit - table C11 allows up to 16mm 4 core and earth
d]
How will you determine the size cable you will need/buy? Work out maximum demand for the shed subboard. Check that voltage drop will be OK.
e]
What else should you buy? Sign to label entry into building if not obvious. Marking tape to bury above cable conduit. Pulling lube (minds out of the gutter) and pulling string.   
8]
You live "way out in the sticks" in a caravan (temporarily, while you are building your new house) & your power supply is not all that good. Sometimes, the power can be off for as long as 1 day (24 hours). As a consequence, you wish to install a generator to supply the caravan in times of supply failure. You have a computer, a sound system, a fax machine, a fridge & an airconditioner in your caravan. 
a]
How will you calculate the size of generator you need? Work out maximum demand by adding up wattages and add some for AC startup load.
b]
What kind of generator will you buy? petrol one single phase
c]
How will you isolate the "normal" supply from your generator supply? changover device with interlocked switching that switched active and neutrals   
9]
You are about to perform a major electrical "upgrade" to your home. A friend has offered you an assortment of RCD's, circuit breakers & main switches for free. These items were previously used in his home but were not required after he had a major electrical upgrade done to his home. He tells you that the items are about 5 years old. He is not an electrician.
Would you accept the items & use them in your upgrade?
If yes, explain why.
If no, explain why not. I would, don't think there has been a recent change providing they are all in working order. 
10]
You are having a shower & when you turn off the metal shower taps with your wet hands, you sense a very small "tingle". 
a]
What could the problem be? loss of equipotential bonding of water pipes or earth raised above 0V eg dry stake or MEN disconnected
b]
What steps need to be taken to ensure that this problem doesn't occur again? ensure that earthing of water pipes is sound and earth system is correctly installed including MEN connection

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## rrobor

May I stop anyone from trying to test their computer with a megger. Most of the major parts are FETS (field effect transistors) they will not withstand any reverse voltage at all, 3 volts incorrectly applied to your nice new Quad processor and its gone. The computer works on a transformer which is tested to 3KV the only other component across that is sometimes a capacitor rated at 1KV and an opto coupler rated at 3KV. Please do not fiddle about or come to conclusions as to switch mode supplies in computers, you have a wee green light to tell you its OK. You will get tickles from USB etc its normal, go into a lift and at times the buttons bite, its normal, Get into bed with nylon sheets and it looks like the bed will catch fire, its normal as is getting out of your car or patting the cat. So leave your computer alone, if you get a tickle its static. Fiddle and you could not only blow up your computer but perhaps if you use an internal modem the telephone relay station and then you are in deep poo.

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## elkangorito

Thanks gentlemen for your submissions. :Biggrin: 
Based on a "quick" look at your answers, I can advise the following; 
Wildman - 4 mistakes. 
Journeyman Mick - 4 mistakes. 
Pulse - 4 mistakes. 
I'll bet that you copied from each other. :Laughing1:  
rrobor is correct. DO NOT MEGGER (insulation test) ANY ELECTRONIC EQUIPMENT!! Conducting an insulation test upon this equipment WILL destroy it.  
I hope some more people contribute. The "sensible" answers so far are very interesting & proves that people are thinking very well. Good on ya guys.  :2thumbsup:  
In a couple of weeks, I will post my suggested answers. In the meantime, have fun & misbehave. :Wink:

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## Wildman

Well I went first so am exempt from the slanderous insinuation of plagerism  :Biggrin:  
Can you define "mistakes". Are these life threatening, not exactly adhering to "the regulations" or not how you would do it? 
Cheers
Ben

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## rrobor

Perhaps Ill get my red blot withdrawn, after all look at all the puter boxes saved, Then again perhaps its my badge of honour, worn with pride.

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## watson

> Perhaps Ill get my red blot withdrawn, after all look at all the puter boxes saved, Then again perhaps its my badge of honour, worn with pride.

  No Way Rob! 
We like it   :Biggrin:   :Biggrin:

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## rrobor

OK have to nominate Noel for funny of the week, that must have taken a bit to do and almost caused me to fall off my perch, well done.

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## Pulse

No copying here, just need to stick to my day job.. 4 mistakes. :Eek:  
Good thing I don't have all those electrical problems currently at my place.. or else I would need to call a sparky. 
Cheers
Pulse

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## elkangorito

> Well I went first so am exempt from the slanderous insinuation of plagerism  
> Can you define "mistakes". Are these life threatening, not exactly adhering to "the regulations" or not how you would do it? 
> Cheers
> Ben

  Hi Ben. 
I'm trying to not use "the rules" as the only correct reference point. I'm basing my judgement on a mixture of rules, common sense & good work practice. 
Don't worry too much about your errors. All will be revealed shortly but in the meantime, I wouldn't proceed with any electrical DIY if I were you. 
I think that you put in a very good effort. :brava:  
I think I'll be submitting my suggested answers on or about the 25th of July, so there will be plenty of time for others to "have a go" at the quiz. 
Don't forget that any & all "sensible" discussion is encouraged. 
Have a great one.  :Biggrin:

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## Terrian

> Kaching!!...1 Cent change sir.

  brilliant, I am now on my way to being able to buy a beer (as long as the missus doesn't find out!)

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## elkangorito

Anybody else wish to "have a go" before the deadline, which is this Saturday night?

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## peter_sm

When I had a new switchbox and RCD fitted to our house, the earth stake was part of the deal. Our house is poly water pipe now also.

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## elkangorito

Answers to the quiz will be posted tomorrow night (24 Jul).

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## elkangorito

My suggested quiz answers as follows. Don't forget, discussion is encouraged about the answers. *Feel free to debate, ask questions or otherwise comment.* :Smilie:  Questions are in red. Answers are in blue.   *Answers 1 to 5.* Answers 6 to 10 in the following post.   1]
In your back shed, you have a "home made" metal bench with metal legs...100% metal. It sits on the concrete floor (not bolted down). On this bench, there is a "plug in" bench grinder. Ocassionally, when using the grinder, you get a small "tingle" from the bench.
What can be done to remedy the situation. Firstly, ensure that the bench is "equipotentially bonded" to the electrical system. This is done by attaching an earth cable from the bench to the earth bar in the sub-distribution board, which should be within the shed. The method of connection to 
the bench is ideally a hole drilled through the bench (probably a bench leg) and a crimp lug attached to the earth cable. The lug (usually a "ring" lug), is then fastened to the bench with a bolt/screw complete with one flat washer & one spring washer on the nut side, and one "star" washer on the other side. The "star" washer ensures a positive bond to the metal leg. This earth cable must be protected against damage (mechanical protection) by installing it in conduit.
NOTE. An appropriate crimping tool MUST be used to crimp the lugs. Using pliers to crimp the lug will not suffice.
Conduct an insulation test upon the bench grinder. If the test reveals a result less than 1 Megohm, the grinder is dangerous & must be repaired or discarded.
Check your Main Earth electrode. It may be damaged. If damaged, it needs to be repaired & an "earth fault loop impedance test" needs to be carried out.
Ensure that the shed power circuits are protected by RCD's.  2]
You have a computer. The tower is metal. Occasionally, you get a "tingle" when you touch the metal tower. What is the problem & what can be done to correct the problem? The problem is either a disfunctional earth or no earth. Ensure that there is an earth supplied to the computer through its supply cable. This can be done by a simple "continuity" test.
Ensure that the Main Earth electrode is undamaged. If damaged, it needs to be repaired & an "earth fault loop impedance test" needs to be carried out.
Ensure that an RCD is protecting the circuit. If there is an RCD, ensure it's proper operation.  3]
You are an "experienced" electrical DIYer & you wish to install 2 x 150 watt driving lights onto your motor vehicle. You already have two other 100 watt driving lights on your motor vehicle.
a]
Before you procced with the work, what must you do? You must check to see that the alternator can carry the future load (add up the amps). 
b]
When you are satisfied that the work can be done, how will you do it? The lights must be switched by a 30 amp relay (minimum) & the cable must be 32 strand (minimum). Ideally, the relay coil will be operated by a separate switch or by the high beam switch & the other contacts supplied directly by a connection to the battery. The cable should be rated at 30 amps (4mm) & be protected by a 30 amp "inline" automotive fuse. The fuse should be placed as close as possible to the battery.  4]
How should a good quality, fully charged car battery be "safely" stored? It should be stored in a cool, dry & well ventilated place & the terminals covered so that a connection between the two terminals will not happen. If being stored for a long period of time (>6 months), the battery should be placed on charge every month for a few hours.  5]
Your existing meter box is old. It only has rewirable fuses in it. You now wish to add a new power circuit to your home. You have contacted an electrician for a quote. The electrician visited your home & after inspection, has given you a "good" price to install the following;
a]
New wiring from the meter box to the new GPO's.
b]
The cost of the GPO's (parts).
c]
The cost of a rewirable fuse. 
Should you engage the electrician to do this work? You should not engage the electrician. It is illegal to install new circuits using rewirable fuses.

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## elkangorito

My suggested quiz answers as follows. Don't forget, discussion is encouraged about the answers. Feel free to debate, ask questions or otherwise comment. Questions are in red. Answers are in blue.      6]
You have noticed that the soil around your solid copper 13mm earth stake is rather parched, cracked & dry.
Do you;
a]
Pour water over the earth stake.
b]
Make a solution of salt & water, & then pour it over the earth stake.
c]
Buy special & expensive chemicals, which are designed to decrease earth impedance, & then pour over the earth stake.
d] Do nothing. Your earth stake can fend for itself. Do nothing. The earth stake can fend for itself.
If you want reasons why, feel free to ask.  7]
You have just built a new shed down the back yard & you wish to save a few bucks. You've decided that you wish to have a couple of fluorescent lights & a couple of GPO's in the shed. You also think that you may like to add some woodworking/metalworking equipment in the future. Your future ideas consist of a woodworking/metalworking lathe, an extraction fan & extra fixed lighting. You've also decided that you wish to run the cable underground, buy the conduit, dig the trench & pull in the cable from the meter box to the shed. You will then hire an electrician to connect everything.
You have 3 phase connected to your house for the purpose of supplying your 3 phase instantaneous hot water heater. All of your future shed equipment will be 3 phase. 
a]
What must be done before you even think about proceeding with this work? You must calculate the future "maximum demand" & add it to the existing demand. This means that you must estimate (preferrably over-estimate) your future load requirements. If you can't do this, an electrician can do it for you. If your total expected demand plus the existing demand (house) does not exceed the current carrying capacity of the aerial conductors & the Main Switchboard, you may proceed with the work. b]
How deep will you dig the trench? If the cable is installed in orange conduit (which is always a good idea), the trench should be a minimum of 500mm. This depth can be reduced by the use of concrete, paving/slabs &/or different cable types. The cables in the conduit need only be
"single insulated" (building wire). That is, they don't need to be TPS, which is double insulated cable. c]
What size conduit will you buy? If in doubt, the bigger the better. In this situation, a minimum size of 32mm should be ok but feel free to use larger sizes. d]
How will you determine the size cable you will need/buy? This can be done in a couple of different ways.
If you want to be super safe, you can add up the amps of your total load (including future load) & go from there.
You can also use a maximum demand calculation as per ASNZ3000. e]
What else should you buy? Unless you wish the sparky to supply it, you could buy a sub-distribution board. Since the installation may have 3 phase equipment, you would be advised to buy a minimum 18 pole sub-board.  8]
You live "way out in the sticks" in a caravan (temporarily, while you are building your new house) & your power supply is not all that good. Sometimes, the power can be off for as long as 1 day (24 hours). As a consequence, you wish to install a generator to supply the caravan in times of supply failure. You have a computer, a sound system, a fax machine, a fridge & an airconditioner in your caravan.
a]
How will you calculate the size of generator you need? The critical things here are the starting currents of the fridge & the airconditioner. The other equipment loads can simply be added to the total expected load.
As a general rule, you NEED to find out the "running" current of all appliances, especially your fridge & airconditioner. For the fridge & airconditioner, finding the LRA (locked Rotor Current) will be very helpful. If you can't find this information, multiply the "run" current by 4. This will be the "start" current for these appliances.
Add up all the "run" currents". This will give you the "full load" (FLA) of the generator. Add the start currents of both the fridge & the airconditioner together & subtract it from the "run" currents. This will give you a "surge" value.
For example, a generator is capable of supplying a 2300 VA (10 amps at 230 volts) & has a "surge" rating of 3200 VA (14 amps). If the "start" currents of both the fridge & the airconditioner exceed 3200 VA when everything is switched on, the generator will not handle the load adequately.
Generator output is given in VA because it does not take into account the Power Factor. b]
What kind of generator will you buy? Since the outage time is longer than 8 hours, a "portable" generator will not do Unless it has a longer "duty cycle" at full load. Most portable generators have a maximum operating time under full load. If this time is exceeded, the life of the generator will be drastically reduced.
As a result & under the circumstances mentioned in the question (24 hour down time), a "stand-by" generator is the correct choice for more than one reason. Many "portable" generators have terrible output waveform characteristics, unless they are the "inverter" type. Generally, a "stand-by" generator does not require inverter technology to produce a clean sinewave. It may, however, use electronics for voltage regulation. Also, the voltage regulation of "cheap" portable generators is not usually good (about 5%) whereas the voltage regulation of stand-by generators is very good (1% or less).
Since sensitive equipment is being used in the caravan (sound system & fax machine), the generator needs to be able to supply a "clean" waveform for long periods of time with minimal voltage drop. c]
How will you isolate the "normal" supply from your generator supply? A BTS or MTS (Basic Transfer Switch or Manual Transfer Switch) MUST be used. If you want the Rolls Royce, you can use an ATS (Automatic Transfer Switch), which usually incorporates phase failure protection (if you have 3 phase) plus automatic startup & shutdown of the generator. Contactors can be used for low "fault current" installations (<5kA) instead of circuit breakers.  9]
You are about to perform a major electrical "upgrade" to your home. A friend has offered you an assortment of RCD's, circuit breakers & main switches for free. These items were previously used in his home but were not required after he had a major electrical upgrade done to his home. He tells you that the items are about 5 years old. He is not an electrician. Would you accept the items & use them in your upgrade?
If yes, explain why. If no, explain why not. Quite simply, you should not accept these items. The "unknown" factor is the important thing here. If the circuit breakers have been subject to high current faults, the contacts may be damaged along with the internal mechanisms, which may mean that they will not operate correctly.  10]
You are having a shower & when you turn off the metal shower taps with your wet hands, you sense a very small "tingle".
a]
What could the problem be? A "small" tingle could indicate a problem with or lack of "equipotential bonding", a problem with an RCD or a problem with the water heater. An electrician should be called to check the situation. b]
What steps need to be taken to ensure that this problem doesn't occur again? If you wish to DIY, ensure that "equipotential bonding" exists & is functioning correctly. The heater in question should be subject to an insulation resistance test. An RCD MUST be installed on the circuit supplying the heater.

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## Wildman

What kind of generator will you buy? My answer to this was one compatible with my UPS. I always use an online UPS (not Line Interactive, they tend to not like generators of any sort) so I dont need clean power from the generator, any generator output, sine, square, stepped sine wave etc will charge the UPS battery and aircon and fridge wont mind either way. Any fluctuations in output will be compensated by the UPS. The only appliance that you would find in a caravan that would require a pure sine wave is a Microwave oven, they will not operate from a square wave or stepped sine wave (in my experience of living off the grid).
Nice to know about the difference in generators from a run time and duty cycle perspective though, I had not given that part any thought. I also have always had batteries rather than full time generator running so only ever ran the genny for a few hours until the batteries were charged. It was an old Ronaldson Tippet single cylinder chug chug diesel and would run forever given a chance. 
Cheers
Ben

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## elkangorito

> What kind of generator will you buy? My answer to this was one compatible with my UPS. I always use an online UPS (not Line Interactive, they tend to not like generators of any sort) so I dont need clean power from the generator, any generator output, sine, square, stepped sine wave etc will charge the UPS battery and aircon and fridge wont mind either way. Any fluctuations in output will be compensated by the UPS. The only appliance that you would find in a caravan that would require a pure sine wave is a Microwave oven, they will not operate from a square wave or stepped sine wave (in my experience of living off the grid). *Nice to know about the difference in generators from a run time and duty cycle perspective though, I had not given that part any thought. I also have always had batteries rather than full time generator running so only ever ran the genny for a few hours until the batteries were charged. It was an old Ronaldson Tippet single cylinder chug chug diesel and would run forever given a chance.* 
> Cheers
> Ben

  Thanks for your thoughts Ben. :2thumbsup:  
"Duty" is with reference to the generator itself...not the motor driving it.

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## elkangorito

Is anybody interested in a "part 3"? 
Would anyone else like to contribute? :Smilie:  Would anyone else like to post some DIY questions? If so, feel free.  :Biggrin:

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## mail2259

I have a Wilco 10A 3ka MCB for my lighting circuit. How much load (amps) can it take before it will trip ?. :Hmm:

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## elkangorito

> I have a Wilco 10A 3ka MCB for my lighting circuit. How much load (amps) can it take before it will trip ?.

  An interesting question Mail but could you post more questions please?

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## Pulse

I think I'd pass that test...  
mmm... 10A?

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## elkangorito

Technically speaking, the answer is >10 amps (slow) or >3000 amps (fast).

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## mail2259

Every protective device has a TCC - time current coordination, or trip curve. A graph which gives a band showing multiples of rated current to trip sec's.  
Which means simply my 10amp mcb can substain a thermal overload for example 1.5 times its rating for between 25sec to 200sec before tripping. A short circuit or higher current will cause an instantaneous trip value. I did a test on my lighting circuit at full load was pulling 14.55Amps without tripping for 90 sec, before I stopped the test.  
A normal nights load for me would be 2-3Amps for lighting. 
So the simple answer is >10amps but depends on the tripping curve, as to how long, as each device has a unique curve.

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## The Bleeder

> My suggested quiz answers as follows. Don't forget, discussion is encouraged about the answers. *Feel free to debate, ask questions or otherwise comment.* Questions are in red. Answers are in blue.   3] You are an "experienced" electrical DIYer & you wish to install 2 x 150 watt driving lights onto your motor vehicle. You already have two other 100 watt driving lights on your motor vehicle.  b] When you are satisfied that the work can be done, how will you do it? The lights must be switched by a 30 amp relay (minimum) & the cable must be 32 strand (minimum). Ideally, the relay coil will be *operated by a separate switch* or by the high beam switch & the other contacts supplied directly by a connection to the battery. The cable should be rated at 30 amps (4mm) & be protected by a 30 amp "inline" automotive fuse. The fuse should be placed as close as possible to the battery.

  Think you better check with the relavent traffic authorites. AFAIK that is illegal and the vehicle will be defected if inspected. Any automotive electricians or vehicle inspectors here want to comment.

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## elkangorito

> Think you better check with the relavent traffic authorites. AFAIK that is illegal and the vehicle will be defected if inspected. Any automotive electricians or vehicle inspectors here want to comment.

  I agree that my wording could've been more specific but I did mean this (see pic below).   http://www.renovateforum.com/picture...&pictureid=157

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## elkangorito

As we all know, Apprentice Electricians are required to undergo certain examinations. 
These are some questions from an examination for apprentices. I will reveal the web address after a while but I suspect that some members already know it. I would ask those members to not reveal anything for a while.   
Here are the questions: 
1] What are the requirements for earthing conductors that are jointed by soldering? 
2] Is it permissible to connect a final sub-circuit protective earthing conductor to any point on the main earthing conductor? 
3] Indicate the minimum side clearance for a recessed halogen lamp luminaire to a building structural member. 
4] List two ways of checking for response from a casualty who has received an electric shock and been safely isolated from supply. 
 5] The following values apply to the attachment below (Q 10.jpg) -
The voltage across points P and N = 100V.
A is 25 Ω; B is 70 Ω; C is 45 Ω and D is 15 Ω.
Calculate:
I. the current flowing through resistor C.
II. the voltage drop across resistor C.
III. the power dissipated in resistor A. 
6] The main switchboard of a 400/230V industrial installation is directly supplied from a 500KVA transformer which has a prospective fault current of 13,990A per phase.
Submains supply a distribution board from the main switchboard.
The following information is known;
a] Impedance of the Consumers Mains = 0.0040 Ω.
b] Impedance of the Submains cables = 0.025 Ω.
Determine the prospective fault current at;
(i) the main switchboard; and
(ii) the distribution board.
Work impedances to 5 decimal places. 
7] A 30 ma RCD is to be installed in the sub-main supplying a distribution board.
 The calculated maximum demand of the sub-main is 25A.
 There are three final sub-circuits supplied from the distribution board.
 The circuits are protected by an 8A, a 16A and a 30 A circuit breakers.
What is the MINIMUM current rating for the RCD?. 
8] On start up, a 3 phase 400V squirrel cage induction motor with an automatic star/delta starter;
A - starts on half the line voltage (200V).
B - changes to delta connection at about 80% of the motors full rated speed.
C - has a starting torque three times that of the DOL starting torque.
D - has a starting current one half of the DOL current. 
9] Unless proven to be de-energised, all electrical equipment must be treated as what?

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## Dutchie

Elkangorito ... and others .. thanks for the interesting thread. Some very interesting info. 
In Holland I would typically do everything electrical myself if it was after the main box, but here no need until now as we were renting. The urge will change now we bought a house in need of a lot of TLC. 
And as I understand you are not even allowed to replace a plug. A different perspective which will take time to adapt to. In Holland nowadays they want kids to learn at school how to change a plug. 
One thing I did notice though was dodgy (unsafe) electrics in both rentals we lived in.. 
But anyway, very interesting to read how things are supposed to be done here. 
Rgds Peter

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