earthing on generators

mikes post 39204

steve

Yes driving an earth stake in is exactly what you have to do for proper earthing. Any half decent generator will provide a lug or similar point to attach the earth cable. You are also absolutely correct in that earth leakage RCD switches will not operate unless you have a good earth. If you have the gennie sitting on a vehicle with rubber tyres you have no earth and therefore no ELB protection. It always scares me when you go to big events where hire generators are sitting all over the place, people everywhere and no proper earthing system is in place. Just relying on it being in contact with the ground is not good enough to provide a guarantee of a satisfactory earth return circuit to make the safety devices operate should a fault occur.

I asked the guys at the 12 volt shop this very question last week. They said it is not necessary.

You need to refer to the pamphlet or to the web for your particular earth leakage safety equipment, but....

Most newer safety swithches are called RCDs (Residual Current Devices).

They are 2 poles wide in your distribution board.

Both the active and the neutral conductors are connected throught the device. They measure the current going out through the active and compare it to the current coming back through the neutral. Any difference - most measure to an accuracy of 15ma - then they trip out. The assumption is someone or something is diverting the current flow to earth.

These do not rely on earth stake.

The protection is downstream of the device, ie there is no earth leakage protection on the lead from the genie to the van.

on safety switches...they only protect against leakage to earth...
RCD's will not protect oneself against being caught between active and nuetral and insulated from earth...you must be earth to be protected.

get a good sparky to do your wiring

If you are only using the generator to power your caravan then the frame of the caravan should be earthed anyway so if you were inside it and a fault occurs then you will be right.

If your using items attached to the outside of your caravan attach an earth stake to your caravan frame.

As an old ex Telecom man.....if you can think you can get a good earth by just driving a stake into the ground , then you live in fairy land....there are lots of variables ....and a bad earth is probably worse than none , and in my opinion a generator does not need to be earthed anyway....cheers

As an interesting side point, what is an earth for anyway? First person with the correct answer I will owe a can of VB to.

This is from a Workcover NSW document titled ' Electrical Practices for Construction Work - Draft Code of Practice' para 6.4

'Earthing of the generator frame is not required or recommended. No earth electrode is required.'

I'll leave it to others more informed on these matters to intrepret what this means.

www.workcover.nsw.gov.au/NR/rdonlyres/C71A75CF-3288-4624-A8EC-3A7A342C2BB2/0/electrical_draftcop_4494.pdf

Hi Steve,
You've raised an extremely important subject here and one that has many experienced electrical engineers devote the whole of their careers to its study, earthing. More importantly, safe and functional earthing.

If you go to your local mine site with a generator they'll mostly require you drive an earth stake and then perform some form of earth bond resistance check. Basically a check to see how well the earth stake is connected to the surrounding ground. They also require the use of Residual Current type Earth Leakage Circuit Breakers.

As others have stated above, Workcover (NSW) doesn't require a generator to have an earth stake but does require an Earth Leakage Circuit Breaker of the Residual Current type. The operation of these has been described above.

As Nudie has quite correctly pointed out an Earth Leakage Circuit Breaker (ELCB) will not protect you from connecting yourself between Active and Neutral. Mind you, no Circuit Breaker will protect someone's life from this type of accident. They will probably protect you from becoming black and crisp. As to the comment regarding the the commonality of this type of accident, the bulk of modern deaths (post compulsory ELCB) from electrical shock are Active to Neutral human connection.

Now, onto your question regarding earthing, generators, camping and your caravan. This is a wholely interesting and little understood subject by almost all users and most electricians! My theory on this is they don't actually draw the circuit then analyse the potential points of failure before happily wiring.

You've raised a valid point regarding the earthing of your caravan, yes it does sit on at least two rubber tyres and a rubber jockey wheel so it isn't actually connected directly to the planet earth. What happens with your caravan is every part of the metal frame, skin and chassis are required to be bonded to the earth conductor of your 240 Volt supply. That bonding point is also required to be accessible for inspection and maintenance.

My take on portable equipment and earthing is this, you absolutely must have a Residual Current type Earth Leakage Circuit Breaker as close as possible to the generator outlet. Everything you run off the generator MUST be downstream of this device.
For me, when running a generator that is NOT subject to a Mines or Workcover ruling, (Both these requirements overrule anything I say or use) I bond the earth to the neutral, UPSTREAM of the Residual Current device.
Why? I'm creating an Multiple Earthing Neutral (MEN) Link just like your house has. What advantage does it offer? There is no path to earth downstream of the ELCB that the ELCB cannot detect. The system is reasonably fail safe.

Note: I did say a couple of paragraphs above to DRAW the circuit and potential fault circuits. Then thoroughly analyse the potential paths for current flow. Don't forget when using portable generating plant it's possible to connect yourself between Neutral and Earth and die. Less than 20mA will stop your heart.

Disclaimer: I offer the above as opinion only. It DOES NOT constitute advice or recommendation of portable generating plant connectivity or offer absolute safety from electric shock whilst operating portable electrical generating and consuming equipment. Hell the generating professionals even blew up a main station transformer in NSW today!!

Geoff.

Hi all,
in the military, they earth all generators, and the rules say that the soldiers are supposed to pee on the earth stake to ensure a nice saline moist earth with good conductivity.
Cheers

Well, here is a question... But then since I know as little as most, the answer may already have been provided above - I just don't understand it

What is the earth pin on the generator outlet connected to, behind it?

The frame of the generator?

What is the use of that?

Is there a any device that will trip when the earth leaking current has nowhere to go, and so therefore will peak (to a low limit) for an infinitesmal time and then be zero?

Surely the purpose of grounding the earth is so that there is something to absorb current for long enough so that the safety devices can detect it?

I hear you about RCD rather than ELCD. Is that all there is to it? A difference in current between active line and neutral line means it is going somewhere else?

So I would expect that a caravan frame/shell could easily be live without any warning, because there is no current going anywhere, until you touch it while you have bare feet on wet ground.

Ken