Generators - To Earth or Not

Submitted: Monday, Feb 09, 2004 at 16:29
ThreadID: 10397 Views:14116 Replies:6 FollowUps:6
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Advice please.

I have a portable generator which comes with an earth connection. The manual says it should be earthed to avoid shock. But if I dont earth it how can I short to earth if I grab active or nuetral (only one at a time).

Is it safer not to earth teh genny or should it always be earthed.

Thanks

Sean
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Reply By: Member - DOZER- Monday, Feb 09, 2004 at 18:16

Monday, Feb 09, 2004 at 18:16
Hi
Quick answer is through touching the gen to turn it off or refuel etc. Static can also build up on an unearthed piece of equipment. My dad used to work for integral, and told me that the 330kv lines can spark to ground and start fires due to static and their isolation to earth. You can put a peg in the ground to attatch earth to (or similar)
I would earth it if it says to. If some leakage occurred accross positive and ended up on the chassis of the generator....and you touch it....zap.
I would also fit an earth leakage circuit breaker in the output just to be safe.
Andrewwheredayathinkwer mike?
AnswerID: 46030

Follow Up By: Member - Ross - Monday, Feb 09, 2004 at 18:38

Monday, Feb 09, 2004 at 18:38
Got it in one Dozer. We've got a Honda which we .... should earth as a matter of course.

Sparky mate of mine questioned the efficacy of a short peg though.

CheersFidei defensor

Rosco
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Follow Up By: Brett - Thursday, Feb 12, 2004 at 23:00

Thursday, Feb 12, 2004 at 23:00
330 kv is a lot different to 240 v. worlds apart. If the same rules applied to 240 volt we would never be able to puug anything in. I think the safe approach distance for 330 kv is 6 meters. within that you are at risk.

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FollowupID: 308430

Reply By: chrisfrd - Monday, Feb 09, 2004 at 19:06

Monday, Feb 09, 2004 at 19:06
G'day guys,

You should earth the unit, no matter what! The unit's genset could end-up floating up to 240V potential and kill somebody, especially if you had a wiring fault in a caravan or something. The battery that you could charge off these units is also a concern, as the -ve is at the chassis potential of the genset.

You should have a deep earth too. If you can't due to rocky ground, then a few earths should be used, made from copper prefferably and they should also be kept wet to aid conductivity.

The 330KV stuff isn't something I'd be going to play with, but the principles are the same, where you get EPR (Equi-potential Rise) events, due to the capacitive effect of the conductors in relation to the ground. It's like a large zenner diode!

I've seen what happens to timber power-poles after their insulators breakdown due to EPR after long dry spells or excessively dusty periods... Lots of burn timber!
AnswerID: 46039

Reply By: Willem - Monday, Feb 09, 2004 at 20:57

Monday, Feb 09, 2004 at 20:57
Dunno...I have a 12 yo Suzuki 800 and it has been used severely. Never been earthed. Handle and on/off fuel switches are made of plastic and it stands on rubber feet. I would have thought that it would be insulated against against possible static shocks. Yes the manual does state it should be earthed. Never had a problem though.........
Willem
Out on the Gibber
AnswerID: 46056

Reply By: sean - Monday, Feb 09, 2004 at 21:12

Monday, Feb 09, 2004 at 21:12
Thanks for the replies but I am not sure I understand. I am basically confused because there are some countries that do not have earthed electrical systems and in these you can hold the active in your and in bare feet nothing happens.

Would this not hold true for a single phase genny that is not earthed (I am not game to try).

Sean
AnswerID: 46060

Follow Up By: V8troopie - Tuesday, Feb 10, 2004 at 01:28

Tuesday, Feb 10, 2004 at 01:28
What are you going to use it for? Use as a stand alone unit to power a light or something at an isolated camping spot, earthing it is not going to make any difference unless you earth all the equipment you plug into it too. And a lot of equipment is double insulated, which you cannot (and should not!) earth.
If the genny develops a fault within it should blow its internal fuse anyway.

If you use it to provide power to a caravan, and the caravan has earthed equipment in it (cooker, micro wave, air con) then earth it to the caravan chassis. Bang a ground spike in if it makes you happy but you have to consider that a fault current has to travel via faulty equipment to ground under caravan and then to earth spike at genny to trip a safety device. If the van is earthed to the genny directly you bypass that dubious through the ground path.
If the genny has a properly wired 3 pin 240V outlet socket and you connect it via a good 3 core mains cable to the van's 240V inlet, you automatically earth it anyway.
Klaus
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FollowupID: 308035

Follow Up By: Brett - Thursday, Feb 12, 2004 at 23:09

Thursday, Feb 12, 2004 at 23:09
<<<Would this not hold true for a single phase genny that is not earthed

Bird on the wire!
Yes, if you could guarantee the generator was and could never contact the earth. You could hold the active or neutral ...not both because then you become the load.

I would not be happy relying on the rubber feet supporting the genny to provide enough insulation.
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FollowupID: 308432

Reply By: Brett - Thursday, Feb 12, 2004 at 22:23

Thursday, Feb 12, 2004 at 22:23
The 240volt single phase genset is basically one single winding/coil. One end of the winding has a differential of 240 v to the other. One end of this winding ends up being the active conductor and the other end of the winding becomes the neutral. This neutral is connected to the frame of the genset. Most portable gensets have insulated rubber feet to reduce vibration and noise thus insulating the frame of the generator from the earth. How does it effect you?

Say you were using an appliance( drill) which had a faulty active and resulting is some leakage of electricity to the handle and in turn the user. In this instance the user would probaby not feel anything and could be actually be walking arould with 240 volts of potential just waiting to escape. No you go up to the generator to turn it off and come into contact with the frame of the genset. This is where the trouble starts. You have just completed the circuit and will get a decent shock..potentially deadly. The same scenario can happen with an extension lead sitting in a puddle of water, because the generator is electrically insulated from the ground/earth there will be no circuit. The generator is decribed as being "above earth potential"

The addition of an earth stake will provide a free electrical path for a fault to be able to activate any electrical protection such as a fuse or circuit breaker. It is standard practice on all building sites that an earth leakage device is to be fitted to every generator set, or, the generator set needs to comply with AS 2790. To my knowledge no-one makes a portable generator which complies with this standard.

The best type of Earth leakage is a core balance type. This personal protection device measures what goes up or down the active and what goes up or down the neutral(remember it is AC). If what goes up one wire and doesn't go down the other at the same time the only other place it could go is to earth. In this instance the switch will automatically throw and it should disconnect the power in approx 20 milliseconds. The amount of current that is acceptable before humans are at risk is 30 milliamps. You will feel it but only slightly.

Another device to reduce fire hazard and high current flow faults is an earth current limiter or earth choke. This "device will allow only a small amount of current to the earth. A common size is 5 amps. This device is described as a equipment protection device.

Problems associated with earth leakage is nuisance tripping whick is mostly caused by electrical water heating devices and multiple fluorescent lights. Occasionally electrical motors can produce enough losses on startup to trick the ELCB.

Hope this helps.
AnswerID: 46533

Follow Up By: Brett - Thursday, Feb 12, 2004 at 23:13

Thursday, Feb 12, 2004 at 23:13
I should add that a properly installed the earth stake will allow enough current to flow in a very short period of time to enable the overload circuit breaker to operate. This switching time may be greatly increased if a poor earth is present. This additional time allows the fault to generate more heat and or damage to humans and equipment.
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FollowupID: 308434

Reply By: Member - StevenL - Thursday, Feb 12, 2004 at 22:37

Thursday, Feb 12, 2004 at 22:37
Guys,

I am a member of the SA Country Fire Service and we use 2 Generators to provide power for a Isuzu Bus that is used as a Field Command unit. They are 3.5 and 6.5Kva Powerchief units that sit in the tube frame and take two people to lift. The small one runs lights and computers and the bigger one runs heavy duty air con for the bus (remember we only go out when it's bloody hot!)

We just set these up about 50ft away from the bus sitting in the grass or dirt and run a lead to them. Naturally we position an extinguisher next to them as part of the safety precustions but not once has earthing been mentioned. Are there risks involved here?

Is there something I am missing here? As a Govt organisation the CFS would surely be up to date on safety issues like this - much more than your average camper!!

StevenLPlaydoe GXL TD Manual
It's on order, Delivery in April '04.
This pic will have to do till then. Can't wait!!!
AnswerID: 46539

Follow Up By: Brett - Thursday, Feb 12, 2004 at 22:54

Thursday, Feb 12, 2004 at 22:54
I would suggest that training is required. or the machines are fitted with ELCB. Earth stakes are provided and safe work practice is for these to be used in the event of your elcb failing. You cannot rely on gravity to provide an adequate earth.
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FollowupID: 308427

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