While looking for information for another thread I rediscovered an article that may be of use to those considering grounding generators.
This is a PDF that I can't directly link to, however I have linked to a Google search that finds it. Portable Generators & OSHA Regulations. The Description - "PORTABLE GENERATORS AND. OSHA CONSTRUCTION REGULATIONS. Draft. monograph by: John “Grizzy” Grzywacz, Professor. OSHA National Training Institute"
The article points out why driving a ground rod for your generator is not a good idea as well as requirements for bonding generator neutrals.
its gives very good reasoning why NOT to ground a portable generator and why NOT to bond the neutral ( unless i mis-read something )
I have never bonded the neutral to frame or grounded a portable genny,
you will notice that the last paragraph and drawing where they advocate bonding the neutral to frame, is a 3 wire dual voltage system (120/240) and they talk about 'a user safety device' and ground fault return protection
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Good link Jon. When reading the first page I thought that the references to ground were unclear as to whether or not they meant an earth ground, but this got cleared up on the next page. I'll add for anybody who doesn't know, the 2008 edition of the NEC added a definition of 'neutral', which I was never able to find in earlier editions. It's very clear from this definition that a 2-wire system does not have a neutral.
My question from this is that when you take a 30 amp RV (which does not have a neutral), and plug it in to shore power (which does have a neutral), does the white wire in the RV become a neutral or not? If I draw a box around the RV and include the shore power wiring, I think the RV does have a neutral. If I draw the box just around the RV, I think it doesn't have a neutral. My 2 sides argued it out, and the result is a draw.
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My question from this is that when you take a 30 amp RV (which does not have a neutral), and plug it in to shore power (which does have a neutral), does the white wire in the RV become a neutral or not?
-----------------------
Trailer has a 7355 power centre.
A. Plugged into house:
three light tester at house says two lights (ground and neutral) and so do trailer receptacles. (With converter on or not)
B. Plugged into Honda gen (which has a floating neutral):
tester shows one bright steady light (open ground)in the Honda receptacles but other two lights faintly flickering, and so do trailer receptacles except other two not lit.
But! If I snap off the converter breaker (the converter has only a black and white wire no ground) the trailer receptacles now show two lights but the neutral light is fainter than the ground light--as somebody here suggested it might be) Turn converter back on and back to one light showing open ground(neutral light goes back out)
C. Plugged into inverter clamped to battery:
tester has all three lights on while in the inverter receptacle and also when plugged into trailer receptacles.
Hope that matters to somebody
My plan is to ignore all this complicated stuff and just keep doing things the same way as always since nothing bad has happened so far (years) If I get killed trying to watch a movie using my 400w inverter, then I'll just have to hope it wasn't a very good movie anyway so I didn't miss anything.
Wayne, think of the white as a "floating" neutral since it has no reference point to say earth ground.
For the most part it could be considered as harmless, but if you consider that the generator sitting on earth loosely couples its self and the RV also is loosely coupled via tongue jack and or levelers/stabilizers to earth ground (I know this is a high resistance when dry). Just add some water to the mix such as the morning dew, light rain or wet snow, now you have a very good connection to earth ground.
Now what you have is a potential that YOU might create a BETTER ground (wet sandles or bare feet). If your gen or RV has some leakage you could now become a very dead camper.
While you can argue the sementics till the cows come home if you like but myself I would rather have my power source wether it is shore/gen/inverter to have the neutral and equipment ground terminated together at one point. This gives a reference point (neutral), a equipment safety ground back to the power source.
In a gen/inverter enviroment without some sort of reference point (floating neutral), you stand a good chance that you yourself may make a better electrical path.
Without drawing diagrams and such it is hard to put into words, but I can tell you this, the most important thing I learned in tech school was to avoid making myself a better conductor. When working on live chassis, I was told to put one hand behind my back. With only one hand you can probe with meters and test equipment much safer than with both hands. With both hands the path of least resistance is between your arms. Your heart is IN THAT PATH. I value my life and others so I do take care that electrical things are done as safe as possible.
On edit, should add in that using a gen/inverter without a bonded neutral/equip safety, you would technically need to interupt both black AND white wires. Why is this? Well you should never interupt neutral, since there is no reference both white and black can be hot or not, so to play it safe interupt both. Not the normal thing to do, is it?
* This post was
edited 10/21/08 05:06pm by Gdetrailer *
Section 1 is giving a very good reason not to ground the genny frame to the earth, something no one does anyway.
Section 2 is moot since the NEC has removed it and OSHA probably will follow suit.
Section 3 seems to say the Neutral and Ground should be bonded at the generator frame. The diagram shows this done on a 120/240v, 4 wire genny, but the only argument against doing this on a 120v 3 wire genny I see is an earlier response saying that a later NEC does not define a 120v 3 wire genny as having a Neutral. To me, that sounds a lot like semantics.
The Onan in my 07 Winnebago came from the factory as a 120v 3 wire genny built in with the Neutral and Ground bonded on the generator (and MH) frame.
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This is the definition of 'neutral' from section 100 of the 2008 NEC. It's very specific, a lot more than semantics:
NEUTRAL CONDUCTOR:
The conductor connected to the neutral point of a system that is intended to carry current under normal circumstances.
NEUTRAL POINT:
The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system.
FPN: At the neutral point of the system, the vectoral sum of the nominal voltages from all other phases within the system that utilize the neutral, with respect to the neutral point, is zero potential.
(end of definition)
Unfortunately. almost everybody except the code writers thinks the definition is "the white wire".
Every 120 volt RV factory generator installation that I'm aware of has the white wire bonded to ground. I don't know why they do it that way, but I do know there are a lot of people out there who mistakenly think the white wire in a 120 volt system is a neutral, and they incorrectly think that the regulations about neutrals apply.
* This post was
edited 10/21/08 10:43pm by Wayne Dohnal *
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