ECN Forum Forums General Topics of the Trade General Discussion Area Portable generator grounding question

If OSHA shows up I would pull out this rule.

Greg, it looks like if you have a straight 120V two-wire generator it would fly, but from what I’ve been reading on the Q&A on the OSHA site, it sounds like if the generator is both 120/240V, it might not be allowed.

Here’s an example reply from the Q&A that has me wondering:

In the OSHA standards for portable vehicle-mounted generators, equipment grounding conductor bonding is mentioned in 1926.404(f)(3)(i)(B) and in 1926.404(f)(3)(ii)(C).Neutral conductor bonding is mentioned in 1926.404(f)(3)(iii).
The intent of 1926.404(f)(3)(iii) becomes very clear when one considers that the term “neutral" is used in its technical sense. A 120/240 volt system has a neutral and therefore must be bonded to the generator frame. A 2-wire 120 volt system has no neutral and therefore bonding is optional. Recall that neither side of a 2-wire derived system is a neutral and when one grounds either side, it becomes a grounded terminal or conductor, but it is not a neutral.

I have still not heard a good reason why you bond the neutral in an ungrounded system. There is certainly no way to have a "ground fault". About the only thing you can have is a frame fault and you artificially created that situation when you bonded the generator.

If you have a floating 120/240 system from a portable generator and a fault developes that connects one of the "hot" legs to earth, is there more risk with the other "hot" leg now being 240 V with respect to earth?

I know that there 120 V breakers and 120/240 V breakers. What is the difference?

Larry

Larry your "earth" question makes my case with an ungrounded generator. If you had the neutral bonded to the frame and one phase got grounded to earth, the whole machine would be 120v above earth, including the case of that drill you are holding.
You might operate a GFCI if you got in the fault path between EGC and earth but not the overcurrent device.

Greg, if you did not bond the centertap of a 120/240 generator and you had the same phase to earth fault, the case of the drill is at an unknown voltage with respect to earth.

I believe the case voltage will be dependant on how much current is flowing thru the holder of the drill.

I would rather have the case floating than at a known 120v above the dirt I am sitting on.

Floating the voltages is a well known protection scheme; it used to be the norm before the advent of inexpensive GFCI outlets, and is still used in bathrooms in Europe and on naval ships, etc. It IS safer than a solidly grounded neutral due to fault tolerance; if one phase suffers a ground fault, it simply changes from a floating system to a corner-grounded system. Fault clearing is diminished, though; if there's a ground fault, you might never know until a 2nd fault occurs.

I'd just never heard of portable generators NOT bonding the neutral.

Small Hondas were all shipped without the bonding. I haven't looked lately.

I have a Honda EU2000. There is no bond between ether of the leads although it has a grounded receptacle and a ground screw. It uses an inverter to generate power out of the multi-pole alternator. I feel real safe using tools in damp or wet locations with it.