[RE-wrenches] Generator bonding discussion

[Drake Chamberlin]

There may be no totally compliant way of using 
the internally-bonded-neutral generators, but 
they are being used a lot in both solar 
applications and emergency generator backup 
systems.  Inlet receptacles and transfer switches 
are being sold in quantity for use with cord  and 
plug connected generators, most of which are internally bonded.

Using a 3 to 2 prong adaptor might be the best 
solution where code rigidity is not the norm.  In 
the old code, the neutral could be separately 
bonded at different structures under the same 
management.  Using the adaptor, the neutral bonds 
to the frame of the generator, so other 
receptacles on it will still be legitimate to use in accordance with 250.34

The building will get its ground through the 
grounding electrode system of the 
building.  There are no parallel neutral 
paths.  All will have normal safety feathers and 
will function well.  It may or may not be 
"code."   Check out 250.34.  I think there is 
some argument for this method being compliant.

Drake


>Content-Language: en-us
>
>The problem of the bonded chassis in most 
>generators has been with us for years, and there 
>is no real solution. With most cheap (and 
>ubiquitous) portables, the AC neutral is 
>internally bonded to the chassis and can’t be 
>easily undone.  When I wrote the HP generator 
>article I attempted to address this issue 
>without getting too technical. I ran this 
>specific issue by John Wiles for his advice, and 
>the final wording reflected his position that 
>the AC ground loop – that is, maintaining the 
>neutral-ground bond in both the generator and 
>the inverter system and accepting that the 
>ground conductor would carry a portion of any 
>current otherwise being carried on the neutral – was the best of the options.
>
>·         The final wording as submitted to HP 
>was: “Quality generators allow the neutral 
>conductor to either connect to the generator 
>chassis (for prime power application) or remain 
>separate from it. Portable generators are seldom 
>properly grounded, so manufacturers ground the 
>neutral output conductor to the chassis. When 
>connected into a grounded power system, however, 
>this presents a safety hazard, as the neutral is 
>now bonded to the ground at two places­one in 
>the power system AC and one in the generator­and 
>the safety ground wire becomes current-carrying. 
>Some units also include AC ground-fault 
>protection, which is incompatible with 
>connection to a grounded power system.  There is 
>no simple, Code-compliant solution to this. The 
>safest noncompliant approach is to bundle an 
>insulated green ground conductor with the power 
>conductors between the generator and the main 
>ground buss, to both ground the chassis and minimize shock potential.”
>
>Inherent in this is that that grounding 
>conductor between gennie and ground buss be 
>bundled in conduit and boxes, rather than being 
>left bare or exposed, as would otherwise be OK with any grounding conductor.
>
>
>Allan Sindelar
><mailto:Allan at positiveenergysolar.com>Allan at positiveenergysolar.com
>NABCEP Certified Photovoltaic Installer
>EE98J Journeyman Electrician
>Positive Energy, Inc.
>3201 Calle Marie
>Santa Fe, New Mexico 87507
>505 424-1112
><http://www.positiveenergysolar.com/>www.PositiveEnergySolar.com
>
>Larry,
>Sounds like there are two neutral ground bonds: 
>one at the generator and one at the house.  This 
>causes part of the neutral current to flow on 
>the ground - a guaranteed way to trip the 
>GFI.  This is the catch 22 of connecting a 
>portable generator, or one with an outlet, to a 
>house system.  The house panel has to have a 
>neutral ground bond.  The generator also has to 
>have a neutral ground bond (Although the small 
>Honda and Yamaha inverter generators don't. How 
>do they get away with that? - No exposed metal 
>to touch I guess.) or the GFI won't work and 
>ground faults won't trip the generator output breakers.
>
>Solutions (unfortunately none of these may be 
>suitable and they all have potential problems):
>
>Permanently wire the generator.  On the 
>generator, remove the neutral/ground bond and 
>remove all of the electric outlets.  In some 
>locations, you aren't allowed to permanently 
>wire a generator unless it is U/L listed.  And 
>most (maybe all) portable generators aren't U/L listed.
>
>Replace the GFI outlet with a non-GFI outlet (so 
>it will be like the old Homelight 
>generator).  Part of the neutral current will 
>flow on the ground wire.  That's a code 
>violation, but for 20 and 30-amp outlets the 
>ground wire has adequate ampacity so nothing is 
>going to overheat.  In fact, even 6 AWG SO cord 
>has a ground wire the same size as the conductors.
>
>Use a 2-prong cheater.  This will prevent the 
>GFI from tripping.  It also prevents any ground 
>fault past the cheater from returning to the 
>generator.  It's probably best to locate the 
>cheater at the load end of the cord; that way if 
>the cord is damaged the GFI will still trip.  If 
>there is ground fault past the cheater, there 
>will be one or probably more than one locations 
>where there is shock hazard.  If you touch the 
>generator frame, it'll tingle; if the ground is wet, it might be severe.
>
>Use a mobile-style inverter that will switch the 
>neutral/ground bond.  Most of these are not U/L 
>for house wiring.  I think this is the best 
>solution but it doesn't cover the circumstance 
>of a grid backup inverter connected to a portable generator.
>
>See. I don't have any good solutions.
>
>Kent Osterberg
>Blue Mountain Solar

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