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 cant 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:al...@positiveenergysolar.com>al...@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
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches@lists.re-wrenches.org
Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out participant bios:
www.members.re-wrenches.org
