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Kent,<br><br>
Thanks for helping sort out this issue. At a minimum, the majority
of the portable generators being connected to wiring systems today are
not code compliant. Fortunately, the connections haven't created
incidents, since these systems have become very common. Off grid
installations must be in the minority. <br><br>
Over the past several years, many major storms have left millions of
people without power. Small generator sales have skyrocketed.
Utility companies pleaded with people not to backfeed breakers, but to
use a transfer switch. Now, as it turns out, the 4 wire connections
to wiring systems via transfer switches, provided by commercially
available generator inlet boxes, create a code violation do to parallel
neutral paths. <br><br>
Maybe portable generators should be arranged like mobile generators,
where available lugs make bonding the neutral to frame (or not) very
simple. Hooking up a 220 KVA mobile generator, for a concert, was really
easy. <br><br>
If the chasis could be un-bonded easily, permanent rod could be
installed, that the portable generator could hook to when moved to its
backup power location. Or, maybe the NEC should be amended to allow
people who have lost power in emergency situations, to connect to a
portable generator. Maybe even extend this to solar backup systems,
if no real world hazards can be demonstrated.<br><br>
I'm still not convinced that it is not legal to hook into a grounded and
bonded wiring system, so long as the equipment grounding conductor is
omitted. Here is the code section on portable generators:<br>
____________________________________________________________________________________________<br>
250.34 Portable and Vehicle-Mounted Generators.<br>
(A) Portable Generators. The frame of a portable generator shall not be
required to be connected to a grounding electrode as defined in 250.52
for a system supplied by the generator under the following
conditions: <br>
(1) <x-tab> </x-tab>The generator supplies only
equipment mounted on the generator, cord-and-plug-connected equipment
through receptacles mounted on the generator, or both, and <br>
(2) <x-tab> </x-tab>The normally
non–current-carrying metal parts of equipment and the equipment grounding
conductor terminals of the receptacles are connected to the generator
frame. <br>
____________________________________________________________________________________________________<br>
<br>
Nothing here says we can't connect to a wiring system via cord and
plug. If we omit the EGC, which runs in parallel with the neutral,
parallel neutral paths don't exist. Maybe it is inferred somewhere
else, or enforced by interpretation. RV and marine inverters do
switch the neutrals, creating separately derived systems. <br><br>
Up until lately, it was permitted to ground the frames of electric ranges
and clothes dryers with a neutral wire. Although this is not
permitted for new systems anymore, I don't know of any incidents that
have occurred. If there is no hazard involved, maybe the NEC
could accept 3 wire connections for 120/240 V portable
generators.<br><br>
It would be good to find a solution to this issue that does not require
hundreds of dollars of additional equipment and installation time,
especially if no real dangers exist. If hazards to exist, equipment
needs to be developed to address them. <br><br>
Drake <br><br>
<br><br>
<br><br>
At 01:06 PM 11/12/2009, you wrote:<br>
<blockquote type=cite class=cite cite="">Drake, I agree with you that
there may not be a code compliant way to connect a portable generator
other than to use a transfer switch that also switches the neutral.
And non-the-less many portable generators are being used for backup power
without a switched neutral -- without incident.<br>
<br>
The older codes only allowed using the neutral to be grounded at separate
structures <i>if there was no other metallic path between the
buildings</i>. It was safe, still would be safe and I think it is a
mistake for the code to be changed to disallow it. But the
"<i>no other metallic path between the buildings</i>"
requirement was often ignored. It is pretty rare to see metallic
water pipes these days; but phone lines (soon to be history too), gas
lines, intercoms, and so on are often added after word. And when
they are grounded at both buildings, they carry a share (a small portion)
of the neutral current.<br>
<br>
NEC 250.34(A) says a grounding electrode isn't required if 1) the
portable generator supplies loads connected by plug and cord and 2)
non-current carrying metallic parts and equipment grounding terminals of
the receptacles are connected to the generator frame. Sorry, Drake,
the intent here is that an EGC is used. Using the neutral to
connect the equipment grounds doesn't comply.<br><br>
NEC 250.34(B) says the same thing for vehicle mounted generators that are
bonded to the vehicle.<br><br>
NEC 250.34(C) requires the generator neutral to be bonded to the
generator frame if the generator is a separately derived system. If
the generator can be used as a portable power source, it will be a
standalone separately derived system and the neutral and ground must be
bonded. Despite advise seen on this list serve, the neutral ground
connection on a portable generator should not be
disconnected. <br><br>
There is a FPN in 250.34(C) refering to 250.20(D) for grounding portable
generators supplying fixed wiring systems. NEC 250.20(D) covers
system grounding for separately derived systems, that is when the
generator neutral isn't solidly connected to the service-supplied neutral
and the load neutral is switched between the two systems. This is the
code compliant method to connect a portable generator to a fixed wiring
system. Unfortunately the inverters we use aren't set up to switch
the neutral; they aren't really set up to connect to a portable generator
at all. And yet many portable generators are being connected to
inverter systems and also directly to buildings for backup power --
without incident.<br><br>
The FPN in 250.20(D) talks about on-site generators that are not
separately derived systems and defines them as having a grounded
conductor that is <i>solidly</i> interconnected to the service supplied
grounded conductor (then the generator neutral ground bond is
omitted). Most inverters are set up for this type of generator
connection: a fixed on-site generator than can have a solid neutral bond
between the different power sources. Yet, often, the customer wants
to use portable generator. Hence our catch 22.<br><br>
I like Alan's work around using the autotransformer as a generator
balancer thereby forcing the neutral current to zero. It is an
expensive piece to add to a small generator. But the Outback x-240
is only large enough to use for a small generator.<br><br>
Kent Osterberg<br>
Blue Mountain Solar<br><br>
<br>
Drake Chamberlin wrote: <br>
<blockquote type=cite class=cite cite="">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. <br><br>
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 <br><br>
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. <br><br>
Drake <br><br>
<br>
<blockquote type=cite class=cite cite="">Content-Language: en-us<br><br>
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.
<br>
<br>
· 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.”<br>
<br>
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.<br>
<br>
<br>
Allan Sindelar<br>
<a href="mailto:Allan@positiveenergysolar.com">
Allan@positiveenergysolar.com</a><br>
NABCEP Certified Photovoltaic Installer<br>
EE98J Journeyman Electrician<br>
<b>Positive Energy, Inc.<br>
</b>3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
505 424-1112<br>
<a href="http://www.positiveenergysolar.com/">
www.PositiveEnergySolar.com</a><br>
<br>
Larry,<br>
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.<br><br>
Solutions (unfortunately none of these may be suitable and they all have
potential problems):<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
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.<br><br>
See. I don't have any good solutions.<br><br>
Kent Osterberg<br>
Blue Mountain
Solar</blockquote></blockquote>
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<x-sigsep><p></x-sigsep>
<font color="#0000FF">Drake Chamberlin<br>
Athens Electric<br>
OH License 44810<br>
CO License 3773<br>
NABCEP </font><font size=1 color="#0000FF">TM
</font><font color="#0000FF">Certified PV Installer <br>
Office - 740-448-7328<br>
Mobile - 740-856-9648 </font></body>
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