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First, I'll say that I agree with William's discussion. Let me add
another way of thinking about this:<br>
<br>
Assume that, instead on two generators, your system is one backup
generator and one utility company serving a commercial building. If
the disconnect switch is your service connection, there will be a
N-G bond located there and none will be allowed in the generator.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar<br>
<p><br>
</p>
<div class="moz-cite-prefix">On 3/13/2024 2:19 PM, Mick Abraham via
RE-wrenches wrote:<br>
</div>
<blockquote type="cite" cite="mid:CABOJ=XQ3uJ1LpTve3Lf63dA2B7MpsKRqHu=8JLB=UgeMbW7gFA@mail.gmail.com">
<div dir="ltr">Hi, Mechanix~
<div><br>
</div>
<div>My off grid project gig has redundant 120y208 generators
that need a 200a "break before make" manual transfer switch so
the clients can choose machine A or machine B. The switch has
a lockable center-off but I think the generators aren't
set up for "lock out tag out". The machines & the xfer
switch will all be indoors and about 10 feet apart. The AC
power wires from each generator will be hard-wired to the
transfer switch & piped in EMT. I had planned for the
transfer switch to have a "solid neutral" bus bar (& I had
planned to bond Neutral to Ground in that box), but a
consulting EE tells me the neutral must be switched along with
the three hots. The project is too remote to have an AHJ, but
the clients have requested a wet stamp from the EE.</div>
<div><br>
</div>
<div>I think his rationale is related to the N-G bond point
location. When I asked about his suggested location, the EE
wrote: "The N-G bond will be at each generator, so the neutral
will be generated at the generator providing power to the
facilities."</div>
<div><br>
</div>
<div>Mick resumes: The genset installation document says "The
generator set is shipped from the factory with the neutral and
equipment ground not bonded together." So...these gensets are
not like those portables where it's difficult to isolate the
neutral. I've attached an image that shows what the EE is
advocating. The manual xfer switch that I wish to use isn't
made in "four poles" without going to the 400 amp version and
the 400a switch won't physically fit the available space.</div>
<div><br>
</div>
<div>Can I make a credible case for the transfer switch being
the "point of first disconnect" instead of each generator
taking turns at being the POFD? If the transfer switch is also
the bond point, can't the Neutral from each generator happily
meet at the neutral bus bar? OR: might the EE have a concern
about a loop (from the Neutral of one genset through the bus
bar then showing up on the terminal strip for the other
genset? Code citations would be appreciated along with your
advice, Wrenchies. </div>
<div><br>
During service intervals, both engines will be running for a
brief interval. Example: Gen A may be carrying the loads while
the mechanic manually runs Gen B as he completes an oil
change. If I wire it as the EE wishes, will both running
machines play well safety-wise if each genset has a N-G bond
(with the equipment ground as their only common connection)?
How would the safety aspects change if both machines are
running but I've wired things per my original concept? <br>
<br>
Thanks as always, Mechanix. "The Wrench List is the Bomb!"</div>
<div><br>
Mick Abraham, Proprietor<br>
</div>
<div>
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<div dir="ltr">
<div><a href="http://www.abrahamsolar.com" target="_blank" moz-do-not-send="true">www.abrahamsolar.com</a><br>
<br>
Landline: 970-731-4675</div>
<div>Cell phone or for text messaging: 970-946-6584</div>
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