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<p>I've gotten into discussions like this before with EEs. They are
not experts at what we do, and can get confused, and go down
strange rabbit holes like the rest of us. I agree with you that
not switching the Neutrals is the way to go. Its how we've always
done it in most scenarios. It only makes sense to have separately
derived systems as he is advocating, if you were including a
portable gen set input, since that gen set might have N-G bonded.
Even if you separated the N-G bond on the portable generator,
there's the chance they could connect up another generator later
that was internally bonded. None of this applies to your
scenario from what you described, though. </p>
<p>The other problem I've had with EEs, is that once they make a
decision, they don't really want to articulate the "Why" behind
that decision. Very frustrating for the rest of us trying to
understand and learn. I've asked for code references, etc. and
they just have blown me off. Another reason I've moved away from
consulting on larger projects. <br>
</p>
<p>I would take a look at 250.30, which says multiple parallel power
sources should be treated as a single separately derived system.
Exception 1 specifically says a single N-G bond is allowed for
multiple power sources.</p>
<p>Ray Walters<br>
Remote Solar<br>
</p>
<div class="moz-cite-prefix">On 3/13/2024 3:19 PM, Mick Abraham via
RE-wrenches wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CABOJ=XQ3uJ1LpTve3Lf63dA2B7MpsKRqHu=8JLB=UgeMbW7gFA@mail.gmail.com">
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<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>
<div>
<div>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">
<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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