my idea for using a 3 phase panel [RE-wrenches]

[Bill Brooks]

Todd,

Any idea like this needs to be cleared with both the AHJ and the utility. I
would think the biggest problem would be with the utility. I would have a
big problem with having an energized buss next to a deengergized buss that
could be easily miswired by someone unfamiliar with the installation. Also,
there is the possibility of putting a load on a two-pole breaker that could
present voltage back through to the main service panel in the event of a
utility outage.

I think the cost of the 3-phase panel and associated potential questions
(those are the biggest problems because they cost time and money to deal
with) far outweigh the benefits. I like to keep things straight and this
seems to muddy the waters. Nice idea for your own home, but I wouldn't put
it on a customer's home.

Although some disagree with me, I think the code is very clear that output
of inverter is an optional standby system and is governed by Article 702.
702-6 seems to address this issue that is must be "designed" to prevent
inadvertent interconnection. I think your idea violates this.

702-6. Transfer Equipment. Transfer equipment shall be
suitable for the intended use and designed and installed so
as to prevent the inadvertent interconnection of normal and
alternate sources of supply in any operation of the transfer
equipment.

Nice idea for your own home, but I wouldn't put it on a customer's home.

Bill.

-----Original Message-----
From: Todd Cory, Bald Mtn. Solar [mailto:toddcory at jps.net]
Sent: Saturday, December 08, 2001 6:43 PM
To: Wrenches
Subject: my idea for using a 3 phase panel [RE-wrenches]


Wrenches,

I have had an idea for years and recently during a conversation with
another wrench this surfaced again so I thought I would throw it out
there for the "critics" to evaluate.   :)

Whenever I do a grid tied system with battery backup (SW4024 etc.) I add
a second breaker panel next to the original one and shift desired back
up load circuits over to the new panel which is fed from the inverter.
Since these panels are usually for 120/240 split phase use, the busses
get jumpered together for 120 volt only use... which really wastes the
second isolated pole since it is not needed.

SO... when using a 120 volt only inverter with new construction, I have
pondered the use of a 3 phase panel. Two of the poles could be for the
usual split phase 120/240 grid feed. The third pole could be used for
the 120 volt inverter feed. Neutrals and grounds all bonded in the same
place, and it has 2 major advantages. One is that it simply looks neater
having only one panel. The other nice thing is only ONE service
disconnect for the building. California requires external disconnects
for power, so this usually means labeling both building panels as
service disconnects "1 of 2" and "2 of 2" respectively.

The only downside I can think of in using a 3 phase panel is the cost.
They are way more than 2 split phase panels.

Other than being an unusual application, can anyone think of why this
idea would not work or be code legal?

Todd

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