interconnection question [RE-wrenches]

[Bill Brooks]

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Keith,

This is not necessarily a California issue. It is an inspector issue since
many inspectors do not understand this issue very well. Code allows us to
connect to any service panel on the premises provided that the sum of supply
breakers feeding the busbar do not exceed the busbar rating. Usually the
commercial panels have supply breakers that match the busbar rating so no
additional breakers will fit. Many subpanels do not have a main breaker, but
are fed by a breaker in the main service (600 Amp in this case).

1.) If the subpanel does NOT have a main breaker and it cannot be
retrofitted with a main breaker, then you should install a new 200-Amp main
lug subpanel upstream of the existing rooftop subpanel and install two
100-Amp branch circuit breakers in the panel--one for the existing subpanel
and one for the PV.

2.) If the subpanel HAS a main breaker, then up to a 100-amp fused
disconnect can be installed on the line side of the rooftop subpanel either
by splicing into the existing 100-amp conductor or using a double lug kit on
the main breaker in the 100-amp subpanel. Since the PV feed is upstream of
the subpanel and is under 100 amps, it will fit on a 100-amp breaker or
fused disconnect and not overload the conductor since loads are all
downstream of the disconnect.

William makes a good point in that the utility disconnect issue would need
to be discussed with the serving utility to make sure your disconnect on the
roof could be used as the visible-break disconnect for the utility. If not,
you are going to have to bring the conductors down from the roof for the
disconnect anyway.

Darryl's suggestion of going to the opposite end of the subpanel for the PV
breaker is technically fine, but many inspectors do not like this method
since it is fairly easy to move breakers around, defeating the assurance
that the PV breaker has no load breakers downstream in the panel.

Does this make sense? Let me know if anything is unclear.

Bill.

-----Original Message-----
From: Keith Cronin [mailto:keith at islandenergy.net] 
Sent: Friday, February 18, 2005 12:33 PM
To: RE-wrenches at topica.com
Subject: interconnection question [RE-wrenches]

Hey gang
 

This might be a Bill question: (no offense to any others- I just figured he
had the pulse of California fresh on his mind!)

If you were looking at putting a 50KW system on a building, and were going
to use a 45KW Trace unit, and they already had a 100 amp, 480 volt feeder on
the roof for mechanical equipment, what are the specific rules governing the
interconnection?

 My mind says, I will be basically neutralizing the load, which is connected
to a distribution panel with a 600 amp electrical service. But, I know
looking at this, it would seem too easy to tie in to the panel on the roof,
and add a curb for the inverter.

Thanks!

Keith Cronin

President

Island Energy Solutions Inc.

270 Kuulei Rd. Suite 106

Kailua, HI 96734

808-262-3268 Tel

808-263-0338 Fax

keith at islandenergy.net

www.islandenergy.net

 

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