Installation details [RE-wrenches]

[Bill Brooks]

Matt,

The code doesn't want you using the conduit going to your hot tub for the PV
Output Circuit. Since the DC and AC are part of the same power system, they
should be allowed. My view of the world is that they are not separately
derived power systems in the way that most people think of those types of
systems. Of course, some inspectors will choose to not see it that way.

Mark Mrohs of AstroPower just wrote up a nice explanation. It makes sense to
me. Again, the inspector is the last word:

1. Basic NEC allowance for AC and DC wiring to be together:
Article 300 Wiring Methods
300.3 Conductors
(C) Conductors of Different Systems
(1) 600 Volts, Nominal , or Less.
“Conductors of circuits rated 600 volts, nominal, or less, ac circuits, and
dc circuits shall be permitted to occupy the same equipment wiring
enclosure, cable, or raceway. All conductors shall have an insulation rating
equal to at least the maximum circuit voltage applied to any conductor
within the enclosure, cable, or raceway. Exception: For solar photovoltaic
systems
in accordance with 690.4(B)”. [The section cited by the exception is
discussed below.]

Comments: The explanation in the Code Handbook goes on to explain

”Section 300.3©(1) makes it clear that it is the maximum circuit voltage
not
the maximum insulation voltage rating 
that determines the minimum
voltage rating required for the insulation of conductors
.The conductors of
a
3-phase, 4-wire, 208Y/120-volt ac circuit; a 3-phase, 4-wire, 480Y/277-volt
ac circuit; and a 3-wire, 120/240-volt dc circuit may occupy the same
equipment wiring enclosure
if all the conductors are insulated for the
maximum circuit voltage of any conductor”.

Thus, if the solar DC conductors and inverter AC conductors are all rated
for
600 volts, they should be allowed to occupy the same gutter box enclosure.

2. The 'PV' section that refers to “different systems”:

Article 690 Photovoltaic Systems
690.4 Installation
(B) Conductors of Different Systems.
“PV source circuits and pv output circuits shall not be contained in the
same raceway, cable, tray, cable, outlet box, junction box, or similar
fitting as feeders or branch circuits of other systems, unless the
conductors of the different systems are separated by a partition or are
connected together”.

Comments: The explanation given in the Code Handbook helps clarify what is
meant by “different systems”:

"For example, 690.4(B) requires the conductors of a yard light located near
a
roof-mounted pv array to be in a separate raceway or cable from the
conductors of PV source circuits or PV output circuits."

The DC and AC wires connected to a Sunny Boy inverter are clearly not from
different systems as interpreted above, and should therefore not be affected
by the section.

Special thanks to Mark Mrohs of AstroPower for assembling the above
information. I hope it helps.

Bill.


-----Original Message-----
From: matthew tritt [mailto:solarone at charter.net]
Sent: Wednesday, November 27, 2002 8:47 AM
To: RE-wrenches at topica.com
Subject: Re: Installation details [RE-wrenches]


David,
 Isn't this mixing separately derived power sources? I thought that was a
big no-no.

Matt

****snip****

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