AC/DC in Same Conduit? [RE-wrenches]

[jberdner at sma-america.com]

Wrenches:

I am afraid I must disagree with Mr. Brooks on this one. 
My opinion is based on exhaustive discussions on this subject with John
Wiles, and UL.

The key phrases in Section 690.4 are "Different Systems" and "other
systems". The input and output circuits of a PV inverter are part of the
same system so this is not a violation of 690.4.  If you have the dc
input circuit and a branch circuit to a water heater in the same raceway
then you would have a violation of 690.4.

Clearly all the wiring must be rated for the highest voltage in the
raceway and you can not >> terminate << the dc and dc in the same
raceway or conduit.  This last point means no wire nuts, split bolts,
etc. in a raceway with both ac and dc in it.

Personally I think it would be a good idea to require the "energized
from multiple sources" labeling on raceways with AC and DC.  I have
already put this one in the 2005 code suggestions box.  

On the topic of 2005 code: 

Now it the time to put in your $0.02 for the 2005 code!! If you have
some ideas on things that need to added, eliminated, or clarified send
your suggestions and comments to John Wiles ASAP (jwiles at nmsu.edu). John
will send them to Ward who will star circulating them for comment.

If you have any questions, or if I can be of any further assistance,
please do not hesitate to contact me.

Best Regards,

John Berdner

SMA America, Inc.
20830 Red Dog Road
Grass Valley, CA  95945
530.273.4595 (voice)
530.274.7271 (fax) 


-----Original Message-----
From: Bill Brooks [mailto:billb at endecon.com] 
Sent: Thursday, July 11, 2002 10:57 AM
To: RE-wrenches at topica.com
Cc: Ward Bower; John Wiles
Subject: RE: AC/DC in Same Conduit? [RE-wrenches]

Brother Todd and others,

The chapter and verse of the requirement is in Article 690.4(b)of the
holy
NEC:

(B) Conductors of Different Systems.
Photovoltaic source circuits and photovoltaic 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.

Here endeth the first lesson.

This doth not refer to DC and AC systems in general. Article 300.3(c)(1)
doth say:

(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).


It appeareth that PV systems are being held to a higher standard
possibly
because of the concerns over miswiring a dc circuit into the utility
grid.
If you would like to use the "Holy Handgrenade" on this particular
requirement this may be a good issue to bring up for the next code
cycle.
All proposals for the 2005 NEC are due by November of this year. Ward
Bower
of Sandia will be conviening a meeting of the technical review committee
some time in the next two months to work through comments to propose to
the
code making panel. It is likely this meeting will be held in California.
If
any wrenches are interested in attending the meeting, please contact me
offlist at <billb at endecon.com>.

Bill.


***snip***
Bill can you quote the code where this is specified. I would like to see
specifically what it says about mixing voltages in one conduit.

Thanks,

Todd


Bill Brooks wrote:

> David,
>
> The NEC gods and goddesses frown on such evil deeds. If you do this
you
must
> live in constant fear of being turned into a newt.
>
> Bill.

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