Richard, when you use your Fluke 87 to measure Vdc, black is negative,
red is positive. The black is labeled common because the meter can also
be used for current measurements. (I have a Fluke 89)
When you start using black wire for positive, it may be allowed by code,
but there just isn't a good reason for it.
Its just too easy to make a mistake, and its just too easy to adhere to
the multimeter convention and keep it safer.
I have personally watched seasoned electricians argue color coding with
me, then minutes later get mixed up and wire two 10 module strings in
series, because they forgot for a moment that they were working on a
positive grounded system. The result was an almost 1000 v arc that
jumped an opened fuse holder (only rated to 600 vdc) and started a small
fire in the inverter, before I disconnected it at the array.
Please give one example where leaving positive unmarked with black wire
makes more sense than taping it. Colored electrical tape, and label
tape are much cheaper than inverters and people. THHN, USE, and PV wire
can all be purchased in red, white, and black. (which saves time with
multiple home runs)
Its not code yet, but it's good sense, all the way back to the color
coded jumper cables you might have in your trunk.
I have discussed this with many electricians over the years, but
eventually every single one sees that's its really easy, no cost, and
still code compliant to make things safer.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 6/28/2013 2:49 PM, Richard L Ratico wrote:
Respectfully:
My Fluke 87 does not use this convention. Black is labeled the COMMON terminal,
the red terminal is labeled according to function, not polarity. Battery based
inverter manus. using this convention typically provide BOS enclosures with OCP
for only one inverter conductor. This requires the other conductor to be
grounded and colored white or gray. Therefore IMHO the manus. should use only +
or - to identify inverter terminals. Many, if not most, battery companies do
this already. Mr. Wiles is, of course, welcome to his opinion.
I would suggest we stay with the NEC required use of any color other than white,
green or gray for ungrounded conductors. This gives installers some flexibility.
It also encourages the guy on the hot roof or the gal in the stuffy mechanical
room to check and double check, maybe triple check polarity, as they should be
doing anyway. I do like the practice of enhanced identification of conductors in
positive ground systems.
Dick Ratico
Solarwind Electric
--- You wrote:
The convention of red for positive and black for negative is not just
automotive. It is also used by all battery based inverter manus, all
battery companies, and all multimeters.
John Wiles also agrees;
red = positive, black = negative for ungrounded systems
red = positive, white = negative for negative grounded systems
white = positive, black = negative for pos grounded systems.
I take it a step further, and use white label tape with red lettering
that says "+ positive ground + ",
because I've seen so many problems with positive grounded systems, and
people not getting polarity correct.
All of this is NEC compliant, and follows standard conventions.
Make it easy on yourself and your journeymen on a hot roof, and have
your color coding match their multimeter.
You might save an inverter or even a life.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 6/28/2013 12:09 PM, Allan Sindelar wrote:
On 6/28/2013 11:47 AM, a...@aramsolar.com wrote:
And of course Red for positive and black for negative.
Most building departments have not pick up on this yet. But they will.
Aram
Where does "of course Red for positive and black for negative" come
from, please? I only know it as an automotive standard that has often
caused confusion when used by DIY offgridders in years past, as black
thus could represent either positive or negative in a DC conductor pair.
Is there yet a convention for ungrounded arrays? While red and black
are technically correct as ungrounded current-carrying conductors, use
of this color convention could cause as much confusion as resolve it
in the future. How about "black and black" or for that matter "yellow
and orange" (if supplied by manufacturers) for ungrounded arrays?
Thanks, Allan
*Allan Sindelar*
_Allan@positiveenergysolar.com_ <mailto:al...@positiveenergysolar.com>
NABCEP Certified PV Installation Professional
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
*Positive Energy, Inc.*, a Certified B Corporation^TM
3209 Richards Lane
Santa Fe, New Mexico 87507
*505 424-1112 office 780-2738 cell*
_www.positiveenergysolar.com_ <http://www.positiveenergysolar.com/>
--- end of quote ---
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