[RE-wrenches] Starting fires for fun with string wiring

Mon Mar 12 09:22:07 PDT 2012

SMA will have AFCI protection built into the inverters. It is integrated into the inside of the inverter, so there are no extra components to install.
They work off of the combined circuit to offer the AFCI protection.

The units are listed but, won't be available for another couple of months. We are in the field testing stage now.

Thanks

SMA America, LLC
Steve Jefferson
Sr. Technical Service Specialist, Sunny Family
6020 West Oaks Blvd, Suite 300
Rocklin, CA 95765 - 3714
U.S.A.
Tel:  +1 916 625 0870
Fax: +1 916 624-2445
Service Line +1 877 697 6283 (Toll Free)
Email: steve.jefferson at sma-america.com
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From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of JRQ
Sent: Monday, March 12, 2012 9:09 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Starting fires for fun with string wiring

I've been wondering about this since I read over the 2011 code:

Are there any listed DC arc-flash products on the market yet, or scheduled to come to market within the next year?

Also: will arc-flash protection come in the form of breakers that need to be installed externally, or will it be something internal to the inverters or charge controllers to which source circuits are wired? Will they need to be installed on each string, or can they function on a combined circuit?

Do systems with DC optimizers or with micro-inverters have arc-fault protection at the module level?

Jeffrey Quackenbush
NABCEP Certified PV Installer
Peripatetic Solar Technician

________________________________
From: "boB at midnitesolar.com" <boB at midnitesolar.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Monday, March 12, 2012 12:37 AM
Subject: Re: [RE-wrenches] Starting fires for fun with string wiring

On 3/11/2012 9:26 PM, Kent Osterberg wrote:
boB,

Most local codes, have granted a delay on implementing arc fault protection. Also, the code only requires series faults to be cleared.

I mentioned this because arc fault is already in the 2011 NEC whether it is adopted or not.

I have a feeling that Jeff was referring to some of the changes that are in the works for 2014.

As far as I understand, the code cannot be required unless there are products that fill the requirement.

Also, the UL spec was not quite complete, but that  didn't stop many of us from starting to work on it
before even 2011 code was out, even releasing "something", even if it did not have a spec
to test to yet.

This code is going to get interesting for sure.   It's also going to make installations more expensive so
it's good that PV prices are falling some to help make up for it !

boB

Kent Osterberg

Blue Mountain Solar, Inc.

www.bluemountainsolar.com<http://www.bluemountainsolar.com>

t: 541-568-4882

On 3/11/2012 8:28 PM, boB at midnitesolar.com<mailto:boB at midnitesolar.com> wrote:
On 3/11/2012 7:35 PM, Jeff Yago wrote:

I just sent a post about people not understanding the dangers of fire in the

array strings between the modules and before the combiner because its high

voltage DC and there are no fuses or circuit breakers to shut down the power

source (at least not until the next code requires arc-fault sensing!).

Jeff,

Arc fault was required as of NEC2011.

boB

Anyway, we have a 3 string, 4-module per string off-grid test system behind

the shop wired for 88 volts peak into a charge controller and 24 volt

battery bank. Last week as a test I temporarily disconnected the charge

controller and re-wired the 3 strings together into a single string of 12

modules with a 264 volt open circuit voltage DC output at about 7 amps at

dead short.  When compared with most grid-tie systems, this is not that high

a voltage or current, so what happened next would be far worse for a larger

voltage array.

I took a 2 x 4 and attached USE-2 single conductor wires using "wire

staples" with the (+) and (-) cables routed side by side and down the 2 x 4.

At the lower wire staple, I deliberately nailed through the wire insulation

which nicked the insulation but did not cut the wires.  After routing the

array power through these test wires nothing happened since the wire staple

was not making a very good contact with the bare wire at the insulation

nick.  I then moved the wires slowly from side to side by hand, which could

have been caused in a real installation from wind, temperature

expansion/contraction, somebody pulling on them, or just the action of age

on the nicked wire insulation.  Anyway, after only a few seconds of slowly

moving these wires, suddenly the wiring where it passed under the wire

staple burst into flame and started to arc.  In about 5 seconds the 2 x 4

was burning and the string wires were burning like a powder fuse running up

the 2 x 4.  As the wire insulation was burning, it exposed the energized

wires and allowed the arcing to continue up the wood 2 x 4 which was now

also in flames .  At times, the arc would pass between wires that were over

1" apart once the arc had started.  In other words, the arc would not

normally jump 1" through the air, but once an arc started it would continue

to arc even when the wires were far apart since the plasma formed from the

vaporized copper wire was conducting the electricity across the gap.

I know the code requires any string wires to be in metal conduit from the

point it enters a building to the first disconnect,  but I am not sure this

is enough protection.   DC voltage is a very strange animal and even trained

electricians do not always realize the strange behavior it has if they have

only worked with AC wiring.  Arc faults in older AC electrical panels are

becoming a real danger to service technicians since sometimes just opening

the panel door can cause something loose to fall across the interior buss

bars and start the arc.

Arc faults are really dangerous because the plasma formed from vaporized

copper can be thousands of degrees in temperature in under a second, and

since it is not technically a "short", an arc-fault condition will not

usually trip the circuit breaker since there is enough resistance in the

higher voltage arc to limit the amp flow to below the rating of the circuit

breaker, which makes it very hard to stop.  I think the solar industry will

start seeing more of this type hazard as these array voltages continue to

increase.  I strongly suggest everyone should wear arc fault rated face

shield and hand protection when working around energized high-voltage DC

string circuits, as electricians gloves alone are not enough.

I will try and down-load this video from my camera and convert to a file I

can send as an email attachment.  If interested, send me your email address.

Jeff Yago

jryago at dtisolar.com<mailto:jryago at dtisolar.com>

804-457-9566

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