array disconnects and code compliance [RE-wrenches]

[John Berdner]

Marco:

The requirements for the PV disconnect are found in 690-13 through
690-17.
Normally, over current protection is required to protect the array
wiring and so a fused disconnect would be used.
There is no code problem using the fused version of the disconnect, it
just costs more.
Also, UL requires a fuse in series with the modules to prevent fires in
the module caused by backfeed current.
If you use a fused disconnect and can make sure the fuse rating is <=
the UL series fuse rating and >= than 1.56* Isc the fuses in the
disconnect  can be used to meet the UL requirement.
While it will provide some protection for the inter-module wiring this
is not the primary purpose.

Steve Jochums (the PV module guy at UL) once gave me some advice I have
found helpful in when thinking about these things.
He told me to think of a PV module as a piece of wire that just happens
to have this weird PV characteristic.
The UL series fuse rating is effectively the "ampacity" of the weird
piece of wire.
As long as the available fault current from all the other sources is
less than the UL series fuse rating then you don't need the UL series
fuse.
Once you start thinking of modules in this way it makes it easy to
figure out what over current protection you need where.

The Sunny Boy has been tested and it will not backfeed a fault in the
array and this is why we can use an unfused disconnect..
No back feeding lets you take advantage of exception (b) in Article
690-9.
Since the inverter will not contribute fault current then you do not
need any over current protection as long as:
1) The ampacity of all the wiring in the system is greater than short
circuit currents from all paralleled strings, i.e. 1.56* Isc, and
2) The UL Series fuse rating of the module is greater than 1.25 * Isc*
(n-1); where n = the total number of paralled strings
When you do the fault current calculations you can show that over
current protection is not needed for one or two strings.
I have a paper on this that I can send to people about this - contact me
offline if you are interested.

If you have any questions or 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
Tel: 530.273.4895
Fax: 530.274.7271




-----Original Message-----
From: Mangelsdorf, Marco [mailto:mmangelsdorf at hei.com]
Sent: Wednesday, January 09, 2002 12:56 PM
To: RE-wrenches at topica.com
Subject: array disconnects and code compliance [RE-wrenches]


Wrenches,
In order to be code-compliant, what is needed between the solar array,
or combiner box, and the inverter in a battery-less system?  Does one
need overcurrent protection in the form of a fuse or appropriately sized
circuit breaker?  Or is an unfused disconnect acceptable?  The Sunny Boy
folks specify an unfused Sq. D HU361RB to act as the array disconnect
before going into the inverter. I've done this with no problem from the
local AHJ but am now wondering whether an fused disconnect is Section
690 acceptable.  Any observations?
marco
proVision technologies
Hilo-town, Hawai'i
- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

==^================================================================
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9
Or send an email to: RE-wrenches-unsubscribe at topica.com

T O P I C A -- Register now to manage your mail!
http://www.topica.com/partner/tag02/register
==^================================================================