Ground fault protection [RE-wrenches]

[Christopher Freitas - OutBack Power]

Allan Sindelar wrote:
> As the PV- and B- are isolated from each other at the SB50, a
> ground fault could indeed send full array current from PV- through
> the controller to the grounded B-, and overcurrent protection 
> wouldn't catch the fault. 

The PV- and B- terminals are not really isolated - just connected 
through a low impedance current measurement shunt.  Much more than full 
array current can flow through this connection when a ground fault 
occurs - such as lots of current from a battery for instance (and a 
reverse current circuit in the controller will not stop flow in the 
negative circuit). 

Breakers will not always trip - the PV is current limited inherently 
below the rating of the breaker.  I can start a fire easily with 3 amps 
at 24 vdc under the right conditions...   

I think that a properly installed ground fault protection system would 
have substantially reduced the damage which occurred.  Its really cheap 
protection - or even "insurance" if you think that way... The cost for 
our OutBack OBDC-GFP/2 is $129 and it can protect two 60 amp PV array 
controllers. It also gives you something to point at when the fire 
marshall / insurance company arrives (...We even installed ground fault 
protection even though the NEC said we didn't have too on a 
non-dwelling/ground mounted installation...).   

The ground fault would have most likely tripped BEFORE the damage to the 
system occurred - most likely during the installation.  This is why I 
have started referring to them as "bad install detectors"...  

Christopher Freitas
OutBack Power Systems, Inc.
cfreitas at outbackpower.com  www.outbackpower.com
Tel 360 435 6030  Arlington WA USA

- - - -
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.bWljaGFl
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
==^================================================================