Misleading fault indications [RE-wrenches]

[Mark Frye]

William et. Al.,

In the diagram you post there is a resister across the 0.5A circuit breaker.
Is it correct to say that the grounded DC conductor becomes "un-bonded" when
the circuit breaker is open?
 
Mark Frye
Berkeley Solar Electric Systems
271 Vistamont Dr
Grass Valley CA 95945
(530) 401-8024
www.berkeleysolar.com
 

-----Original Message-----
From: William Miller [mailto:wrmiller at charter.net] 
Sent: Tuesday, March 04, 2008 6:47 PM
To: RE-wrenches at topica.com
Subject: RE: Misleading fault indications [RE-wrenches]


John:

Thanks for the detailed background on the fault scenario and the 
code-making process.

I try to differentiate between a fault in which the negative current 
returns on the equipment grounding conductor, the positive current returns 
on the grounding conductor or a plain old pos. to neg. short circuit.  I 
don't know if it is important to differentiate these faults here but I 
suspect it is.

I have some questions:

1. John, do you have any concerns about the scenario I presented?  It just 
does not seem right that a fault in an inverter indicates as a fault in the 
PV and that the inverter continues to have power supplied to it.

2. Also, do you share my gut reaction that un-bonding a neutral just to 
accomplish ground fault detection is somehow not the straightforwards 
approach?  The drawing that indicates this scenario is located at:
http://mpandc.com/case_studies/ground_fauilt/ground_fault.html  It is the 
second study from the top.

3. Has anyone attempted to detect ground faults by monitoring the 
difference in current on the positive lead versus the negative?

BTW, the top study on that page indicates a scenario as you mentioned in 
your reply and illustrates the importance of ground fault detection.

Sincerely,

William Miller


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