Xantrex XW [RE-wrenches]

[Mick Abraham]

John Raynes wrote: "What would happen in a system with more than one XW 
charge controller tied into the same DC bus?  Wouldn't each controller 
see the other's GFP as an external ground fault?"

Mick says: In a system with multiple XW controllers, the manual says to 
remove the fuses from all the controllers except for one. I think this 
is not because the other controllers would look like a ground fault but 
rather the opposite: the other fuses would provide alternate links 
between negative and ground so that a 1 amp GFP fuse could not be relied 
upon to blow at that low value.

John wrote: "I would hope that there would be some way of 
disabling the internal GFP", and Dan Rice wrote: "negative and ground 
must be kept isolated so the GFP will work correctly, and probably for 
the controller to work at all."

Mick says: There's nothing you can do within the charge controller 
itself to disable the GFP. Regarding the recommended isolation of 
negative and ground elsewhere in the system, the manual says: "Bonding 
the negative to ground disables PV ground-fault protection and causes 
improper unit operation." The manual says other things to discourage 
this...things like "WARNING: Shock Hazard" and "NEC requirements".

In spite of these intimidating words, I suspect that the XW control 
would still work normally (in a retrofit system where there's already a 
negative/ground bond) except for the GFP feature. If there is a 
neutral/chassis bond exterior to the XW controller, this would prevent 
any voltage potential from developing across that fuse so the fuse could 
never blow, but to the controller that would look just like  normal 
operation with no ground fault. Confirmation or refutation of this 
theory would be welcomed. Not all installations require DC ground fault 
protection, after all...


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