Xantrex XW [RE-wrenches]

[Mark Edmunds]

Hi Mick,

You are correct, the note in the manual is to ensure the ground
connection remains fused at a maximum of 1A, even when addition
controllers are connected to the same battery. The units will work
normally if there is already a dc neg-ground bond in an older system
without ground fault protection. In this this case the built in GFP is
essentially disabled, as the fuse cannot ever be blown by a fault
current.

Cheers,

Mark



Mark Edmunds
Xantrex Technology Inc.

-----Original Message-----
From: Mick Abraham [mailto:mick at abrahamsolar.com] 
Sent: Tuesday, November 06, 2007 7:46 AM
To: RE-wrenches at topica.com
Subject: RE: Xantrex XW [RE-wrenches]



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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