Xantrex XW [RE-wrenches]

[Dan Rice]

Mark,

Please clarify the point about using the XW controller on a system with an
existing negative-ground bond. Do I understand correctly, that the
controller requires the 1A fuse be installed to operate, even if there's an
external bonding conductor? If so, and there's already an existing
negative-ground bond in the system, this amounts to having two "bonding"
points, which is prohibited by NEC. Besides the fact that, with parallel
current paths, the fuse may blow because current may be flowing through it
(it's become a parallel conductor in the negative conductor current path).
Please clarify.

Dan Rice
Abundant Sun, LLC.

----- Original Message ----- 
From: "Mark Edmunds" <mark.edmunds at xantrex.com>
To: <RE-wrenches at topica.com>
Sent: Tuesday, November 06, 2007 11:46 AM
Subject: RE: Xantrex XW [RE-wrenches]


|
| 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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|
|
|
|


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