[RE-wrenches] Supply Side Tap Overcurrent Protection

Dave Click daveclick at fsec.ucf.edu
Mon Mar 29 05:47:14 PDT 2010


Looks like your question is answered but something else to look out for- 
this is pretty straight-forward for batteryless systems but for 
battery-backup and a line-side tie, you're adding a big load to the 
service conductors for battery charging and pass-through current to 
critical loads. If you're tying in your battery-backup system as a load 
side connection, if you have a high house load and a high 
battery-charging load then the main breaker trips to protect those 
service conductors. However, by bypassing the main here you could be 
pulling enough power in to overload them and cause a meter fault.

But at least when the meter fails you have your important stuff on 
battery-backup...

Dave Palumbo wrote:
> Wrenches,
>
> I am tasked with reviewing an installation by a licensed electrician in
> Vermont and would like help with the following:
>
> Grid-tied PV system with battery back-up. AC point of connection is a
> supply side tap (done on customer side of utility meter ) then traveling
> 5 feet of #2 THHWN in 1” EMT to the 60 Amp 240vac Lockable Utility
> Disconnect (unfused) and continuing 15 feet #2 THHWN 1” EMT to Xantrex
> XW 60 Amp breaker.
>
> I had said that the 60amp 240vac lockable disconnect needed to be fused,
> and received the following reply from the installing electrician.//
>
> / /
>
> /<< “The Xantrex XW Power Distribution Panel contains the required over
> current protection (60 amp/
>
> /double pole circuit breaker) negating the need for a redundant fuse at
> the Utility Disconnect switch.” >>/
>
> / /
>
> I am on a short trip in Florida and away from my code books. Can someone
> provide guidance and code reference please? I am concerned about the 20
> foot distance of the un-protected circuit from the supply side tap and
> also the interrupt rating of the 60 Amp breaker in the Xantrex
> distribution panel.
>
> David Palumbo
>
> Independent Power LLC
>
> Offices in Lamoille and the Champlain Valley
>
> 802.888.7194
>
> www.independentpowerllc.com
>
>
>
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