[RE-wrenches] Critical Loads Panel Wiring

William Miller william at millersolar.com
Tue May 8 07:14:38 PDT 2012


Darryl:

I respectfully disagree with the use of the bonding screws.  In general, 
there are two panels that require bonding:  The service and a separately 
derived system.  The service needs a neutral-ground bond screw but the 
second panel is a sub-panel and must have an isolated neutral.

William

PS:  When considering how to bond and feed neutrals to a critical loads 
panel, think about how the neutrals are connected in the inverter.  Unless 
the inverter is a "mobile" unit, the in and out neutrals are connected 
together in the inverter.   When using an integrated BOS AC cabinet, only 
one neutral is required.  Therefore one neutral buss is technically all 
that is needed for the described scenario.  Your inspector may very likely 
not be comfortable seeing no neutral buss in one panel.  If required, you 
can feed the new panel neutral from the inverter or from the service 
panel.  With proper low impedance connections, they are all the same 
potential and complete the circuit path back to the service transformer, 
the ultimate duty for a neutral buss.

Wm


At 06:42 AM 5/8/2012, Darryl Thayer wrote:
>Locally if you have two service panels next to each other, inspectors want 
>both bonded and grounded, by allowing a bonding jumper from panel one to 
>panel 2, and both panesl use the bonding screw, and both have to have a 
>neutral bus.
>
>From: Corey Shalanski <cshalanski at joule-energy.com>
>To: RE-wrenches at lists.re-wrenches.org
>Sent: Tuesday, May 8, 2012 6:51 AM
>Subject: [RE-wrenches] Critical Loads Panel Wiring
>
>Wrenches,
>
>Batt backup system: When placing a critical loads panel directly adjacent 
>to the main service panel (in the next stud bay), must the neutral and 
>ground conductors be pulled into the new subpanel? or can only the hots be 
>pulled? Any Code references would be appreciated.
>
>--
>Corey Shalanski
>Joule Energy
>New Orleans, LA
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