FW: Gen Set / Xfer switch sizing [RE-wrenches]

[John McNicholas]

Dan,
First off I am not an electrician, but we get involved in gen installs here
in hurricane country - Florida. If you are backing up the main panel with a
gen, then the auto xfer switch must be rated the same as the service, since
all possible current coming into the panel is going through the xfer switch
first. 200 amp main breaker in panel - 200 amp xfer switch. There is no
requirement for the gen output to be as large as the switch or the service.
Rather than back up a whole panel, we often move critical circuits to a
subpanel - we can use a smaller xfer switch just for the subpanel, and size
the gen for those loads. If you back up the main panel with a smaller gen,
someone may have to perform load shedding when running on the gen since
there isn't enough power to run everything, which sounds simple but in
reality leads to problems. Here in FL, they are now requiring loads calcs
specifically for backed up loads, in an attempt to avoid overloading the gen
and tripping a breaker, leaving nothing running in non-occupied homes (which
we have lots of) that people presumed were backed up (but they aren't there
to load shed if they left too much running). 
Make sure the transfer switch you buy has a built-in gen starting battery
charger and a weekly gen exercise capability. 
John

John McNicholas

FL Solar Contractor
License - CVC56676
(239) 290-6040 cell
(239) 389-5497 fax
 
E-mail keypowerservices at comcast.net

Web www.keypowerservices.com 
 
____________________________________________________________________________
_________ 
-----Original Message-----
From: Dan Brown [mailto:Cvsolar2 at aol.com] 
Sent: Thursday, April 19, 2007 8:11 AM
To: RE-wrenches at topica.com
Subject: Gen Set / Xfer switch sizing [RE-wrenches]





hey everyone;
       I'm working on a stand by Gen Set (12k kohler) project for our local 
Fire Dept. one of the other members (w/ masters ticket) wants to use a 200
Amp 
auto Xfer switch (kohler) to automatically switch between line and gen set.
we 
figure the place should run just fine on about 8k. but it does have a 200A 
main entrance.
       issue is, there's another electrician (master ) , who says that the 
code says that the gen set must be rated at the same size as the xfer switch
-- 
i.e., 200Amp. 
       I've talked to a few folks -- they say they know there's exceptions
in 
the code for inverters, but have never heard of gen set sizing issues. 
       so, distinguished colleagues, any one ever heard of this issue?
pros?, 
cons? logic? any advice would be greatly appreciated? thanks db 

Dan Brown

Foxfire Energy
Professional Renewable Energy Systems 
Service, and Installation
(802)-483-2564
www.Foxfire-Energy.com


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