[RE-wrenches] Busbar rating with multiple main breakers

[William Miller]

Eric:

 

Here is another distinction to make:  

 

1.    In PG&E territory, the largest service that is direct metered is 320
amps (continuous).  This may be likely in many other areas.

2.    Above that, the metering is all done with CTs (current transformers).


3.    If you pull a direct meter, you disconnect the feed to the service.  

4.    Fire responders and line workers will pull the meter as a foolproof
way to disconnect a service.

5.    If you pull a CT meter, you do not disconnect the service.

6.    If you have a CT service and a grid-interactive system in PG&E
territory (and likely many other utilities) you have to install a locking
disconnect within 10 feet of the service disconnecting means that
disconnects the grid-tie or the entire feeder.

7.    The information above was derived from many sources and should be
verified.

 

The service you are describing is likely a class 320 direct metered service.
Here is a link to information on a common variety.

 

http://www.hqs.sbt.siemens.com/gip/general/dlc/data/assets/us/SIILV/Brochure
_400A_Combinations_Siemens.pdf

 

I hope this information helps (and is not something you already knew).

 

William

 

 

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Chris Mason
Sent: Thursday, December 19, 2013 2:41 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Busbar rating with multiple main breakers

 

The 120% rule refers to source breakers, not load breakers. 

 

On Thu, Dec 19, 2013 at 3:16 PM, SunHarvest <eric at harvesthesun.com> wrote:

Hi guys -

 

Concerning the 120% rule: I've encountered several circumstances recently
where a 400A nameplate-rated (listed on inside label) main panel has two
200A main breakers. One of the breakers will be feeding the busbar in the
main and the other will feed a subpanel. I had previously thought the main
busbar is rated at the nameplate rating (400A in this case) regardless of
quantity of main breakers. My lead electrician says the main busbar in these
types of panels is derated to 200A because of the split. However, I have two
other reliable electrician friends who disagree with my lead electrician.
One of my C10 buddies says it depends on whether or not the busbar in the
main is broken up into 2 sections (200A) or it is continuous (400A). Can
anyone clear up, beyond doubt, our disagreement?

 

Thanks!

 

Eric Stikes
SunHarvest

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