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Joined: Jul 2004
Posts: 136
cgw Offline OP
A service with a main distribution panelboard with a main circuit breaker and 6 or less feeder circuit breakers. Is the main circuit breaker redundant, a potential weak point, or a good idea?
(assume no need for future expantion)

Joined: Jan 2005
Posts: 5,316
Cat Servant
I have encountered this situation twice recently.

One was a strip mall where the owner wanted to divid his largest space. This project became untenable, simply because of the work that would be required to separate / upgrade the electric for the new spaces. In building the strip mall, every trick had been used to keep the required meters / disconnects to a maximum of six - and adding the main disconnect that additional meters would have required in turn meant the wholesale replacement of the entire switchgear.

In hindsight, it would have been far better had the main disconnect been included at the start. That's what happens when you use the NEC as a design manual!

The other job was the opposite situation; I added a 'main' before just one service. Why? Because there are plans to add two more, and having the disconnectwill make the future work much easier to do.

IMO, a good design allows for future uses, and makes provisions for future maintenance work. While a good design is almost certain to meet code, a 'code minimum' design may be poor design.

Joined: Aug 2006
Posts: 356
I will echo what reno said, do a good design that is practical for now and plan for future.

Be kind to your neighbor, he knows where you live

Joined: Jul 2004
Posts: 136
cgw Offline OP
In my case it is a single owner building with the meter before the MDP. Right now 5 feeders out of the MDP. There is space for for a feeder circuit breaker large enough for any conceivable addtion. (that would bring it up to 6 if it ever happened). Is there any good reason to have a main circuit breaker in the MDP.

Joined: Jan 2005
Posts: 5,316
Cat Servant
Heck yes.

First of all, that main disconnect is another place you can add a fuse - one way to keep track of problems. There's no way that feeder can supply everything to maximum load.

Secondly, the main disco gives you a way to work on the system without having to cut the PoCo wires at the weatherhead.

Here's a pic of a place that just kept growing:

[Linked Image]

Last edited by renosteinke; 08/30/09 02:21 PM.
Joined: Jul 2007
Posts: 85

Joined: Nov 2005
Posts: 826
What about the advantage of knowing what your overcurrent protection is by the size of your main breaker or fusing?

Joined: Jan 2005
Posts: 5,316
Cat Servant
Depends upon WHERE the main disco is located. If it's on the PoCo side of the meters, you won't have access to the fuses.

Joined: Mar 2003
Posts: 849
Point of Info.
230.90 (A) Exception # 3.
Allows the six disconnects to total more then the service conductors ampacity.(see calculated load requirements).
Example service conductors good for 3200 amps with six
600 amp breakers . This is done quite often so the GFI rule does not come into effect.(230.95)

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