Main Service CB - Electrician's Opinion

[Gshell82]

I am wondering if it is more practical/cheaper to have a separate external Main Circuit Breaker for a new service or to a have a Service Rated Panelboard with a MCB as the main disconnect instead?

Is there a benefit one vs. the other, maybe ease in ordering equipment for the electrical contractor?

 

[Dennis Alwon]

Cost could be a factor and obviously, 2 panels will cost more than a single panel. The advantage to having a separate service disconnect is that the sub panel can then be installed in other locations rather than directly inside the structure from the meter.

 

[Gshell82]

ok thanks. The location of the panel isn't a concern in this application. So I guess cost wise it's best to have the MCB integral to the Main panel.

Also, would you just then ground the Main panel similar to how you'd ground the separate external MCB?

Thanks

 

[Dennis Alwon]

Yes, only the main service panel gets the grounding electrode conductor's so if you have an exterior then that one gets those conductors. If the main service panel is the one inside with other circuits in it then that panel gets the grounding electrode conductor's.

No equipment grounding conductor is required to the main (service) panel.

 

[wbdvt]

The other factor to consider is the arc flash hazard. With the main breaker installed in the same panel, it has to be ignored in the analysis for incident energy which leads to a high incident energy level on the main panel. Having a remotely mounted main breaker allows for that breaker to be considered the interrupting device for an arc flash on the main panel.

 

[Gshell82]

at what type of fault current levels does this become an isssue?

IE - this current project is a 2 level apartment building with basement and attic. roughly 4,000 sq. ft. per level.

My very rough estimate at this point for the available short circuit current is 6,800A