How to size main disconnect.

[Liteitup]

I want to install a main disconnect for a group of 7 meters in a building. (6 apartments and 1 common) How do I size the disconnect? Fusible or breaker? Interrupt Rating? Any suggestions?

 

[ericsherman37]

I usually size things with a tape measure.

HA! Thank you thank you, I'll be here all week.

No seriously though. Is your "main disconnect" a service disconnect? I suspect that it probably is. If so, it needs to be sized not less than the load to be served.

That, sir, would require a load calculation. Check out NEC Article 220 for calculation stuff and Article 230 for requirements for services, including disconnecting means.

 

[IamJonscranium]

I think we need more info... The only answers I can see giving are "see section xxx in the code" as posted above, or going through the details of sizing a breaker.

{Moderator's Note: Removed statements that questioned another member's credentials}

 

[Dennis Alwon]

I want to install a main disconnect for a group of 7 meters in a building. (6 apartments and 1 common) How do I size the disconnect? Fusible or breaker? Interrupt Rating? Any suggestions?

What is your calculated load?

 

[don_resqcapt19]

Where are the disconnects for the 7 panels?

 

[malachi constant]

If this is a service with utility-owned meters, then in addition to the code references mentioned by others I recommend coordinating with the metering department of your local utility. They may take issue with a disconnect ahead of their meters, esp in front of the house meter.

Just basing that on my many experiences with one utility (Xcel). Not sure how other PoCos handle services to apartments.

 

[Buck Parrish]

I want to install a main disconnect for a group of 7 meters in a building. (6 apartments and 1 common) How do I size the disconnect? Fusible or breaker? Interrupt Rating? Any suggestions?

If the owner knew of the cost of adding the 7th meter. He or she may figure out away to install the common areas to the 6 other panels. If allowed.
The PC may provide out door lights at a monthly flat rate.

 

[IamJonscranium]

If this is a service with utility-owned meters, then in addition to the code references mentioned by others I recommend coordinating with the metering department of your local utility. They may take issue with a disconnect ahead of their meters, esp in front of the house meter.

Just basing that on my many experiences with one utility (Xcel). Not sure how other PoCos handle services to apartments.

It seems as though each utility is different. Some prefer the meter upstream of the disc, some downstream. You are correct, the utility should be contacted.... unless OP is the utility


Fused or breaker depends on your preference. Fuses operate over a time by heating up due to the overcurrent. Breakers are an instantaneous device primarily to handle fault conditions.

I *believe that if you purchase a service entrance rated disconnect, that will take care of your interrupt rating.

 

[don_resqcapt19]

...
Fused or breaker depends on your preference. Fuses operate over a time by heating up due to the overcurrent. Breakers are an instantaneous device primarily to handle fault conditions. ...

Standard breakers are thermal magnetic and provide short circuit, ground fault and overload protection.

 

[raider1]

I *believe that if you purchase a service entrance rated disconnect, that will take care of your interrupt rating.

Interrupting rating is part of the overcurrent protective devices rating not the disconnect rating. The fuses or the breaker must have an AIC rating equal to or greater than the available fault current at the disconnecting means.

The disconnecting means must have a short circuit current rating that is equal to or exceeds the avaliable fault current.

Chris