tap rule

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pat1il

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A restaurant currently has a three phase service with #2 copper wire coming from the meter to a 100 amp main breaker. The restaurant currently is maxed out on its current load center but wants to install a 30 amp air conditioner.

Is it possible to tap before the main breaker into a fused subpanel to run the air conditioner. #2 copper should be able to handle 130 amps. Can I use #10 copper wire for the tap?

Is there anything that I am missing.

Pat
 
Re: tap rule

Service conductors are permitted to be tapped ahead of service disconnectings means as long as the tap is performed in an approved manner. #2 CU is actually only good for 115-amperes at 75?. You will have to perform a service calculation to determine the existing loads and how much you will be adding in.

Since this tap will be before the service main, the new panelboard will not be a "subpanel", but an additional service disconnecting means. This will require the equipment to be identified for use as service equipment.

If you are are only going to install a single branch circuit off this new service panel, the minimum rating can be as small as 15-amperes, so your #10 would be fine. If you plan on adding a panel that can be used for additional loads or more than one branch circuit, I feel the disconnecting means must be sized at least 60-amperes and you will need to install overcurrent protection and properly sized conductors for the load to be served.
 
Re: tap rule

I guess I was not precise. Can a 30 amp fused switch box for the air conditioner be tapped before the service disconnect (100 amp circuit breaker)?

The #2 copper wire from the meter runs about 50 feet to the service disconnect. Assuming that the current load center is practically maxed out (100 amps), will the #2 copper wire be overloaded if we tap it?
 
Re: tap rule

The 30-ampere A/C disco is permitted to be tapped ahead of the service main only if it is identified as service equipment. This bascially means it will need to be wired with each phase conductor and a service grouned (neutral) conductor that is bonded to the enclosure. See 230.66 of the NEC.

The #2 is only good for 115-amperes, so if you figure the current load to be 100-amperes, you only have 15-amperes of available load capability.
 
Re: tap rule

It would be less trouble and more benefiscal to upgrade the service to 200a. I know,these people don't have much money,and------.It sounds like the 100a service is just making it, do yourself and the customer a favor and fix it up properly.JMO

frank
 
Re: tap rule

Thanks, I think that the restaurant is going to have to upgrade to 200 amps or forget about adding additional ac. Not the answer hoped for, but that's life...
 
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