Total Amperage in a circuit breaker panel

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Trovmar

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Hi guy's i have asked this question to about every electrician i know and no one has given me a straight answer. Here it is, how do you know how much amperage you can use from the cb panel? Maybe thats not clear enough, let's say you have 100 amp service and all the breakers are in. There are no empty slots, how do you know you can add let's say a couple of tandem breakers for some more circuits. Is there a formula to figure this out? Today a customer asked to add a 20 amp GFCI to the back yard. There was 100 amp service and when you add all of the breakers ratings up they equal 315 amps. Is this ok? And also can i add another 20 amp circuit by removing a 20 amp breaker and installing a tandem with two 20 amp circuits? Please help:confused:
 
Trovmar said:
Hi guy's i have asked this question to about every electrician i know and no one has given me a straight answer. Here it is, how do you know how much amperage you can use from the cb panel? Maybe thats not clear enough, let's say you have 100 amp service and all the breakers are in. There are no empty slots, how do you know you can add let's say a couple of tandem breakers for some more circuits. Is there a formula to figure this out? Today a customer asked to add a 20 amp GFCI to the back yard. There was 100 amp service and when you add all of the breakers ratings up they equal 315 amps. Is this ok? And also can i add another 20 amp circuit by removing a 20 amp breaker and installing a tandem with two 20 amp circuits? Please help:confused:
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Trovar you can have a circuit breaker for every receptacle in the house and that will not change the load.

You would have to do a load calculation. I can't imagine that adding a 120 volt GFCI recep would be a problem but you never know.:smile:
 
You Have To Be Careful With Tandem Circuit Breakers If You Have Class Ctl Assemblies You Have To Use A Breaker Listed For A Ctl Listed Panel. Non Ctl Rated Circuit Breakers Are Rated For The Old Style Non Ctl Equipment. And Are For Replacement Use Only. Your Panel May Be Rated For A Max Of 20 Circuits And Installing A Non Ctl (cheater Breaker) Will Void The Listing Of Your Equipment.
 
SEO said:
. Your Panel May Be Rated For A Max Of 20 Circuits And Installing A Non Ctl (cheater Breaker) Will Void The Listing Of Your Equipment.
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i don't know that it would "void" the listing of the panel but it would be a code violation.
 
SEO said:
You Have To Be Careful With Tandem Circuit Breakers If You Have Class Ctl Assemblies You Have To Use A Breaker Listed For A Ctl Listed Panel. Non Ctl Rated Circuit Breakers Are Rated For The Old Style Non Ctl Equipment. And Are For Replacement Use Only. Your Panel May Be Rated For A Max Of 20 Circuits And Installing A Non Ctl (cheater Breaker) Will Void The Listing Of Your Equipment.
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"Replacement use" does not mean that they can be used in any "old" loadcenter. The load center must still be rated for tandem breakers. I know that the CTL requirement has been in existence for at least 30 years, so non-CTL should be only used in really really old loadcenters.
 
I had the same question when i started my career. The best analogy i heard is the checking account.

You have a checkbook (breaker panel) and your checking account (incoming service). Now just because you dont have any more checks left in your check book, you may still have money in the account. THis also works in the opposite, you may have checks left in the checkbook, but you cant write a new check without having the funds in your account.
 
"but you can't write a new check without having funds in your account."


I've been telling my wife this for years.
 
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