Adding circuits in an existing panel

[StevieP007]

I'm having trouble finding a code article regarding extra circuit breakers in an existing panel.

I know art.408.15(2002NEC) says no more than 42 OCD shall be installed in any 1 cabinet. Is there a rule of thumb or code law that limits the amount of mini's or sub-main breakers that you can add?
As an example; you go into an existing restaurant or small store, and it's Main panel is a 100A 20 ckt panel. of course,over the years, lights,plugs, and machines are added, so what do people do? when the breaker slots are all full, they throw in minis. if the total load on that small store is under 100A, the main will not trip. How do you know if adding another mini will overload the panel, and if you amprobe the mains and you're under the rating or the busbars, is it acceptable?

Thanks in advance

 

[charlie b]

Re: Adding circuits in an existing panel

A one-time reading with an amp-probe will not be sufficient. Article 220.35 has a discussion of adding load to an existing facility. You either use 12 months of utility records, or you can take a 30 day load reading at the panel. Multiply the peak load observed during that period, add 25%, and then add your proposed new load. If you are still within the panel?s rating, you can add the load.

 

[StevieP007]

Re: Adding circuits in an existing panel

Thank you so much CharlieB

I really appreciate it. I looked through 408,240, and 220, obviously I breezed over 220.35

Have a good day

 

[mc5w]

Re: Adding circuits in an existing panel

A panelboard also cannot have more circuits than for what is was designed. If it was only designed for 20 circuits you cannot put in more using twin circuit breakers.

Some companies make twin circuit breakers for use in old panels that were built before the circuit limiting feature was required.

 

[electricmanscott]

Re: Adding circuits in an existing panel

Originally posted by mc5w:
Some companies make twin circuit breakers for use in old panels that were built before the circuit limiting feature was required.

Also most, if not all companies make panels that are designed to take twin breakers. Example: a panel may take 30 full size breakers or 20 full size and ten twins. A good option when you need more circuits but there is limited space to place the panel.

[ March 24, 2005, 06:42 AM: Message edited by: electricmanscott ]