Panelboard current rating
Panelboard current rating
(OP)
If I have a 400 amp panelboard, what is the highest combination of breakers I can possibly have? Is there a formula? Would I be able to have say 5 100 amp breakers in a 400 amp panel?






RE: Panelboard current rating
RE: Panelboard current rating
If I have a 400 amp panelboard,
///This size or frame of panelboard is overlapping switchboard size. There is a difference between the panelboard and switchboard.\\\
what is the highest combination of breakers I can possibly have?
///There is not really limit theoretically. Practically, there are often as many as needed by the downstream power distribution.\\\
Is there a formula?
///The number of the circuit breakers increases as their frame goes down, e.g. down to 100A frame\\\
Would I be able to have say 5 100 amp breakers in a 400 amp panel?
///Yes, especially if they have 100A frame, i.e. 100AF.\\\
RE: Panelboard current rating
jthjr, that is the basic idea behind load diversity. It is fairly common that the sum of ratings in branch breakers in a panelboard to be greater than the main bus rating.
RE: Panelboard current rating
1. If the 400-amp panel has 400-amp protection ahead of it, the panel can have any combination of circuit breakers totaling up to 4200 amps (42 branch circuits, each at 100 amps). (This assumes the panel is one typical 42 circuit branch panel with 100 amp maximum branch circuit breaker frame sizes.)
(The 42-circuit limitation is for "mixed load" panels serving lighting and other loads. If the panel does not have any lighting loads, there is no limitation on the number of circuits (and hence circuit breakers) in any given "panel". Functionally however, panels are manufactured with a maximum of 42 circuits. Panel boards with greater than 42 circuits are comprised of one or more normal panels connected in series or parallel. In this instance, with a number of parallel panels all connected electrically as a "single panel", there is theoretically no limit to the number of panels, and circuits.)
2. If the panel is to provide overcurrent protection where a main disconnect is required, AND where the main disconnect is provided by using the six disconnect rule, then there IS a total sum of the handle rating limit.
For example: a separately derived system requires a 400 amp overcurrent protection on the secondary side; a 400 amp main lugs only (no single main overcurrent device installed ahead of the panel)panel is used. Up to a maximum of six handles (6 separate circuit breakers)can be used as long as the sum of their ratings does not exceed 400 amps total; e.g., 5 circuit breakers at 20 amps, 1 circuit breaker at 300 amps.
3. You would have received a lot more answers to this question had it been posted under the "IEEE (electrical) Code Issues" forum.
RE: Panelboard current rating
e.g. visit
http://www.ecmweb.com/ar/electric_sizing_circuit_breaker/
for: Circuit Breaker Sizing),
then 5 x 100A x 0.8 = 400A which is the main circuit breaker nominal rating. However, the main 400A circuit breaker should not be loaded more than 0.8 x 400A = 320A. This would leave 4 x 100A x 0.8 = 320A or four 100A circuit breaker limit rather than five 100A circuit breaker limit.
RE: Panelboard current rating
Your commentary on the derating of circuit breakers is partially correct (for long continuous loads), is incorrect for "100% rated" circuit breakers, and is hardly germane.
I illustrated an example where THERE are limitations on the "sum of the handles".
RE: Panelboard current rating
1. secondary overcurrent protection for a transformer, where the sum of the breaker ratigns must not exceed the rating required for a single device.
2. services, where the sum of the breaker ratings must be adequate to carry the total load as calculated per Article 220.
RE: Panelboard current rating
" For a panelboard to be considered for lighting and appliance branch circuit more than 10% of the overcurrent devices must be rated for 30A or less"
Any guesses as to where it might have come from?
Checkout the above website at:
http://www.sea.siemens.com/step/templates/lesson.mason?pan:1:3:5
RE: Panelboard current rating
Please, notice that 100% rated circuit breakers still may be derated because of ambient temperature, altitude, harmonic currents, unbalanced currents, etc.
Visit
http://www.sea.siemens.com/speedfax04/sec06/06-54_55.pdf
for 80% and 100% rated circuit breakers. 100% rated circuit breakers are more expensive and not every circuit breaker manufacturer offers them.
RE: Panelboard current rating
Further, "A power panelboard is one having 10% or fewer of its overcurrent devices protecting lighting and appliance branch circuits."
Lighting and appliance branch circuit panelboards are required to have dedicated overcurrent protection. Power panelboards are not.
RE: Panelboard current rating
Panelboard. A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front.