PanelBoard size calculation

[electricaleng30]

Hey all,

We have a 150A breaker feeding 2 sub panels at our plant. Those 2 sub panels are full and have a certain rating on them for capacity in amps and lug rating(which I don't have on hand right now, but is irrelevant to my question). What I would like to know, is how do you go about determining the size of those sub panels (calculations)? How would you know, if you wanted to add other sub panel on a specific service breaker, whether or not that panel is the right size or not when compared to the breaker feeding that panel? Maybe its me not being familiar enough with the terminology, but there is a bit of confusion as to how one goes about determining all the appropriate information to size a panel from the service amperage, to the breaker size and so on. Any technical information on that subject would really be appreciated. Thanks.

 

[waross]

The NEC and CEC have basic procedures for determining loads on panels and services.
Under the CEC, you may increase the loading if you can show the inspection department that there is adequate unused capacity on the breaker or service, based on load recordings over a period of time acceptable to the inspection department.
For service load increases, the maximum demand as shown by the revenue meter is often acceptable. Even though your plant may not be on a demand schedule, the meter may retain maximum demand information.
respectfully

 

[alehman]

The NEC also permits use of metering as a baseline for adding loads to existing systems in some situations.

For "lighting and appliance branch circuit" panelboards as defined by the NEC, you must provide overcurrent protection based on the panel bus rating. Panelboards not fitting that definition do not have that requirement. In that case, the bus must be sized at least for the load.

You should probably grab a copy of the applicable code book and read the sections on feeders, overcurrent protection and panels.