Can you tell the amperage of a panel by how many breakers it has.

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Eddy Current

Senior Member
I was wondering if there is a mathematical way of figuring the amount of breakers and if that will give the the amperage of the overall panel/main breaker?
 

kwired

Electron manager
Location
NE Nebraska
I was wondering if there is a mathematical way of figuring the amount of breakers and if that will give the the amperage of the overall panel/main breaker?
No.

First if you have a main breaker you will never load it beyond the rating of the main breaker (for very long anyway) and the main is going to trip. It will not matter one bit what combination of load breakers is installed once the main is overloaded it is going to trip.

If you have the allowed up to six mains current will be limited on each of the mains by the rating of those mains, but you could legally have a 600 amp rated panel with 6 - 200 amp main breakers (that comes to 1200 if evenly divided but yet there is no tripping) if the total load calculated using article 220 is 600 amps or less.
 

jeremysterling

Senior Member
Location
Austin, TX
IMO, the question in analogous to asking, "Can you tell how fast a car can go by how many wheels it has?"

The rating of the main breaker is determined by various factors including panelboard nameplate rating and/or tap rules.

The load rating in amps of the panel is determined by things like bus size, not breaker count or breaker size.

The actual load can be determined by amp clamp meter on the feeders. If you wanted to get theoretical and had time on your hands, you could validate Kirchoff's current law by measuring the load on each branch circuit and adding the (same leg) currents together.
 

Speedskater

Senior Member
Location
Cleveland, Ohio
If the question is: How much current is presently flowing through the panel, then a current probe/meter will give you an answer, but the reading will change minute by minute, day to night and summer to winter.

If the question is: What is the continuous rated current of the panel, then somewhere in the fine print on the panel label it's listed.
 

kwired

Electron manager
Location
NE Nebraska
If the question is: How much current is presently flowing through the panel, then a current probe/meter will give you an answer, but the reading will change minute by minute, day to night and summer to winter.

If the question is: What is the continuous rated current of the panel, then somewhere in the fine print on the panel label it's listed.
Easy way with main breaker panels is to look at the main breaker. Even if bus can handle more the main is still the limiting factor.
 

Eddy Current

Senior Member
If the question is: How much current is presently flowing through the panel, then a current probe/meter will give you an answer, but the reading will change minute by minute, day to night and summer to winter.

If the question is: What is the continuous rated current of the panel, then somewhere in the fine print on the panel label it's listed.


The question was a hypothetical, i was trying to remember if there would be a rating on the panel how do they come up with those ratings?
 

kwired

Electron manager
Location
NE Nebraska
The question was a hypothetical, i was trying to remember if there would be a rating on the panel how do they come up with those ratings?
I think you are trying to figure it the wrong way. You can easily have sum of branch breakers total well above the capacity of the panel. Majorrity of the time not all loads run continuously, not all loads run simultaneously, not all breakers are loaded to their maximum rating. The panel has a fixed rating it can handle. Common bus sizes are usually 125, 225, 400, 600, 800 ... Any size in between is limited only because of a main breaker whose setting falls in between.
 
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