Panel Board is Rated at 125A - How Much Load Can IG Handle?

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bm03801

Member
Location
Georgia
Occupation
Engineer
Hi all,

I have 125A rated lighting panel (16 slots) and was wondering how to determine how many breakers, and what sizes I can put in it. For example, can I have 6-60A double pole breakers or is that too much?**note this is 120/240V** This lighting panel is protected by a 200A rated main disconnect (separate of the lighting panel) with two 125A fuses. The lighting panel would feed six small sheds with their own lighting panels. I sized the cables from the disconnect to the lighting panel at 3#1,1#6 GND and the lighting panel to the shed’s lighting panel cables at 3#4 and 1#8 GND.Thanks!
 

kwired

Electron manager
Location
NE Nebraska
If panel is rated to have 125 amp breakers plugged onto it you could have 15 or 125 amp breaker on every space, or anything in between. You can't have total load exceed 125 amp rating of the panel though.
 

bm03801

Member
Location
Georgia
Occupation
Engineer
If panel is rated to have 125 amp breakers plugged onto it you could have 15 or 125 amp breaker on every space, or anything in between. You can't have total load exceed 125 amp rating of the panel though.
Can you please explain? You’re saying I could have any number of breakers that will fit as long as they’re 125A breakers or less?
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Max breaker size on any stab is 125A, you can have as many breakers as needed as long as the total load doesn't exceed the limit of the panel.
 

kwired

Electron manager
Location
NE Nebraska
Can you please explain? You’re saying I could have any number of breakers that will fit as long as they’re 125A breakers or less?
What I am saying is your panel likely rated to accept 125 amp breakers in any position. Just because you plug a 125 amp breaker in a particular position doesn't automatically mean that the connected load will be 125 amps, though there is good chance if you used a 125 it will be pretty significant load. Even if you put all 20 amp breakers in there (8 per bus if it is a 16 space panel) but only had 12 amps of load on each breaker you only have 12 x 8 = 96 amps of load and not 20 x 8 = 160 amps of load.

Plus you said this was a 125 amp panel - so you can't put total load of more than 125 amps on it, but at same time as long as nobody replaces the 125 amp fuses with 200's it is protected from overloading.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
Technically speaking, you can fill the sub-panel with all 60A breakers. However, in reality you have to figure out what the worst case scenario of what the actual loads are and make a determination as to whether the feeder fuses will not trip. You're not supposed to load a fuse or breaker to more than 80% of its value. 80% of 125 is 100A. In addition the loads for each shed are protected at a max of 60A. 80% of 60 is 48A

That said, I can't imagine that the lighting loads in your sheds are going to come anywhere close to the max amperage of your design, but I could be wrong IMHO.
 

kwired

Electron manager
Location
NE Nebraska
Technically speaking, you can fill the sub-panel with all 60A breakers. However, in reality you have to figure out what the worst case scenario of what the actual loads are and make a determination as to whether the feeder fuses will not trip. You're not supposed to load a fuse or breaker to more than 80% of its value. 80% of 125 is 100A. In addition the loads for each shed are protected at a max of 60A. 80% of 60 is 48A

That said, I can't imagine that the lighting loads in your sheds are going to come anywhere close to the max amperage of your design, but I could be wrong IMHO.
You can have 100% for non continuous loads.

Base rules for conductors and overcurrent protection are basically the same - 125% of continuous load plus 100% of non continuous load is minimum ampacity or overcurrent protection setting.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
What matters is the total electrical load on the sub-panel, not the total of breaker handle numbers.
 
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