Maximum branch breaker size?

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e57

Senior Member
How can I figure out the limit of the main-panel. The labels are destroyed. The main barker is 100A.
You say the main is 100? - then its 100A. Are you looking to change the breaker to something larger? What are you looking to accomplish? The original wire size and insulation if rated for over a 100A may be the limit in this case - if looking to change both the breaker (MOCP), and SECs you may have to do some more research on what make, and model you might have. The breaker 'should' give you a clue to the make - start there... As for max branch - I have seen several at 80a for either one side of a stab or combined both.
 
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Dennis Alwon

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Location
Chapel Hill, NC
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Retired Electrical Contractor
I have worked on 100A Murry main panels that stated maximum branch circuit = 50A. I believe this limitation is not related to ?load calculations?.

I am sorry I missed the heading on your post. I believe in the newer panels a 100 amp breaker is allowed with a 100 amp panel. I have not noticed the restriction on older panels.
 
125% x continuous loads
100% x non-continuous loads


If this is a residential location, most likely you do not have continuous loads in the building.


If you mean, how do you find the loads of the other breakers installed in the panel, you could take a meter and record the loads over several days.
Or
Take an educated guess based on the existing loads.


If
You are wondering if the 100A breaker is going to hold, unless it has tripped, it is holdiing.
 

toaduu

Member
I think my question is not clear.

I think my question is not clear.

Thank you all. I think my question is not clear. I always read the main panel labels before adding any branch breakers. Many cheep main panels I have worked on state a maximum branch breaker rating of 50A. I believe this limitation is due to the breakers socket maximum amperage limitations.

I want to add a 60A branch circuit but the socket rating may only be good for 50A.
My issue is that I can’t read the label so I am unaware of the breakers socket rating.
 
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I looked at a 100 amp rated buss panelboard and a 225 amp rated panelboard in my stock. On the sticker it states maximus size of horizontal breaker to not exceed 100 amps. Which I belive is a moot point sice the biggest size sub breaker they make is a 100amp. These however are panelboards and Im sure have higher ratings that a loadcenter type panel. I hate to say this but since the identification is not there you really should get a new panel, not sure thats a possibility but better safe than sorry.


I will have to look at some loadcenters on my travels and see if there are max sub breakers numbers listed
 

e57

Senior Member
Thank you all. I think my question is not clear. I always read the main panel labels before adding any branch breakers. Many cheep main panels I have worked on state a maximum branch breaker rating of 50A. I believe this limitation is due to the breakers socket maximum amperage limitations.

I want to add a 60A branch circuit but the socket rating may only be good for 50A.
My issue is that I can?t read the label so I am unaware of the breakers socket rating.
What make and type of panel? Many of the older BR styles like Westinghouse, CH, Bryant don't have max sizes in excess of the total panel rating in the larger sized panels or main combo's - but some do.... On the same note a lot of the smaller sub-like panels like say a 12/24, or an 8/16 would have a greater chance of having a limit of 80A usually, only from memory have I noticed possibly one or two with a 70A or 50A limit on a BR style - but FPE would have a 50A limit most likely. Never noticed a branch max on a SqD QO, and am sure I have not seen one on any QOB, or other bolt-on type panel of any make.
 

frizbeedog

Senior Member
Location
Oregon
Thank you all. I think my question is not clear. I always read the main panel labels before adding any branch breakers. Many cheep main panels I have worked on state a maximum branch breaker rating of 50A. I believe this limitation is due to the breakers socket maximum amperage limitations.

I want to add a 60A branch circuit but the socket rating may only be good for 50A.
My issue is that I can’t read the label so I am unaware of the breakers socket rating.

Right...You may be limited on the rating of the buss in the panel in regards to maximum allowable circuit breaker you may install. Most panels list that rating...but you have no label. Now what?
 
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