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Can I have a main circuit breaker in the basement & also in my apartment?
* There is a main circuit breaker for my apartment in the building basement.
* The apartment has a circuit breaker panel in the apartment but here is no main circuit breaker in the apartment panel box.
Question: In addition to the main in the basement, can I have a main installed in the apartment circuit breaker box so that in he event of an overload, the main in the apartment will trip and I would not have to go to the basement?.
Can I have a main circuit breaker in the basement & also in my apartment?
* There is a main circuit breaker for my apartment in the building basement.
* The apartment has a circuit breaker panel in the apartment but here is no main circuit breaker in the apartment panel box.
Question: In addition to the main in the basement, can I have a main installed in the apartment circuit breaker box so that in he event of an overload, the main in the apartment will trip and I would not have to go to the basement?.
Thank U
depending on the panel it may be main lug only in which case it can't take a main breaker kit . the whole panel would have to be ripped out to do it right .
the main in the apartment would have to be sized quite a bit smaller so it trips before the basement which may not let the apartment get enough power at times .
There is no hard and fast rule other than that the upstream circuit breaker should be at least one frame size larger than the downstream circuit breaker. What the ratio actually turns out to be in a specific application is dependent on the electrodynamic withstand capability of the upstream circuit breaker, the peak current (Ip) let through by the downstream circuit breaker and the available short circuit current where the downstream circuit breaker is located.
this is likely not worth doing
Last edited by mathjak107; 11-29-2019 at 02:28 AM..
I would be content to have the in-apartment lines to be separate and lower amp rated. That way if anything overloads only that leg of wiring will trip out. A simplified example: 100 amps downstairs and six 15 amp breakers upstairs (to make a point.)
If your upstairs breakers are working you should never trip the downstairs breaker.
I would be content to have the in-apartment lines to be separate and lower amp rated. That way if anything overloads only that leg of wiring will trip out. A simplified example: 100 amps downstairs and six 15 amp breakers upstairs (to make a point.)
If your upstairs breakers are working you should never trip the downstairs breaker.
Not quite as easy .this is called breaker coordination.
The code has standards that need to be met in breaker coordination....there is a time curve factor that determines how de-rated the main downstream has to be reduced to ...it is a lot smaller then the upstream and I mean a lot . It is based on how fast the downstream breaker can get off line compared to upstream ...it is very complex ...because we are not dealing with over current issues , we are dealing with massive short circuit potential it is not as easy as just use slightly smaller breakers .
Do you consider a 15 amp breaker only "slightly smaller" than a 100 amp breaker?
he is talking adding another main breaker not branch breakers to the 2nd panel. breaker coordination is done a lot of times but it is governed by code and trip times unlike fuses which are coordinated by amperage rating and fuse type .
Last edited by mathjak107; 12-01-2019 at 07:14 AM..
Do you consider a 15 amp breaker only "slightly smaller" than a 100 amp breaker?
breakers are typically thermal / magnetic and provide both short circuit protection and over current protection ... the 15 amp breaker vs a 60 amp breaker tripping sooner applies to just over current not the short circuit protection time curve ...they are two different things ......
in a short circuit , .if the same type of breaker is used but just different amperage , they both carry the same aic interrupting rating of stopping 10,000 amp .( all resi is 10k aic ) in half a cycle
so the short circuit interrupting times usually have to involve two different breaker styles that are used as mains . in other words i won't have proper short circuit protection if both main breakers or even branch breakers are the same type . as an example all murray mp breakers regardless of current rating or all ge thql breakers carry the same short circuit rating regardless of their over current ratings .
so the time curve of a breaker for over current may be a 500% overload beyond it's rating for 30 seconds before tripping . that is pretty slow . on the other hand that breaker needs to interrupt up to 10,000 amp in a short in half a cycle . that is incredibly fast.
so the code requires the down stream main curve to trip before the upstream curve in a short ...see the difference ?
do you need me to explain the difference between short circuit fault currents vs over current conditions ? that is key to understanding so you understand why just using a smaller breaker will not stop a short from popping the upstream breakers ......
Last edited by mathjak107; 12-01-2019 at 07:16 AM..
Do you consider a 15 amp breaker only "slightly smaller" than a 100 amp breaker?
this is about the easiest explanation i could find as to why it is not as simple as just use a smaller amperage breaker down stream . that only effects over current not short circuits which are determined by the breaker type not the amperage rating since all residential plug in breakers are the same 10,000 aic with the same instantaneous trip curve . .
If all residential breakers are the same 10,000 aic, why are we quibbling?
We aren’t ,, what I said is he can’t just use a smaller amperage breaker in the apartment...he needs to see first what the model number is on the main breaker in the basement .. then he needs to get an instantaneous trip curve ....then he needs to see if there is a main kit available that can fit in the apartment panel .. most panels in apartments are not convertible and there is no kit ....
If there is no kit then he is done ...there is nothing he can do... if there is a kit he needs to check the trip curve to see if it is shorter .
He is likely out of luck here as in residential apartments there is not a lot of breaker coordination you can do.
When you are going to have a another main breaker down stream that you want to protect the up stream these are highly sophisticated engineered projects .....
Last edited by mathjak107; 12-02-2019 at 11:20 AM..
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