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Thread: House electrical Main breaker question

  1. #1
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    House electrical Main breaker question

    A question about the main breaker in a house breaker panel. I googled and found no real answer. For a big one say 100-200 amps is it actually a breaker? Or is it just a switch. I always called it the main breaker but that is just the vocabulary I learned over time. If it was a fuse block it would be called a disconnect since it is physically pulled out and totally disconnected. It does not really matter either way I would just like to know.
    I have a Square D circuit breaker on my desk right now. I see nothing that says it is a overload breaker. Just the maximum amps it can disconnect about 10,000 and it meets FCC regulations about interference.
    Bil lD
    Last edited by Bill Dufour; 01-10-2021 at 1:58 AM.

  2. #2
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    It is a breaker or as you said an overload breaker. It will trip if overloaded or surged. A disconnect can also be a nonfused circuit interrupter. No fuses in the disconnect.
    Last edited by John Terefenko; 01-10-2021 at 2:15 AM.
    John T.

  3. #3
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    The 10,000A is a reference to the maximum short circuit that the supply can deliver. If the service has a short feeder length from a large transformer, then the short circuit current could be very large, even hundreds of thousands A. A 10KAIC breaker might explode or otherwise pose a safety problem if it is called upon to interrupt a short circuit higher than 10,000A. Most residential services are much less than 10,000A short circuit capacity.

  4. #4
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    Some HVAC and water heater disconnects are just a switch for the serviceman and some have an over current feature. On Square D breakers the current rating is on the tip of the lever. Those large 100 or 200 ones are breakers, the rating is per leg.

  5. #5
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    Quote Originally Posted by Frank Pratt View Post
    The 10,000A is a reference to the maximum short circuit that the supply can deliver. If the service has a short feeder length from a large transformer, then the short circuit current could be very large, even hundreds of thousands A. A 10KAIC breaker might explode or otherwise pose a safety problem if it is called upon to interrupt a short circuit higher than 10,000A. Most residential services are much less than 10,000A short circuit capacity.
    Yes, mine is approximately 2,300 amperes on a 100 ampere service. My panel is approximately 18 metres from the transformer...Rod

  6. #6
    If it is not a breaker, it will be marked as a "Molded Case Switch" it provides no overcurrent protection if a MCS. The standard AIC, Ampere Interrupting Capacity is 10,000, the next is 22,000, then 42,000, 64,000, the price of the breakers escalates with each increase of AIC. A lot of newer residential panels come with a 22K, AIC rated main as standard now.

  7. #7
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    I always thought it was just a switch. Good to know, thanks for the info. It does explain why they cost so much. I also thought folks who wired in a big breaker and back fed it as the main breaker were rednecks. Now I am not so sure.
    Bil lD

  8. #8
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    Go to a store that sells electrical items and ask them.

  9. #9
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    Quote Originally Posted by lowell holmes View Post
    Go to a store that sells electrical items and ask them.
    His question has already been answered.

  10. #10
    Quote Originally Posted by Bill Dufour View Post
    I always thought it was just a switch. Good to know, thanks for the info. It does explain why they cost so much. I also thought folks who wired in a big breaker and back fed it as the main breaker were rednecks. Now I am not so sure.
    Bil lD
    Some panels have a back fed breaker on the branch bus as their main. It has to be mechanically fastened to the panel so it can't be pulled out like a regular breaker. They don't seem as common as panels with a dedicated main anymore though.

  11. #11
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    Quote Originally Posted by Andrew Seemann View Post
    Some panels have a back fed breaker on the branch bus as their main. It has to be mechanically fastened to the panel so it can't be pulled out like a regular breaker. They don't seem as common as panels with a dedicated main anymore though.
    Almost all residential panels I've installed use a conventional breaker that is back fed through to the buss bars. It's still the most common configuration.

  12. #12
    My house has a switch of some kind where the power enters the house and that feeds to two boxes in the house. One with a main for the residential part of the house and another box with a main for the shop area..

  13. #13
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    The code since about 2000 says something like a disconnect switch for the whole house must be near the power meter if the cable run to the main panel is more than 10ft. Once you run the cable up to the ceiling height and then down to the panel it will be over 10ft so basically the interior main panel has to be on the same wall as the power meter or you need a disconnect. I put two 200 amp panels on my previous house and had two disconnects outside. I used 200 amp breakers.

  14. #14
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    The 2020 NEC now requires an exterior disconnect switch for all houses. The 2020 NEC is only in effect in eight states so far. I installed one on my house back in October even though the 2020 NEC was not yet in effect. I was replacing the meter base so I decided to add the disconnect because future plans might require it.

  15. #15
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    Does just a main breaker in the panel next to the meter meet that new code? Sounds like it does to me.
    Bil lD

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