100A Service Panel with 3Main breakers

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  #1  
Old 03-15-16, 06:29 AM
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100A Service Panel with 3Main breakers

I bought an old house a few years back, that I have completely re-wired with the exception of the main service panel. The service panel has 100A stamped on the plaque, but it has 2) 50A breakers and 1) 40A breaker. It's also stamped with our utility provider (Central Maine Power) So I know the panel was installed by them.
Currently one 50A breaker services the new service panel I installed as a sub.
The other 50A is for the Stove (Restored, vintage 50A stove)
The 40A currently is empty, but I want to run service out to my barn, which is currently serviced by a 120V 20A branch circuit running from the sub. The barn is 100' wire length away from the service panel.

I have been trying to figure out since I moved in why the 100A service panel has 140A of breakers in it. Yes, I do plan on upgrading the service to the house in a few years to 200A underground service, but that's a few thousand dollars away.

The house has only ever had one meter, and no other breaker between the meter and the service panel.

Any thoughts on the panel or my plan to use the 40A breaker for the barn
 
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  #2  
Old 03-15-16, 07:00 AM
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The installed breakers can sum up to be more than the amp rating of the panel. The actual highest amp usage at one time should not exceed 100A. You can use the 40A for the barn but be mindful that the total load in-use at one time on the panel doesn't exceed 100A. You should consider putting in a new panel and maybe upgrading the service size sooner than later.

Did you run a 4 wire feeder to the new subpanel?
 
  #3  
Old 03-15-16, 09:23 AM
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Yes, I am running a 4 wire 8Ga. It was 1/2 price at Lowes, so I figured it was time to start this project. 74' of Direct burial in NM conduit. 30 feet inside on regular 8/3.

I know the sum of the breakers can and often is greater than the panels rating. I just can't figure out how the combination of the Main breakers can be higher than the panel's rating, and this is the way it was installed by the power company.

If you look at the connections inside the panel, you will see each pair of breakers is fed directly off the service feed.
 
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Old 03-15-16, 11:06 AM
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Residential services are designed with the knowledge that in a typical house, all of the appliances do not run all at the same time. Furnace, fridge, AC, sump pump, all cycle on and off as needed; residents only use appliances for a few hours of the day at most. It is also designed to take temporary overloads (less than 3 hours) for the rare cases (Thanksgiving dinner) when all the stove burners are oven are on high and all the lights and everything is on.
 
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Old 03-15-16, 11:31 AM
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Are those breakers even code compliant as two pole 240 volt breakers? No handle ties and obviously no common internal trip.
 
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Old 03-15-16, 11:46 AM
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Grandfathered, sure. They still would be ok for mains, just like fuses are. They really shouldn't be used as branch circuit breakers due to the lack of common trip, but it could be OK if you also provided a 2-pole disconnect like an AC pull-out somewhere in the circuit or a lock-out shackle on the box cover if it effectively covers the handles.
 
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Old 03-15-16, 07:21 PM
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What I will probably do then is get a small 100A sub panel, put two 50A Breakers in it, and connect it to the 50A Range breaker in the main panel. put the stove and the barn on the two 50 amp breakers in the new Sub. It's not likely the stove will be going full tilt when I'm in the barn, it has two ovens, and we have only used both of them once.

I will be upgrading the service to the house in a year or two. we would occasionally trip one of the legs on the main panel if we used the oven and the dryer together when they were running of the same 50A line. Since it trips asymmetrically, all kinds of weird things would happen with the electronics and whatnot in the house!

The house runs pretty well off one 50A breaker after I moved the stove to the other one. It hasn't tripped since!
 
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