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I just found out my parents breaker box is 200 amp in there mobile home but the underground electrical service line is 100 amp. The mobile home park has existed since 1979 and landlord has said electric line has never been upgraded. I am not sure if the meter box outside that does 4 mobile homes at once has a 100 amp shutoff, if it does than the indoor 200 amp breaker box shouldn't be a problem. They have lived in the mobile home for over 10 years and hasn't any problem with it.

I do believe they have never used over 100 amps at once. I have already told there landlord that the breaker box needs replaced to 100 amp or the underground wire needs upgraded to 200 amp wire and there landlord has already given me attitude and refuses to do anything about the problem.

I only have an issue with it since they do have all electric heat and because of that it should be a 200 amp service line. Its a tiny mobile home, so 100 amp line should be enough. I want professional opinion on the problem.

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    Can you just replace the main breaker from 200A to 100A? You shouldn’t have to replace anything else in the box. – kponz Oct 7 '18 at 3:33
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    What make and model is the breaker box? Can you post the square footage of the mobile home, and how many watts or BTUs of heat they have? Also, is there an outdoor shutoff? That matters quite significantly in this case. – ThreePhaseEel Oct 7 '18 at 3:45
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    Is there a main breaker somewhere before the breaker box? If that is 100A, then all is good. How did you arrive at the 100A rating for the underground service line? Is this before your electric meter? – Harper - Reinstate Monica Oct 7 '18 at 9:13
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    Is the breaker box rated for 200A but has a 100A breaker? Or is there a 200A breaker on it? – mmathis Oct 7 '18 at 14:56
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    @ThreePhaseEel What I know is the electric baseboard heat is on 2 breakers that total 60 amps, but also there are multiple high amp breakers on the breaker box, there is also a 50 amp breaker for the dryer/stove , 30 amp breaker for the water heater. I just had to check to see if there is a outdoor shutoff and there is a 100 amp shutoff breaker outside on the meter-box. The Outside 100 amp shutoff breaker has never tripped , so I am sure they are probably never using over 100 amps of power at once. – Michael Weaser Oct 7 '18 at 16:16
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Service lateral

The service lateral (underground version of the service drop) before the meter is the power company's responsibility. They have a smart meter on it. They know what is installed in the ground (it could be #4Al for all we know) and they know when you draw on it hard enough to cause thermal problems or voltage drop. So go ahead and install your Bitcoin miners and horticulture lights if you're in a state that's into that... The power company will let you know if you need a service lateral upgrade.

Service laterals are not subject to NEC. The power company has a different codebook.

Your responsiblity is to have overcurrent protection (breaker) that is appropriate to the power the power company has promised to provide you (provisioned you) i.e 100A. The service lateral may be wholly inadequate to the task if you really drew all that; but it's their right to undersize the cable on the bet that you won't, and their job to bird-dog that.

A downline (sub) panel can always have a bigger breaker

Since you have a 100A main breaker at the meter, it's perfectly fine to use a larger 200A panel downstream of it. There is nothing that requires the subpanel's "main breaker" agree with the breaker that is actually feeding it.

  • if the subpanel's "main" is bigger than the supply breaker, it is merely a shutoff switch. Given how panels are priced, it is often the cheapest way to get a shutoff switch if one is required (e.g. In an outbuilding).
  • If the subpanel's "main" is smaller than the supply breaker, then each has different jobs. The supply breaker protects the wire/Cable to the subpanel. The subpanel "main" protects the subpanel itself.

In this case, since the "sub" panel is in fact the domicile's main panel, using a 200-225A panel is the only sane choice. 100A panels are quite small panels, typically not much larger than 20-space. You need as a "desperation minimum" 30 spaces in a main panel, and 40 spaces or more is a better choice. That is especially so in an all-electric home, where otherwise-gas appliances are gobbling up breaker spaces 2-4 at a time.

The traditional desperation move when you run out of spaces is "double-stuff" breakers, but that is becoming less viable as more and more circuits require AFCI or GFCI. Those breakers are not available in double-stuff. Given the price difference you are far better off just buying a 42-space or two 30’s, rather than painting yourself into a corner and having to spend much more to get out of it.

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  • Since the op only states 100 amp disconnect we need to know if it was fused quite common for this age and type of service or a breaker it would be fine but if only a disconnect as in a switch it would not meet code back then or now. – Ed Beal Oct 7 '18 at 22:51
  • @EdBeal in comments he indicated it was a breaker. – Harper - Reinstate Monica Oct 7 '18 at 22:55
  • My comment was written 6 hours prior to the op comment, my answer at the same time as the op's comment I don't think anyone on this forum is clairvoyant. – Ed Beal Oct 8 '18 at 15:32
  • @EdBeal i was referrring to your comment here. Regardless it is okay, it's not a race. Anyway now you know, you can edit your answer. Below your answer are the words "share edit delete flag". Past versions are stored so it's not like you lose anything. – Harper - Reinstate Monica Oct 8 '18 at 15:57
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You stated the supply to the 4 homes was 100 amp. If this is a circuit breaker you are totally fine. We commonly install large sub panels like 100a or larger being fed from 40-60 amp breakers in the main panel. This would be the exact same case if the disconnect is fused at 100 amp (quite common for this age of disconnect) or if it is a breaker. If it is just a disconnect it would have been a code violation at the time of installation. I would check the disconnect if fused it was a code compliant install and there is nothing to worry about.

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Ok you have asked one specific question in your title. That answer is: Using a 200A breaker one 100A service conductors is bad and needs to be corrected. In short you have insufficient over current protection of the feeder and circuit. That means in the event of a failure is is most likely your 200A beaker will not trip out thus causing an electrical fire and/or shock hazard that is life threatening.

So get it addressed and make the necessary repair to bring into a safe installation. NEC Table 310.15(B)(6) will give you the proper conductor sizing.

Above all make the installation safe. You might discuss with the landlord that if both of you cannot come to an agreement, you might bring in the AHJ to help arbitrate the matter.

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    I just found out , the outside subpanel for the meters that do 4 mobile homes each. each has a 100 amp shutoff breaker. I am going to say the 200 amp indoor breaker box isn't a problem than? because if more 100 amp gets used at once the outdoor shutoff breaker is going to go off. But do you think the 200 amp breaker box, I could just have the landlord replace it with a 100 amp breaker inside to be extra safe? @retired – Michael Weaser Oct 7 '18 at 16:25
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    No your fine if the service is protected by the 100A breaker. – Retired Master Electrician Oct 7 '18 at 19:47

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