50 amp receptacle breaker: 60 amp OK?

[NormDunn]

The function of the main breaker is to protect the wire feeding the panel and the rating of the panel. A 200amp main would most likely have a minimum size 2/0 cu which 2/0 cu is suitable for 200 amps. The panel would then contain multiple breakers 15,20,30 amp and so on. Some single pole and some double pole. The reason you don't exceed the rating of the wire on eithere the service entrance conductors or the lower amp branch circuits by simply installing a larger breaker is to avoid thermal breakdown of the insulation on the wire. For example: pulling anything above 50 amps thru a wire rated at 50 amps, will cause melting of the insulation on the wire resulting in short circuit and or fire. Speed at which the the insulation melts down is relative to the level of current above the rating of the wire and, heat generated. Also, the combined load, not the numbers of breakers on a 200 amp main, exceed the 200 amp main, the main should trip. Notice I said should trip. They are man made electro mechanical devices subject to a failure of correct operation. Doesn't happen often on the overload, more likely to start having a premature trip. Hope that helps.

[NormDunn]

I didn't answer part of your question. It is not ok, by use of a cheater as you indicated, to connect a 30 amp rv to a 50 amp receptical. What you have is a 30 amp circuit protected by a 50 amp breaker. Again, thermal breakdown of the insulation causing a short or fire. I know fully it's done all the time across the USA. Doesn't make it right or more importantly safe for you and your family. If the 50 amp receptical is protected with a 30 amp breaker, I would then say it's ok, not ideal but the most likely failure point would be the cheater not melting down the insulation.

[nothermark]

Originally Posted by NormDunn

The function of the main breaker is to protect the wire feeding the panel and the rating of the panel. A 200amp main would most likely have a minimum size 2/0 cu which 2/0 cu is suitable for 200 amps. The panel would then contain multiple breakers 15,20,30 amp and so on. Some single pole and some double pole. The reason you don't exceed the rating of the wire on eithere the service entrance conductors or the lower amp branch circuits by simply installing a larger breaker is to avoid thermal breakdown of the insulation on the wire. For example: pulling anything above 50 amps thru a wire rated at 50 amps, will cause melting of the insulation on the wire resulting in short circuit and or fire. Speed at which the the insulation melts down is relative to the level of current above the rating of the wire and, heat generated. Also, the combined load, not the numbers of breakers on a 200 amp main, exceed the 200 amp main, the main should trip. Notice I said should trip. They are man made electro mechanical devices subject to a failure of correct operation. Doesn't happen often on the overload, more likely to start having a premature trip. Hope that helps.

Make that "may" instead of "will" cause a fire and you have the point. It will cause a slightly higher than desired temperature rise in the overloaded conductor. As a fraction of overload it is less of an overload than replacing a 15 A breaker with a 20 A breaker in a 15 A circuit. That is a fairly common practice. Anyone worried might find this discussion interesting:

14 AWG allowable ampacity - Electrician Talk - Professional Electrical Contractors Forum


Given that the current ratings are purposely conservative for wire in a bundle in a conduit sitting in the Texas sun on a hot day the only place I get worried is where the wire is running through an enclosed pipe. I will give you that a 3 or 4 wire insulated cable will get warm laying in the sun but it is well below the rated maximum temperature for the cable.

It also assumes the power cord will dissipate an extra 10 A somewhere between the receptacle and the 50A breaker at the input of the Motor Home. If you have 10 A of leakage current you already have a bad power cord and probably a fire despite the breaker size.

All that assumes the MH will draw 50A on either leg under normal usage.

Altogether too many assumptions for me to get worried about putting a 50A receptacle on a 60 A protected circuit.

[NormDunn]

Thanks, I looked at and liked the link. Upon reading it I quickly noticed they were talking about a/c circuits and motor load circuits and not a multipurpose circuit. Personally, I don't believe and it has not been my experience that any electrical inspector has, would, will allow a 20A breaker on a comercial, residential or rv circuit that is not specifically dealing with a dedicated ac or motor circuit. Again, that's just been my experience.

I like to think of any code book as the absolute worst job you can do and still get a green tag.

[NeilV]

Doesn't really matter what we are personally worried about it is what code enforcement requires balanced against what your insurance companies inspector will allow to be covered when an incident has occurred with local conditions taken into account that may require a step up in specs. Too late then to say well Dan/Bob/Bill/Sue at IRV2 said electricians in other jurisdictions feel that the code is too strict and that I could get away with it.....

You do it to exceed code. As was mentioned Code is many times not best practice but just good enough to get by and still get paid for the job.

Where I live we have long running low voltage events that will increase amperage and heat well above design specs. A good local electrician and local electrical engineer will keep that in mind and exceed code due to local conditions and not take liberties in their designs. A good local electrical inspector may also on inspection take exception to special circumstances that he notes and require components be upgraded.

[Santara]

most all rv have a inside main breaker 50a can only draw that much ,so all that is fused at 60 is the cord

[draboo]

Originally Posted by Santara

most all rv have a inside main breaker 50a can only draw that much ,so all that is fused at 60 is the cord

I had a electrician look at what I wanted to do and he said the same thing. The coach won't draw any more than a max of 50A. The cord and wiring between the coach and the breaker will be protected for 60A.

I m going to be doing this in a few days and will post a few pics for y'alls amusement!

[TQ60]

NEC is just that...national code.

The breaker is rated for wire and all parts of the circuit up to and including the outlet.

Breaker is not designed to protect the wiring past that point thus smaller loads like wall wart used in a 15 amp ckt.

A 30 amp cord will trip a 50 amp breaker...

If there was a fire and the inspector found the 60 amp breaker on conductors or outlet rated for less than breaker then sn insurance adjuster can deny claim.

I believe op stated they were going to use correct size so it should be done to NEC or local code.

[Santara]

Originally Posted by draboo

I had a electrician look at what I wanted to do and he said the same thing. The coach won't draw any more than a max of 50A. The cord and wiring between the coach and the breaker will be protected for 60A.

I m going to be doing this in a few days and will post a few pics for y'alls amusement!

that was my racket also

[cimplexsound]

Make sure your power inverter can handle the extra power. Otherwise I would recommend upgrading to a higher power, power inverter.

[nothermark]

Originally Posted by cimplexsound

Make sure your power inverter can handle the extra power. Otherwise I would recommend upgrading to a higher power, power inverter.

What does your power inverter have to do with the coach service wiring?

[H. Miller]

Originally Posted by hdossett

That said, match the breaker to the wire, i.e. #8 wire (3/wG), no more than 40 amp DP breaker.

Not all the time! A #8 THWN or THHN wire is rated at 55 amps...

[cimplexsound]

All your electrical house wiring is serviced by your power inverter. You could say your power inverter is the central nervous system or brain of your RV's electrical system. If you cause it an overload, your in trouble. Meaning lights out? Just saying it's better to be safe than sorry.

[peggwn]

Thanks, OLYLEN, I think you answered a question I was about to ask. We are about to add electrical to a new barn for our 30amp service RV. I want to go ahead and wire for 50amp service now, so when the DW decides we need to upgrade we'll probably need it - and we'll have it without having to upgrade the electrical service as well (which will probably cost more than the original install). Of course we'll get a 30amp-to-50amp adapter for our current RV for now.