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I'm looking to install a shore power panel for an RV, which will have a 50-ampere, 30-ampere, and 20-ampere receptacle in it. Each receptacle is protected by an appropriately sized circuit breaker, that is built right into the panel. The panel will be similar to this one.

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I have a 50 ampere GFCI breaker in my main service panel, as well as a length of 6/3 with ground cable (decommissioned Hot Tub circuit). Can I re-purpose this circuit to feed the RV panel, or do I need a larger feeder?

Reading through the National Electrical Code section 551, it seems to me that I should be fine.

National Electrical Code 2017

Chapter 5 Special Occupancies

Article 551 Recreational Vehicles and Recreational Vehicle Parks

551.73 Calculated Load.

(A) Basis of Calculations. Electrical services and feeders shall be calculated on the basis of not less than 12,000 volt-amperes per site equipped with 50-ampere, 208Y/120 or 120/240-volt supply facilities; 3600 volt-amperes per site equipped with both 20-ampere and 30-ampere supply facilities; 2400 volt-amperes per site equipped with 20-ampere supply facilities; and 600 volt-amperes per site equipped with 20-ampere supply facilities dedicated to tent sites. The demand factors set forth in Table 551.73(A) shall be the minimum allowable demand factors that shall be permitted in calculating load for service and feeders. Where the electrical supply for a recreational vehicle site has more than one receptacle, the calculated load shall be calculated only for the highest rated receptacle.

According to this, it seems as though the calculated load for the panel would be 50 amperes (based on the highest rated receptacle), and the feeder should be based on 12,000 VA (12,000VA / 240V = 50A). So I should be fine with a 50-ampere breaker and 6 AWG conductors, right?

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    Can we assume that you will never need more than 50A at one time from the panel even tho it seems capable of providing 100A? – JPhi1618 Sep 7 '17 at 14:46
  • @JPhi1618 My current RV will use the 30 amp receptacle. Just figured I'd futureproof, since I already have a 50 amp breaker and 6 AWG cable. This is going to be for a trailer parked in my driveway. If I didn't already have all the stuff, I'd just install a 20 amp circuit. – Tester101 Sep 7 '17 at 18:51
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Where the electrical supply for a recreational vehicle site has more than one receptacle, the calculated load shall be calculated only for the highest rated receptacle.

clinches it. However, this presumes this is one site. If it is reasonably plausible that this is 2 sites, and Junior could roll up and park his TT30 right next door -- then yeah, you'll have a problem.

And I would address that problem by fitting a generator interlock so both the 50 and 30 can't be on at once. I wouldn't worry about the 20.

Also, build a birdhouse with a door over that thing. You'll thank me later (actually you won't though).

  • No chance of any other RVs plugging in, but the interlock is still a great idea. Also, in my case this panel will be inside my garage, so no need to protect it from weather. – Tester101 Sep 7 '17 at 18:47
  • Does it make a difference that this isn't technically an RV park? It's just a place to plug in my RV, when it's parked at my house. – Tester101 Sep 7 '17 at 18:56
  • The difference is you are doing what would be required for an RV park even though it isn't one. And, that's the best thing to do. Just makes good sense. – ArchonOSX Sep 7 '17 at 19:21

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