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I want to connect a RV sub panel with a 50a RV receptacle a 20a gfci receptacle totaling 70a. I have 200a overhead wires feeding a metered box with a 200a main breaker. Connected is a 20a double that runs the well pump and then feeds the 200a house breaker box through underground. I will use a 70a double breaker to feed the sub panel. Here are the 2 questions.

  1. The main has the ground and neutral on same bar. Do I connect both the neutral and ground from the sub panel to that same bar? (With the actual sub panel unbounded)
  2. Would the physical location and connection of the panel as shown in picture be ok?

Metered entrance:

enter image description here

RV Panel:

enter image description here

Proposed installation location:

enter image description here

  • What size are the wires from the pole to the house? By tapping it heere, you may change their effective rating. What is the hreaker that is in there now? – Harper - Reinstate Monica Jan 1 at 3:18
  • @Harper-ReinstateMonica -- they're already tapped here, and NEC 310.15(B)(7) point 3 means that the feeder sizes given in NEC 310.15(B)(7) point 1 don't need to be upsized because of a tap – ThreePhaseEel Jan 1 at 4:58
  • @ThreePhaseEel Thanks, I had never actually laid eyes on that part of Code, my searchable PDF is 2011. – Harper - Reinstate Monica Jan 3 at 22:25
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You don't need to provision 70A to your RV box

RV receptacles have standard loads, based on the largest capacity receptacle present at a RV site, as given in NEC 551.73(A):

(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 only 20-ampere supply facilities; and 600 volt-amperes per site equipped with only 20-ampere supply facilities that are 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.

Since this is a one-RV-site situation, we don't need the demand factor table; however, the last sentence is what holds here, as any given RV only has one electrical plug on it! So, we need only provision for 12,000VA, or 50A, of current to the box.

As to running the feeder...

Your plan to run out the back of the panel and down through the top hub on the RV box is probably not the wisest idea, given the proposed box positioning, as it requires some rather funny field bends to avoid exiting the back of the meter panel at a funny angle, and can't be done with flexible conduit as a liquidtight connector won't mate properly to the hub fitting on top of the RV box due to mismatched threading (straight vs tapered). Instead, I would use 1" liquidtight flexible conduit to come out the back of the meter panel with a 90° connector, then enter the side of the RV box at the knockout with another 90° connector. This allows the liquidtight run to be mostly straight and near the pole, while keeping a leak in the meter panel from showering the innards of the RV box.

As for the wires inside the conduit, 8AWG copper THHNs for the hots and neutral with a 10AWG bare or THHN ground will suffice here, as we can use the 75°C ampacities when wiring something upwards of 30A between two panels using something other than NM or UF. The neutral and ground wires for this feeder circuit land on the combination N/G bar in the meter-panel, as meter-panels generally don't ship with separate bars due to the fact they can't be used as subpanels. When they reach the RV box, though, they go their own separate ways, with the neutral wire heading to the neutral bar next to the breakers and the ground wire going to the box grounding lug on the far right. The hots, of course, land on the two line lugs above the breakers.

Finally, you'll need a BR250 for the breaker in the meter-panel for this 50A feeder. If you wish to run 70A, or already have the BR270 fitted, your feeder will consist of 6AWG copper THHN instead of 8AWG with an 8AWG ground wire, but the routing is unchanged.

TORQUE ALL LUGS TO SPEC

There is one more thing that needs to be kept in mind here; namely, that NEC 110.14(D) (new in the 2017 Code) requires that you use a torque wrench or torque screwdriver (generally reading in inch-pounds, as that's what the torques on the labels are specified in) to tighten the various connection screws on the panels and breakers you're installing to the torques specified on the breaker or panel's labeling. Even if your jurisdiction hasn't adopted the 2017 NEC, it's still a good idea to do this anyway, lest your electrical system develop a case of the loose lugnuts!

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First you don’t add the amperage totals that way. A single RV has a load requirement by code I think it is article 551 but this is an old code book , 9600va at 240v is the required RV supply for a 50 amp 240v service. A single unit requires 100% . Yes I have had a larger feed on a large RV with dual ac’s , after downsizing I am back o a 30 amp 120v (single ac) on a 30 amp breaker as required by code. So look at article 551 in the national electric code, would I upsize my feeder with my last big class a yes I did. But not on my small one that I have today after the kids left.

  • I did not simply add the values I got it from GE panel itself. You could see it below. So are you saying that it can’t simply come off a 70a double breaker? dropbox.com/s/up80a76lo6j6cpa/… – Ram Rubicon Jan 1 at 2:59
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    @RamRubicon You can if the wires are large enough for 70A. It isn't unsafe or anything... but that's only by sheer chance. If you're lifting the number off the subpanel, then you obviously don't know what you're doing. This particular blunder isn't dangerous, but there are lots of others that are. Maybe you should leave this to the pros, instead of coming on here and arguing with pros... – Harper - Reinstate Monica Jan 1 at 3:27
  • I. agree with Harper+. I have had several motor homes and have installed permitted connections for my own MH’s as a spare room. I have also installed multiple 30/ 50 amp RV parks the latest for my current company that required 30+ locations with 50/30 connections. Code has minimums and these may be different than the panel. Your understanding of the supply is lacking. The largest motor home service currently allowed by code is 50 amp 240v . Check out the national electric code a single unit even if it has a 50amp 240v , 30 amp 120v and a 20 amp 120v power pedestal can be supplied by a 50a bkr – Ed Beal Jan 1 at 7:24
  • Sorry Harper but it was not argumentative. I simply stated and posted a picture of where I got the number from. I thank everyone for the info and the time spent to help. – Ram Rubicon Jan 1 at 22:15

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