I want to run a couple of lines from my main box, 1 for 50 amp for my RV and then I want to have 9 shop lights installed (4 to run on one switch and the other 5 on a second switch) and 5 110 outlets between 2 sheds. Should I run a sub panel to the sheds and run everything from it, or just go with 1 big breaker in the main box and split the wires down as I need?? Going to have help with this, but trying to price everything out ahead of time and just not sure which way is best.

  • Can't just split wires. Running lots of circuits will likely cost more than a subpanel. Also grounding issues. How far are the sheds from the main panel? – manassehkatz Feb 11 at 22:05
  • Depends on your locality. Generally a sub board per building is a legal requirement, and for me a licenced electrician must do the board work and connections. Homeowner can do donkey work to reduce labour costs, but ultimately your local code requirements are the authorative call. – Criggie Feb 11 at 23:10
  • I want to have 2 separate runs, 1 for my boat shed which will only have 4 outlets, 4 overhead shop lights, and 1 light switch. Most I will run in there will be a small air compressor, table saw, or small tools but not all the same time of course. That shed is about 115' from main panel. Other shed will have 5 overhead shop lights, and only 1 outlet but will also have a 50 amp outlet for my rv and thatch shed is about 130' from main panel – Jerry C Gillette Jr. Feb 12 at 0:16
  • Are the sheds located near each other, or way off in different directions? – ThreePhaseEel Feb 12 at 1:28
  • They are about 2' apart from each other – Jerry C Gillette Jr. Feb 12 at 1:43

Going with a sub is really the only option you need over current protection for the lighting and GFCI's for the outlets then your RV. You don't mention what size loads will be in the sheds . NEC 551.72 can be used to calculate the load for the RV not less than 12000va or 50 amps, so you will probably will want at least a 75 amp feeder, I would get a 100 amp panel so there is plenty of room for expansion. Go with the largest feeder (wire size) you can afford, I have never been told to down size panels but have come back on quite a few jobs and upsized feeders and panels with 1 job I returned a 3rd time and the owner said he wished he had listened the first time because now he paid 3x for what I recommended the first time. Go big and save in the long run. You did not say what the distance to the shop is from your panel, this will be important so we can verify the voltage drop.

  • Ed it is about 150', give or take a few, to the furthest point. The sheds are like 2' apart from each other. Only thing in 1 shed will be small tools, ex. table saw, small air compressor, skill saw, drill, but they will NEVER be going all together at all. Other shed is just the RV and nothing else – Jerry C Gillette Jr. Feb 12 at 22:18
  • Here are some numbers 150' at 80 amps would take #3 copper or #1 aluminum the breaker in the main would be 80a. A 70 amp in the main would use #4 copper, or #2 aluminum. I always recommend to go big. You will probably not be working in the shop when the RV is fully utilized so that can be part of your sizing choice. Hope this helps the reason for the larger wire than the tables show is to keep the voltage drop below 3% this is not a hard requirement by code but many AHJ's require it to be met. I would install a sub with a main since it is a long way back to the house a 100 amp panel will work – Ed Beal Feb 12 at 23:10

Yeah, that's not salesmanship when we (pretty much everyone here) says "Go Big" on service panels. The critical factor is spaces -- lots of people come here and say "my panel is full, I'm out of spaces, what can I do?" Never seen a question like "Help, I have all these extra spaces in my panel".

The trick is the subpanel itself has an amp rating, and its master breaker (if equipped) has an amp rating, and those are allowed to be larger than your feed. So for instance, running a 75A feeder to a 200A rated subpanel with a 150A master breaker, that is fine. The master breaker in a subpanel is only thereto be a shutoff switch, and its value doesn't matter. The shutoff switch is required because this is an outbuilding. Using a panel with a master breaker is the cheapest way to do that.


Fat conduit is your friend here

First off, I would be running this project in conduit, and Schedule 80 PVC to be precise, provided burial depth is not an issue. Why? It is far cheaper to pull fatter wires through conduit than it is to dig up and replace a direct buried cable, and it also provides a bit of protection against oopsies when digging. You also need a somewhat shallower trench with conduit (18" to top of conduit for Schedule 80, which translates into a 21-22" trench depth) than you do with a cable (24" to top of cable).

As to sizing, I would use 2" Schedule 80 here, which provides plenty of space for pulling larger conductors to the sheds and RV pedestal in the future. As to running it, I would run conduits from the house and both sheds to the RV pedestal, as that's probably the most obvious place logically speaking to make the feeder splices/taps.

Wire sizing and making your connections

Given that you are using conduit, this gives us the flexibility to size our wires for today's needs without precluding tomorrow's upgrades. As a result, I'd use 3 6AWG THHNs (hot/hot/neutral) with a 10AWG bare copper ground in the conduits, protected by a 70A breaker (using the NEC 240.4(B) "round up" rule). At the pedestal, we use a trio of insulated mechanical tap connectors (Polaris™ or equivalent) to connect the incoming feeder wires from the house to the feeder wires to the sheds and to the tap wires going up to the pedestal's lugs.

As to the panels and pedestal

You will need a main breaker subpanel at each shed in order to provide a disconnecting means for power to the shed. Using a subpanel here instead of a lesser solution also provides more upgradeability compared to the alternatives, provided you size the subpanel properly, which is where most folks fall short, as they buy the cheapest panel that will work.

Instead, what you want to do is provision plenty of panel spaces now for expansion, as they are far cheaper to install now than they are to add later. This leads us to select a 100 or 125A, 24 or 30 space, main breaker panel, preferably with factory fitted ground bars -- if your panel comes without ground bars, you will have to add a set yourself in the field.

As to the pedestal, the configuration I would look at is a dual-receptacle, 50A/20A configuration in an unmetered, earth burial style -- this provides both a 50A/240V receptacle that will provide sufficient power for just about any RV you can find, and a 20A/120V duplex GFCI as a general utility receptacle at the RV location. (If you wish, you can go with a 50A/30A/20A configuration that also provides a TT-30 30A/120V receptacle, but that is strictly optional.)

Other notes

As of the 2017 NEC, 110.14(D) now requires that all lugs be tightened to the manufacturer's specified torque using an (inch-pound, by the way) torque wrench or torque screwdriver. Even if your jurisdiction does not enforce this requirement, I would do it anyway, lest your electrical system do what Greg Biffle's infamous lugnuts did!

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