From the RV Travel reader comments
Q: I want to install a 30-amp box hookup on a stand in my RV concrete slab in my back yard. I hear of several methods, but some don’t sound so safe. What is the proper and safe way? I know it has to be totally separate with its own breaker and the wire needs to be at least 6-12 inches underground, and that wire is expensive. I’d like it to be in a PVC pipe so if there is digging at least the pipe will be visible. Yes, I realize I need an electrician, but not all electricians deal with RVs. Would like your input.
A: According to the 2011 National Electrical Code NFPA-70, any non-protected wire over 20 amperes must be buried at least 18 inches below grade. And since plastic (non-metallic) conduit does not protect the wiring from penetration due to a shovel or whatever, it still needs to be 18″ deep for a 30-amp circuit, unless it’s buried under a concrete slab, in which case the depth can be 12″. However, if you use metallic conduit then your wiring may only need to be 6″ below grade. These cover depths can vary from state to state, county to county, and municipality to municipality, so you’ll need to check with your local electrical inspector (aka the AHJ for Authority Having Jurisdiction) before you start digging the trench.
BTW: I just dug an 18″ deep trench for my dad and rented a small Ditch Witch for the job. His 125 ft. trench took me less than 90 minutes to dig, so that’s under 1 minute per foot of trench, which I thought was amazing. And always remember to check with your local utilities such as Miss Utilities a least a few days before you plan to dig your trench. That trencher would easily slice though any previously buried electrical wires, and you certainly don’t want to do that. It’s not only dangerous, the utility can fine you and require you to pay for the repair.
Also, many residential electricians will take one look at a TT-30 receptacle and assume it’s an early 30-amp dryer outlet and has to be wired for 240-volts, and that’s simply not the case. If you look carefully at the front of the receptacle you’ll see that it’s rated for a maximum of 30A-125V (30 amperes at 125 volts). Can’t these residential electricians read?
So your 30-amp RV outlet is indeed a 120-volt electrical service which only needs a single-pole circuit breaker to power it. Take a look at the graphic on the right for proper wiring. NEVER let any electrician convince you that a 30-amp outlet for an RV is a 240-volt/2-pole service, as plugging into it will generally destroy your RV’s electrical system in a few seconds. And yes, the electrician may blame you for his mistake and ask that you get your own insurance company to come up with the $10,000 it will take to fix your RV’s electrical system. No kidding.
As far as how heavy the wire needs to be, in most instances you can get away with 10-gauge direct burial wire for a 30-amp service. I always run it in schedule 80 non-metallic conduit, even if I’m going 18″ deep. But your local AHJ might allow thinner-wall Schedule 40 to be used instead. In any case, if there’s any significant length of run (100 feet or more) it’s much better to use the next heavier 8-gauge wire in order to reduce the voltage drop under load. Your air conditioner will thank you for it later.
Email me at mike (at) noshockzone.org with your questions.
Mike Sokol is an electrical and professional sound expert with 40+ years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.