Miady RV and generator plug guide

Read the code, not the shape

RV, generator and shop plugs look alike at a glance, and most of them do not fit each other. The NEMA code molded on the plug or printed beside the outlet settles it. In most codes the number before the dash names the family, which fixes the voltage and whether there is a ground, and the number after it is the amp rating. An L in front marks a locking plug that you push in and twist. A P at the end is the plug, an R the receptacle it fits. TT-30 is the exception to the pattern, a name kept from travel trailers.

TT-30 and 14-50 at the campground

Campground pedestals usually offer a TT-30 outlet, a 14-50 outlet or both, often beside an ordinary 5-15. A TT-30 gives a camper a single 30 amp circuit at 125 volts. The 14-50 brings two 50 amp legs, 125 volts each and 250 volts across the pair, so a 50 amp rig has far more to share between its appliances.

Our RV power plugs cover both sides: 30 amp and 50 amp replacement male plugs, a 50 amp female plug, and TT-30R and 14-50R outlet boxes for a site of your own. Those outlet boxes are installed by a licensed electrician.

The dogbone: a 30 amp camper on a 50 amp pedestal

A dogbone adapter is a short cord with a different end at each side. Ours has a 14-50P male plug on one end and a TT-30R female socket on the other, with 18 inches of 10 gauge cord between them. Plug it into the 50 amp outlet, plug your camper's 30 amp cord into it, and you can use the 50 amp side of a pedestal when the 30 amp outlet is taken or worn.

The camper gains nothing from the bigger outlet. It still draws 30 amps at most, because its own cord, inlet and breaker are built for 30. What the adapter changes is where you can plug in, not how much power you get.

Generators and the L14-30

Many portable generators carry an L14-30R twist-lock outlet: 30 amps, 125/250 volts, four prongs. The plug turns into place, so engine vibration does not shake it loose. Our L14-30P generator plug takes a 10 gauge cord and suits generators up to about 7,500 watts with a 30 amp outlet, and the matching L14-30R connector goes on the far end of the same cord.

Replacement plugs: match two things

A replacement plug has to match the configuration of the outlet it goes into and the wire gauge of the cord it goes onto. Configuration decides whether it fits. Gauge decides whether the conductors seat properly in the terminals and the cord clamp holds. Each of our plugs states its range: the 30 amp RV plug is made for 10 gauge cord, the 50 amp one for 10 to 4 gauge, the 6-30P/6-50P plug (interchangeable blades) for #10 to #6 wire, and the 15 amp cord ends clamp cords from 18 to 12 gauge.

Fitting a plug to a cord is electrical work. An electrician or another qualified person should do it, following the instruction sheet in the box.

Inlet boxes, transfer switches and backfeed

A power inlet box gives a generator a proper connection point on the outside wall of a house or shop. Installing one is a job for a licensed electrician, who fits it together with a transfer switch or an interlock that separates the building from the utility line while the generator runs. Of our inlet boxes, the 30 amp one takes a cord with an L5-30 connector at 125 volts, and the 50 amp one runs at 125/250 volts.

Never plug a generator into a house outlet with a double-ended cord. Power then flows backward through the panel and out onto the utility lines, where it can reach a line worker far away who expects the line to be dead. OSHA names this danger directly, and it is the reason the electrician's switch exists.

Extension cords: rating first

Every extension cord carries a rating in amps or watts, and the load on it has to stay under that figure. Our short 8 inch cords are 16 gauge and rated 13 amps at 125 volts, about 1,625 watts. They exist to clear space on a crowded power strip or wall outlet, where one bulky plug would otherwise block its neighbor.

• Add up the watts of everything on one cord before you switch it all on.
• Do not plug one extension cord into another to reach further. Use one cord of the length you need.
• Keep cords out from under rugs and furniture.
• Treat an extension cord as temporary. A load that needs power every day needs its own outlet.
• Many space heaters are labeled 1,500 watts, which takes most of a 13 amp cord by itself and leaves almost nothing for anything else. Plug a heater into the wall outlet.

For the shop, our 25 foot welder cord runs 8 gauge wire between 6-50 ends, so a welder can move closer to the work instead of staying beside the one 250 volt outlet.