Making Connections

Many campground electric pedestals are wired for 20-, 30- and 50-amp hookups. If you pull into a new resort featuring only 50-amp service in a rig built for 30-amp power, however, you’ll need the appropriate adapter.

Demystifying 30- and 50-amp hookups from shore or generator power

By Mike Sokol

etting outdoors and “roughing it” in an RV means different things to different people. Some go all-out and load up the RV for a weekend or more of off-the-grid camping. Others, however, will opt to leave their hectic lifestyle for a few days and find the nearest campground or RV resort that allows them to plug into enough power to enjoy life’s comforts while still shedding the everyday stress that tends to walk in our shadows.

50-, 30- and 20-amp plugs

A typical campground electric pedestal with 50-, 30- and 20-amp connections.

Being able to tap into the park’s power, however, requires being able to connect the electric pedestal to an RV’s power cord — and there will be times when that may not be possible. Your RV, for example, may have been built with 30-amp onboard power — but the resort may only offer 50-amp plug-ins.

So, you’ll need an adapter.

All modern RVs come in one of two flavors of power service: 30-amp and 50-amp. While a third option of a 20-amp outlet is available, there are no currently produced RVs (that we’re aware of) which have a 20-amp shore power cord. It’s either a TT-30 connector, which is 30 amps at 120-volts AC, or a NEMA 14-50 connector, which is 50-amps at 240-volts AC (split down two separate circuits of 50 amps at 120-volts AC each, for a total of 100 amps of current at 120 volts AC). There are also a few variations of generator outlets available that must be considered when you’re running from a generator rather than shore power.

In order to be able to plug your RV into whatever power is available, there’s a plethora of possible adapters you can purchase. Most of them are in “dogbone” style, so named because they look like a cartoon version of a big bone held in a dog’s mouth. There are a few versions of adapters that resemble a tall hockey puck, but they tend to put a lot of twisting strain on the outlet they’re plugged into.

Adapters can be divided into three basic categories: 50-amp and 30-amp RV shore power cords, and generator twist-lock connectors. We’ll take a look at some of the most popular connectors; however, keep in mind that this is by no means an exhaustive overview.

Just remember that you can’t get blood out of a turnip. So even if you’re using a 30- to 50-amp dogbone adapter to power your 50-amp RV, you still only have 30 amps of total current to use. The same goes for a 50-amp pedestal to 30-amp shore power dogbone connection: your RV is still limited to 30 amps total current, no matter how much more you wish for. Know, too, that all quality dogbone adapters will properly split 240-volts from a 50-amp pedestal outlet or generator, to the proper 120-volts for a 30-amp shore power cord, or 120/240-volts for a 50-amp RV shore power cord. However, if in doubt, use a meter to confirm anything new before plugging in your RV.

30-amp RV adapters

If you have a 30-amp RV there are fewer options to consider. If you need to plug your 30-amp RV into a 50-amp shore power outlet, you’ll need a 50- to 30-amp adapter. Note that a properly wired dogbone adapter will only use one of the 120-volt legs in the 50-amp outlet to feed to the single leg of your 30-amp shore power cord, so you will indeed be feeding 120 volts to your RV’s electrical system, not 240 volts. However, your power will still be limited to 30 amps total since your RV’s power center will have a 30-amp master circuit breaker. This adapter is also useful if the pedestal you’re plugging into has a worn 30-amp outlet but a newer 50-amp outlet. You won’t get any more power, but you may get a more solid outlet connection.

50-amp to 30-amp
“dogbone” adapter.

This is a 15 to 30-amp adapter that will allow you to connect your 30-amp RV to a standard 15/20-amp home outlet. Note that all outside 20-amp outlets are required by code to be protected by a GFCI breaker or outlet set to a 5mA trip point. However, many RVs have normal leakage that can exceed that 5mA threshold, which may cause nuisance tripping. But that’s another entire article.

50-amp RV Adapters

Some RVs use a 50-amp 120/240-volt shore power cord. Note that while this is indeed a 240-volt service, it’s split down the middle to two separate 120-volt feeds (commonly called legs) with a four-pin plug (two hot, one neutral, one ground). Each leg feeds a separate side of the RVs service panel. So, when you need to plug your three-pin, 30-amp RV into a 50-amp outlet (from a pedestal or generator), your 30-amp RV uses only one 120-volt leg at a maximum of 30-ampers of current. Conversely, when you plug your 50-amp RV into a 30-amp shore power outlet, that single leg of 30-amp power is sent to both legs of your 50-amp shore power cord to share. However, the maximum current is always determined by how much amperage and how many power legs (1 or 2) are available from the outlet.

This 15- to 50-amp adapter will allow an RVer to plug a 50-amp RV into a standard Edison/Home outlet. Note that even though we call this a 15-amp outlet, it’s usually wired with 12-gauge conductors and powered by a 20-amp circuit breaker. So it’s actually rated for 20-amperes of current at 120 volts.

Below is a typical 30- to 50-amp adapter, allowing you to connect a 50-amp RV to a 30-amp pedestal outlet. In a properly wired dogbone adapter this will connect the pedestal’s120-volt, single-pole, 30-amp outlet to both legs of the RV’s shore power connector. This will ensure that both halves of the RV receive 120-volt power, albeit with 30-amperes of available current instead of the 100-amperes total current normally available from a 50-amp outlet.

You can “stack” adapters by using a 15 to 30-amp adapter connected to a 30 to 50-amp adapter which you can plug your 50-amp RV cable into. This will feed the 20 amperes of current into both legs of the RV’s shore power cord, powering everything in the unit, albeit with a total of 20 amperes of power. So running multiple high-power appliances while plugged into a 20-amp outlet won’t work. That’s when you’ll begin tripping the main circuit breaker feeding that outlet.

Generator Power

There are three basic categories of generator outlets typically used to power RVs: 2,000-watt, 3,000-watt and 6,000-watt. So if you want to connect your RV shore power cord into a generator, you’ll need an adapter that matches your generator output on the one side with the appropriate RV shore power plug on the other side. On 2,000-watt generators with 20-amp duplex outlets, for example, you would use a standard 15-amp to a 30- or 50-amp dogbone adapter described earlier.

Keep in mind, too, that even though your generator will have some sort of ground connector, portable generators powering an RV are NOT required to be connected to any kind of grounding rod. However, any 2,000 to 7,500-watt inverter generator may require a ground-bonding plug if you’ll be connecting it to an EMS/Full-Protection Surge Protector.

Adapter for a 6,000-watt 240-volt 4-prong generator with twist-lock outlet to 30-amp shore power cord.

A Southwire Ground-Neutral generator bonding plug

Sources
Camco Manufacturing Inc.
(800) 334-2004
www.camco.net

Conntek Integrated Solutions
(877) 267-3788
www.conntek.com

Park Power by Marinco
(800) 307-6702
www.park-power.com

SmartPlug Systems
(206) 285-2990
www.smartplug.com

Southwire Co.
(770) 832-4242
www.southwire.com

Valterra Products
(818) 898-1671
www.valterra.com

Voltec Power & Lighting
(866) 486-5832
www.voltec-industries.com

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