30 vs 50 amp service

[jerry d]

Unless the adapter has 30 amp fuses then it is not only a bad idea to use it but violates numerous Nat Electrical Code sections. The circuit breaker in this case is a 50 amp breaker, with a cord rated at 30 amps. The circuit breaker will not trip until 50 amps is exceeded, A previous poster pointed out that the trailers main would prevent damage to the trailer, this is true, but the trailers main breaker is downstream of the un-protected cord. If an adapter is on the market that has internal fuses then go for it, otherwise Bad Idea.

[markdoane]

Originally Posted by richinny

ok i'm confused. i thought that campground 50 amp plugs provided two 25 amp/120 volt hot wires, one neutral and one ground.

do the adapters in fact use one of the hots thereby providing 25 amps or do they combine the two hots and provide 50 amps?

Ricky, the 50 amp receptacle provides two 50 amp legs, for a total of 100 amps at 120v. The power cord is #6 AWG - 3 wires plus ground.

The adapter uses just one of the hot legs, and is capable of 50 amps. The 50 amps is limited to 30 amps only by the main breaker in your trailer.

[SteveH]

Originally Posted by Hodum

In the 50 amp receptacle there are 2 prongs that have 120 volts but are opposite polarity, so if they are supplied to 240 volt equipment they provide the necessary 240 volts. In this case the neutral (white) is not energized. When only 120 volts are needed as in an airstream only one of the power legs is used and the neutral completes the circuit back to the source. The ground (green) is only there incase of a fault and should never be energized under normal conditions. In 50 amp RV's though 240 volts are available it is not supplied to any 240 volt equipment but each leg of the power providing 120 volts each feed two separate bus bars and each bus provides 120 volts for the equipment. When using a 50 amp to 30 amp adapter you connect to only one of the hot legs of the 50 amp supply thus bringing your chord in contact with only 120 volts. It is safe.

This is accurate, folks, and the best description I've read here. I did not want to get into explaining how the two 120 VAC legs make a 240 VAC circuit, did not want to use the word polarity, or especially the word phase, (really more accurate because we are talking about AC)because that brings up a whole other argument.

Anyway, Hodum's description is accurate.

[richinny]

ok, thanks Mark.

[chegard]

Thank you all. I should have studied my physics in college more extensively!
Chegard

[A W Warn]

Another thing to consider when using the adapters: I have seen the 30 amp (120v) single pole breakers that are GFCI. Not all of them, but some. I have never seen a 50 amp two pole (240v) breaker. When you use those adapters in wet weather be cautious how you place your trailer cord. If the connection point is in a puddle or the chord is wet and you walk through the puddle or touch the chord, it could be shocking!

Is there an adapter with a GFCI built in?

[Hodum]

There are some RV boxes that are equipped with 50 amp 240 volt double pole GFCI breakers. I have had one for several years. They are more expensive but GFCI is the safest thing going whether single pole or double pole. They are designed to detect the slightest amount of current flow going to ground for any reason and trip the breaker immediately. In case there is a short circuit to the metal of your trailer the ground wire should carry the current back to the breaker box and the breaker would trip from an overload condition. In case the ground wire had lost connection for any reason the trailer would be setting as a electrical death trap waiting for someone connected to the ground to touch it. However if there is GFCI protection it will sense the fault as soon as someone touches the trailer and trip the breaker before damage is done. GFCI measures the amount of current (in 1/1000's of an amp) that is being supplied by the hot leg and balances it against the current returning on the neutral leg and trips the breaker when the slightest imbalance occurs. Safety is paramount.