From the stupid questions department .....A fellow told us last weekend that when we plug our 30 amp plug into a 50 amp plug through a 50 amp to 30 amp adapter we still get 50 amps. That doesn't seem reasonable somehow, but is that true?thx ....

You get 30 amps through 1 leg at 120V. With a 50 amp plug, you get two 120V 50 amp "legs" for a total of 100 amps on two different 50 amp circuits.Edited, my mistake on understanding he is tying into a 50 amp 2 leg pedestal with a 30 amp cord. He'll have the full 30 amp capacity in his RV /TT.2oldman below is correct.

No. Although it may be possible to draw 50a through the wire, your onboard main 30a breaker will see to it that doesn't happen.If I may read into your question a bit, amps are not "pushed" like voltage, so if the fellow was trying to caution you that you may have too much power for some things, it's not true.

This is what happens when you plug a 50A (MALE) to 30A (FEMALE) adapter at the camp ground pedestal...As you can see only one HOT leg of the 50AMP service is being used. Even if you are plugged into a higher amps leg your internal 30A circuit breaker will only allow you to use 30A of current.Usually the connections are much cleaner on the 50AMP side as they really don't get used as much as the 30A service does...We use the 50A(M) to 30A(F) adapter all the time in order to get better 120VAC service sometimes... We have never had any problems using the RV50A(M) to 30A(F) adaptersRoy Ken

Simple way to look at it - if you could get 50A thru a 30A plug why would they ever have installed 50A plugs? And, would a 30A plug then really be a 30A plug, or would it be a 50A plug?Bill

What is your MAIN Breaker.............30AThat is it......30A regardless if using a 50A/30A Adapter Point that out to 'that guy' and please do NOT allow 'that guy' to do any electrical rewire/wiring job for you

50 amp down to 30 amp plug -- still 50 amp? | Good Sam Community

22 Replies

babun
Explorer
Aug 25, 2015
Old-Biscuit wrote:
wnjj wrote:

True except the 50A has 2 phases to choose from and one may well be lighter loaded than the other. If you want the perfect setup, you'd have 2 dogbones to choose from with each one using a different 50A leg. :p

Wish I saw that one before I bought my single dog leg!!
:(
Old-Biscuit
Explorer III
Aug 25, 2015
wnjj wrote:

True except the 50A has 2 phases to choose from and one may well be lighter loaded than the other. If you want the perfect setup, you'd have 2 dogbones to choose from with each one using a different 50A leg. :p
babun
Explorer
Aug 25, 2015
wnjj wrote:
DrewE wrote:
mkirsch wrote:
IMHO if you can plug into a 50A circuit, do it unless you know the campground has decent wiring. Often times campgrounds have less than adequate wiring and the heavier circuit will give you better power with less voltage drop.

If they're in the same pedestal, the wiring supplying both the 30A socket and (one leg of) the 50A socket is the same (with the exception of the few inches of wire between the breaker and the socket itself). The 30A socket itself may well be in poorer condition and make poorer contact than the 50A one, which is a different story and a reason in that case to prefer the 50A socket. At identical loads, however, the voltage drop from the campground wiring will be the same for either receptacle.

Put another way, a campground isn't going to have a separate distribution grid for the 30A socket and the 50A socket at the same campsite. If the voltage is low on one, it will also be low on the other.

True except the 50A has 2 phases to choose from and one may well be lighter loaded than the other. If you want the perfect setup, you'd have 2 dogbones to choose from with each one using a different 50A leg. :p

I'm a retired electrical contractor new to RV'ing.
you have a great idea!!

Other than carrying my ohm meter into the store, is there a way to tell which 30/50 dogleg is wired to which phase {side of the 50 plug}
Do any manufacturers used a std layout, such as always one side all the time?
wnjj
Explorer II
Aug 25, 2015
DrewE wrote:
mkirsch wrote:
IMHO if you can plug into a 50A circuit, do it unless you know the campground has decent wiring. Often times campgrounds have less than adequate wiring and the heavier circuit will give you better power with less voltage drop.

If they're in the same pedestal, the wiring supplying both the 30A socket and (one leg of) the 50A socket is the same (with the exception of the few inches of wire between the breaker and the socket itself). The 30A socket itself may well be in poorer condition and make poorer contact than the 50A one, which is a different story and a reason in that case to prefer the 50A socket. At identical loads, however, the voltage drop from the campground wiring will be the same for either receptacle.

Put another way, a campground isn't going to have a separate distribution grid for the 30A socket and the 50A socket at the same campsite. If the voltage is low on one, it will also be low on the other.

True except the 50A has 2 phases to choose from and one may well be lighter loaded than the other. If you want the perfect setup, you'd have 2 dogbones to choose from with each one using a different 50A leg. :p
DrewE
Explorer II
Aug 25, 2015
mkirsch wrote:
IMHO if you can plug into a 50A circuit, do it unless you know the campground has decent wiring. Often times campgrounds have less than adequate wiring and the heavier circuit will give you better power with less voltage drop.

If they're in the same pedestal, the wiring supplying both the 30A socket and (one leg of) the 50A socket is the same (with the exception of the few inches of wire between the breaker and the socket itself). The 30A socket itself may well be in poorer condition and make poorer contact than the 50A one, which is a different story and a reason in that case to prefer the 50A socket. At identical loads, however, the voltage drop from the campground wiring will be the same for either receptacle.

Put another way, a campground isn't going to have a separate distribution grid for the 30A socket and the 50A socket at the same campsite. If the voltage is low on one, it will also be low on the other.
mkirsch
Nomad II
Aug 25, 2015
When you attach to a 50A plug, that does not mean that suddenly 50A is being forced through your RV. Only the electricity that is demanded by appliances in your RV is going through your RV. For example, 10A for your air conditioner, 2A for your converter, another 1A to run the TV... 13A total, not 30A or 50A.

IMHO if you can plug into a 50A circuit, do it unless you know the campground has decent wiring. Often times campgrounds have less than adequate wiring and the heavier circuit will give you better power with less voltage drop.
ECones
Explorer
Aug 25, 2015
As I understand it, it could also keep him from having to go outside in the rain to reset the 30 amp breaker on the pole if he manages to overload it. It would trip inside.

Maybe that's his goal.
wnjj
Explorer II
Aug 25, 2015
ECones wrote:
The fellow we talked to said he always plugs his 30 amp trailer into the 50 amp plug through an adapter so he'd have 50 amps available, and being that I'm no electrician I didn't argue. But I did understand that we're really only using half that plug (Roy's post above) so I seriously doubted it.

Luckily, I knew who to ask. ;)

Thanks for all the kind responses and, once again, nobody pointed out my mental deficiencies. ;)

Technically he does have 50A available at the other end of his cord. Using only half of the 50A service just means there is only 50A and not 100A available. As some others have stated, the current coming from the pedestal depends upon what is limiting it. With a 30A pedestal receptacle, the 30A breaker on the pedestal will limit you to 30A.

If you now use a dogbone to connect to the 50A receptacle, there is indeed 50A available. If the trailer does not have a 30A "main" breaker there is nothing stopping it from pulling up to 50A. The setup in the picture a couple of posts above without a main breaker could use (15+20) = 35A if plugged into a 50A dogbone.

This situation is no different than a light-duty extension cord plugged into a 20A receptacle at home. If you then plugged an electric heater into the extension cord, you could overload the cord without tripping the 20A breaker. In this case, just like the RV dogbone into 50A you can't just rely on the receptacle supply's breaker to limit the current if the device plugged into it isn't capable of the load.

Many RV's with 30A cords have 30A main breakers to prevent this.

The reality is his trailer is limited by the lower of his main or the pedestal breaker. By using the 50A service, his effectively now only limited only by his 30A main. This may result in slightly more power available for him if the pedestal 30A breaker would have tripped at something less than 30A.
ECones
Explorer
Aug 25, 2015
The fellow we talked to said he always plugs his 30 amp trailer into the 50 amp plug through an adapter so he'd have 50 amps available, and being that I'm no electrician I didn't argue. But I did understand that we're really only using half that plug (Roy's post above) so I seriously doubted it.

Luckily, I knew who to ask. ;)

Thanks for all the kind responses and, once again, nobody pointed out my mental deficiencies. ;)
wa8yxm
Explorer III
Aug 24, 2015
Well. this may sound strange but...

YES: you can still GET 50 amps.. BUT.. You can only accept 30 of 'em.
(SO what happens to the other 20? They are simply left in the box as it were)

IF you try to draw more than 30 amps you still get the CLICK OF DARKNESS (Sound of a circuit breaker tripping) only it is INSIDE the RV, not out where you need to put your shoes on to reset it.

Some folks worry about the posibility of a short that draws say 45 amps and overheats the shore cord.. Possible in a lab,, Basically impossibly in real life.. So do not worry about it (You might do it if you use an extension cord adn the plug/outlet junction is in a puddle but only the extension cord would be at risk not your RV's cord)