50 amp to 30 amp pigtail question

[Rawn77]

From what I understand a 50 amp RV receptacle has 2 hot wires, 1 neutral and 1 ground. I guess that's why there are 4 prongs on a 50 amp cordset.

So my dumb question is, when you use a 50 to 30 pigtail adapter what happens to one of the 4 wires since a 30 amp cordset has only 3 wires; hot, neutral & ground. Does the pigtail simply discard one of the hots coming from the 50 amp side?

I was just wondering.......

[mimiandrews]

Originally Posted by Rawn77

From what I understand a 50 amp RV receptacle has 2 hot wires, 1 neutral and 1 ground. I guess that's why there are 4 prongs on a 50 amp cordset.

So my dumb question is, when you use a 50 to 30 pigtail adapter what happens to one of the 4 wires since a 30 amp cordset has only 3 wires; hot, neutral & ground. Does the pigtail simply discard one of the hots coming from the 50 amp side?

Yep. That's how it works.

I had the same question until I took a meter to our adapter.

This is electricity we're talking about here. There are no dumb questions!

[Rawn77]

Thanks!
Kind of what I thought


Sent from my iPad using Airstream Forums

[Wayward]

Maybe I can simplify the background . (or not )

This is an oversimplification because I will omit a few safety/grounding points that might make it harder to understand the basics

There are really only 3 wires coming in to the typical 50/30amp campsite hook up box.

--------------HOT1

--------------Neutral

--------------HOT2

All 110v consumer appliance/devices really only "need" 2 wires to work. Current comes into the appliance via HOT1 and then current flows out of the appliance through the 2nd wire to Neutral. OR Current comes into the appliance via HOT2 and then out to Neutral.

If you have a 30amp setup like most Airstream it is all 110v. In the RV campsite your 30 amp outlet is really only using 2 wires - either HOT1 and Neutral or, HOT2 and Neutral. The third wire in your 30amp plug/cord is for safety/ground.


220v consumer appliance/devices also really only "need" 2 wires to work. You hook 2 wires across HOT1 and HOT2 you get 220v and more current/power.

By bringing all 3 wires into an RV (not most Airstreams) it can run both 220v appliances (HVAC) or 110v appliances and have far more current and power. This 50amp service outlet at the campsite is really only using 3 wires - HOT1, HOT2 and Neutral. The fourth wire in a 50 amp plug/cord is for safety/ground.

To answer your question, YES. The 50-to-30 amp pigtail simply picks up Neutral, the saftey ground wire, and either HOT1 or HOT2. There is no electrical connection to the other Hot wire..

[Wayward]

30amp vs 50amp service is misnamed and causes some of the confusion.

It should be 110v service vs 220v service.

[airdreamers]

Originally Posted by Wayward

30amp vs 50amp service is misnamed and causes some of the confusion.

It should be 110v service vs 220v service.

It's both 110 volts. 220 volts will blow your whole wiring system. A friend plugged into 50amp at a FL campground which was wired wrong and, yes cooked the RV wiring. Nothing should be 220 volt in a RV of any kind. Be careful, when in doubt check with an electrician. Don't take casual answers as fact.

[DKB_SATX]

The "painfully accurate" (read: nerdy, pedantic) way to describe how it's actually used would be 30A vs 2x50A, since what the 50A receptacle at the pedestal provides to an RV that is set up for 50A is 2 circuits at 120v, each capable of providing 50A. That will probably confuse people even more, though.

"Nominal" supply for most residential and light-commercial applications in the US has been 120 or 240 for a long time, rather than 110/220.

[Rawn77]

So let me add to the confusion:
Does that mean when I hook up the RV with a 50A cordset that only a single 50A 120V is going to the RV?

[Minno]

Depends if you're plugging in a 30 Amp trailer or a 50 Amp trailer.

If it's a 30 Amp trailer, and you use a 50 to 30 Amp adapter, then you have a single 50A 120 VAC circuit feeding your trailer. The 30 Main breaker in your trailer will prevent you from pulling more than 30 Amps and frying your shore power cord.

If it's a 50 Amp trailer, then you have two 50 Amp circuits feeding your trailer (the 2 hot wires mentioned previously). The 50 Amp main breaker in your trailer is a dual breaker, and each side feeds half the circuit breaker box. After that, it's up to the trailer manufacture to determine what circuits run on which half on the breaker box. A typical distribution would be to have one a/c unit in each half of the breaker box. Then other circuits are spread out however they see fit.

Chris

[Rawn77]

Originally Posted by Wayward

Maybe I can simplify the background . (or not )

This is an oversimplification because I will omit a few safety/grounding points that might make it harder to understand the basics

There are really only 3 wires coming in to the typical 50/30amp campsite hook up box.

--------------HOT1

--------------Neutral

--------------HOT2

More questions, please don't shoot me:

At the pedestal for 50A service, there's 2 HOTs, 1 Neutral and maybe 1 Ground??

So if I was theoretically to create my own 50A -> 30A Pigtail, I wouldn't have to worry which of the 50A HOTs to discard or are there times at the pedestal that only one of the two 50A HOTS are used?

It would seem that after reading all of the above comments that there are two 50A-100V HOTS at the 50A receptacle on the pedestal but that only one of them is ever used. Then why is it there? Especially if no one is combining the two to create a 240V connection.

[Rawn77]

Originally Posted by Minno

Depends if you're plugging in a 30 Amp trailer or a 50 Amp trailer.

If it's a 30 Amp trailer, and you use a 50 to 30 Amp adapter, then you have a single 50A 120 VAC circuit feeding your trailer. The 30 Main breaker in your trailer will prevent you from pulling more than 30 Amps and frying your shore power cord.

If it's a 50 Amp trailer, then you have two 50 Amp circuits feeding your trailer (the 2 hot wires mentioned previously). The 50 Amp main breaker in your trailer is a dual breaker, and each side feeds half the circuit breaker box. After that, it's up to the trailer manufacture to determine what circuits run on which half on the breaker box. A typical distribution would be to have one a/c unit in each half of the breaker box. Then other circuits are spread out however they see fit.

Chris

Thanks Chris
You've explained everything!
I feel much better now.... I'll sleep tonight

[Minno]

Originally Posted by Rawn77

More questions, please don't shoot me:

At the pedestal for 50A service, there's 2 HOTs, 1 Neutral and maybe 1 Ground??

So if I was theoretically to create my own 50A -> 30A Pigtail, I wouldn't have to worry which of the 50A HOTs to discard or are there times at the pedestal that only one of the two 50A HOTS are used?

Shooting is not allowed... Like someone else said, this is electricity. No dumb questions. better to be safe than zapped.

No maybe on the ground - it's there. The ground, is literally that. It's connected to a ground rod somewhere. If not at the campsite post, then wherever the main circuit panel that feeds the campground is located. The ground rod is a 10 foot copper rod that's pounded into the ground, and provides a safety for the electrical service, each RV, each appliance, and you.

If you make your own adapter, you are correct. Pick one of the 50 Amp hots (black) to connect to the 30 Amp hot (black). Simply do not connect anything to the other 50 Amp hot in the 50 Amp plug. Be sure to connect neutral to neutral (white) and ground to ground (green). Since this is providing 30 Amp service, use at least 10 Gauge wire.

Chris

[TG Twinkie]

Many 240 volt appliance require the neutral as well as 2 hot legs. The light inside a dryer is 120 volts as well as the motor that rotates the drum. The heating element in most dryers is 240 volt. The controls are low voltage requiring 120 volts.

[Rawn77]

Chris
Help me understand something:
If I'm trying to adapt a 30A RV to a 50A pedestal, dropping one of the 50A HOT's makes sense if I'm making my own pigtail.

But, if I'm connecting my 50A RV to a 30A pedestal with a pigtail, wouldn't I need the single 30A HOT to connect (or perhaps better to say...split) to both 50A HOTs in the pigtail?
Look at this cordset from Park Power

If the 50A RV indeed has two sides to it's circuits, the 30A single HOT wire would have to feed both sides, correct?

How do you think the above cordset is wired at the female end?

[Wayward]

Originally Posted by Rawn77

if I'm connecting my 50A RV to a 30A pedestal with a pigtail, wouldn't I need the single 30A HOT to connect (or perhaps better to say...split) to both 50A HOTs in the pigtail?
Look at this cordset from Park Power

If the 50A RV indeed has two sides to it's circuits, the 30A single HOT wire would have to feed both sides, correct?

How do you think the above cordset is wired at the female end?

An RV wired for 50 amp service has some outlets and appliances connected to one 110v leg while other outlets and appliances are connected to the other leg. If the RV has two air conditioners. each would would be connected to a different 110 volt leg.

The 4 prong plug going into an RV with "50 amp" service is actually carrying two 50 amp circuits at 110v (HOT1 and HOT2). A 30amp RV adapter like you are considering could power either leg , or both.

If you wire the single 30amp 110v hot line from the campsite into both HOT1 and HOT2 on the 4 prong 50amp female plug, all 110v circuits in the RV would be live. Any 220v appliance would not work.

If you turn on both AC units, or power up too many 110v appliances you will be sure to kick the 30amp campsite circuit breaker.

(ps: if you buy such an adapter, look at the female end carefully. Some are 4 prong but some are 3 prong. The three prong ones are appear to be special for 50amp/220v RVs with detachable power cords. )

One like this powers both legs