Running 50 amp circuit Need Expertise

[5picker]

Originally Posted by D W

These days, many of your high-end ranges require the NEMA 14-50 configuration as opposed to the standard 3 prong NEMA 10-50.

Originally Posted by Tiggerdad

Same for dryers.

Correct.
A 50 amp R/V outlet is no different than either of these.

The CONFUSION comes when folks try to wire up a 120v 30a R/V outlet like the old 240v 30a range/dryer outlets.. Bad things happen.

[Larry-NC]

Originally Posted by Bama Rambler

In the U.S. the standard residential split phase power is 120/240 volts. Your RV is the same. Any certified electrician will be very familiar with how that connects. The wires will be L1 (hot), L2 (hot), Neutral & Ground. The receptacle is a 14-50R and it has terminals X,Y,W,G. X is L1, Y is L2, W is Neutral & G is Ground.

There's not nearly as much confusion about how to hook up a 50 amp service as there is for 30 amp RV service.

You can do it by the colors:
W(hite) is Neutral
G(reen) is Ground
L1 and L2 are the two hot wires. It doesn't matter which phase goes to which terminal.

Larry

[b bob]

Originally Posted by Herk7769

To understand the relationship between voltage and current is not "overly" complicated, so bear with me.

As many have stated previously, a 50 amp wired coach has what is called a "split phase" 50 amp 120 VAC service. The 220 VAC supply panel is "split" with 120 VAC L1 on one side and 120 VAC on L2 on the other, with a "Neutral" that is common to both circuits.

Alternating Current (AC) means that the direction of the current alternates between the "hots" (L1 or L2) every 1/60th of a second (called 60 cycle AC).

Voltage measured between L1 and L2 would be 220 volts AC with the direction of flow alternating between the two.

When a Neutral is used, the source phased voltage is "split" in the middle with 120 volts AC available on each (L1 and L2 when measured relative to the Neutral).

Then, every 1/60th of a second, when voltage between on L1 is "positive", the Neutral becomes the return path for that leg of the circuit. Concurrently, it ALSO becomes the "positive" for the L2 120 volt current flowing through to the L2 side ("negative" if you will). Then 1/60th of a second later everything alternates the other direction from L2 through the Neutral to L1.

Because of this relationship, the identical current is available on both sides of your 120 volt AC panel ALL THE TIME.

How MUCH of the current YOU have available to use is "limited" by the protection that is installed at the source to protect the wiring and equipment being used down stream. That protection, (the circuit breaker), is "Ganged" so that an overload on one leg will trip both legs OFF to protect the Neutral source wire.

Remember that BOTH sides "see" the same available current. If the campground's 50 amp service is wired correctly, each leg will always have 50 amps of service available to be used because it is limited by the campground's pedestal breakers and not for any other reason.

Because of the purpose of your camper's circuit breakers is to prevent circuit current from exceeding the rating of your camper's wires (including your connecting wire from the camper to the pedestal) and your installed equipment (like outlets and direct wired appliances) and not the campgrounds (which is protected by the pedestal breakers).

Remember also that the breaker is there to keep you from exceeding the maximum current that is safe for your wires on each leg. The actual current you are using on each leg is the sum of everything you have turned "on".

You can have 28 amps of stuff on one leg and still have 45 amps of stuff on the other because you can be using a total of 100 amps (just never more than 50 on a side).

Most campground's also have other service connections (sockets) on their service panel (typically a 30 amp and a 20 amp duplex each on their own breaker).

Those sockets can be wired "upstream" of the 50 amp service breaker or "downstream" of the 50 amp breaker depending SOLEY on the campgrounds pedestal service wires!

In order to be wired "upstream", the campground's service wires to the pedestal must be capable of "serving" 100 amps of service to the pedestal. In this case, all the sockets are capable of providing their full rated power without tripping any others.

However, many older campgrounds are wired for only the service rated on that campground's loop. So for the 50 amp loop, the supply wires are sized/rated only to provide 50 amps to each campsite.

In this case, the additional sockets are wired "downstream" of the 50 amp "main" protection breaker. Normally, the 50 amp socket is fed directly from the breaker and another breaker "out" wire takes the L1 and Neutral go to the 30 amp socket and the L2 and Neutral go to the 20 amp Duplex.

You are welcome to use any combination of outlets, provided the total load does not exceed 50 amps on any circuit leg. For this example, if you are using the 50 amp service on your camper and the L1 camper circuit is pulling 40 amps and you connect another extension cord to the 30 amp socket, any attempt to use more than 10 amps will trip the 50 amp campground breaker.

Herk, if the pedestal is wired "downstream" as you described, would the 50 amp pedistal breaker need to be on for the 30 amp and/or duplex outlets to be powered?

[RVBuff]

Question for Herk or wmtire...This may be just idle curiosity, but you've raised a question in my mind. Suppose you are in a 50-amp RV and using two interconnected devices...say a desktop computer physically connected to a printer. And say the computer is plugged into an outlet served by L1, while the printer is plugged into an L2 outlet. Is there any potential hazard from having the devices on out-of-phase "hots"? Would the neutral side in the two devices be out of phase, thus yielding a 120-volt potential across them?

[cavie]

Electricians have trouble with the 30 amp plugs. Not the 50's. The 50 amp 4 wire plug in your rig is exactly like a 50 amp 4 wire range outlet in a house. It's called 50 amp 220 volt 4 wire. The 30 amp plug is different. It is 30 amp 120 volt 3 wire. 45 year master electrician.

[cavie]

Originally Posted by formerFR

don't rely on this forum for professional electrical advise, as your own electrician is the final word on what you need, HE's the one wiring it!....if he's never 'done it' before, seek another electrician. It's not complicated.

There is no difference between the 220 volts 4 wire plug in your trailer than the 220 volts 4 wire rang plug in your house.

[cavie]

Originally Posted by BuzzWolfAR

We are putting a 50 amp circuit at the end of our driveway for the Cedar Creek 29ik. It runs on a 50 amp circuit. I have a progressive ems 50 amp PTX, I think it is.

The sticker on the fifth wheel says 120/240v, 4 wire ………… and the EMS on the outside where the plug is says 240v. I KNOW the unit runs with 120volt, two hots, common neutral and one ground.

My electrician who is a certified electrician has never done a 50 amp circuit for an RV before, and keeps saying he can run 240volt. I need an electrician who has done these to respond so my guy is clear on how to run this. I don't know the language and am afraid to pull drawing off the internet, as there is so much bad stuff our there.


Please give me something I can print and give to him so we don't screw this one up. Thanks in advance.

There is no difference between the 50 amp plug in your trailer than there is in your 220-volt range plug in your house. Tell your electrician to hook it up. It's the 30 amp plugs that cause problems.

[mawilson]

RVBuff, the first stop for 110v AC in either the computer or the printer is a transformer. The (typically these days) USB cord only has provision for 5v DC. Unless computer or printer has a dead short from AC past the transformer, there's path for AC between the two. BTW, there is no guarantee that any two outlets in your house are on the same phase.

In 38 years of building, programming and integrating computers, the only computing devices I've ever run into that were sensitive to AC phase were the SGI Onyx and Origin computers. Mixing phases for the two 208V feeds for each rack could scramble the ECL logic used to interface CPUs and RAM. That also applied to racks that were interconnected by Craylink cables. I suppose that the phase restriction also applied to Cray computers since the ECL logic and Craylink hypercube interconnections resulted from SGI's purchase of Cray in the 90's.

[cavie]

Originally Posted by Brewhedd

The difference between say a residential stove and your rv is the stove is wired with 2 hots and ground. The rv needs 2 hots, a neutral and ground. While the full 220 is applied to the stove the rv is 2 120 circuits.

220 volts is exactly 2 120 volt circuits. 1 neutral and 1 ground. They have been wired this way since about 1990. just like your trailer.

[cavie]

Originally Posted by RVBuff

Question for Herk or wmtire...This may be just idle curiosity, but you've raised a question in my mind. Suppose you are in a 50-amp RV and using two interconnected devices...say a desktop computer physically connected to a printer. And say the computer is plugged into an outlet served by L1, while the printer is plugged into an L2 outlet. Is there any potential hazard from having the devices on out-of-phase "hots"? Would the neutral side in the two devices be out of phase, thus yielding a 120-volt potential across them?

No.

[wmtire]

Originally Posted by RVBuff

Question for Herk or wmtire...This may be just idle curiosity, but you've raised a question in my mind. Suppose you are in a 50-amp RV and using two interconnected devices...say a desktop computer physically connected to a printer. And say the computer is plugged into an outlet served by L1, while the printer is plugged into an L2 outlet. Is there any potential hazard from having the devices on out-of-phase "hots"? Would the neutral side in the two devices be out of phase, thus yielding a 120-volt potential across them?

Not sure you phrased your concern correctly at the end there, since 120 volts is what you DO want.

But to answer your question, NO there is no problem in plugging in a computer and/or printer to outlets on possibly opposite power legs.

Your home is wired with an L1 and L2. So you could have some outlets on either, depending on how it's wired.

I think what you are getting at is the shared neutral carrying the load imbalance.. This has to do with amperage than voltage.

Mark has the real technical answer in his post above.

[Herk7769]

Originally Posted by b bob

Herk, if the pedestal is wired "downstream" as you described, would the 50 amp pedistal breaker need to be on for the 30 amp and/or duplex outlets to be powered?

Yes indeed. That is one of the best ways to find out if you can "use" the Duplex outlet for an extra kick if there is only a 30 amp and a duplex.

If you trip the 30 amp off and it kills the duplex you will know for sure you won't gain anything.


Speaking of which; what is wrong with THIS picture …

[Herk7769]

Originally Posted by RVBuff

Question for Herk or wmtire...This may be just idle curiosity, but you've raised a question in my mind. Suppose you are in a 50-amp RV and using two interconnected devices...say a desktop computer physically connected to a printer. And say the computer is plugged into an outlet served by L1, while the printer is plugged into an L2 outlet. Is there any potential hazard from having the devices on out-of-phase "hots"? Would the neutral side in the two devices be out of phase, thus yielding a 120-volt potential across them?

No. The reason was answered previously. This also explains why, if there is 100 amps available between the L1 (50 amps) and L2 (50 amps) circuits, why the neutral wire isn't twice the diameter of the hots. It never sees more than 50 amps (ever) due to the alternation of current flow.

[RVBuff]

Thanks.

[Kaadk]

Originally Posted by Herk7769

No. The reason was answered previously. This also explains why, if there is 100 amps available between the L1 (50 amps) and L2 (50 amps) circuits, why the neutral wire isn't twice the diameter of the hots. It never sees more than 50 amps (ever) due to the alternation of current flow.

That's assuming it was wired correctly. If it was miswired to have L1 and L2 of the outlet on the same phase (doubtful, but possible) then the shared natural would see the combined load from both legs.

[Herk7769]

Originally Posted by BuzzWolfAR

I KNOW the unit runs with 120volt, two hots, common neutral and one ground.

My electrician who is a certified electrician has never done a 50 amp circuit for an RV before, and keeps saying he can run 240volt.

In order to save some money he might want to run "240 volt" with no neutral; just a black L1, red L2, and safety green. Most 220 volt appliances, like your water heater will work just fine with those 3 wires. The camper will not.

Print the attachment out for your electrician. Full credit to NOSHOCKZONE.ORG for the illustration!

Oh and BTW, in the box below, the 20 amp GFCI duplex is wired "upstream" of the 50 amp breaker (by that buss tie metal clip). The 50 amp breaker's position does not effect the operation of the 20 amp circuit in this case.

[5picker]

Originally Posted by Kaadk

That's assuming it was wired correctly. If it was miswired to have L1 and L2 of the outlet on the same phase (doubtful, but possible) then the shared natural would see the combined load from both legs.

And once that L1/L2 same phase load reaches 50a, the breaker pops and no harm to the neutral. But we speculate...

[Herk7769]

Originally Posted by Kaadk

That's assuming it was wired correctly. If it was miswired to have L1 and L2 of the outlet on the same phase (doubtful, but possible) then the shared natural would see the combined load from both legs.

Originally Posted by 5picker

And once that L1/L2 same phase load reaches 50a, the breaker pops and no harm to the neutral. But we speculate...

Youwser ...

[Herk7769]

Originally Posted by Herk7769

in the box below, the 20 amp GFCI duplex is wired "upstream" of the 50 amp breaker (by that buss tie metal clip). The 50 amp breaker's position does not effect the operation of the 20 amp circuit in this case.

So from the "looks" of the incoming wires, it seems to me to be correctly sized for 50 amps. Since the 20 amp breaker is upstream from the 50 amp breaker in this box, if both are used to capacity, 70 amps would be on the L2 and Neutral feed wires.

Seems a recipe for eventual burned up wires...

[5picker]

Originally Posted by Herk7769

So from the "looks" of the incoming wires, it seems to me to be correctly sized for 50 amps. Since the 20 amp breaker is upstream from the 50 amp breaker in this box, if both are used to capacity, 70 amps would be on the L2 and Neutral feed wires.

Seems a recipe for eventual burned up wires...

I'd agree.