Finding a lost leg

[remoandiris]

Somewhere between the plug into the coach and the main breaker, I lost one leg of power. Is there a "common" cause for losing one leg of a 50 amp circuit? I have 240 V at the end of my shore power cable where it plugs into the coach, but only 120 V at the main breaker inside the coach.

[Devilishjim]

I believe that other leg is in your converter being as the two legs split for different sections of your coach, What I am curious to find out is how does one breaker control both legs ?

[dennisvr]

I had a bad transfer switch that did the same thing. That would be the first place I would check.

[AFchap]

I had a bad transfer switch that did the same thing. That would be the first place I would check

Yep, same for me. One leg was hanging in the transfer switch. I got a new ATS at a great price from dyersonline ...problem gone.

[Kirk W]

We really don't have nearly enough information here to give you anything specific. Am I correct in assuming that your RV is a 50A one and that it has a cord with a 4 pin plug into the 50A receptacle of the pedestal? Just to be clear I'll post a picture of the typical RV pedestal box.

The next question is what you have inside of the RV as the power distribution panels found in the RV are not standard but come in a wide range of versions and manufacturers from standard one used in housing to unique ones built for the RV industry. The circuit breaker that supplies a 50A outlet has two handles that are mechanically tied together and if one trips, it will open the other as well. It is possible for one side to open, leaving the other closed but that is pretty unusual and means that the supply breaker has failed.

 

Inside of the RV, if it is a 50A type there will be two separate load supply bus-bars with about half of the circuits supplied by each one. In the event that you loose one hot leg from the power supply, there will then be circuits inside of the RV which have no power at all. If you connect a 30A RV to a 50A outlet by using one of the adapters for a 30A RV cord, you will only be connecting to one of the two hot legs in that pedestal. Also as others have said, you could have a bad contact inside of the power transfer device that has failed and so only get one side, but it would still mean that some circuits would have no power at all.

 

Part of the question of 120V versus 240V is where you are measuring inside of a 50A RV. The only place inside of a typical RV that you could measure 240V is inside of the 50A distribution box, where you would then measure between the two hot legs. Is that where you are measuring? When you measure inside of the RV distribution box you should have two hot leads, L1 & L2 as well as one neutral leg and one ground leg. When all is working properly you can measure 120V between L1 and either neutral or ground and the same is true for L2. In order to measure 240V you measure between L1 & L2. If one leg is open and one is good, the one of the two legs to neutral or ground will measure 120V and the other should measure near 0V.

[oldjohnt]

Remo, I think I can help you and perhaps answer your questions, but more info would sure help.

 

WARNING those who don’t like in depth comprehensive responses which attempt to educate as well as answer specific questions, you don’t have to read this. NOTE Based on what you stated and spoke of 240 volts, I am assuming you have a 50 amp RV and I’m “guessing” you “might” have a Transfer Switch or Transfer Device/Method that serves your Panel from EITHER a Generator orrrrr Utilty.

 

1) YOU STATE: “Somewhere between the plug into the coach and the main breaker, I lost one leg of power”

 

If you actually lost one leg there??? and IF??? you have a Transfer Switch or Device in between plug and main breaker, and assuming it switches the two hot legs L1 & L2 independently, and assuming the two poles are NOT mechanically tied together, MY GUESS IS the Transfer Switch or Device IS BAD.

 

QUESTION do you have any sort of an EMS between the Utility and your RV panel???? Iffff so and ifffff it can individually control L1 & L2 separately ?? THAT COULD BE THE PROBLEM, but if one leg goes out and in turn neither can continue as I expect, that wouldn’t account for only one hot leg IE NOT an EMS problem. ALTHOUGH IT COULD STILL BE A WIRING OR CONNECTION PROBLEM THERE.

 

2) YOU STATE: “Is there a "common" cause for losing one leg of a 50 amp circuit?”

 

Typical causes of the loss of one leg, depending on what equipment you have, ASSUMING the Utility is fine, may be:

 

a) Transfer switch or device

Loose, burned or open connection in the RV panelboard

c) Open or burned wire or connection somewhere from plug to TS to Panel or plug to panel

d) Bad/Open power cord

e) I DOUBT the main breaker is bad and its two poles are generally mechanically joined together.

 

INFORMATION in case you don’t already know it.

 

At the Utility Pedestal, if alls well, you would measure 120 VAC from EITHER L1 or L2 to Neutral or Ground,,,,,,,,,,,,,240 VAC from L1 to L2.

 

At the RV main panel, if alls well and if there’s a good TS and/or a good non tripped EMS in between, you would measure 120 from L1 or L2 to Neutral or Ground but 240 VAC from L1 to L2

 

If one leg is bad/open or the TS is bad or there’s an open wire or connection or a panel problem (for whatever reason) any appliances and receptacles fed from that bad/open leg WILL SEE NO USEABLE VOLTAGE while appliances and receptacles fed from the good leg CAN STILL WORK FINE.

 

If one leg is bad/open, from it to Neutral or Ground, you would NOT read 120 volts, but subject to inductance and capacitance and type and quality of volt meter, still read some voltage

 

If one leg is actually open, you likewise would NOT read 240 volts L1 to L2.

Since the two legs are split up so one serves some of the RV and the other the rest, the ONLY place 240 is available is between the two incoming L1 & L2 legs.

 

FINAL BEST GUESSES BASED ON LIMITED INFORMATION

Transfer switch or device,,,,,,,,,,,,,Open or loose wire or connection,,,,,,,,,,,,Panel problem like open wire or lug or connection,,,,,,,,,,,,EMS problem (if it could switch L1 & L2 independently and still allow one if other goes down which I doubt)

 

I would check all connections and wires and terminals and lugs and any TS then start where voltages are good then work back through the circuit until you see where voltage is lost.

 

Nuff said,

 

John T Long retired power distribution electrical engineer and rusty as an old nail so no warranty

[remoandiris]

Thanks much for your reply.

 

Am I correct in assuming that your RV is a 50A one and that it has a cord with a 4 pin plug into the 50A receptacle of the pedestal? Just to be clear I'll post a picture of the typical RV pedestal box. Yes.

 

The next question is what you have inside of the RV as the power distribution panels found in the RV are not standard but come in a wide range of versions and manufacturers from standard one used in housing to unique ones built for the RV industry. The circuit breaker that supplies a 50A outlet has two handles that are mechanically tied together and if one trips, it will open the other as well. It is possible for one side to open, leaving the other closed but that is pretty unusual and means that the supply breaker has failed. Neither breaker is tripped.

 

Inside of the RV, if it is a 50A type there will be two separate load supply bus-bars with about half of the circuits supplied by each one. In the event that you loose one hot leg from the power supply, there will then be circuits inside of the RV which have no power at all. Yes, that is my situation. Some circuits have power and some do not.

 

Part of the question of 120V versus 240V is where you are measuring inside of a 50A RV. The only place inside of a typical RV that you could measure 240V is inside of the 50A distribution box, where you would then measure between the two hot legs. Is that where you are measuring? Yes, that is where I am measuring. I get 120V measuring between L1 and L2 inside the panel.

 

BTW, I do NOT have a generator. That means I do not have a transfer switch, correct?

[remoandiris]

NOTE Based on what you stated and spoke of 240 volts, I am assuming you have a 50 amp RV and I’m “guessing” you “might” have a Transfer Switch or Transfer Device/Method that serves your Panel from EITHER a Generator orrrrr Utilty. Yes, it is a 50 amp fifth wheel without a generator.

 

1) YOU STATE: “Somewhere between the plug into the coach and the main breaker, I lost one leg of power”

 

If you actually lost one leg there??? and IF??? you have a Transfer Switch or Device in between plug and main breaker, and assuming it switches the two hot legs L1 & L2 independently, and assuming the two poles are NOT mechanically tied together, MY GUESS IS the Transfer Switch or Device IS BAD.

 

QUESTION do you have any sort of an EMS between the Utility and your RV panel???? I have a portable Progressive Industries Surge Guard. It (and the power cord) are fine. At the end of the power cord that connects to the coach, I have 120 V AC from two of the connections.

 

2) YOU STATE: “Is there a "common" cause for losing one leg of a 50 amp circuit?”

 

Typical causes of the loss of one leg, depending on what equipment you have, ASSUMING the Utility is fine, may be:

 

a) Transfer switch or device

Loose, burned or open connection in the RV panelboard

c) Open or burned wire or connection somewhere from plug to TS to Panel or plug to panel

d) Bad/Open power cord

e) I DOUBT the main breaker is bad and its two poles are generally mechanically joined together.

 

INFORMATION in case you don’t already know it.

 

At the Utility Pedestal, if alls well, you would measure 120 VAC from EITHER L1 or L2 to Neutral or Ground,,,,,,,,,,,,,240 VAC from L1 to L2.

 

At the RV main panel, if alls well and if there’s a good TS and/or a good non tripped EMS in between, you would measure 120 from L1 or L2 to Neutral or Ground but 240 VAC from L1 to L2 Measuring between L1 and L2 at the RV main panel gets me 120 VAC.

 

If one leg is bad/open or the TS is bad or there’s an open wire or connection or a panel problem (for whatever reason) any appliances and receptacles fed from that bad/open leg WILL SEE NO USEABLE VOLTAGE while appliances and receptacles fed from the good leg CAN STILL WORK FINE. This is the symptom I have. Some circuits work and others do not.

 

FINAL BEST GUESSES BASED ON LIMITED INFORMATION

Transfer switch or device,,,,No generator, so that means no transfer switch, correct?

Open or loose wire or connection A loose wire is my guess, I just have no idea where to start searching for it.

Panel problem like open wire or lug or connection All screws in the panel I could reach are tight.

 

Thanks much for your input. This is very frustrating.

[MrSeas]

Check you 50 amp plug at both ends of the power cord.

[Chad Heiser]

Just because you do not have a generator, does not mean you do not have a transfer switch. If your coach was generator ready, it should have a transfer switch installed.

 

Since you have verified the park power panel has power to L1 and L2, I would do as MrSeas said and start with the cord and all connections in between (including your portable EMS).

 

Plug the portable EMS in without the cord. Check power on the loose end of the EMS. If that is working, plug the cord in to the EMS and unplug the other end from the coach and check power there. If that is fine then plug the cord into the coach and find the transfer switch and check power there. If that is fine then the next point of connection would be the power panel inside the coach. You need to check each point of connection systematically to find were it is failing.

[oldride]

Just my 2 cents . I had the same or like issue dropped power on 1 leg and the main A/C would not come one. Finally i turned power off at outside pole breaked unplugged cable cleaned both ends with spray contact cleaner. Plugged back in and I had both A/C working again. BTW I had already reset the main outside breaker a couple of times.

[remoandiris]

FIXED!!!

 

The problem - L2 was loose at the plug on the coach's exterior wall. I unscrewed the 4 screws and pulled the plug out. After loosening the plastic connections, I slid back the plastic cover housing the wires for L1, L2, neutral and ground. Copper wire for L1 and L2 were showing, L2 showing more. I loosened the L2 connection, slid the wires in, and tightened the screw. In my haste, I failed to perform the same act on L1. When I get home, I will redo this AND put some Vibra Tite on the threads.

 

Once I put everything back together and plugged back into shore power, my wife exclaimed that power was restored to the outlets that had been inop.

 

Thanks all.

[Chad Heiser]

Congratulations! It pays to be systematic when diagnosing electrical issues.

[oldjohnt]

CONGRATULATIONS a simple loose wire or connection was all it was YAYYYYYYYYYYYYY

 

Its the old KISS principle at work lol but at least maybe something was learned in this fun discussion

 

THANKS for your feedback

 

John T

[Kirk W]

FIXED!!!

 

Once I put everything back together and plugged back into shore power, my wife exclaimed that power was restored to the outlets that had been inop.

Great work! Some of us tend to overlook the connection between the power cord and the RV side as many do not have them. None of our RVs have had that type of connection with the removable cord, but I have considered converting our present one to that type of cord connection. It is always good to look at the simple things first as they seem to be the most frequent source of problems. As previously mentioned, if the RV was sold as "generator ready" then it very likely does have a power transfer device, but since most fifth wheel trailers don't come that way, most likely you do not have one and with no generator on-board, that is a good thing. One less thing to fail. You did the right thing to find the power to one side and not the other as that is by far the most common indication of the loss of one leg of a 50a power supply. When trouble shooting, it is best to check each end of the circuit, then try to spit the possible problem area into halves, looking for power in the middle and thus cutting the possible locations in half as well. Once you knew the cord was good, you hit the next most probable site.

 

Most of us who have traveled a lot in our RVs have learned that loose connections is one of the most common sources of electrical power loss. Many of us make the checking and tightening of those connections in the main power system a part of our annual maintenance. When you get home, it would probably be wise to go through your power distribution box and tighten all connections there as well.