50 Amp Coach

[Mike in GA]

50 amp service is really two 50 amp lines, right?
Well, I was wondering a while back why I couldn't seem to run more than one roof air at a time in my all-electric coach at a 50 amp campground. Turns out I have only one of the two 50 amp lines passing power through the latched double 50 A main breaker at the distribution panel. I checked outside, and both red and black lines are hot where they come into the coach, and at the screw end of the main breaker, but only one side of the double 50 main is passing power, which is serving all the breakers, but apparently with only half the intended amperage available. Questions:
1.   Do these double 50 latched breakers often go bad?
2.   Trust there will be no unintended consequences when I swap the double 50 out, so long as it's the same mfgr, power off at the box, etc.
Thanks in advance for any thoughts.
Mike in GA

[Melbo]

That should work

Direct replacement and power off ---- you should be fine

Melbo

[HighTechRedneck]

but only one side of the double 50 main is passing power, which is serving all the breakers, but apparently with only half the intended amperage available.

If the one leg is powering all breakers in the panel then I believe it was set up that way and both branches in distribution panel are tied together.  If that is the case and you try to feed both inbound legs into the one, it will be be a short circuit of the two hot legs in a big way with lots of fireworks.  If it was a faulty breaker, then one leg of the distribution panel would be dead.

[bevans6]

Exactly.  Just like in a house breaker panel, every second breaker is tied on a different side of the dual line feed.  If half of your outlets are not working, then the duplex 50 amp breaker may be bad.  If all your outlets work, then your setup was designed and installed wrong for 50 amp pedestal power and you are only using one side of the 50 amp feed.  Which can be fine, if it's done right, but you are still only getting half the power you have available.

Trace the power cord as  it comes into the isolation switch or directly to the panel if no isolation switch.  The cord should have blak and red for power, white for neutral and green for ground.  Trace the path of the two power feeds.  Both should go to the main breaker.  They are the opposite of the load breakers - you should see voltage on them even if the breaker is tripped off when the bus is plugged into a 50 amp service,  since they pass power from the cord into the panel.

Brian

[JackConrad]

Mike,
   Using a voltmeter, check power from the red wire to the white wire and from the black wire to the white wire, both should be 120 volts. Check power from red to black, that should be 240 volts. If it is not, I would start by checking campground source using same method. If the wiring in you panel checks out as above, your panel is connected properly for a 50 amp 120/240 service. In a properly wired 120/240 panel you have 2 vertical rows of breakers. I am pretty sure that in each row, every other breaker is on the same circuit, the others are on the other circuit. Under one of the hot wires in the main breaker circuit numbers 1,3 5,7 should be on one circuit, circuit numbers 2,4,6,8 will be on the other circuit. The same holds true for the other vertical row of circuits. If I remember correctly the top circuit breaker in each vertical row connects to the wire color on that side of the main breaker (Red or Black).
   If all your breakers are fed by 1 side of your double pole main breaker, do not install a standard double pole breaker connecting red and black wires to the top of the breaker (if they are truly 240) You migh end up with an early July 4th fireworks display.  Jack   

[Lin]

It is not uncommon for someone, like myself, that has no need of 240 volt to run both legs of the panel off one 50 amp feed.  This would be rare in an all electric coach though.  If that is the case, there will be a jumper wire somewhere to connect the two legs at or before the panel.  In my case, I have removed one of the prongs from the 50 amp plug and only have a 3 wire cord (hot, neutral, ground).  If you have a store bought 50 amp cord with a molded plug, you might have one of the hot wires just terminated somewhere.  Check to see where each of the four wires goes and is connected.  Also look to see any place that there may be a jumper connecting the two legs.  It could be right in the panel or anywhere there is a connection along the way, like a receptacle.  Before trying to do anything to correct or alter the system, you want to make sure that you have a complete understanding of what you have.  It may be done safely or may be truly dangerous.  People do all sorts of things.

By the way, one 50 amp supply is enough to run two AC's.  The breaker could be bad, or you could have another issue.

[bobofthenorth]

It took me 4 years to discover that our coach had a 3 conductor "50 amp" power cord.  I've always blamed Doofus (the PO) but I suppose Bruce Coach may have wired it that way.  Both sides of our panel were served by one leg of the 50 amp service.  I had 50 amp plugs on both ends of the power cord and the cord was big enough to have been a 4 conductor cable but it turned out it wasn't.  Given that it took me 4 years to notice that fairly major wiring error I guess maybe doofusness might be a requirement for owning this coach. 

[Lin]

Bob,

I disagree about denigrating the PO over this wiring or even calling it an error(there may be other reasons for the title).  The fact that it took you four years to find you had a three wire, one leg 50 amp system would suggest that it worked fine.  This is my second bus with such a system.  The first, I did it myself.  The second came to me that way.  Since I knew it was a three wire power cord, I was prompted to search out why.  The system works fine, the cord is 25% lighter, and I have no need for 240v.  Actually my system is genuine 240 when switched to the generator and faux 240 when plugged in to the shore.

[robertglines1]

what kind of breaker box do you have? did it work well before?If so change breaker they do get weak and go bad.

[Sean]

I disagree about denigrating the PO over this wiring or even calling it an error...

Lin, I think Bob has more reasons than just this one for his nickname for the PO.  We've discussed some of them here before.

That said, I must agree with him on this count as well: an error it is.  A 3-wire, 50-amp service is not a permitted configuration for a coach.

RV's must be equipped with one of only three permitted services.  For larger rigs, there are only two: either a three-wire, 30-amp, 120-VAC service terminated with a NEMA TT-30P, or a four-wire, 50-amp, 120/240 or 120/208Y service terminated with a NEMA 14-50P.  Other "home brew" configurations are not permitted by code.

Moreover, if the rig has either more than five total circuits, or more than two thermostatically controlled appliances, then there is no choice: the larger, four-wire service is required.  That probably includes most of us with coaches larger than 35'.

Now, the code is not explicit about arranging loads across the two legs of such a service. So it is technically possible that someone could legally build a coach with a 50-amp service wherein all the loads were wired to one side, instead of balanced.  But it is definitely not legal to have a 3-wire cord with a 50-amp connector.

All of that applies here in the US.   Bob, I am sorry I am not well enough versed in such matters north of the boundary to tell you whether Bruce Coach ought to have done otherwise or not.  But since Canada tends to follow suit in such matters, I would guess the code there is more or less the same.

-Sean
http://OurOdyssey.BlogSpot.com

[Lin]

Sean,

I suspected that there might actually be some code issue, but do not see what the safety problem would be.  What danger do you see lurking?

[Sean]

Lin,

In this case, one chief "danger" has to do with expectations.  Another is the issue of load imbalance.

With regard to expectations, one reason why codes and standards exist is so that others who come along after the fact, whether that be a new owner, maintenance worker, or whoever, can make reasonable assumptions about how things work.  Whenever anyone sees a 14-50P connection at the end of an RV power cord, that person could reasonably expect that a full 12,000 watts of power are available to the devices inside the RV.

Bob's situation is a case in point:  Seeing that connection on the rig, he had every right to expect that all four wires were present, connected, and available for his use.  It should never be necessary to disassemble these sorts of things and count wires, or have to measure wire gauges for that matter: a 50-amp service should deliver the full capability of a 50-amp service, not half that capability.  When he ran his load up to 4-5kW, he would be within reason to expect that he was using only about half his capacity or less, and had plenty of safety margin for wire heating, motor starting, or whatever.  Instead he was, in fact using 80-100% of his available capacity and had no margin whatsoever.

The load balance issue by itself can also be a matter of safety, in the sense that unbalanced systems which are designed to be balanced tend to use up the engineered capacity before the expected fill rate is achieved.  This can cause main service breakers to trip, which itself can be a safety hazard.

This kind of load imbalance can also contribute to excessive conductor heating, higher voltage drop, and ultimately reduced performance of appliances such as air conditioners.  Drawing 5kW on a 50-amp three-wire system will actually overload it, tripping the breaker over time, but more importantly, the 42-amp draw will cause significant voltage drop and heating, whereas drawing the same 5kW on a four-wire system will be using only half the capacity, and, at a draw of just 21 amps, far, far less conductor heating and voltage drop.  All of these are factors in why the code requires the 4-wire service for more than, say, two air conditioners -- not because there is an expectation that all 12kW will be needed at once.

In any case, the code is clear: 50-amp systems must be four wire systems accepting 120/240 split phase and 120/208Y, and are required whenever more than two thermostatically controlled appliance or five branch circuits are present.

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

Lin,

In this case, one chief "danger" has to do with expectations.  Another is the issue of load imbalance.

With regard to expectations, one reason why codes and standards exist is so that others who come along after the fact, whether that be a new owner, maintenance worker, or whoever, can make reasonable assumptions about how things work.  Whenever anyone sees a 14-50P connection at the end of an RV power cord, that person could reasonably expect that a full 12,000 watts of power are available to the devices inside the RV.

Bob's situation is a case in point:  Seeing that connection on the rig, he had every right to expect that all four wires were present, connected, and available for his use.  It should never be necessary to disassemble these sorts of things and count wires, or have to measure wire gauges for that matter: a 50-amp service should deliver the full capability of a 50-amp service, not half that capability.  When he ran his load up to 4-5kW, he would be within reason to expect that he was using only about half his capacity or less, and had plenty of safety margin for wire heating, motor starting, or whatever.  Instead he was, in fact using 80-100% of his available capacity and had no margin whatsoever.

The load balance issue by itself can also be a matter of safety, in the sense that unbalanced systems which are designed to be balanced tend to use up the engineered capacity before the expected fill rate is achieved.  This can cause main service breakers to trip, which itself can be a safety hazard.

This kind of load imbalance can also contribute to excessive conductor heating, higher voltage drop, and ultimately reduced performance of appliances such as air conditioners.  Drawing 5kW on a 50-amp three-wire system will actually overload it, tripping the breaker over time, but more importantly, the 42-amp draw will cause significant voltage drop and heating, whereas drawing the same 5kW on a four-wire system will be using only half the capacity, and, at a draw of just 21 amps, far, far less conductor heating and voltage drop.  All of these are factors in why the code requires the 4-wire service for more than, say, two air conditioners -- not because there is an expectation that all 12kW will be needed at once.

In any case, the code is clear: 50-amp systems must be four wire systems accepting 120/240 split phase and 120/208Y, and are required whenever more than two thermostatically controlled appliance or five branch circuits are present.

-Sean
http://OurOdyssey.BlogSpot.com

[bobofthenorth]

Just so we're clearly not bashing Bruce Coach, I don't think they were responsible for this particular wiring "feature".  There was some blowup between Doofus and Bruce near the end of construction of the frenchy-bus and Bruce didn't actually finish it.  After 6 years of ownership I can pretty quickly identify who did what and I'm certain that Bruce did not hang the 3 conducter "50 amp" cord on the coach.

[Len Silva]

I don't know anything about that particular situation but it makes sense that installing the power cord would be among the last things done on a professional conversion.