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Topic: Air Conditioner Power Question - 240 Volt Power (Read 12 times) previous topic - next topic
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Air Conditioner Power Question - 240 Volt Power
Yahoo Message Number: 158473
I am probably a bit off subject. However , there was discussion of 240 volt power in an RV and I thought that I would contribute my two-cents worth.
 Joan provided the following link: http://www.myrv.us/electric/ and the site provides good information.
 240 volt power in most RV's is handled the same as 240 volt power in a stick house or at least any house less than 50 years old that conforms to NEC.
 240 volt shore power enters the RV via a "main breaker" in the AC power distribution panel. The power is then divided into two 120 volt phases which are referenced to the incoming neutral line; for discussion purposes Phase A and Phase B. The power distribution panel is physically organized such that the circuit breakers for external loads are alternately connected to Phase A and Phase B; specifically if a load circuit breaker is connected to Phase A,  the two load circuit breakers next to it are connected to Phase B.  In rigs with 2 A/C units, the two units typically run on 120 volt power and are connected to opposite phases of the 240 volt power. No doubt there are cases in larger RV's where 240 volt power is used to run A/C's or something like a clothes dryer.
 In most RV's, particularly Class C's,  you find only load circuit breakers that provide 120 volt AC power. To get 240 volts out of this distribution panel one must install a 2-pole circuit breaker that occupies two adjacent load circuit breaker positions in the panel. This is not to be confused with a "twin breaker" that installs in a single load circuit breaker position and provides two external load circuits; both connected to same 120 volt phase.
 To provide a 240 volt load circuit breaker, an experienced electrician might install single pole (1-pole) breakers in two adjacent load breaker positions and physically connect their "trip/reset" handles with a jumper; thus if one breaker trips, it will trip its partner. I have seen this done where there are "twin-breakers" installed in adjacent load breaker positions. The "closest" breaker of each twin breaker is one pole for the 240 volt load circuit breaker. Such tricks are common when trying to install additional circuits in an existing power distribution panel where available load breaker space may be limited or non-existent. Probably 95% of all 240 volt power distribution panels have the "alternate phase connections" for the load circuit breakers. However, there may be panels for RV's that are not built this way.

A few side notes on related subjects: ØCampground  "power pole's"  that have a 30-amp service connection and a 20-amp duplex are typically being fed by a 240 volt power source. The 30-amp connector and the 20-amp outlet are connected to opposite phases of the 240 volts. There may also be a 50-amp connector in the box. It is just connected to the two phases of the 240 power in parallel with the 30-amp connector and 20-amp duplex outlet. Whether you can concurrently use both the 30-amp service and the 50-amp service depends on the campground wiring that is feeding the "power pole." Often this "feed" is just a 50-amp or 60-amp 240 volt circuit, which precludes obtaining maximum power from both the 30-amp and 50-amp connectors.
ØSomeone mentioned that electricians often do not know how to wire campground electrical connections. This is typically the result of the electrician not knowing how to associate the "hot, neutral, and ground" wires with the pins on the connectors. Most of these connectors come with an instruction sheet that identifies the pins. However, one must read the instructions. Twice I have helped a campground electrician replace a 30-amp connector in the power pole.
ØA major problem in campground power poles is deterioration of the contacts in the power receptacles which is caused by two things: weather and people connecting and disconnecting with the receptacle "hot." The latter causes arcing and burning of the contacts. The deterioration causes increased resistance between the receptacle's contacts and the pins on a shore power connector and as a result, heating. This is quite common in older campgrounds. On several occasions I have noted significant heating of the plug on my shore power cable even when drawing limited current. I carry a small spray can of "contact cleaner" and will spray some into the receptacle on the power pole if it looks dirty.
ØCampgrounds in the USA are required to meet the requirements of NEC (&UL) which says that the power pole must contain a circuit breaker that turns off the power. Older campgrounds may not have a circuit breaker but are "grandfathered" in. As I recall in Canada the CSA does not require such a breaker, although it is common to find them.

Doug Baker
Re: Air Conditioner Power Question - 240 Volt Power
Reply #1 –
Yahoo Message Number: 158477
Thanks, Doug! Very "current" and "enLIGHTENING" information. (Sorry, that's the best I can do in the early a.m.!) ;-)

Joan
2003 TK has a new home
Re: Air Conditioner Power Question - 240 Volt Power
Reply #2 –
Yahoo Message Number: 158480
Doug's post has me feeling uncertain of my knowledge.  Doug said "In most RV’s, particularly Class C’s, you find only load circuit breakers that provide 120 volt AC power. To get 240 volts out of this distribution panel one must install a 2-pole circuit breaker that occupies two adjacent load circuit breaker positions in the panel."

My 30 amp system has a power line, a neutral line and a ground line.  It enters the ATS where the power and neutral are switched by a relay controlling the feed from shore or generator into the power panel.  In the power panel, there is a single power buss and a neutral and ground buss.

My understanding of this setup is that a 30 amp service for RV's provides 120 volts, 30 amps, not 240 volts.  I think there is no way to get 240 volts from my power panel, regardless of what you do with breakers.  There is only 120 volts in that box.

As I understand it, a 50 amp service has 2 power or hot lines, a neutral line and a ground.  Each power or hot line carries 120 volts.  If the two 120 volt power lines are phase shifted, they can be wired with a breaker connecting to each of two power busses to provide a 220 volt circuit, but that is not how our LD's are wired.

What am I missing?

Ken F in NM
'08 MB
Re: Air Conditioner Power Question - 240 Volt Power
Reply #3 –
Yahoo Message Number: 158481
Doug is speaking in general - including both 50A and 30A RVs. What he is referring to is the fact that even in 50A RV panels, most breakers will only provide 120V, from one side or the other of a split-phase 240V supply. Note Doug, ASFAIK, has not yet returned to a LD from his 50A class-A, so he is familiar with both types of services.

Steve
2004 FL
2013 Honda Fit
Re: Air Conditioner Power Question - 240 Volt Power
Reply #4 –
Yahoo Message Number: 158490
"Note Doug, ASFAIK, has not yet returned to a LD from his 50A class-A, so he is familiar with both types of services."
 Brain fart - Doug does not have a class-A nor 50A service - but he knows of which he speaks...'

Steve
2004 FL
2013 Honda Fit
Re: Air Conditioner Power Question - 240 Volt Power
Reply #5 –
Yahoo Message Number: 158491
You are correct. Doug does not have a Class A with 240 volt 50 amp shore power. I used to have an LD but now have an SOB Class C. However, I have done electrical work on a couple of Class A's that belong to friends.

AC distribution panels for RV's come in at least two flavors: ØVersion 1 is strictly for 30 amp service and has a single AC distribution bus to which the load circuit breakers attach.   The old Magnetek 6300 series boxes, and most other units from that era, were of this type.  (I had to replace the AC distribution bus in one of these as a breaker came loose and arced, burning the bus.)  As RV's advanced they needed more power and the 240 volt 50 amp service was developed. This required a different AC distribution system.
 ØVersion 2 can be configured to work with either a 120 volt 30 amp service or a 240 volt 50 amp service. It has two AC distribution busses to which load circuit breakers attach. When configured for 240 volt 50 amp service, one AC distribution bus is connected to each phase of the 240 volt shore power.   If configured for 120 volt 30 amp service the two AC distribution busses are tied together. The way in which you configure the unit to work with a specific type of shore power differs from one manufacturer to the next.
 I have never seen one, but I suspect that there are AC power distribution units that will work only with 240 volt 50 amp service.
 I do not know what power distribution system LD is using currently. For many years they used Parallax 7300 Series devices. I rebuilt mine once but cannot remember the configuration of the AC distribution busses. I would guess that it is a single bus unit as it holds a very limited number of circuit breakers. My current coach has a Progressive Dynamics PD4560K power center that can be configured for either 240 volt 50 amp service or 120 volt 30 amp service. Mine is the latter. However, the manual tells me how to configure it for 240 volt 50 amp service should the need arise. (By definition it will never arise.)

Doug Baker
 
Re: Air Conditioner Power Question - 240 Volt Power
Reply #6 –
Yahoo Message Number: 158492
Ken, You are not missing a thing.  Your thinking is correct.  AFAIK the standard AC power configuration for LD's is 120 volts 30 amps.  That does not say that a 240 volt 50 amp service could not be installed.  However, it won't be cheap.  I don't know why you want 240 volts, but I would look for an alternate solution.
 I neglected to say that you must have a 240 volt 50 amp shore power service and an a 240 volt 50amp AC power distribution box before you can get 240 volts to use for a load.   I guess that I thought it was obvious.
 The shore power cable you describe is strictly for 120 volt 30 amp service.  The AC power distribution unit in your coach is built, or configured, for that type of service.  To get 240 volts to use in your coach you will have to install a 240 volt 50 amp shore power cable.  In addition you will have to install an AC power distribution panel that will handle the 240 volt 50 amp service.  Only then can you plug in circuit breakers that can feed 240 volts to some load.  Depending on the age of your coach, it may be possible to convert your existing AC power distribution panel to work with the 240 volt 50 amp service.  If this is even possible, at a minimum the existing 30 amp 1-pole main breaker will have to be replaced with a 50 amp 2-pole breaker. (Prepare for sticker shock when you shop for this breaker.)  Converting your existing AC power distribution panel may also require wiring changes within the panel.  (I made some comments of panels in another post.)
 Unless you have done a significant amount of electrical work, I would advise you to engage the services of a qualified electrician, with RV experience, to do the work.   I have done a fair amount of this type of work and the projects never go as planned.  You are often required to develop "alternate solutions" to solve problems that occur.   Doing this type of work in a stick house is one thing but doing it in an RV is a different game.  If you have problems with work in a stick house, you can run down to Home Depot or Lowe's and generally get free advice (sometimes good, sometimes not so good).  But don't ask these guys about RV electrical problems.

Doug Baker