KTM Camper
California
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Joined: 02/28/2007
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I am installing a new 50A service for the MH and am looking for electrician advice on sizing the neutral. The distance between my house main panel and the new 50A receptacle will be 143'. Calculating voltage drop assuming a full 50A load I have determined I need to use #2 wire for the two 120V hot wires (this results in a voltage drop of 2.87%).
Question is this, since my MH is utilizing two independent 120V services and there are no 240V loads, how do I size the neutral wire to accommodate unbalanced loads? Can I use #2 wire for the neutral or do I need something larger?
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WayneZat
Tucson, AZ
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Joined: 04/17/2004
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I haven't looked but I would say no, it #2 carries the load, you can only pull 50 amps then your breaker trips. Your breaker will trip at 50 amps not 100, and I don't see where you will ever pull the full 50 amps.
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smkettner
Southern California
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Joined: 03/21/2005
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Neutral should be the same size as the hot connections.
http://www.myrv.us/electric/
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Hurricaner
Hurricane Utah
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Joined: 02/17/2007
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The neutral can be sized the same as the hots as it is impossible for it to carry more current under normal operating conditions. I would also use 240 volts for your calculations. Although it is possible for a 50 amp service to use 120 volts exclusively, it is highly unlikely especially at anything over 30 amps. I would use #4 for that distance, #2 is overkill.
Sam
Sam & Kari
Hurricane, Utah
2004 34' Damon Challenger 315
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Chris Bryant
DeLand, Florida, USA
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Nope- the most the neutral will every carry is 50 amps, and that is unlikely, though possible.
-- Chris Bryant
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Roadpilot
Lakes Region of New Hampshire
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Joined: 09/16/2006
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The two hot wires on 50 amp service are out of phase, i.e. 180 degrees out of phase. Therefor the two neutral currents are subtracted. If the loads on each phase were perfectly balanced, the neutral current would be zero.
As an example, say you have to matched AC units, one on each phase, each drawing 12 amps. Each hot would measure 12 amps, but the neutral would measure zero amps.
If the campground were wired incorrectly or possibly a long time ago, the two hot wires may not be out of phase. If this were the case, the neutral currents would add. In the example above, each hot would measure 12 amps and the neutral would measure 24 amps. The breaker is in the hot lead, not the neutral, so it wouldn't be able to protect against this problem.
They sell inexpensive checkers that will tell you if the 50 amp service is wired correctly.
Bottom line is use the same size wire for the neutral as the hot wire, because you could have a load on only one phase so the neutrals wouldn't cancel. Then just in case, buy a checker.
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enblethen
Moses Lake, WA USA
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Joined: 01/05/2005
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The grounded conductor (neutral carries only the unbalanced loads.
Sizing should be calculated same as the feeder circuit. Yes, you could downsize by calculating this number.
"Exception: For 3-wire, 2-phase or 5 wire, 2 phase system, the maximum unbalanced load shall be the maximum net calculated load between the neutral and any one ungrounded conductor multiplied by 140 per cent" NEC article 220.61
I would not recommended downsizing in an RV application to start with. Newer products using heavy non-linear loads such as converters, inverters, and fluorescent fixtures throws out a bunch of harmonics.
I would suggest you add an additional receptacle, a 15 or 20 ampere GFCI at the RV end. It comes i handy for work lights, drills or such.
Bud
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dontay
Mims, Florida
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I agree that the #2 wire is way overkill and over-expensive. I used #4 from the house 220' to the workshop for 60 amp 240 V service. From the workshop to the RV garage I used 110' of #6 for the 50 amp service.
We are living in the MH while building a new house so we are at the end of a 65' 30 amp extention cord since we don't want to be in the garage except during storms. (Waiting delivery of a 50 amp extention cord.) But even with all that length the AC Volt meters I installed in the MH (see pictures on webshots) never drop below 110 Volts with one a/c running. One time it droped down to 100 V when I turned on the a/c but switching the water heater from 110 V to gas made the voltage rise back to 110 V.
50 amp service is really two 50 amp lines wired to 240 V. I do not know if any MH's have 240 V appliances. Ours does not. In fact, the generator puts out 120 V on each leg that in in phase with the other. That is if you measure across the legs with a meter you get 0 V. But each is 120 V to neutral.
* This post was
edited 04/21/08 12:24am by an administrator/moderator *
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LarryJM
NoVa
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Joined: 11/09/2007
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While it was only 6' CLICKY the 50A range cord that is used for my dual 30A dogbone has two 6Ga (black and red hot sides) and 8ga for the white common and green ground.
Larry
2001 standard box 7.3L E-350 PSD Van with 4.10 rear and 2007 Holiday Rambler Aluma-Lite 8306S Been RV'ing since 1974. TRAILER MODS
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Buffalobilly
Holiday Island, AR
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Joined: 07/15/2001
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I agree that the neutral should be the same size as the legs.
Now there is a know problem with the neutral in most RV boxes. Look at this RV electric. Be sure to read the open neutral section.
Bill
Buffalobilly
95 Safari Sahara
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