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Author Topic: Why rewire a bus from 50A back down to 30A shore power?  (Read 1340 times)
HighTechRedneck
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« on: April 02, 2009, 01:42:04 PM »

I'm just curious.  I've seen several posts lately of people rewiring their buses back down to 30A shore power connections.  What is the benefit?

I am very happy with my 50 amp x 2 leg shore power setup.  I have a 30A adapter that ties the single leg of a 30A to both legs of the distribution panel. Then I have a 30A to 15A adapter for those times when 15A is the only thing available.  I don't have anything that uses 240V, just two legs of 120. 

I spend most of my time attached to 30A connections or less, but it sure is nice when I can connect to a 50A and not have to turn off the air conditioner to run the microwave, refrig and cooktop to make dinner.  And soon I will have two roof air units installed and then it will be even nicer on 50A2 service.
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luvrbus
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« Reply #1 on: April 02, 2009, 01:50:16 PM »

Hightech, if they ever visit AZ or Texas in July they will miss the 50 amp but each of us has our own reasons   

Good luck
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Frank @ TX
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« Reply #2 on: April 02, 2009, 02:56:27 PM »

Hightech,
I have the same set up as you have.
We have 3 AC's and sometimes in TX or AZ we us the 3 at the same time to get the temp down quickly.
After the temp is down only one or somethims two are needed.
I would have no idea why anyone could wish to be limited only to 30 amps.
Frank
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belfert
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« Reply #3 on: April 02, 2009, 06:36:23 PM »

My bus is 50 amp, but I rewired my 8KW generator for 120 volt only.  I don't have anything that needs 240 volt.

Powertech designed things so that the same hot wires for 240 volt also both supply 120 volts (when so configured) so a standard 50 amp transfer switch can still be used.  A jumper does need to be added inside the generator between the 35 amp breakers so the breakers don't trip once total load exceeds 35 amps.
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JackConrad
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« Reply #4 on: April 03, 2009, 04:27:29 AM »

We have a 10 KW PowerTech generator.  I was told by PowerTech that if it is wired for 240/120 (another option is 240 only, no 120), each leg would be 5 KW. So if you only use 1 leg of the 240 , you are limited to 1/2 of the generator's capacity.  Wiring the generator for 120 only, allows full 10 KW capacity with no worries about load sharing or exceeding 1/2 of generators capacity. Of course, you have to use wire large enough to handle maximum power you will use.  If you need 240, please disregard this post.  Jack
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John316
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« Reply #5 on: April 03, 2009, 05:25:01 AM »

We won't rewire for 30 because we need 50. We have five roof airs, and use 120v in the coach. To be off grid for a while isn't a big deal, since we have one bank of four 8d's right now, and we are going to add another bank soon. Our 20kw generator charges us up, and allows us to run the airs. We take 240 from the generator and then split the legs to get 120.

We use anything from 50 amp all the way down to 15 amp (granted that is when we are somewhere with very little usage). We have two trace 4500 watt inverters, which helps the charging differences.   

God bless,

John
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Lin
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« Reply #6 on: April 03, 2009, 08:43:40 AM »

We are wired for 50 amp.  The generator puts out two legs of 120v each, so it is genuine 240 even though we do not have any 240 equipment.  However, the shore line draws only one leg of 120v through a 50 amp cord.  There is a jumper in its receptacle to energize both legs of the panel.  It is sort of faux 240v.  It runs our two roofs airs fine.  If there were a problem, I could see going after that extra 120v leg, but so far none.  It seems that 50 amp service is rather rare, but it nice when there.  We have an electric hot water heater, and the 30 amp campground breaker has popped when we are running one A/C, the water heater, and frig on it.
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Sean
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« Reply #7 on: April 03, 2009, 09:39:11 AM »

My bus is 50 amp, but I rewired my 8KW generator for 120 volt only.  ... so a standard 50 amp transfer switch can still be used.  A jumper does need to be added inside the generator between the 35 amp breakers so the breakers don't trip once total load exceeds 35 amps.


Brian,

If you re-strapped your 8k genny for 120-only, you can be supplying up to 65 amps of current to your mains.  I hope you ran appropriately sized wire for that much current;  in particular, even if you are splitting the output between two separate hot leads, you will still carry the full total current on the neutral.  A "standard" 50-amp transfer switch, for instance, can't be used in this configuration, unless you limited the neutral current (by using, say, a three-pole breaker) to 50 amps, which would thus limit you to drawing only 6,000 watts from the genny.

This is the key reason why RV generators over 6kW are almost universally wired for 120/240; it allows for use of smaller wire and breakers while at the same time remaining consistent and compatible with 50-amp shore service, which is universally 240 by law.  (And yes, I know some campgrounds break this law routinely, before anyone jumps on me for saying that.)

As to the OP question, I don't have a clue why anyone would downgrade a 50-amp system to a 30-amp one.  You can always use a 50-amp coach on 30-amp power, but you can't squeeze any more power into a coach that is only wired for 30-amps no matter what you do.  Besides which, most of us are required by code to have a 50-amp system (any more than 5 circuits, or two thermostatically controlled appliances requires 50 amps).

We get around the biggest nuisance of the 50-amp system, the "elephant trunk" power cord, which is heavy, hard to fake, and stiff as a rod in cold weather, by carrying a completely separate 10-gauge cold-weather-rated cord for cases where only 30 amps are available.  We'll use the 10-gauge unless we need to run two air conditioners; at that load, the voltage drop on the 10-gauge (which happens to be 50' long) becomes a problem, and we switch to the 6-gauge four-wire with a "dogbone" on the end.

-Sean
http://OurOdyssey.BlogSpot.com
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