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Old 03-28-2014, 10:01 AM   #1
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240 volt into two 110 15A circuits

Hey folks, I have a wiring question or situation that needs validating. Apologies for my lack of knowledge, but have been trying to make sense of this and will try to explain to the best of my ability.

I am re-wiring my 59' tradewind for a music studio, and not a camper, so no 12volt is required or will be installed. All I require are four 110 outlets in the coach, for a heater, lights and music gear. I have a 2200 generator [20A circuit], and also intend to sometimes use a 15A shore hookup from a house circuit. I have purchased a 30A RV inlet, I have lots of 3/C 12 300 volt gauge cable to wire the outlets inside, and make external extension chords with [donated by a kind brother].

So here is my question;

I have been told of an option of wiring the 30A inlet into a soon-to-be-purchased 2 pole sub-panel [riveted to the inside skin] using 240 volts, then onto two 110 volt 15A circuits. This is to assure that if my heater throws a breaker, my music gear won't as it will be on another circuit [this is important to avoid missing important recording takes due to power cuts].
Therefor shore hook-up from the 30A RV inlet would consist of splitting the 240 volts into two 110 volts [using adapters?], thus I could use two shore plugs, and two extension chords, creating two possible sources of shore hook-up.

Is this a sound idea, or am I complicating it too much?
Does anyone have an idea of a good cheap sub panel to buy, I don't need anything large?

Many many thanks, I am learning, and plan to hire someone, but want to buy the right gear for the job.
Muskie
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Old 03-28-2014, 10:06 AM   #2
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The 30A RV inlet has 3 conductors... Hot, Neutral, Ground. Hot is nominally 120v compared to either Neutral or Ground.

You'd need a 50A inlet (and 50A sources) to have 240v to work with.

Unless the breaker you throw is the 30A main, you should be able to have the smaller circuits on individual breakers so they are protected individually... e.g. the heater can throw its breaker while the main and the breaker for your music equipment will not necessarily be affected.
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Old 03-28-2014, 10:07 AM   #3
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You won't find a 30 amp 240 V outlet to hook up to. You can easily split a single 120v 30 amp service into two 15 amp circuits, just use a cheap circuit breaker panel with slots for two breakers, and install a jumper across the two buss bars.
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Old 03-28-2014, 10:09 AM   #4
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Quote:
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I have been told of an option of wiring the 30A inlet into a soon-to-be-purchased 2 pole sub-panel [riveted to the inside skin] using 240 volts, then onto two 110 volt 15A circuits.
Don't. 30amp 110vAC plugs are not quite the same as 30amp 240vAC plugs. Do not use one in place of the other. If you wire for 240v, use a 240v socket for your inlet, not an RV inlet.
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Old 03-28-2014, 10:12 AM   #5
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Thanks, so that decides it then. 30A into two 15A circuits.
What will or can I get away with for the shore power extension? Does it have to be 10 gauge, or can I get away with 12 if the draw is small and no heater is being used?

In other words, will a 30A always require the compatible cord?

Thanks folks, a real help!
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Old 03-28-2014, 10:18 AM   #6
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Thanks, so that decides it then. 30A into two 15A circuits.
What will or can I get away with for the shore power extension? Does it have to be 10 gauge, or can I get away with 12 if the draw is small and no heater is being used?

In other words, will a 30A always require the compatible cord?

Thanks folks, a real help!
When you only have a light electrical load you can use a regular 12 ga extension cord with no problem. When I'm loading my trailer and cooling the fridge down, I just run an everyday outdoor extension cord across the lawn. You need a heavy cord and a high-capacity circuit if you're running high-demand equipment like resistive heat or if you're running the AC.
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Old 03-28-2014, 10:21 AM   #7
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Another note: If you're adding a 30A circuit to your home and/or business for this, make SURE the electrician knows it's a 120v RV outlet, and before you plug in, check the voltage at that outlet with a meter. Quite a few people have had to replace equipment in their trailers because an electrician "knew what he was doing" and wired a 120V RV 30A outlet with 240v service.
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Old 03-28-2014, 10:27 AM   #8
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Local electrical Code?

Quote:
Originally Posted by Muskie View Post
...
What will or can I get away with for the shore power extension? Does it have to be 10 gauge, or can I get away with 12 if the draw is small and no heater is being used?...
Perhaps you should be guided by the requirements of the applicable electrical code for your modification. The code will keep you out of trouble most of the time, even when an inspection is not required.

Just Saying.
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Old 03-28-2014, 10:31 AM   #9
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You should only use a 12 ga extension cord if you are at home using the 15a service, or using your 20a rated generator. If you are in a campground using a 30a shore power connection you will need 10 gauge.
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Old 03-28-2014, 10:40 AM   #10
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Use a four conductor #10 wire cable (red and black are power, white is neutral, and bare copper is ground) from the house panel on a 30 amp 240 volt breaker. Put a 30 amp 240Vac rated disconnect in the trailer box. You can then easily have two 15 amp 120Vac circuits on each leg in a four circuit box.

Fot TW or UF copper wire

#14 wire for 15 amps
#12 wire for 20 amps
#10 wire for 30 amps
#8 wire for 40 amps
#6 wire for 55 amps
#4 wire for 85 amps
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Old 03-28-2014, 11:21 AM   #11
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Thanks folks, learned more in an hour than a week!
Off to find a box of some sort, any suggestions?
-m
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Old 03-28-2014, 01:22 PM   #12
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You mentioned 240 volts split to 120 volts in your original question and stated 30amp....

240 volts should only uses a 50amp circuit, a 50amp cord to connect from shore to trailer, and #8 or #6 (depending on length of run) wire from outside connection to panel. The panel also needs to be rated for 50amp.

Based on your needs stated, it is my opinion that 30amp would be more than fine. You will need to wire a 3 plug box with a 30 amp breaker to your main panel at home. You need to make sure you have enough room, space, or amps on one of the two legs in your main home panel to full fill that need, many do not!

You want a 30amp cord from three prong (shore) to trailer and wire with #10 wire from connection to breaker box. You also want to use #10 wire from gen to breaker box. Both the shore and gen would be wired into a 30amo transfer switch before the breaker box. From there you can in most cases have up to 90 amps ready at the breaker box. So that means four 20amp circuits and one 10 amp or nine 10amp circuits, point being you can not go over a total of 90 amp in the box. If you trip a circuit it will be at the trailer first 20amp or 10amp and then go to the main circuit (30 amp) and not the main at the house or shore power source. You want to supply the 20amp circuits with #12 wire, and dedicated your large items with only one item per circuit. Like one 20amp to air, or oven, or heater or other high use items. That way you will not over load the circuit and pop the breaker. I would also place a surge protector from the 30amp transfer switch to your breaker box. Yes they are expensive but your equipment my guess is way more that $250.00.
Hope this helps!
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Old 03-28-2014, 02:49 PM   #13
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50Amp!

I reiterate what others have said: If you want 240V in an RV, you MUST go to 50amp service!

Now, that is not a big deal. I converted my 34 footer to 50amp and will never look back. Just get a Progressive Dynamics PD4590 panel (about $200) and some 6-wire. Rewire the coach for 50amp RV service. You'll have more power available than you'll know what to do with. The 50 amp panel feeds two bus bars, and each one is 50 amp (as opposed to a single 30amp bus bar with the other setup). So Watts = Volts x Amps. With a 30amp RV setup, you have one bus, so you get Watts = 120V x 30amp = 3600 watts. Not bad, but try to run the electric water heater, the a/c, and a hair dryer and you'll blow the breaker. With the 50amp RV service, you have TWO bus bars at 50 amp, so Watts = (2) x 120V x 50 amp = 12,000 Watts.

If you need more than that, better plug into a nuclear reactor

On edit, The way you get 240V is to tap into both bus bars and the common neutral. 120+120 = 240. So you need the 50amp panel for that.

Really though, just get a PD4590 and be done with it. I did, and it's worked out great. It has a superior battery charger built into it than the original too.

Take care!
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Old 03-28-2014, 07:31 PM   #14
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Thanks again folks, and more homework is needed for me for sure.
I think the way i will go is as simple as possible. I have no A/C or water heaters, and will only be running some small recording devices and a 1500w heater plus a couple lights. Having 2 circuits of 15A each from my 30A inlet I suspect will be fine. Again, I won't be camping in this.
My recording gear when all fired up is probably no more than 300w. I have surge protection power bars, and that with the breakers at the sub panel box should do the trick. My goal is to have things trip in the trailer before the shore.

I will take notes on the type of wires I need that you all recommended, and again thanks for the pics and input from all.
Cheers
-muskie
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