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Old 04-16-2010, 12:16 AM   #1
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110/120V Wiring

I plan to install a rooftop A/C unit, 40 amp DC charger, television, DVD/Blueray player, and some outlets for plugging in cellphone chargers and other convenience items. My lighting system will be completely on the DC system so I am not running extra lights and switches. I plan on installing an AC inverter to run everything except the A/C and the charger when I am not hooked to shore power, as well I have a 5000W generator that I want to be able to plug in to run everything if need be. The generator has a 4 prong twist-lock connector that provides 120/240V service.

Few questions regarding the AC portion of my wiring...

1) Do I need a breaker box with a 'main' breaker or could I just use a subpanel with individual breakers only?
2) Is a 30 Amp RV plug enough to run everything? Or should I wire up for 50 Amp service?

I will have other questions...
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Old 04-16-2010, 12:48 PM   #2
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Re: 110/120V Wiring

Thanks for the quick reply Smitty. I wasn't sure if having a main breaker was required or not, but like you said, I have a disconnect (unplug the cord), and most sites have a breaker on the pedestal. As far as wiring my lighting for 12V, I plan to do quite a bit of dry-camping in the mountains where I will not have shore power. The fridge is LPG (actually 3-way), no coffeemaker, no crockpot, may put in a microwave later. Basically my survival items are the fridge, the lights, and heat (which will be LPG as well). I am thinking that the 30 amp service will be sufficient. Anyone know the power consumption of a typical 13,500 btu A/C unit and 40A charger?
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Old 04-16-2010, 01:34 PM   #3
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Re: 110/120V Wiring

I have thought about this some more. 30A service is a single 120V 30A line that you split off with breakers for different circuits. 50A service is a pair of 120V 50A lines that are 180* out of phase to eash other allowing you to run 240V appliances as long as the campground is wired correctly. I have learned that most of the RVs that have 50A service do not actually use any 240V appliances and are set up to run everything from a single 120V leg except for the second A/C unit which is tied to the second 120V leg. The larger coaches, on the other had, often have 240V appliances and actually use both legs to get their 240V power. (Isn't electrical theory fun!) What this means to me (and others here) is that if we wire up for 50A service using a standard 50A plug, we get two 120V 50A lines coming into the bus. We could then wire the 'essentials' to one leg and the 'luxuries' to the other leg. I found that my generator is similar, it is wired with two 120V 20A legs that are capable of running 240V at 20A. I could then wire the bus for 50A (two leg service) and make a generator adapter to plug the 4 wire cord into the 4 wire twist-lock connector on the generator. Then I would have 20 amps to run the battery charger and outlets, and 20 amps to run the rooftop A/C unit. If I have lost anyone, I can clarify, but it helps to think these things out loud (in the forum), besides if anyone else finds it useful, I can feel good about helping others.
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Old 04-16-2010, 10:35 PM   #4
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Re: 110/120V Wiring

Smitty, you have got one of the largest and quietest power system I have ever seen. And the best thing is that solar provides 'free' power. Of course, I bet it doesn't feel so free at the moment! Thanks for the help with the AC system so far. I looked at breaker panels today, and plugs, and breakers, etc. I need to reassess my AC requirements, this stuff gets expensive quick!
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Old 04-16-2010, 11:41 PM   #5
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Re: 110/120V Wiring

Smitty, I have been going back and forth on lighting, 12v or 110v. I completely understand what you are saying, but here is my mentality. First of all, most 110v volt lights take up more space. If you have your lights centered on your ceiling, 12v pancake lights have a strong advantage...unless you have a roof raise, which may be one reason you have a different perspective. Second, I already have a battery bank to run my inverter, so why not use it for lighting as well. I'm not adding anything by using 12v for lighting. My electrical system is VERY simple. I don't even have a converter. If I am plugged in, my inverter has a built in 3 stage charger to keep my 12v system charged. One negative is that 12v lighting rules out florescents, but I can use led bulbs if I want (negative would be more expense). Anyway, each way has advantages. I finally went with 12v. Hopefully I don't regret it To be honest, if I had a raised roof, I would probably go with 110v.
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Old 04-17-2010, 12:45 AM   #6
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Re: 110/120V Wiring

Quote:
Originally Posted by jkindt
I have thought about this some more. 30A service is a single 120V 30A line that you split off with breakers for different circuits. 50A service is a pair of 120V 50A lines that are 180* out of phase to eash other allowing you to run 240V appliances as long as the campground is wired correctly. I have learned that most of the RVs that have 50A service do not actually use any 240V appliances and are set up to run everything from a single 120V leg except for the second A/C unit which is tied to the second 120V leg. The larger coaches, on the other had, often have 240V appliances and actually use both legs to get their 240V power. (Isn't electrical theory fun!) What this means to me (and others here) is that if we wire up for 50A service using a standard 50A plug, we get two 120V 50A lines coming into the bus. We could then wire the 'essentials' to one leg and the 'luxuries' to the other leg. I found that my generator is similar, it is wired with two 120V 20A legs that are capable of running 240V at 20A. I could then wire the bus for 50A (two leg service) and make a generator adapter to plug the 4 wire cord into the 4 wire twist-lock connector on the generator. Then I would have 20 amps to run the battery charger and outlets, and 20 amps to run the rooftop A/C unit. If I have lost anyone, I can clarify, but it helps to think these things out loud (in the forum), besides if anyone else finds it useful, I can feel good about helping others.
You are basically correct. However, the goal is balancing the 120-volt loads between the two legs to keep the current down. For example, putting one air conditioner on the black leg and a second on the red is a start. Put a chest freezer on one and a fridge on the other. The 50-amp to 30-amp plug adapters commercially available connect the black 30-amp pin to both the red and black. It is up to you to only draw 30% of full capacity to keep the breaker on the pedestal from tripping.

In your case, you may already be balanced with one air conditioner on one leg if the other loads don't add up to more than that on the other. Plus, with a 20-amp 240-volt plug on the genny you bought, wiring for 240 volts makes a lot of sense.

Any imbalance between the current draws on the red and black legs must return on the neutral. If the two hot legs are balanced, the neutral isn't required to carry any current. Let's say you wire to run on your genset, and you put 20 amps of load on each leg. At full load, the current is red 20, black 20, white 0. If instead, you divide the same loads so the black has everything on it except an outlet that serves a 2-amp laptop charger. You now have black 38, red 2, white 36 (the difference). In both cases you are only drawing 4800 watts. In the balanced case, the total of the currents in the wires heating them up is 40 amps. In the unbalanced case, the total of the currents is 76 amps, so you have a much warmer cord and connectors.

The most dangerous place is in a vehicle with a full 12,000 watt draw - a full 50 amps on each leg. You plug into a mis-wired campground, where both the red and black pins are wired to the same phase, and turn everything on. Any 240-volt appliances won't work, because the leg-to-leg voltage is zero. All the 120-volt appliances will, but the cord will be overloaded. Instead of carrying 50-50-0, the neutral must return BOTH legs, so you get 50-50-100! And the white wire isn't sized to carry 100 amps.

I have seriously thought of using a 3-pole main breaker off of a 240-volt shoreline, so an overloaded neutral can cut the power as well as the hots.

The only thing more dangerous (and expensive!) is a 50-amp pedestal with an open neutral. My brother-in-law found one of those on his second extended trip. Without the neutral to balance the legs, the 240-volts is divided between them by resistance, or the inverse of the draw. In the previous example, the 2-amp laptop charger was 5% of the load, so it would get 228 volts, and the 38 amps of other loads would get only 12 volts, or 5% of the voltage. The pedestal, breakers, and shoreline would all be happy as your appliances go up in smoke.
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Old 04-17-2010, 01:17 AM   #7
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Re: 110/120V Wiring

Quote:
Originally Posted by Smitty
Initially, I was going to do as much on 12VDC as I could... the stuff is overpriced if you ask me. Then after learning a little more, I knew I needed a sine-wave inverter. Once I went that far, may as well go the rest of the way. I found a 2800watt Magnum inverter on Amazon for under $1700 delivered.

I've got a 110VAC fluorescent mounted on the ceiling that's less than 2" deep. I had to switch one of the standard fixtures since the pantry door hit it. I went total fluorescent lighting, even a CF in the bed reading light, and the range hood light. Sure you can get 12VDC fluorescent lighting....it's expensive (as I was saying), I'm not overly impressed by LEDs, though I did buy them for the exterior bus lighting (clearance, stop, turn, etc). So what are you're going to use incandescent lighting?

To be honest, ceiling height had nothing to do with my choice, matter of fact it never even entered the picture. Again, simplicity....I have 1 electrical system, other than circuits for my 12VDC fresh water pump and amplifier for a Winegard (TV) antenna. If something craps-out...I can go anywhere to buy a replacement, and in an emergency (pump failure) I can still have running water.

Smitty
Yeah, having everything on one electrical system would be a big advantage, as would being able to go to any dept. store and buy replacements. One thing I forgot about was that I am only going with a 30 amp service for now because I already had what I needed from my tent trailer. I am going to wire it so that I can upgrade later. By putting as much as possible on 12v, I am reducing the load on my inverter or shoreline. By moving what I can to 12v, I know that I can get by with a 30 amp service. Maybe I should just go with everything on 110v in anticipation of going to a 50 amp service later. I hate decisions, haha! How will you still have water if your pump fails? I'm just not tracking with what you are saying there. Thanks for being willing to share your reasoning behind things. It helps the rest of us think things through better.
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Old 04-17-2010, 10:56 AM   #8
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Re: 110/120V Wiring

I see, if your water pump takes a crap, you don't necessarily need to replace it right away. Thanks Smitty!
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Old 04-24-2010, 06:30 PM   #9
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Re: 110/120V Wiring

When you wire up your electrical panel, should you run a ground wire to the chassis of your bus? I know you run a ground wire to each outlet box and ground the metal boxes there, but should you ground the actual bus itself? At first I thought, of course you do, but then thinking about it more, houses are not made of metal. My background is in automotive electronics (DC) not AC so I am not familiar with wiring codes and such.
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Old 04-24-2010, 07:31 PM   #10
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Re: 110/120V Wiring

You ground the panel box to the frame of your bus. Make sure you get a good ground.
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