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Old 04-15-2010, 11:16 PM   #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, 11:48 AM   #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, 12:34 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, 09:35 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, 10:41 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 04-16-2010, 11:45 PM   #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, 12:17 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.

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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, 09:56 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, 05:30 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, 06:31 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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Old 04-24-2010, 07:31 PM   #11
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Re: 110/120V Wiring

Yes, the ground wire should go to all the boxes and devices, and since they are attached to the bus frame, the bus is in effect grounded.

DO NOT bond the shoreline neutral to the shoreline ground. The campground provides this tie where the commercial power comes in. You can have a neutral to ground bond in your genset when it is connected instead of a shoreline.

It would be good practice (though rarely if ever done) to drive a ground stake at the campsite and connect it to the bus frame before plugging in. This would drain off any voltage induced into the campground ground, so touching the bus will not be a memorable experience.
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Old 04-24-2010, 08:11 PM   #12
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Re: 110/120V Wiring

Quote:
Originally Posted by Smitty
. . . . If I were to ground the panel to the frame, and plug into shore-power at a CG without checking the polarity, what's preventing my bus from being "hot"? lol....today is slow-Saturday for me (so be gentle) ...what am I missing here?

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You are missing absolutely nothing. Plugging into a mis-wired pedestal can kill you, and can kill you faster touching a metal skoolie than the walls of a plastic product. Isolating your electrical system can help, because unless you have outside outlets, or the battery negative attaches to ground through the AC charger, it is unlikely you can stand outside and touch something electrical. It still is a danger inside if the bus is connected to a water supply with high mineral content.

The answer, of course, is never plug into a pedestal without checking the wiring connections. Or buy one of those in-line analyzers that checks the power and voltage for several minutes before flowing it to your bus.
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Old 04-25-2010, 08:43 AM   #13
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Re: 110/120V Wiring

The point I was trying to make about campground mis-wiring is don't use it! Find another site with a properly wired pedestal. There are other ways to find your body connected across the power feed besides standing on the ground with your hand on the bus door handle. Trying to "live with" the wrong set up, such as employing ground isolation, is asking for trouble.

FWIW, Our radio trucks have a ground rod aboard with a wing nut top to attach a wire to the frame, but I've never seen one of the drivers set one up.
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Old 04-25-2010, 08:43 PM   #14
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Re: 110/120V Wiring

You are correct. Extra protection from shocks is provided by having all the grounded electrical components mounted on non-metallic parts of the conversion, such as wooden studs, etc. It is sort of like using the double-insulated power tools that only require 2 prongs instead of 3.

The problem I worry about is allowing a sense of complacency to develop, having the idea that "I can't get a shock no matter what I do, because the bus chassis is isolated." There are ways, such as the water supply I mentioned, that can provide grounds which are acceptable targets for alternate circuit paths.

If there is a chance for an accidental ground path, like through an inverter-charger negative, or an outlet box with a mounting screw sticking out the back scratching through the paint, then I would suggest installing a deliberate and quality bond that you control. Most conversions will have something in the electrical system mounted to the frame. Perhaps it could be one of the appliances, so the bus chassis to third wire ground connection will be present through the appliance, and isolation will be lost.

I have two images when you mention "ground fault." One is a loose hot wire inside a piece of equipment contacting ground, or water getting inside some wiring. If the connection is good and draws high current, it will trip a standard breaker. If a poorer, high resistance connection is made, it may heat up and maybe start a fire, and may make the case electrically hot to touch.

The other image of "ground fault" is completing a circuit outside of the wiring components, like grabbing a hot wire in the breaker box while standing on wet concrete in your bare feet. This can kill you before you are able to draw enough current to trip the breaker.

If you have GFCI "ground fault" breakers, they will trip first. Based on the way they are wired to both hot and neutral, I presume they measure the current going out the hot, and compare it with the current returning on the neutral, and shut off the power right away if any of the current is missing, such as going through your body. I do know from experience that if you so much as put a meter between the hot and ground, they shut down the power. My problem is that some of them can also shut down falsely in the presence of radio transmitters, so there are places I would like to use them and can't.
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Old 05-14-2010, 02:20 PM   #15
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Re: 110/120V Wiring

If I can jump in here...Redbear is right. RVIA requires that all RVs have the AC panels tied to chassis since the ground plane is the alternate return path to the pedestal. ABYC requires boats to do the same. In case of a short (hot touching the body of the bus), the breaker trips as it should. If your chassis is completely isolated from the pedestal, and a hot wire touched the body, you'd have a hot skin that would not trip the breaker, but still bite you when opening your door. Admittedly, if a pedestal were reverse wired hot/ground, it would create the same issue IF the ground wire were not bonded to neutral. If all three wires are connected to the receptacle, and the hot were not in the right location, nothing would work and the first camper would report it, and it would get changed.

You're probably okay now, but a few years down the road as your electrical system ages, you're probably better off rolling your dice toward the campground being wired correctly, than your electrical system never scuffing a hot wire.

Dozens of comittees on the subject couldn't be wrong...oh...wait...nevermind that part.
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Old 05-15-2010, 08:59 AM   #16
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Re: 110/120V Wiring

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. . . Dozens of comittees on the subject couldn't be wrong...oh...wait...nevermind that part.
HMMMM . . Dozens of committees stacked with people who make stick 'n staples for a profit? HMMMM . . . . .

By the way, (no personal experience since we boondock) based on family members' experiences, I would trust my wiring more than that of an average campground. Even if it started out right, campground wiring is subject to insect nest infestation inside the panels, sockets fatigued from repeated plugging and unplugging, breakers switched too many times or loaded with dew. All these possibilities could all cause less than stellar electrical performance. Plus, the Mom & Pop campgrounds with reasonable rates may have been wired as a favor by old Uncle Harry, who LOOKED like he knew what he was doing.
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Old 05-15-2010, 09:55 AM   #17
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Re: 110/120V Wiring

Here is a link to a site that explains RV electrical very well. Especially how to test the campgrounds pedestals. I have read through it a few times and it still amazes me how dangerous it can be to hook up to a worn out or improperly wired outlet. Great info about making a tester too. HERES THE LINK
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Old 05-15-2010, 10:50 AM   #18
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Re: 110/120V Wiring

Great Site! I love this line, repeated on multiple pages:
Quote:
DO NOT TRUST anyone, yourself, friends, relatives or ANY Professional Electrician. ALWAYS check out all RV Electric Service BEFORE plugging in the first time.
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