Power outlet panel

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  #1  
Old 01-02-13, 06:29 PM
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Power outlet panel

I am making a simple power outlet panel to power equipment in a work truck. The panel will be powered by an 10/4 SOOW 100' cable plugged into 30amp dryer receptacles (240/120VAC, NEMA 14-30). The power they need at the truck is two 30amp, 120VAC L5-30R receptacles and a GFCI protected 15A duplex receptacle. I will set up a small break out panel within the truck.

I see three possibilities:
  1. wire the 15A duplex receptacle onto one of the 120V legs, without having a 15A breaker at the truck. So, using junction boxes, I would just split everything into the two L5-30R and the duplex 15A receptacle. I would probably include a simple 30A double pole switch to allow for an easy disconnect. In portable/extension cord settings I see that 15A receptacles are put onto 30A circuits (see this splitters), and I'm confident that the load will stay under 30A a leg usually. If it doesn't, the breaker at the building will throw.
  2. A separate breaker at the truck, maybe using something like this. So, 30A protected cable feeds the box, and at the box it would be split into two 30A/120V and one 15A/120V circuits. There would be no main bus breaker at the truck.
  3. Run a completely separate run to the truck for the 15A receptacles (AKA a normal extension cord).

Suggestions to use a $500 prewired box aren't going to be very helpful to me.

I have rewired houses, but haven't worked on this kind of thing, so appreciate your advice.

Thanks.
 
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  #2  
Old 01-02-13, 07:08 PM
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I'd purchase an 8-space panel at the big box, backfeed a 2-pole 30A breaker, then use 2 30A single poles for the 5-30's and a 20A for a GFCI convenience receptacle.
 
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Old 01-02-13, 07:20 PM
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Unless the cord is hard wired to something (more on that later) you will need an inlet at the truck. DO NOT build a suicide cord!!

Are you expecting all houses will have a 4 wire dryer receptacle for your use or is this at some other building? How is this going to attach to your truck?

If it was me, I would want a disconnect, and overcurrent protection for each branch circuit at the truck. Using a small 4-8 circuit panel would fit the bill at a minor cost.

*Justin beat me to it* =P
 
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Old 01-02-13, 07:34 PM
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Are you expecting all houses will have a 4 wire dryer receptacle for your use or is this at some other building?
Keep in mind most homes (at least here anyway) have 3-wire dryer and range receptacles. I learned that the hard way and hopefully you don't do the same.
 
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Old 01-02-13, 07:53 PM
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Tolyn: Please help me understand your first paragraph. If by 'suicide cable' you mean that I would use a plug to input power into a receptacle - that is not my intention. I am going to hard wire the cable directly into the breakout panel at the truck. Because the switch will be adjacent to where the power inlet plug would be, I don't see any safety benefit to a power inlet plug - although I am interested in what you think.

Also, for buildings that do not have a dryer receptacle, we will add one temporarily or permanently. I bought 'space covers' to use for when these are pulled out. It doesn't make any sense to me to hard wire both sides of an cable attached to a vehicle, so we'll skip that.

Thanks for the advice on back feeding a cheap 8 space breaker box by back feeding a 30A breaker. So, 30A double pole breaker back fed as input. And two single pole 30A, and one 15A, out. Seems like overkill... but I guess this is the only way to overload protect the 15A circuit.
 
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Old 01-02-13, 07:56 PM
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Keep in mind most homes (at least here anyway) have 3-wire dryer and range receptacles. I learned that the hard way and hopefully you don't do the same.
Do they make adapters that let you separately bond the ground? Kind of like a common 2-prong to 3-prong adapter?
 
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Old 01-02-13, 10:26 PM
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Do they make adapters that let you separately bond the ground
Bond the ground to what ?
If you only have 3 wires at the receptacle then you technically don't have a ground there.
 
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Old 01-03-13, 10:05 AM
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all you need is a single slot panel on one leg for the 15 amps, they cost like 12 dollars at big box and the then put one of the 30 amp 120v outlets on each leg mount this on a 12/12 piece of plywood
 
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Old 01-03-13, 03:57 PM
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A "suicide cable" is a cord that is made with both ends a male cord end. By doing this you would have hot prongs hanging out and is very unsafe.

Hard-wiring the cord to a panel, or j-box, is the way to go.

If you only have 3 wires at the receptacle then you technically don't have a ground there
You do have a ground, you don't have a neutral on a 3 wire connection.
 
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Old 01-03-13, 07:43 PM
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If you only have 3 wires at the receptacle then you technically don't have a ground there
You do have a ground, you don't have a neutral on a 3 wire connection.
We were talking about using an old style dryer receptacle (NEMA 10-30). These are three wire, hot-neutral-hot, with the neutral used as the ground. So, at the dryer plug, I'd either need to combine the neutral and ground, or else run a pig tail from the cable ground to a ground. Best option is to go to the panel, and add a 4 prong dryer receptacle.

BTW, our old timer all tells us to just climb a utility pole and clamp onto the transformer outputs, as they used to do.
 
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Old 01-03-13, 07:54 PM
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Yes... but, it's nice to have a disconnect at the panel (so another $15 for the 30A double throw switch and box), and it's nice to blow breakers in the truck, rather than in the building, and the whole thing is a little safer and flexible wired up like they describe maybe. So, I just went with a sub panel with back fed breakers for about $65.

But, you are right, I think.
 
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Old 01-03-13, 08:10 PM
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And what do you do at houses with a gas dryer and gas stove? Not a single 240 or 120/240 receptacle in my house. Whatever you need to use the power for it seems a shorted sighted idea.
 
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Old 01-03-13, 08:12 PM
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Rather than adding a 14-30 receptacle everywhere (which is not always feasible, either as a lot of places have full obsolete panels or fuses) have you ever considered a generator, too?
 
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Old 01-03-13, 08:34 PM
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Yes, there is a 15,000W generator, which they usually use. For situations where we are on site for a few days, though, it is probably worth the effort to tie in to the shore power. And, if the generator goes down, having this as backup can save a lot of time/money. Where there already is a 4 prong dryer receptacle, this is a no brainer.
 
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Old 01-04-13, 07:11 PM
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These are three wire, hot-neutral-hot, with the neutral used as the ground.
I know I am nit picking here but, no, it is hot, hot, ground. It is the ground being used as a neutral.

Back in the day electric dryers did not need a neutral because everything used 240 volts. Then came fancy electronics (timers, etc) and they allowed that minor current to be put on the ground. Well, the current became greater and greater so the code changed in the 90's. The same thing goes for 3 wire electric oven feeds.
 
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Old 01-04-13, 08:11 PM
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I must respectfully disagree. Haven't dryers basically always been 120 volt appliances with a 120 volt motor and either a gas or 240v electric heat source? Tolyn can you post a cite for your statement?
 
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Old 01-04-13, 08:48 PM
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On a dryer cable, is the neutral/ground treated like a ground or a neutral? For example, can it be a bare wire, or must it be insulated? When the other end is wired into a subpanel, is it connected to the neutral bar, or the ground bar?

I think it makes sense to call it a neutral, or a 'neutral ground', but seems like there is a risk of confusing people like me if it is just called a ground.
 
  #18  
Old 01-04-13, 11:56 PM
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3 prong 240VAC plugs use the neutral wire as a chassis ground. However, in my opinion, they should always be treated as a current carrying conductor because the neutral carries the phase-to-phase current imbalance under normal operation. In your scenario of jacking in to a 10-30 plug for various truck loads, including 110 VAC loads, you will be creatung imbalances loads. Therefore, insulate the neutral wire.
 
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Old 01-05-13, 07:39 AM
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Haven't dryers basically always been 120 volt appliances with a 120 volt motor and either a gas or 240v electric heat source? Tolyn can you post a cite for your statement?
As fas I know, the electric dryers of the 60s and 70s all had 120 volt motors and 120 volt timers.
 
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Old 01-05-13, 07:50 AM
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Tolyn can you post a cite for your statement?
No, I can't. This is just info I have heard through the years and it made sense to me as a ground wire is typically bare, while the neutral is not. I also find it hard to believe that the Code would ever have allowed bonding the chassis to a neutral wire, with the amount current of a 120 volt drum motor.
 
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Old 01-05-13, 08:10 AM
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And I have always heard or maybe just thought different. In areas where non-metallic cable is used it is easy to think of the hookup with ungrounded cable as two hots and a neutral with no ground. This seems to be verified by the fact that in the dryer the white goes to the neutral terminal and a bond strap to the chassis not directly to the ground and a neutral strap to the neutral terminal.

The reason I have read for allowing bonding chassis to neutral is the copper shortage surrounding WWII but I can't provide a cite either.

P.S. Gee, where's Furd when you need him?
 
  #22  
Old 01-05-13, 08:34 AM
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Furd is not feeling well. Early clothes dryers were 120/240 volt machines. Some/most European machines sold in the United States are straight 240 volt volt machines. I don't know about Asian machines.
 
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