Amps

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  #1  
Old 11-11-02, 10:16 AM
KIRKD
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Amps

I am adding a circuit to my breaker box. This circuit will have three hot plates that will plug into three receptacles. Each hot plate will pull as many as 1000 watts each. I am using a 30 amp circuit breaker with 10/2 grounded wire. My question is can I use 15A/125V CU receptacles or is there a 30A/125V CU receptacle that I should be using.

Thank You
Kirk
 
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  #2  
Old 11-11-02, 11:01 AM
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If your running a 30 amp breaker then you require 30 amp 125v receptacles which are available from any electrical supply house.
 
  #3  
Old 11-11-02, 03:16 PM
DaveB.inVa
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I think a much better question would be, what is the configuration of the plug at the end of the cord?
 
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Old 11-11-02, 03:59 PM
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You absolutely may not plug standard 1000-watt appliances into a 30-amp circuit. I suggest you install two or three 20-amp circuits. Use tandem breakers if panel space is an issue.
 
  #5  
Old 11-12-02, 12:43 AM
HBB
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Kirk,

My insatiable curiosity begs this question: What are you going to do with those three hot plates, which I assume would be operated simultaneously?
 
  #6  
Old 11-12-02, 11:24 AM
KIRKD
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John

Why am I unable to use a standard 1000 watt appliance on a 30 amp circuit. Is the plug configuration on the appliance different from the receptacle or is there a safety reason. The 1000 watt hot plates I will use have a standard two prong plug.

Kirk
 
  #7  
Old 11-12-02, 11:43 AM
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You can not install a standard 3 prong recepticle on a 30 amp circuit. You have to install 30 amp plugs which have a different pin configuration. You can only install the standard type plugs on 15 and 20 amp circuits.
 
  #8  
Old 11-12-02, 12:32 PM
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"Is the plug configuration on the appliance different from the receptacle or is there a safety reason. "

Answer: Yes, there is a different plug configuration on 30A circuits, and it is different for safety reasons. Your appliance is designed assuming that if for some reason (internal fault) it draws more than 20A, the circuit breaker will trip. If you change to 30A, it is possible for the appliance to pull enough current in a fault situation to burn up but still not trip the breaker.
 
  #9  
Old 11-12-02, 02:17 PM
HBB
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Kirk,

Here's a workaround for your situation, which may or may not conform to the NEC, but it will work and it isn't likely to burn your house down:

This assumes your three hot plates draw a maximum of 1,000 watts each.

We're dealing with:

One hot plate: 1,000 watts / 120 = 8.33 amps

Two hot plates: 2,000 watts / 120 = 16.66 amps

Three hotplates: 3,000 watts / 120 = 25 amps

Your initial problem is how to get 3,000 watts to all the hot plates through conductors which will have the ampacity to handle a total 25 amps. No. 10 AWG wire will handle that.

Your next problem is how to distribute that into circuits for each hot plate without having to install three separate outlets in a wall or somewhere. Since two hot plates will draw a total 2,000 watts -- 16.66 amps -- a combination 15/20-amp receptacle will handle that and also will accept the plug from your hot plates.

Here's how you do it:

1. Run the 30-amp circuit with NM-B 10/2 AWG w/ground and 30-amp breaker to a 30-amp 125v 2-pole 3-wire grounding receptacle in an outlet box.

This outlet is the point at which you need to split that circuit into two, each of which will handle a maximum of 20 amps. To do this you simply create what is basically an extension cord with a 30-amp 125v 2-pole 3-wire grounding plug (for the 30-amp outlet) connected to a large 2-gang workbox containing two combination 15/20-amp duplex receptacles.

2. From the 30-amp plug run NM-B 10/2 AWG w/ground into the 2-gang box and secure it with a Romex connector. Buy a 2-gang raised duplex outlet cover for this box, the type that allows the two receptacles to be secured to it, giving you more work room for wires.

3. Inside the workbox, with red or larger wire nuts, bring two 10 AWG pigtails each off the black hot and the white return wires. Get a box grounding screw and secure the bare ground wire around that, leaving enough wire to pigtail two grounds off it.

4. Connect each black hot pigtail to the copper-colored screw terminals on each receptacle and the same with the white returns to the silver-colored screws. Connect the bare grounding pigtails to the green terminal screws of each receptacle. Curl these wires clockwise completely around the screws but not extending beyond. Tighten the screws securely and also screw down the unused terminal screws.

5. Install the receptacles on the cover, push it all into the box and secure the cover to the box. When you push this assembly into the box, pay attention to where the wires are going so there's no chance the bare grounding wires will come into contact with the hot or return terminals on the receptacles.

You now have what amounts to a heavy-duty "splitter" extension cord. It's basically just running a series of receptacles inside a workbox, rather than along a wall.

You can plug two hot plates into either of the duplex receptacles and the third into the other. You CANNOT plug in a fourth hot plate, because the 4,000-watt total -- 33.33 amps -- will exceed the ampacity of the 10 AWG wire and, hopefully, trip the 30-amp breaker.

Since you've used 10 AWG wire and 15/20-amp receptacles, nothing SHOULD exceed the ampacity of either the wire or either receptacle.

This is my opinion from personal experience, but I consider it IMPORTANT: Buy Leviton brand plugs and receptacles, rather than Eagle or some other, especially cheaper, brand. No. 10 AWG wire is heavy, stiff and very difficult to work with. Just getting it around a terminal can tax the physical limits of a receptacle.

CAUTIONARY NOTE: As mikewu99 says, your hot plates are not provided with equipment grounding plugs. If one suffers an internal short, that short will not be conducted safely to ground. Just a chance you'll have to take if you want to do this. I would NOT go off and leave those hot plates unattended.

NOT-SO-FINE-PRINT DISCLAIMER: If any of this fails to function properly, shocks you, burns your house down or upsets your dog, I disclaim any and all responsibility.

You're on your own there, good buddy.

OTHER BOARD MEMBERS: I've done this and it's always worked without problems. I realize this is very likely nonconforming with the NEC. Beyond that, I welcome any comments -- positive, negative or whatever.
 

Last edited by HBB; 11-12-02 at 02:42 PM.
  #10  
Old 11-12-02, 02:40 PM
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I can confirm that this would work. I can also state my opinion that this setup "probably" won't burn your house down. But I can also confirm that this does not meet the minimum safety standards of the NEC. I recommend against it.
 
  #11  
Old 11-12-02, 02:41 PM
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"CAUTIONARY NOTE: As mikewu99 says, your hot plates are not provided with equipment grounding plugs. If one suffers an internal short, that short will not be conducted safely to ground. Just a chance you'll have to take if you want to do this. I would NOT go off and leave those hot plates unwatched."

THIS WAS NOT MY POINT AT ALL! I never mentioned equipment grounding plugs.

MY POINT IS THIS: Inside the hot plate there very likely are components (switch, wiring, thermostat) which are designed to operate safely when the current is limited to 20A. If you do not limit the current to 20A (by plugging into a 30A circuit) you run the risk of burning something up.

Please just run two circuits for the three hot plates.
 
  #12  
Old 11-12-02, 03:15 PM
HBB
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John,

It does work, and it's always worked safely for me. I've made many heavy extension cords like this with various drills, circular and table saws, small compressors, etc., plugged in and operating more or less simultaneously. I admit, however, that I made those mostly for convenience on a job site and to lessen voltage drop. Never used them for hot plates, though.

Your advice to Kirk is well taken by me.

mikewu99,

Yes, I see your point about the internal components of hot plates. I still don't think it would be a problem, but I'm not an electrical engineer and I'm certainly not about to argue the finer points of that discipline with one.

And I, too, would say Kirk would probably be more properly served, if not conveniently, by two 20-amp circuits, each on its own 20-amp breaker.
 
  #13  
Old 11-12-02, 04:12 PM
texsparky
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Wink

It won't be any harder to run 2 circuits of the proper size than it would be to run 1 of the wrong size !
 
  #14  
Old 11-12-02, 05:15 PM
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Why is it there's never enough time or money to do it right the first time but always enough to do it right the second time after it's burned down??

Just a thought ............
 
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Old 11-15-02, 01:37 PM
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An alternative connection is a 20 amp 3-wire branch circuit. Two 20 amp receptacles would connect Black-to-White and one 20 amp receptacle would connect Red-to-White.Presuming 10 amp loads on each receptacle,the current in the Black wire= 20 amps.,the current in the Red wire=10 amps.,and the current in the White (Neutral) wire = 10 amps.
 
  #16  
Old 11-15-02, 01:43 PM
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Afterthought-----a 3-wire 20 amp branch circuit allows for connecting a 4th 10 amp load. 120v X 30ampps.= 3600 watts.-----240v. X 20 amps. = 4800 watts.
 
  #17  
Old 11-16-02, 07:06 PM
bwetzel
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HBB,
Why don't we just install a bunch of recpts next to the panel and run these cord setups all around the house. I take it personal when someone gives out unsafe electrical advice to the unskilled homeowner that is not trained to know any better. This is the reason our code books are as thick as they are. Do it right the first time or call someone who is willing to do a safe and neat job!
Brian
 
  #18  
Old 11-16-02, 08:37 PM
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I'm with Brian shoulder to shoulder Either do it right or don't do it
 
  #19  
Old 11-21-02, 09:27 AM
KIRKD
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Thanks for all the replies and very helpful information. I ran 20 amp circuits and everything works fine.

Kirk
 
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