# How are 30amp & 50 amp plugs connected?



## Scott447 (Jul 8, 2009)

I have to connect a 30 amp (shop heater) plug and a 50 amp welder plug.
The two plugs are connected with green (or copper) wire to ground terminal, and black and red wires to the two other terminals on the plugs.
However, the wires I have have red, black, green/ground and white.

What happens with the white?  Four wires leave the cb panel to thress on the plugs.
The plugs are Not placed in metal boxes, they are stand-alone type.

Any thoughts?

Thanks, Scott


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## Blue Jay (Jul 8, 2009)

Newer standard outlets for at least the 50 amp would be 4 pole. The welder would be straight 220V so would not need a neutral (white) not sure about the heater, if it has a fan it could be a 110 or 220V motor for 110 you would need a neutral.


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## speedy petey (Jul 8, 2009)

Just cap off the white. It is not needed for these straight 240v circuits.


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## speedy petey (Jul 8, 2009)

Blue Jay said:


> Newer standard outlets for at least the 50 amp would be 4 pole. The welder would be straight 220V so would not need a neutral


HUH???
The second sentence contradicts the first.

The first sentence only applies to120/240v household cooking appliances and electric dryers. The code exception that allowed us to omit the ground was removed years ago.


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## Blue Jay (Jul 9, 2009)

speedy petey said:


> HUH???
> The second sentence contradicts the first.
> 
> The first sentence only applies to120/240v household cooking appliances and electric dryers. The code exception that allowed us to omit the ground was removed years ago.



Yea I must have been brain dead. Should have gone to bed instead of turning the computer on, at least I screwed this up instead of between the sheets.
   I plead "parts-himer"  part of the time I remember :banana:


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## Scott447 (Jul 9, 2009)

Hey speedy petey and blue jay - thanks guys,

But to keep at it...
I know i'm asking the same thing, but really want to get it right.


When the 30 amp line was connected the red & black wires went to the CB, the white to the bus bar and the copper to the ground.  So all I have to do is cap the white?  

Is this the same for the 50 amp wire?  (I was going to use a length of new stove line)
I connect red & black wires to the CB, the white to the bus bar and the copper to the ground.  Cap off the white?  

Thanks again,
Scott


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## Blue Jay (Jul 9, 2009)

Yep that's right, just cap off the white wire at the plug.


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## Scott447 (Jul 10, 2009)

Hi Blue Jay,
Thanks again, Scott


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## Nestor_Kelebay (Jul 11, 2009)

Scott:

     Electric power comes into a house through a three wire 220 volt electric cable.  The three wires will have black, red and white insulation.  Both the black and red wire carry 110 volts AC relative to the white wire, but they're 180 degrees out of phase.  So, when the black wire is at +110volts relative to the white wire, the red wire will be at -110 volts relative to the white wire.  Similarily, when the black wire is at -110 volts relative to the white wire, the red wire will be at +110 volts relative to the white wire.  The best way of thinking about it (which is technically incorrect) is that the power comes from the generating station along the red and black wires and goes back to the generating station along the white wire.

You make a 110 volt circuit by connecting the circuit between the white wire and EITHER the red wire or the black wire.  If you put a 15 amp fuse on that circuit, you have a 110 volt 15 amp circuit which is a standard household circuit for lights and fans and such.  If you want to make a 220volt circuit for an electric dryer or stove heating element, you put that heating element between the red and black wires.  If it's a dryer heating element, then you would put 30 amp fuses on BOTH the red and black wires going to the dryer.  Similarily, if the heating element was a stove, you'd need to put 50 amp fuses on BOTH the red and black wires going to the stove.  So, 220 volt appliances like your shop heater and welder will have two fuses or circuit breakers; one on each power line going to the appliance.  You need to remove both fuses or trip both breakers before all the power is shut off to a 220 volt appliance.

     There's a convention in wiring any 220 volt appliance like an electric stove or dryer.  I expect your shop heater and welder are special cases of this general rule because they might not need the neutral wire.

The general rule is that on 220 volt appliances, either on the wiring terminal or on the plug or receptacle, you will see three connection points in a row.  The white wire ALWAYS goes to the middle connection point and the red and black wires are connected on either side.  It doesn't matter which side you connect the red and black to (because in 1/120 th of a second the polarity will have reversed anyhow), as long as white is in the middle and red and black are on either side.

220 volt appliances like electric dryers and stoves will still need a white neutral wire.  That's cuz some of the circuits on a 220 VAC stove or dryer will run on 120 volt power.  The electric motor in the dryer, for example, uses 120 VAC power.  The indicator lights on a stove's console or the light bulb inside the oven will also use 120 VAC power.  To make a 120 VAC circuit, you need to connect between the red and white wires or between the black and white wires.

I think what other people are saying is that there aren't any 120 VAC circuits in either your electric heater of arc welder, and so it's not necessary to even have a white neutral wire, and so you can just stick a big wire nut on the white neutral wire to insulate it's end.

But, look on the space heater or welder to be sure.  any indicator lights that are supposed to light up when the heater or welder are turned on are likely to run on 120 VAC power, and that means there's a need for a white wire to be run to the appliance as well.

Hope this helps.


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## bkplasma (Jul 11, 2009)

Nestor:  Thanks for that great explanation. I think you did a great job clearing it up.


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## Nestor_Kelebay (Jul 11, 2009)

bkplasma said:


> Nestor:  Thanks for that great explanation. I think you did a great job clearing it up.



Thanks for the fan mail, Bkplasma.  Think how much better it woulda been if I was sober when I wrote it.

jk

I just re-read the original question and Scott is saying he has to wire a 30 amp plug and a 50 amp plug.  A 220 volt 30 amp space heater will use exactly the same receptacle and plug as a 220 volt 30 amp electric clothes dryer, which you can buy in any hardware store.  Similarily, a 220 volt 50 amp arc welder will use exactly the same plug and receptacle as a 220 volt 50 amp stove, which you can also buy at any hardware store.

Now, I'm not a licenced electrician, so if I say anything not quite right in this post, would the electricians in here please correct me.  I'd rather be corrected than have all the newbies in here getting the wrong information.

What you need to do is first add up the amperage on all the fuses in your electrical panel and find out if the panel has enough capacity to add another 80 amps of load.  If having both the space heater and arc welder running at the same time as all the other lights and receptacles and stove and dryer currently on the panel will exceed the panel's rated amperage, then you'll have to install a new panel, and that's way over my head.

If adding the space heater and welder doesn't overload your panel, then you need to run a three conductor cable (what gauge wire I don't know but the electricians in here should) to the main panel of your house, and connect the red, black and white wires.  Now, don't assume that by connecting to breakers on opposite sides of the panel that you're connecting to opposite voltage sources.  That is, one side of the panel isn't always powered by the red wire and the other side the black wire.  It's the bus bars inside the panel that determine which circuit breakers get connected to the black wire and which get connected to the red wire.  Typically, a panel will have several ADJACENT breaker locations where adjacent breakers get connected to opposite voltage sources.  Electrical panels are designed this way so that two breakers servicing the same appliance can be "ganged together" so that you can't trip off one breaker without tripping off both of them.  If you only have two locations like that on your panel, they are probably already being used for your electric stove and electric clothes dryer.  If you have 4 such locations, you can move the 15 amp breakers that may be in those locations to other slots on the panel and use the "gangable" locations for your space heater and arc welder as it's better to have both breakers to a 220 volt circuit adjacent to one another.

You will be putting TWO 30 amp circuit breakers in the panel for the space heater, and preferably those two breakers will be on the same side of the panel and in adjacent locations so they can be ganged together.  (Your electrical inspector might hassle you if they're not together and even ganged together somehow.)  The red wire of your cable will connect to one 30 amp breaker and the black wire to the other.  The white wire of your cable will connect to the bus bar in the panel where all the other white wires connect.

At the other end of the cable, you will install a receptacle intended for electric dryers.  Inside that receptacle, you will see three connection points in a row on the back of the plastic female receptacle, as well as a fourth connection point for the ground wire.  Connect the white wire to the middle point on the row of three connection points and the black and red wires to the connection points on either side.  If the space heater doesn't need the white wire, then having the white wire connected to the middle connection point in the receptacle won't do any harm.  To find out if it does use that white wire, maybe open the space heater and see if the white wire from it's cord is connected to anything or just has a big wire nut on it.  If the space heater doesn't have a cord, use a cord from an electric clothes dryer.

Now, just plug your space heater into that dryer receptacle, flip your two 30 amp breakers on at the panel, and the space heater should work when you turn it on.

Wiring your welder is exactly the same process except that you would use a female receptacle for a stove, (and a cord for a stove if the welder doesn't have a cord) and you would use 50 amp breakers in your panel instead of 30 amp breakers.  You'll have to find out from someone more knowledgeable about what size of three conductor cable to use for the welder.  Also, when I say "three conductor cable", it means three wires BESIDES the ground wire.  That's cuz normally, there shouldn't be any current in the ground wire, so it's pessimistic to call it a "conductor".  Calling the ground wire a conductor is predicting there will be a short in the space heater circuit.

In the hardware store, the plastic bag that stove or dryer cords come in will say "range cord" or "dryer cord".  Similarily, the cardboard boxes that range receptacles or dryer receptacles come in will say "receptacle for range" or "receptacle for dryer".  This is only to keep things simple for homeowners, who, as a general rule, don't know squat about electrical wiring.

The way it really works is that the people that oversee the electrical standards in the United States have designed mating plug and receptacle configurations for all combinations of voltages and amperages and you simply use the designated plug and receptacle configuration for the appliances voltage and amperage.  So, a 110 volt 15 amp receptacle and plug will have the standard polarized plug/receptacle configuration we see all the time, and a 110 volt 20 amp receptacle and plug will be different, with one horizontal prong instead of both being vertical.  And, there are other prong and slot configurations for every combination of voltage (110, 220 and 440) and amperage (15, 20, 25, 30 and 50).

So, it's not like there's a special "dryer" plug and receptacle configuration that dryers use or a "range" plug and receptacle configuration that stoves use.  There is a special 220 volt 30 amp plug and receptacle configuration that all 220 volt 30 amp appliances use, whether they're an electric clothes dryer or a 220 volt 30 amp space heater or a 220 volt 30 amp air compressor in an auto body shop.  Ditto for stoves.  There is a 220 volt 50 amp plug and receptacle configuration that all 220 volt 50 amp appliances use whether they're a stove or an arc welder or a milling machine in a machine shop.

Obviously, those plug and receptacle configurations only apply if the appliance has a cord that plugs into a receptacle.  Often appliances will be "hard wired" to the appliance with no receptacle and plug to "unplug" the appliance.  If you see a cable going directly into a 220 volt appliance, then that cable will be wired to a "terminal block" inside the appliance and the "white in the middle, red and black on either side" rule applies to the three wiring connections on the terminal block.

Now you know enough to start the legwork, which is finding out the rated capacity of your existing panel to see if it has sufficient capacity to also accomodate the space heater and welder.  And, at the same time, find out how many locations in your panel will allow you to connect to opposite voltage sources with adjacent breakers so they can be ganged together for safety.

Hope this helps.


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