Dryer circuit.

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  #1  
Old 09-01-06, 08:31 AM
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Cool Dryer circuit.

I am looking for confirmation of information supplied by my dryer manufacturer.
From information gathered from other threads here, I was figuring I would need a 120/240v 30a circuit.

I asked the manufacturer about the amps required for this dryer.

I was told that 30 amps would be fine, and that it could be wired 3 or 4 wire and that they could tell me which wires to put where when I was ready to install it. Mute point, the dryer is already four wire and the laundry will be wired as such also.

Now for the question, I was told that a straight 240 circuit was fine, that I didn't need 120/240. Is this determined by the breaker that is selected? Is this mfg. rep. a bit off-base by saying straight 240, or am I the one that is "up in the night". Do they internally get 120 for the timer motor or tap just one of the hots?

Thanks
 
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  #2  
Old 09-01-06, 08:49 AM
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New dryer circuits in the US are required to be 30 amp four wire circuits. This means they are 120/240 volts. It used to be allowed for dryers to be three wire circuits, and many three wire circuits still exist in houses, apartments and condominiums. The reason for the four wire requirement is that electric dryers have 120 volt components. The drum motor, the electronics, and light bulb(s) are typically all 120 volts, while the heater is 240 volts.

Since you are wiring a new laundry room (from other posts), your circuit needs to be four wire. The only difference between a 120/240 volt circuit and a straight 240 volt circuit is the extra wire, which is the neutral wire. The circuit breaker is exactly the same. The extra neutral wire connects to the neutral buss at the panel. The two hot wires and the ground wire connect to in the same way regardless of whether the circuit is 120/240 or straight 240.

A new dryer is made to be connected to a four wire circuit, and is usually sold with a four wire cord and plug. However, it is legal to install this new dryer in an older existing three wire receptacle. This is done by making a change at the back of the dryer and by using a three wire cord and plug.

I donít know exactly what questions you asked the manufacturer or what exactly they told you, so I donít know if they flat out gave you wrong information or not.
 
  #3  
Old 09-01-06, 09:03 AM
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Cool

Thanks Racraft, that was the confirmation that I was looking for. I think the mfg. was going down the path of 3 wire, rather than 4 wire. The dryer is in storage until this house is done, I needed to know the dryer amps., thus called the mfg.

I asked them specifically if it needed to be 120/240, and was told no it needed a straight 240. I feel it is miscommunication of what will work, not what code requires, etc.

I will do the four wire, and move along my project.

Thanks for the input.
 
  #4  
Old 09-01-06, 09:08 AM
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If you are wiring a new circuit for an electric dryer, it MUST be four wire.

Even if you had an existing dryer that was set-up for three wire, if you were putting in a new circuit it would have to be four wire, and you would have to change your dryer. Likewise, if you were moving into a house that already had a four wire circuit, you would have to change your dryer.
 
  #5  
Old 09-01-06, 09:47 AM
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Smile

ramiron,

If you're supplying the dryer with a 240V circuit you have by default also supplied it with a 120V circuit...2 of them actually.
A 240V single phase circuit is actually two 120V circuits that are out of phase with each other by 180 electrical degrees. In other words, each leg of the 240 will read 120V to ground and 240V between each other. The dryer is wired internally to use one leg (120V) and the neutral of the 4 wire circuit (2 hots, 1 neutral and 1 ground) to provide a 120V circuit for the dryer 120V loads. On older existing dryer 3 wire circuits (2 hots and 1 neutral) the dryer uses the neutral (3rd wire) for the 120V circuit and also for grounding the dryer too. The neutral and ground are bonded (tied) together at the main breaker panel on 240V (residential) systems. In a ideal installation (and required on new ranges and dryers) the ground wire will never have any current flow unless there is a ground fault (short circuit). On older systems, it was allowed.
 

Last edited by DIYaddict; 09-01-06 at 10:46 AM. Reason: Removed quote as it's unnecessary
  #6  
Old 09-01-06, 11:03 AM
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I concur with racraft's recommendation of installing a proper 30A 4 wire circuit.

But a _slight_ clarification: _Most_ clothes dryers in the US are 120/240V appliances as racraft described. A 120/240V circuit requires two hots and a neutral. Circuits in your home also require an equipment ground conductor (safety ground), making a total of 4 conductors. Prior to 1996, the NEC _permitted_ the neutral to serve dual duty as the equipment ground; this was 'safe enough' but not as safe as having a proper _separate_ equipment ground. This code allowance dates to WWII, and was there to save on materials. Current code does not permit the neutral to serve as the equipment ground, and if you are installing a _new_ 120/240V circuit, then you _must_ use 4 conductors.

However it is entirely possible (though uncommon) that your dryer is a pure 240V appliance. In this case you could install a pure 240V circuit, using only three conductors, with two hots and an equipment ground, but _no neutral_. More pure 240V appliances are being seen as European manufacturers sell to North America. This is entirely legal, though IMHO not advisable. A 120/240V dryer circuit will be the most common new circuit, and will permit the use of 120/240V appliances in the future, and will likely have the correct receptacle for the plug on the dryer. If you have a pure 240V appliance, then the neutral conductor will remain unused; at slight cost but without any safety or code issues. If, on the other hand, you install a pure 240V circuit but use a 120/240V appliance, you will have saved a few pennies, and will have both code and safety issues.

-Jon
 
  #7  
Old 09-01-06, 11:57 AM
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Jon is, as usual, correct. If the dryer in question is a strsight 240 volt appliance then you COULD install a straight 2450 volt circuit.

However, as Jon has also stated, this would not be recommended. I further state that it would most likely turn out to be a poor decision. Perhaps not for you, but almost certainly for the next person who owns the house.

While straight 240 volt appliances are becoming more common, they are by no means becoming commonplace. The chances that the next owner of the house will own one or will buy one is not great. When this happens, they will have to change the circuit to be four wire.

So, my advice remains, install a 30 amp four wire dryer circuit for your electric dryer, whether you absolutely positively need need one or not.
 
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