New dryer: NEMA 10-50 converting to 10-30?

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  #1  
Old 03-01-06, 06:53 AM
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New dryer: NEMA 10-50 converting to 10-30?

Hi,

We just bought new washer and dryer from Sears last week. The delivery took place last night. The washer was installed just fine, but we ran into a problem with the dryer. The installers said that my old dryer used to be on 50 Amp line and the new dryer requires 30 Amp. They recommended to rewire the outlet.

After they left I went online and did a little research. Apparently my old (current) outlet for dryer is NEMA 10-50 standard. The new one requires NEMA 10-30. However, even though the current outlet (NEMA 10-50) is rated at 50 Amp, it connects to a 30 Amp curcuit breaker at the panel. Does it mean my old dryer was using only 30 Amp line all this time? And if I don't change my 30 Amp circuit breaker for a higher rated breaker at the panel, that line for the dryer will be 30 Amp line? So, to finish the conversion I just need to swap the 10-50 outlet for 10-30 outlet and be done with it? (Both NEMA 10-50 and NEMA 10-30 are 3 pole/3 wire configurations) Sound easy enough, but I want some confirmation from the gurus about my assumptions.

Thanks!
 
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  #2  
Old 03-01-06, 07:23 AM
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Assuming that 10 gage or larger (lower gage number) wire is in place, then yes you could swap out the receptacle for a proper receptacle.

However, if this is only three conductor cable (ie three wires) and not four conductor cable (ie four wires) then you should replace the cable as well.
 
  #3  
Old 03-01-06, 07:35 AM
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Thanks! Yes, I assume that 10 gage wire is currently installed. But I believe it has three wires (10/3) not 4. Why would I need four conductor cable (with four wires) to feed NEMA 10-30 receptable that only requires 3 wires?

(I understand that NEMA 14-30 that requires four conductor cable is probably better than 10-30, but since Sears left me with 10-30 power cord I guess three wires should be enough for this appliance?)
 
  #4  
Old 03-01-06, 07:40 AM
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Just replace the receptacle and you'll be fine.

Bob comment about replacing the cable was a suggestion, not a requirement. It's a good idea if feasible, but if it would be difficult, I wouldn't worry about it.
 
  #5  
Old 03-01-06, 07:45 AM
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Just make sure that you use a three wire receptacle if you only have three wire cable.

The dryer can be installed with either a three or a four wire cord and plug, and there will be different instructions for each of them. Make sure that you follow the instructions.

By the way, your use of 10/3 is not correct terminology, and can be confusing. Most people understand 10/3 to mean 10/3 with ground. You do have three conductor cable, but it apparently is not 10/3 with ground.
 
  #6  
Old 03-01-06, 08:08 AM
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Sorry, I am not a trained electrician, just a curious DIYer who likes to do projects and learn stuff. I was under assumtion that 10 gage wire with 3 wires would be called "10/3" wire. Apparently, that's not the case So, I learned something new today!

I have another question. My new dryer stands on top of the washer (stackable) and it appears that 6 ft power cord that came with the dryer would be a little too short. I understand I have two options: 1) move the receptacle couple of feet closer to the dryer, 2) try and find 8' or 10' power cord. I looked everywhere but I was not able to find a place that is selling appliance cords more than 6' long. Do they exist? Maybe I will be better off doing option one (moving the receptacle?)
 
  #7  
Old 03-01-06, 09:37 AM
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Unfortunately, the meaning of 10/3 differs depending on what type of cable it is and what decade it was manufactured in. In some cases, 10/3 has three wires, and in other cases, it has four. It pays to be explicit.
 
  #8  
Old 03-01-06, 10:32 AM
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I was reading through older posts and found one that discusses the possibility of moving receptacle to a new location. It appears that it is not advisable to "extend" 3-wire setup with an add-on piece of wire that will run from an old box/recetacle to a new receptacle in a different location? Is it true? If yes, why is this not advisable?

(The same post says that it is perfectly fine to do this with a 4-wire setup.)
 
  #9  
Old 03-01-06, 11:13 AM
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Most of us would agree that extending a three wire circuit for a dryer would create a code violation., although it would not be any less safe than using the three wire circuit where it presently is located.

Again, if at all possible, I would run a new circuit for the dryer. Relocating the existing three wire circuit would be okay, if it will allow the cord to reach.
 
  #10  
Old 03-01-06, 11:39 AM
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Originally Posted by v1rok
It appears that it is not advisable to "extend" 3-wire setup with an add-on piece of wire that will run from an old box/recetacle to a new receptacle in a different location? Is it true? If yes, why is this not advisable?...(The same post says that it is perfectly fine to do this with a 4-wire setup.)
This reason is a technicallity in a sense. A three-wire dryer is ungrounded: it has hot-hot-neutral. A four-wire dryer is grounded: hot-hot-neutral-ground. Even though extending the three-wire circuit would work just fine and be no less safe than it is in its current location, extending an ungrounded circuit is forbidden by code. The only code-compliant solution is to install a new, grounded circuit to the new location.
 
  #11  
Old 03-02-06, 06:41 AM
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On a subconscious level I understand that 4-wire circuit (grounded) is better than 3-wire circuit. But what exactly are the benefits of 4-wire vs. 3-wire? In what situations 4-wire circuit would save the day? (Examples would be nice.)
 
  #12  
Old 03-02-06, 07:09 AM
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Extending a dryer circuit is not the subject of this thread. The original poster is not doing this.

A four-wire dryer circuit is safer than a three-wire dryer circuit precisely because it has a fourth wire, i.e., a grounding wire. Consider just one failure scenario: a three-wire dryer circuit where the neutral wire becomes disconnected. In this example, the chassis of the dryer would become energized to 120 volts whenever the drum motor is receiving power. Then just touching the dryer frame could kill you. This is clearly very bad. The reason that the exception is allowed is because it is felt that the neutral becoming disconnected is not very likely since it only has two terminations, one at the panel and one at the dryer. Obviously, each time you splice this cable, you create additional failure possibilities.

The only reason that the code even allows you to continue to use a three-wire dryer circuit is that because the code committee realizes that it would be an incredible burden to try to upgrade tens of millions of homes. But if you make modifications to the circuit, code revokes the exception and requires you to upgrade.
 
  #13  
Old 03-02-06, 07:15 AM
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First, if you have 10 gauge wire and a 30 amp breaker, that 50 amp receptacle was completely illegal. I would be interested to know what the previous owners had plugged in to that!


Now, in the past, it was considered acceptable to have an appliance like a dryer run without an actual grounding (bare wire) connection. A pure heat load like a water heater needs only two hot wires and a ground, but not a neutral (white wire ). A dryer may have both 240 volt loads ( heating element) and 120 volt loads ( control circuits, timer, etc.) so they ran 2 hots and a neutral. Because the laod is nearly balanced, very little current flows in the neutral wire, so it was allowed to connect the chassis ground to the white neutral at the receptacle. This was not completely safe, so codes have changed to require a dryer to have 4 wires ( black,red = hots; white=neutral; bare = ground).
 
  #14  
Old 03-02-06, 07:30 AM
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A 50-amp receptacle on a 30-amp circuit is not illegal if it's the only receptacle on the circuit.
 
  #15  
Old 03-02-06, 08:37 AM
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Thank you all! I understand the situation a whole lot better now. Actually, after learning from this board I am leaning toward running completely new 4-wire circuit from the panel to the new dryer and installing a new receptacle. This would be fun!

Yes, it appears previous owners used 50 amp (NEMA 10-50) receptacle on 30 amp circuit breaker and were running an electric dryer on it. I guess the dryer did not really need 50 amp and was just fine with 30 amps. But the whole mismatching thing does not look good. So, I will try to do something about it...
 
  #16  
Old 03-02-06, 08:37 AM
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Originally Posted by John Nelson
A 50-amp receptacle on a 30-amp circuit is not illegal if it's the only receptacle on the circuit.
Correct. This is done all the time on circuits for welding machines, most all of which come with a "standard" NEMA 6-50P 50A plug, even the ones that only need a 20A circuit. Would be the same for dryers, though it wouldn't exactly be typical, like it is with welders.
 
  #17  
Old 03-02-06, 08:34 PM
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Originally Posted by John Nelson
A 50-amp receptacle on a 30-amp circuit is not illegal if it's the only receptacle on the circuit.
OK, I'm curious about this. According to 210.21(B)(3), a 50A receptical can be on a 40A or 50A circuit. Where does the allowance of a 50A receptical on a dedicated 30A circuit come from?
 
  #18  
Old 03-02-06, 08:52 PM
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210.21(B)(3) does not apply when there is only one receptacle on the circuit. You missed the words, "Where connected to a branch circuit supplying two or more receptacles or outlets". Go back and read 210.21(B)(1).
 
  #19  
Old 03-03-06, 01:16 AM
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Originally Posted by 594tough
Because the load is nearly balanced, very little current flows in the neutral wire, so it was allowed to connect the chassis ground to the white neutral at the receptacle.
That would be nice if it were true -- and the manufacturers should do this.
Even assuming that there is no lightbulb in the dryer, all that I have examined had 120V motors.
Only the heating element is 240V. It takes only milliamps to kill. So the neutral current to run a motor is plenty more than the fatal shock current.

But it I suppose it would be too confusing if gas dryers and electric dryers used different motors.
 
  #20  
Old 03-04-06, 06:46 AM
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Originally Posted by John Nelson
210.21(B)(3) does not apply when there is only one receptacle on the circuit. You missed the words, "Where connected to a branch circuit supplying two or more receptacles or outlets". Go back and read 210.21(B)(1).

Thanks John! I never caught that. In my "Pocket Guide" version of the 2005 NEC, the actual text of 210.21(B)(3) is not right by the table (and the table is before the text), so I never noticed that wording.

So, by the same logic, code would allow a single, simplex, 20A receptical on a 15A circuit, correct? (Not that I would want to do that...I don't even HAVE any 15A breakers. lol)
 
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