Why I need 10/3 for dryer?

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robert pitre

Member
Location
Houma,la
Today I had a electrain ask me a question, if my meter pan is back to back with my main panel,and my neturals and grounds are bonded in together, why do I need to run 10/3 wire for my dryer?
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Today I had a electrain ask me a question, if my meter pan is back to back with my main panel,and my neturals and grounds are bonded in together, why do I need to run 10/3 wire for my dryer?
Because except for old work where only three wires (two hots plus ground) were originally pulled the NEC requires you to disconnect the neutral to ground bond in the dryer and run a four wire cord to a four wire receptacle (two hots, one neutral and one separate EGC) the home run can use raceway as EGC if suitable metallic raceway is used. But if you pull UF/NM you need to include separate neutral (white or gray) and EGC (green or bare). There are many old threads in the forum that discuss this.

If the dryer has a permanent connection from neutral to ground you cannot use it in a new work installation. Period!

Congratulations on asking questions when necessary!

Take a good look at 250.140 [2011] with close attention to the exceptions. If you have questions about that wording, come back to us. :)
 

mbrooke

Batteries Included
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United States
Occupation
Technician
Conductors fail, connection can get loose. Grounding through the neutral is usually fine until something goes wrong. Would you rather have the dryer simply not turn on or become energized at 120 volts?
 

degupita

Member
Location
Boulder Colorado
I think people might be misunderstanding who was asking.

It sounds like the electrician asked you why you would need a 10/3 for your dryer. Is that right Robert Pitre?

If I can make the assumption. It sounds like he is trying to talk out of running a new 10/3 cable and that there is an existing 10/2 running to a three prong dryer receptacle?

He might be doing that because it would, with whatever your current layout is, really hard or require a lot of demo, to put the cable in.

If you got a new dryer with a four prong cord, 2 hots, neutral, and ground. I can see why you would want the change.
 

kwired

Electron manager
Location
NE Nebraska
It sounds like the electrician asked you why you would need a 10/3 for your dryer. Is that right Robert Pitre?

If I can make the assumption. It sounds like he is trying to talk out of running a new 10/3 cable and that there is an existing 10/2 running to a three prong dryer receptacle?

That is a clarification I would like to see before too many more comments are made. Is the question why two "hots" and a grounded conductor?
Or is it why do we need a separate equipment grounding conductor? Or maybe a little bit of both questions?
 

jaylectricity

Senior Member
Location
Massachusetts
Occupation
licensed journeyman electrician
Electrician is trying to get out of running 10/3. Either he quoted a price and it'll be too much work or he's just trying to save money.

If he really is asking that question, he sounds either inexperienced or dishonest.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
10-2 NM cable was never permitted. 10/2 SE cable was permitted if the circuit came from the service panel.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Today I had a electrain ask me a question, if my meter pan is back to back with my main panel,and my neturals and grounds are bonded in together, why do I need to run 10/3 wire for my dryer?
If you don't run an EGC then you have to bond the frame of the dryer to the branch circuit neutral. That works fine if everything stays intact. Loose your neutral and the frame of the dryer heats up to 120V. Not good.
 

user 100

Senior Member
Location
texas
That is a clarification I would like to see before too many more comments are made. Is the question why two "hots" and a grounded conductor?
Or is it why do we need a separate equipment grounding conductor? Or maybe a little bit of both questions?

I agree- we don't yet know the full scoop behind the inquiry-I too think this may end up being one of those "since they are essentially connected together in the panel, why can't the neutral be both egc and ccc?" kind of things.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I agree- we don't yet know the full scoop behind the inquiry-I too think this may end up being one of those "since they are essentially connected together in the panel, why can't the neutral be both egc and ccc?" kind of things.
And the simple answer is still "One of them carries normal current and the other does not, carrying only fault current."
 

growler

Senior Member
Location
Atlanta,GA
Today I had a electrain ask me a question, if my meter pan is back to back with my main panel,and my neturals and grounds are bonded in together, why do I need to run 10/3 wire for my dryer?


Years ago (back in the good old days ) dryers didn't use a neutral so there was no reason to run one. Two hots and a ground were safe enough ( same as an AC unit).

The manufacturering process changed and they did need a neutral because they tapped one leg to neutral ground) to get the 120V for the controls . If they had used a transformer the dryer would have cost more but we wouldn't need a neutral.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Years ago (back in the good old days ) dryers didn't use a neutral so there was no reason to run one. Two hots and a ground were safe enough ( same as an AC unit).

The manufacturering process changed and they did need a neutral because they tapped one leg to neutral ground) to get the 120V for the controls . If they had used a transformer the dryer would have cost more but we wouldn't need a neutral.

I disagree, dryers have always needed a neutral. In fact the NEMA 10-30r receptacle has always been classified as none grounding 3 pole 3 wire.

Also, its not just the controls:
 

iwire

Moderator
Staff member
Location
Massachusetts
I disagree, dryers have always needed a neutral. In fact the NEMA 10-30r receptacle has always been classified as none grounding 3 pole 3 wire.


I agree, we were allowed to use the neutral as the grounding means, we were not allowed to use the EGC as the neutral.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
I agree, we were allowed to use the neutral as the grounding means, we were not allowed to use the EGC as the neutral.



Hence why 10-2 has always been illegal. Although I will admit is was common around here. Even I am guilty of doing it. :ashamed1:
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
I think you can still get a 240 only dryer. I installed a new one about 2-3 years ago.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
I think you can still get a 240 only dryer. I installed a new one about 2-3 years ago.

Most Euro and import based models are like that. Exact same design just adapted to 60Hz.


I think (and I could be wrong) the reason why US dryers use 120 volt motors is because the same ones are used on 120 volt gas models. Therefore less to keep in stock.
 

mbrooke

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Location
United States
Occupation
Technician
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