Dryer - Neutral Size

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DSamson

DSamson

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San Francisco, CA
Hello All,

I'm running up against a capacity problem in an existing piece of 1/2" EMT. Three of the conductors in the pipe are for an electric dryer. The installation instructions say it needs 4 10-AWG conductors. The pipe will be the equip. ground, so I'm down to 3 conductors.

Here's my question: Why does the neutral in an electric dryer need to be 10-AWG? What's it running, a light bulb, maybe a blower? The GE Answer center was no help, neither is the nameplate. It just says "120V/240V 24 amps, 4 wire."

Do any of you ever size the dryer neutral smaller than the ungrounded conductors? If so, what's your authority.

Thanks,

David
 
I don't think there is any help for you in the NEC. If the vendor says 4#10, then the NEC is going to tell you that that is what you need to provide. Just out of curiosity, does this existing conduit have other conductors as well? A 1/2 EMT can hold five #10 conductors, and you are talking about three.
 
To respond to Charlie b -- This pipe only has the 3 #10s right now, but I want to use it to run some other cirucuits. 1/2" pipe at 40% fill is .122, I've got .1226, with my new circuits.

Thanks for your reply
 
DSamson said:
Here's my question: Why does the neutral in an electric dryer need to be 10-AWG?
Click to expand...
Table 250.122


Edit to add:
I read that ? wrong....not EGC, but neutral conductor.
Sorry
Looking up the "why" now.


EDIT #2:
charlie b said:
I don't think there is any help for you in the NEC. If the vendor says 4#10, then the NEC is going to tell you that that is what you need to provide.
Click to expand...


Charlie knows the code better than me..so there's your answer ~ 110.3(B).
 
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Dryer - Neutral Size - Interesting Observations

Dryer - Neutral Size - Interesting Observations

So, I clamped a meter on the conductors. The Neutral shows an almost constant 4 Amps. L1 (Black) shows - zero in some states, and 21.7-23.9 as the heating element cycles on and off. L2 (Red) shows - 4 Amps in some states, and 23.7-25.6 in other states.

So, I conclude the motor and / or blower run at 120V, and the heating element runs at 240V.

So, I'm required to run a 10 AWG neutral, for a max load of 4 amps. I hear you about 110.3(B), but when the code (or an appliance manufacturer) ignores physics, it's a little annoying.

Thanks as always for your good counsel.
 
We can't ignore the physic either.
The heating elements are connected at 240V. It is not known if it is phase-phase or phase-neutral loads. If it is phase-neutral, what happens to the neutral current if one of the phase-neutral heating elements fails open? Answer, the neutral current goes to 24 amps. A failed open heating element could cause the neutral to overheat and cause a fire, how strange is that?

Also, and even harder question. How is the next dryer that the home owner buys wired?

-- Now the flip side --

Like you said, "the heating elements run at 240V" and likely are phase-phase. And by code I believe you have to provide the branch circuit required for the dryer that you now have. So I really don't know, but I would definitely "feel" better with a full size neutral conductor.
:smile:
Ed Jackson, P.E., Charlotte, NC
 
DSamson said:
So, I conclude the motor and / or blower run at 120V, and the heating element runs at 240V.
Click to expand...
Correctamundo, which is why they work fine (albeit at a lower heating level) on 208v.
 
Wouldn't the heating elements operate at 120v for low heat and 240 for high heat?

This schematic seems to de-bunk this theory, but are all dryers the same?
speedqueendryschematic.jpg


Or is low heat accomplished by either:
- 1/2 the element energized at 240
- entire element at 240, but less "run time"


Looking at this schematic, I think less "run time".
 
I have replaced elements in a dryer before and found that at least that one had more than one element so the temp is controlled by the number of elements called on.

It looked like two different sized elements so it would work like a three way lamp, Low (the smallest element) Med (the largest element) High (both elements)
 
celtic said:
Wouldn't the heating elements operate at 120v for low heat and 240 for high heat?

This schematic seems to de-bunk this theory, but are all dryers the same?
speedqueendryschematic.jpg


Or is low heat accomplished by either:
- 1/2 the element energized at 240
- entire element at 240, but less "run time"


Looking at this schematic, I think less "run time".
Click to expand...
Notice the two thermostats, 'hi' and 'lo'. The fabric switch chooses which one controls the single heating element. There is no dotted line between the three sections of the 'fabric' switch, meaning they don't close and open together. This is actually a hi, lo, air switch.

The heavy lines denote that pathway of the heating element. Notice that the timer motor only receives power when the selected thermostat opens from the exhaust air reaching the set temperature. The third (top) section bypasses the thermostats.

This is how an automatic dryer works; by advancing the timer when a certain temperature is reached. In other words, the lower setting merely energizes the timer motor at a lower exhaust temperature. And yes, these dryers are almost identical.

Also, the push-to-start button works by being paralleled with a centrifugal switch that opens the start winding and simultaneously bypasses the start button.
 
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LarryFine said:
This is how an automatic dryer works; by advancing the timer when a certain temperature is reached. In other words, the lower setting merely energizes the timer motor at a lower exhaust temperature. And yes, these dryers are almost identical.
Click to expand...

Yes but not all dryers have only two temps.

Mine has 'Air' (no heat), Low, Med, Med High and High.
 
iwire said:
Yes but not all dryers have only two temps.

Mine has 'Air' (no heat), Low, Med, Med High and High.
Click to expand...
No argument, and it may even have an electronic controller. Do you have the schematic handy?



Disclaimer:
LarryFine said:
And yes, these dryers are almost identical.
Click to expand...
You don't have one of "these" dryers.
 
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