neutral size for appliances
- Thread starter kimrichi
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Good question, but one I cannot answer. I do need to point out that the 70% factoring is only for service and feeder sizing, not the branch circuit.
A finer point to your question is the part stating: where the maximum unbalanced load has been determined in accordance with Table 220.55 for ranges and Table 220.54 for dryers. There is no maximum unbalanced load determined with those tables???
Does anyone consider range or dryer neutral current in their service and feeder calculations for neutral sizing?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Most dryer motors and range blowers are 120V not 240v. Most of the loads are 240V but the 120V load can be more than the electronics. Now why is a dryer motor 120V-- I don't know. I have seen some models that are straight 240V.
- Location
- Massachusetts
I have read, and it seemed plausible to me that the motor is 120 so that the dryer can be supplied with 240 or 208 without effecting the motor.
240 volt is too high for a 200 volt motor and 208 volt is to low for a 230 volt motor.
What this means for a straight 240 unit I do not know, I wonder if they are actually listed for use on 208 volt systems.
Keep in mind that the different heat factors in ranges and dryers are being done by applying different voltages to the elements:
Take 2 elements at 240V and 5KW each.
At 240 parallel they are 10KW.
At 240 Series they are 5KW
at 240V one and 120V the other is 7.5KW
One at 120V is 2.5KW
Both in series at 120V is 1.25 KW
So you can see where the heat can be controlled by just using different voltages across the elements(from 10KW to 1.25KW) by using the neutral.
The 70% would come from the fact that the highest phase to phase is about 40A while highest neutral to phase is around 21A, which a little more than 50%, and the other 20%? I guess just better to be safe than sorry
And considering the other answer that puts the motor at 120V there's your other 20%
Take 2 elements at 240V and 5KW each.
At 240 parallel they are 10KW.
At 240 Series they are 5KW
at 240V one and 120V the other is 7.5KW
One at 120V is 2.5KW
Both in series at 120V is 1.25 KW
So you can see where the heat can be controlled by just using different voltages across the elements(from 10KW to 1.25KW) by using the neutral.
The 70% would come from the fact that the highest phase to phase is about 40A while highest neutral to phase is around 21A, which a little more than 50%, and the other 20%? I guess just better to be safe than sorry
And considering the other answer that puts the motor at 120V there's your other 20%
I agree with ranges using the different voltages... but there is a huge variation on how they do it.
Here's supposedly a typical wiring schematic:
http://www.tpub.com/content/construction/14026/img/14026_215_1.jpg
And here's one for a Kenmore:
http://c.searspartsdirect.com/lis_png/PLDM/P0401166-00005.png
I know the example I gave wasn't even near what the manufacturers actually do.
I was just giving an example on how you can change the heat output by playing with the voltage applied to the elements, including 120.
And also I was saying that it's easy to reach at least 50% of the ungrounded conductors ampacity on the neutral doing that.
I was just giving an example on how you can change the heat output by playing with the voltage applied to the elements, including 120.
And also I was saying that it's easy to reach at least 50% of the ungrounded conductors ampacity on the neutral doing that.
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