Electric Dryer wattage

[Grouch1980]

I went through a thread from back in 2010, where the question was asked if you use a 240 volt rated, 4500 watt hot water heater on a 208 volt system, what would be the wattage of the heater... and the answer is 3380 watts, since the water heater is a resistive load.

Does the same apply for an electric clothes dryer? Let's say it's a 5000 watt dryer, rated at 240 volts. If I use this dryer on a 208 volt panel, will the wattage of the dryer now be 3755 watts? [(5000w / 240v) x (208v/240v)] x 208v

 

[jaggedben]

Yes, more or less.
The heating element will just stay on for more of the time. The thermostat will typically have it cycling on and off during a drying cycle in any case.

 

[jaggedben]

Unlike most water heaters, you need to separate out the motor load from the heating element load to calculate the total more accurately.

 

[infinity]

Do clothes dryers now come with both wattage/voltage combinations on the nameplate?

 

[hbiss]

I have not seen any probably because it's not all that common to supply them with 208.

-Hal

 

[jaggedben]

Do clothes dryers now come with both wattage/voltage combinations on the nameplate?

I've seen some like that. Or volt / amp combinations.

 

[Grouch1980]

Thanks everyone. As a follow up question, let's say I use the standard calculation to size an apartment feeder. The minimum load for an electric dryer is 5000 watts. If I have the situation described in my first post, where it's rated 5000 watts at 240 volts, and I'm plugging the dryer into a 208 volt panel, do I use 3755 watts in my calculation, or am I still obligated to use 5000 watts minimum? I believe it is the latter.

 

[jaggedben]

If that's the way the rating is stated then arguably yes, you still have to use 5000W. If the appliance has a separate amps or watts rating for 208V then you could use that.

FWIW in my experience datasheets and manuals rarely have such detail. A 208V rating, if there is one, would most likely only be found on the label on the appliance itself.

 

[HEYDOG]

If that's the way the rating is stated then arguably yes, you still have to use 5000W. If the appliance has a separate amps or watts rating for 208V then you could use that.

220.54 says nameplate rating or 5,000 watts which ever is greater!

 

[Tainted]

When you apply 208V on a resistive appliance that is 240V, only 75% of the wattage is applied:

(208^2)/(240^) = 75%

It doesn't matter which appliance as long as it's completely resistive.

But remember, NEC says to use nameplate, not the actual applied wattage. Also if standard method is used for a dryer then you must do 5000VA or nameplate, whichever is higher.

I do see in a lot of apartment building 240V public dryers getting connected to 208V. You would have to ask manufacturer if it would be ok to do that.

 

[Grouch1980]

Ok I got it. Right... the NEC specifically states for an electric clothes dryer... 5000 VA minimum or nameplate, the higher of the two.

So for a hot water heater, or any purely resistive load, THEN I can use the lower applied wattage... at 75% when i plug a 240 volt resistive load like a hot water heater into a 208 volt panel.

 

[Tainted]

Ok I got it. Right... the NEC specifically states for an electric clothes dryer... 5000 VA minimum or nameplate, the higher of the two.

So for a hot water heater, or any purely resistive load, THEN I can use the lower applied wattage... at 75% when i plug a 240 volt resistive load like a hot water heater into a 208 volt panel.

What is the hot water heater for specifically? Radiant heating?

 

[Grouch1980]

What is the hot water heater for specifically?

for an apartment... sinks, shower, etc.

 

[Tainted]

for an apartment... sinks, shower, etc.

what about radiant heating?

 

[Grouch1980]

what about radiant heating?

Sure, let's assume it includes that as well.

 

[Tainted]

Sure, let's assume it includes that as well.

Funny thing is 220.82, 220.83, and 220.84 calls for nameplates for water heaters but I don't see it telling you to use the nameplate on the standard method. I think you should use the nameplate at 100% using the standard method anyway. As a devils advocate you could argue and say 220.51 tells you to use 100% of the connected load (3755W) but even that's a bit vague.

 

[Grouch1980]

I just checked:
Section 220.53, part of the standard calculation, mentions the use of nameplate ratings for the appliance loads (which includes water heaters).
Sections 220.82 and above, part of the optional calculations, mentions the use of nameplate ratings as well.

So for hot water heaters, are we allowed to use the adjusted wattage, at 75%, if we use a 240 rated appliance on a 208 volt panel? Both standard and optional calculations mention 'nameplate'.

Funny, my dryer question morphed into water heaters

 

[Tainted]

I just checked:
Section 220.53, part of the standard calculation, mentions the use of nameplate ratings for the appliance loads (which includes water heaters).
Sections 220.82 and above, part of the optional calculations, mentions the use of nameplate ratings as well.

So for hot water heaters, are we allowed to use the adjusted wattage, at 75%, if we use a 240 rated appliance on a 208 volt panel? Both standard and optional calculations mention 'nameplate'.

Funny, my dryer question morphed into water heaters

I don’t think the water heater is subject to 220.53 because you said the water heater is used for spaceheating

 

[Grouch1980]

I don’t think the water heater is subject to 220.53 because you said the water heater is used for spaceheating

Let’s assume it’s not for space heating, just for sinks and showers.

I think I got it…. For the feeder / service calculations, which is article 220, you use the actual nameplate ratings.

For calculating branch circuit sizes… THEN you can use the wattage brought down by 75% to accommodate 240 volt equipment on a 208 volt panel.

Is this right?

 

[Tainted]

Let’s assume it’s not for space heating, just for sinks and showers.

I think I got it…. For the feeder / service calculations, which is article 220, you use the actual nameplate ratings.

For calculating branch circuit sizes… THEN you can use the wattage brought down by 75% to accommodate 240 volt equipment on a 208 volt panel.

Is this right?

I don’t want to misinterpret what you are saying so I think it’ll be better if you upload the load letter here so we can see your intent