Electric Dryer wattage

[Grouch1980]

No load letter. This is just a general question

 

[Grouch1980]

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?

Bumping this up again. From awhile back. Is the lower wattage for a resistive appliance (a 240 volt rated appliance connected to a 208 volt panel) used for branch circuit sizing? I understand that for feeder / service calcs, you use nameplate ratings, regardless if the wattage is lower on 208 volts.

 

[Tainted]

Bumping this up again. From awhile back. Is the lower wattage for a resistive appliance (a 240 volt rated appliance connected to a 208 volt panel) used for branch circuit sizing? I understand that for feeder / service calcs, you use nameplate ratings, regardless if the wattage is lower on 208 volts.

I would say yes it would make sense to size the branch circuit using the lower wattage. 125% at the next size up for circuit breaker. (Check if 422.13 applies)

But still do due diligence and check with manufacturer if they will allow you to apply 208V on a 240V resistive appliance. Maybe they have special instructions for that? Some allow you to rearrange the coils

 

[Tulsa Electrician]

Copy of a dryer name plate

 

[Grouch1980]

Copy of a dryer name plate

So since in my area we use 120/208 volts, I would work with the second line, and use 5000W in the load calculation since that's the minimum allowed.

 

[Tainted]

So since in my area we use 120/208 volts, I would work with the second line, and use 5000W in the load calculation since that's the minimum allowed.

When doing a load letter, use 5000W or nameplate (whichever one is higher). Branch circuit you would use the actual wattage.

 

[Grouch1980]

Is this correctly done (using the standard calculation)?

I came across an electric range, rated 240 volts, 32 amps as stated on its cutsheet. In my load calc, I would use 7,680 watts since that would be the nameplate rating. (240V x 32A).

When I have my total VA load for all equipment in the apartment however, at the end I would divide the total VA load by 208 volts (since my area is 120/208 volts).

And then for the branch circuit sizing, I would size the circuit breaker based on 5,768 watts, since the range is plugging into a 208 volt supply (approximately 75% of the 240 volt rating).

 

[Grouch1980]

Actually for the branch circuit sizing, since I mentioned the standard calculation, I would apply table 220.55 and apply 80% from column B to the 5,768 watt value, thereby getting 4,614 watts... and size the breaker based on this (4614 watts / 208 volts = 22.18)... so I would use a 2 pole, 25 amp circuit breaker. Is everything I mentioned in posts 27 above and this one correctly calculated?

 

[Tainted]

Is this correctly done (using the standard calculation)?

I came across an electric range, rated 240 volts, 32 amps as stated on its cutsheet. In my load calc, I would use 7,680 watts since that would be the nameplate rating. (240V x 32A).

When I have my total VA load for all equipment in the apartment however, at the end I would divide the total VA load by 208 volts (since my area is 120/208 volts).

And then for the branch circuit sizing, I would size the circuit breaker based on 5,768 watts, since the range is plugging into a 208 volt supply (approximately 75% of the 240 volt rating).

Why use a 240V range when you can use a 208V range?

 

[Grouch1980]

Why use a 240V range when you can use a 208V range?

I don't specify the kitchen appliances... they are chosen by the architect or kitchen consultant. They are then passed on to me. I could potentially point this out to them, to select a 208 volt range. But assuming they stuck with the 240 volt range, is the calculation I showed correct?

 

[Tainted]

I don't specify the kitchen appliances... they are chosen by the architect or kitchen consultant. They are then passed on to me. I could potentially point this out to them, to select a 208 volt range. But assuming they stuck with the 240 volt range, is the calculation I showed correct?

I think you are in my shoes cause I work on residential building projects. Honestly I would just tell them the performance of the range will lose 25% of power if 208V is used on the 240V appliance. You could still apply 208V to it but size the branch circuit using the actual demand load of the equipment. I believe 220.55 note #4 explains branch circuit may be calculated using 220.55

 

[Grouch1980]

I think you are in my shoes cause I work on residential building projects. Honestly I would just tell them the performance of the range will lose 25% of power if 208V is used on the 240V appliance. You could still apply 208V to it but size the branch circuit using the actual demand load of the equipment. I believe 220.55 note #4 explains branch circuit may be calculated using 220.55

Woops... I should've used the 80% on the feeder calc... Please let me re-write this :

I came across an electric range, rated 240 volts, 32 amps as stated on its cutsheet. In my load calc, I would use 7,680 watts since that would be the nameplate rating. (240V x 32A). I would then apply 80% from column B from Table 220.55... 7680 watts x 80% = 6144 watts.

When I have my total VA load for all equipment in the apartment however, at the end I would divide the total VA load by 208 volts (since my area is 120/208 volts).

And then for the branch circuit sizing, note #4 from Table 220.55 states "it shall be permissible to calculate the branch-circuit load for one range in accordance with table 220.55". So... since I'm dealing with a branch circuit, I'll use 75% of the 7680 nameplate rating, bringing it down to 5760 watts (since we're connected to 208 volts). And since note #4 says I can use Table 220.55 for a range, I can then apply 80% to the 5760 watts... I am now at 4608 watts. 4608 watts / 208 volts = 22.15 amps... next size up is a 2 pole, 25 amp breaker.

Is all this correct?

 

[Tainted]

Woops... I should've used the 80% on the feeder calc... Please let me re-write this :

I came across an electric range, rated 240 volts, 32 amps as stated on its cutsheet. In my load calc, I would use 7,680 watts since that would be the nameplate rating. (240V x 32A). I would then apply 80% from column B from Table 220.55... 7680 watts x 80% = 6144 watts.

When I have my total VA load for all equipment in the apartment however, at the end I would divide the total VA load by 208 volts (since my area is 120/208 volts).

And then for the branch circuit sizing, note #4 from Table 220.55 states "it shall be permissible to calculate the branch-circuit load for one range in accordance with table 220.55". So... since I'm dealing with a branch circuit, I'll use 75% of the 7680 nameplate rating, bringing it down to 5760 watts (since we're connected to 208 volts). And since note #4 says I can use Table 220.55 for a range, I can then apply 80% to the 5760 watts... I am now at 4608 watts. 4608 watts / 208 volts = 22.15 amps... next size up is a 2 pole, 25 amp breaker.

Is all this correct?

Yes you may use 25 amps since this is the absolute minimum, also there is nothing wrong with using a 30amp breaker too as long as the wires are #10

 

[jaggedben]

I bet the range actually has a rating at 208V on it. I can't recall seeing one that didn't have that. That's what you should use.

And you really can't extrapolate the current from the 240V rating. I actually looked at two different ranges today. One was 12.1kW at 240V vs 9.1kw at 208V, and the other was 11.6kW vs 9.8kW.

 

[infinity]

And you really can't extrapolate the current from the 240V rating. I actually looked at two different ranges today. One was 12.1kW at 240V vs 9.1kw at 208V, and the other was 11.6kW vs 9.8kW.

I would bet that the second one is incorrect.

 

[Tainted]

I would bet that the second one is incorrect.

Agreed. second one seems to violate the laws of physics.

I bet the range actually has a rating at 208V on it. I can't recall seeing one that didn't have that. That's what you should use.

And you really can't extrapolate the current from the 240V rating. I actually looked at two different ranges today. One was 12.1kW at 240V vs 9.1kw at 208V, and the other was 11.6kW vs 9.8kW.

This is a purely resistive load. Therefore you can indeed find the 208V current on the 240V appliance

 

[jaggedben]

Agreed. second one seems to violate the laws of physics.

It might be because it's got an induction stovetop. Anyway, it doesn't necessarily violate physics because...

This is a purely resistive load. Therefore you can indeed find the 208V current on the 240V appliance

That's true for an ideal resistor, but you don't know how ideal the behavior of the heating element is. Plus there may a fan or two.

 

[jaggedben]

Also if you cut it too close, the savings in wire isn't worth the return service calls when the breaker trips.
If you don't have the unit itself to look at the markings, then just go by what the manual says for the branch circuit size.

 

[Tainted]

It might be because it's got an induction stovetop. Anyway, it doesn't necessarily violate physics because...


That's true for an ideal resistor, but you don't know how ideal the behavior of the heating element is. Plus there may a fan or two.

Comparing two internal fans to a large resistive load is like comparing the size of the earth to the sun... Heating elements are designed to be extremely close to 100% efficiency. There is also a reason why the ratings are in watts and not VA.

 

[kwired]

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

-Hal

It is pretty common on larger multifamily applications. The motors and controls are normally 120 volt so they still work the same when on a 208/120 system, you just have a reduction in heater watts is all.