208V Appliance Circuits

[ericlemmon1]

The typical 12kW electric range requires a 50 ampere circuit when operated on the common residential 240 VAC. However, many condos, apartments, and cluster homes are fed 120/208 VAC derived from a three-phase transformer bank. I know of several cases where a resident purchased a 240 VAC-rated electric stove, clothes dryer, or water heater from an appliance store and was disappointed in its lackluster performance. Further investigation revealed that the resident lived in a facility that had 120/208 VAC power. In each case, the resident was unaware of the available voltage, and the appliance salesperson never asked about it. Ohms Law will prove that a resistive heating appliance rated for 240 VAC will produce only 75% of its capacity when operated at 208 VAC.


My concern is that some appliance manfufacturers do make 208 VAC-rated ranges, but a 12kW range at 208 VAC will require a 60-ampere circuit. The NEC does not acknowledge this fact, and I submit that this is a significant oversight that needs to be corrected. Likewise, electric clothes dryers and electric water heaters intended for 208 VAC operation will require higher-rated circuits to handle the higher currents. I don't think the average appliance buyer is aware of the practical implications of a 208 VAC service.

 

[david luchini]

Per T220.55, a 12kW, 240V range (with its 8 kw demand) would be fine on a 40A/240V circuit.

A 12kW, 208V range (with its 8kW demand per T220.55) would likewise be fine on a 40A/208V circuit. I don't see it as a problem.

But the code does address it anyway. See 210.19 and 210.20. The branch circuit must be sufficiently sized for the load to be served.

 

[ActionDave]

My concern is that some appliance manfufacturers do make 208 VAC-rated ranges, but a 12kW range at 208 VAC will require a 60-ampere circuit. The NEC does not acknowledge this fact, and I submit that this is a significant oversight that needs to be corrected. Likewise, electric clothes dryers and electric water heaters intended for 208 VAC operation will require higher-rated circuits to handle the higher currents. I don't think the average appliance buyer is aware of the practical implications of a 208 VAC service.

I think you are a little over the top here. All of my electric appliances; two dryers, one electric double oven, and one electric range have a rating for both 240V and 208V.

 

[iwire]

I think you will find all US made ranges, dryers and water heaters for dwelling units are rated at both 208 and 240 volts and yes the stove tops burners performance is less than impressive.

 

[jumper]

I believe most residential/small commercial HVAC equipment is rated at 208 or 230 also.

 

[Hv&Lv]

The typical 12kW electric range requires a 50 ampere circuit when operated on the common residential 240 VAC. However, many condos, apartments, and cluster homes are fed 120/208 VAC derived from a three-phase transformer bank. I know of several cases where a resident purchased a 240 VAC-rated electric stove, clothes dryer, or water heater from an appliance store and was disappointed in its lackluster performance. Further investigation revealed that the resident lived in a facility that had 120/208 VAC power. In each case, the resident was unaware of the available voltage, and the appliance salesperson never asked about it. Ohms Law will prove that a resistive heating appliance rated for 240 VAC will produce only 75% of its capacity when operated at 208 VAC.


My concern is that some appliance manfufacturers do make 208 VAC-rated ranges, but a 12kW range at 208 VAC will require a 60-ampere circuit. The NEC does not acknowledge this fact, and I submit that this is a significant oversight that needs to be corrected. Likewise, electric clothes dryers and electric water heaters intended for 208 VAC operation will require higher-rated circuits to handle the higher currents. I don't think the average appliance buyer is aware of the practical implications of a 208 VAC service.

A range is a resistive load. In a resistive load, the voltage and current are directly proportional. If the voltage is reduced, the current will be reduced.
At 240 volts, and 12kW I=50 R=4.8
At 208 volts, the resistance will stay the same, so I=43 P=9kW

 

[norcal]

Most modern domestic appliances have dual rating for 120/240V, & 120/208V, I looked at my Whirlpool built Kenmore range, it has a 12.5 KW @ 120/240V, & 9.5 KW, @ 120/208V rating just to give a EZ example.

 

[ericlemmon1]

I think we're mixing apples and oranges here. Of course, a 12kW range that is intended to operate at 240 VAC will, indeed, operate at reduced power when connected to a 208 VAC supply. The point I was making is that some appliance makers do, in fact, make 12kW ranges that are designed to produce full power when operated on 208 VAC. Such appliances are usually special-order items that are found in the back of the sales books, and are often available at extra cost. Being a resistive heating device, a 12kW appliance will draw 50 amperes at 240 VAC and 57.7 amperes at 208 VAC. Despite the NEC diversity provision, a full-size 12kW range will draw close to maximum power when all elements and the oven are in use.

 

[iwire]

I think we're mixing apples and oranges here. Of course, a 12kW range that is intended to operate at 240 VAC will, indeed, operate at reduced power when connected to a 208 VAC supply. The point I was making is that some appliance makers do, in fact, make 12kW ranges that are designed to produce full power when operated on 208 VAC.

And the code knows that and address that, as was pointed out.

Being a resistive heating device, a 12kW appliance will draw 50 amperes at 240 VAC and 57.7 amperes at 208 VAC. Despite the NEC diversity provision, a full-size 12kW range will draw close to maximum power when all elements and the oven are in use.

Feel free to put in a code change proposal, you have until this fall to get them in for the 2017 NEC.

But I suspect it will be shot down as unneeded.

 

[don_resqcapt19]

...

Feel free to put in a code change proposal, you have until this fall to get them in for the 2017 NEC.

But I suspect it will be shot down as unneeded.

The proposal deadline for the 2017 code is 5pm EST on the first Friday of November 2014.

 

[iwire]

The proposal deadline for the 2017 code is 5pm EST on the first Friday of November 2014.

Thanks, I thought I had seen you post it was this fall.

 

[Hv&Lv]

Being a resistive heating device, a 12kW appliance will draw 50 amperes at 240 VAC and 57.7 amperes at 208 VAC. QUOTE]

I can't see how you come up with these numbers. Must be a weird type of stove that doesn't follow Ohms Law. :?

 

[texie]

While I agree with the others that this is not an NEC issue, but it is a customer satisfaction issue. Used to get a fair number of complaints about this. Typical scenario was high rise luxury second home condo. Primary residence a typical single family home with 120/240 service. They notice that the heating appliances just seem don't seem right and not like their primary home.

 

[david luchini]

Being a resistive heating device, a 12kW appliance will draw 50 amperes at 240 VAC and 57.7 amperes at 208 VAC.

I can't see how you come up with these numbers. Must be a weird type of stove that doesn't follow Ohms Law. :?

Seems pretty straightforward.

The point I was making is that some appliance makers do, in fact, make 12kW ranges that are designed to produce full power when operated on 208 VAC.

A 12kW/240V range: 12000/240=50

A 12kW/208V range: 12000/208=57.7

 

[hurk27]

While I know we are allowed to use the single range demand load (Table 220.55) when sizing the circuit for a range (210.21(B)(4) )

But since the largest receptacle we can use is a 50 amp range receptacle and table 210.21(B)(3) will only allow us to protect that 50 amp receptacle with a 50 amp OCPD, so the only way I could see a larger range would be to have it hard wired?

I have done some searching but I can not find a range with a 12kw rating at 208 volts which if there was it would have a 16kw rating if it was to be installed on a 240 volt system, what would keep a homeowner who purchased their own range then move out to a house or apartment that has 240 volts to try to use it? it would pull 66.7 amps and most likely trip the OCPD on Thanksgiving day and you would have an unhappy cook.

I'm just curious as while gas appliances is the norm around here, just wondering if that is why the table 220.55 goes up to 12kw and you don't see many single stand alone ranges above 12kw, I have seen an LG that was 13.5kw but it only have a 10.5 rating on 208 and it had a double oven.

 

[broadgage]

Being a resistive heating device, a 12kW appliance will draw 50 amperes at 240 VAC and 57.7 amperes at 208 VAC. QUOTE]

I can't see how you come up with these numbers. Must be a weird type of stove that doesn't follow Ohms Law. :?

I think that two different issues are being confused here.
If a resistive heating appliance designed for 240 volts is used on 208 volts then it will use less amps and less kilowatts, and have reduced performance.

If however the appliance designed for 240 volts is removed and replaced with a similar appliance, of the same KW loading, but designed for 208 volts, then the current will be greater.
A 12KW, 208 volt appliance will use more amps than a 12KW 240 volt appliance.
A 12KW 240 volt appliance connected to a 208 volt supply will use less amps.

In practice the reduction in average actual amps used by a real world cooking appliance may less than expected by reducing the supply voltage from 240 volts to 208.
The assumed demand for a range is less than the total loading of each element, because in normal use the elements are cycled on/off to maintain the required temperature.
At a lower voltage the element produces less heat and to cook the same food the element must run for more minutes in each hour to do this.
For example, an oven element might use 12 amps at 240 volts and only 10.4 amps at 208 volts.
However the element might run for 30 minutes in each hour on 240 volts but for 40 minutes in each hour on 208 volts.

A stove top element might run at full power to boil a pot, but take 6 minutes to this on 240 volts, and 8 minutes on 208 volts.

 

[Hv&Lv]

Seems pretty straightforward.



A 12kW/240V range: 12000/240=50

A 12kW/208V range: 12000/208=57.7

My point was I believe you are using the wrong formula. By your formula the resistance of the range is changing. A range will have the same resistance at whatever voltage you use for it whether it is 240, 208, or 120.(I will admit, it wont get hot at all on 120, just warm)

The actual kW will be reduced by the lower voltages, as the resistance isn't changing.
So for your example,
A 12kW range: 12000/240=50 to expand, the resistance is 4.8 ohms
12000/208=57.7 the resistance is 3.6 ohms
the resistance doesn't change in a range.

R=P/I²: 12000/2500(50²)=4.8ohms
for the 208 range the resistance doesn't change,and the formula needs to take the resistance and the voltage in consideration.
I=E/R: 208/4.8=43.33 amps on the 208 range
The current will be reduced proportional to the voltage in a resistive circuit.

 

[kwired]

I believe most residential/small commercial HVAC equipment is rated at 208 or 230 also.

And you run into HVAC guys that don't realize that the voltage is 208 and they size their unit on the 240 volt rating.

Then it is my fault they only get 75% of the rating they were looking for.

I can transform to get proper voltage but getting right size HVAC unit is a lot less cost.

 

[kwired]

My point was I believe you are using the wrong formula. By your formula the resistance of the range is changing. A range will have the same resistance at whatever voltage you use for it whether it is 240, 208, or 120.(I will admit, it wont get hot at all on 120, just warm)

The actual kW will be reduced by the lower voltages, as the resistance isn't changing.
So for your example,
A 12kW range: 12000/240=50 to expand, the resistance is 4.8 ohms
12000/208=57.7 the resistance is 3.6 ohms
the resistance doesn't change in a range.

R=P/I²: 12000/2500(50²)=4.8ohms
for the 208 range the resistance doesn't change,and the formula needs to take the resistance and the voltage in consideration.
I=E/R: 208/4.8=43.33 amps on the 208 range
The current will be reduced proportional to the voltage in a resistive circuit.

Resistance will change if the unit is designed to be 12kW at 208 volts vs 12kW at 240 volts. In that case the kW is what remained the same which is what this comment was about, a special order 208 volt unit.

 

[david luchini]

My point was I believe you are using the wrong formula. By your formula the resistance of the range is changing. A range will have the same resistance at whatever voltage you use for it whether it is 240, 208, or 120.(I will admit, it wont get hot at all on 120, just warm)

The actual kW will be reduced by the lower voltages, as the resistance isn't changing.
So for your example,
A 12kW range: 12000/240=50 to expand, the resistance is 4.8 ohms
12000/208=57.7 the resistance is 3.6 ohms
the resistance doesn't change in a range.

I am not using the wrong formula, you are misunderstanding the OP's point. Reread his posts #1 & #8.

He is decrying the fact that a 12000W/240V range will under-perform on a 208V circuit. He further suggests that one can install a 12kW/208V rated range. The 12kW/208V range on a 208V circuit will have a higher load current (57.7A) than the 12kW/240V range on a 240V circuit (50A.)