voltage question

[Matt Mckenzie]

Will a 3 phase service with a wild leg that is 240 volts leg to leg support a 3 phase 240 volt heater vs. a 3 phase service that is 208 volt leg to leg would not a support a 240 volt 3 phase heater. Unless listed for both voltages? The heater spec sheet says one model for a 3 phase 208 volt and another model for a 3 phase 240 volt.

 

[iceworm]

I'm not understanding your question. Could the MFG be saying that the 10KW heater rated at 240V 3ph is only puts out 7.5KW at 208V 3ph?

ice

 

[ActionDave]

Some are either or but if the unit only says 208V or 240V that is what should be used respectively.

 

[MasterTheNEC]

Will a 3 phase service with a wild leg that is 240 volts leg to leg support a 3 phase 240 volt heater vs. a 3 phase service that is 208 volt leg to leg would not a support a 240 volt 3 phase heater. Unless listed for both voltages? The heater spec sheet says one model for a 3 phase 208 volt and another model for a 3 phase 240 volt.

Matt,If you are asking can you run a 240V rated heater (and I will assume an infrared heater, since I can) on a 208V system the answer would be yes. However, you will have to expect about a 60% of the heating energy versus its stated output. The real issue is what you stated in the specs....If the manufacturers specifications call for a specific system for the specific heater you have selected then you should install it in accordance with the manufacturers instructions. If I was doing this for a paying customer I would never try to put a 208V heater on their 240V system...but that's just me.

 

[iceworm]

Matt,If you are asking can you run a 240V rated heater (and I will assume an infrared heater, since I can) on a 208V system the answer would be yes. However, you will have to expect about a 60% of the heating energy versus its stated output. ....

Really - How did you calculate that?

ice

 

[MasterTheNEC]

Really - How did you calculate that?

ice

well it is probably more than 60% but I was being lazy...

if the output was 100% at the rating of the unit at 240V then reducing the voltage to 208V only serves to reduce the potential output value....so it's more like 86% output due to the voltage difference. Hey....i have 3 glasses of wine in me...can't I be lazy. (even if I slighted him 26%)..

 

[Matt Mckenzie]

voltage question

I guess what I am saying is... If I have a 3 phase service in my shop and I have a wild leg but I am 240 volts leg to leg and I want to order some ceiling mount heaters that have blowers on them do I order the model that is 208 3 phase or a 240 volt 3 phase? I am assuming I need to order 240 volt 3 phase but I just want to be sure.

Thanks

 

[gar]

141108-2146 EST

Quite obviously you need to order the 240 V three phase heater. Your source is 240 V leg-to-leg.

If your source was 208 leg-to-leg, then you could put either a 208 or 240 V heater on it, if there was no motor. But with a fan as part of the package don't put a 240 on a 208 source.

A 240 V heater operated at 208 V will provide approximately (208/240)^2 = 0.75 of the rated power. P = V * I and heater resistance is approximately constant. From no current to normal full rating current a typical resistive heater resistance will increase about 10%. So from 208 V to 240 V the resistance will change considerably less than 10%.

.

 

[MasterTheNEC]

141108-2146 EST

Quite obviously you need to order the 240 V three phase heater. Your source is 240 V leg-to-leg.

If your source was 208 leg-to-leg, then you could put either a 208 or 240 V heater on it, if there was no motor. But with a fan as part of the package don't put a 240 on a 208 source.

A 240 V heater operated at 208 V will provide approximately (208/240)^2 = 0.75 of the rated power. P = V * I and heater resistance is approximately constant. From no current to normal full rating current a typical resistive heater resistance will increase about 10%. So from 208 V to 240 V the resistance will change considerably less than 10%.

.

Glad math was not my specialty..:slaphead:

 

[Sierrasparky]

Glad math was not my specialty..:slaphead:

Have another glass of wine,
The numbers will look better.

 

[ggunn]

I guess what I am saying is... If I have a 3 phase service in my shop and I have a wild leg but I am 240 volts leg to leg and I want to order some ceiling mount heaters that have blowers on them do I order the model that is 208 3 phase or a 240 volt 3 phase? I am assuming I need to order 240 volt 3 phase but I just want to be sure.

Thanks

The voltage of the high leg doesn't figure into a three phase load; only the phase to phase voltages matter. The high leg is 208V referenced to the center tap between the other two phases, but a 240V three phase load doesn't connect to it.