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Thurman 12-29-2010 11:40 PM

Not good at calculations
 
I have a heat strip from a central unit HVAC. The A/C part is shot and has been removed. The heat strips and fan work just fine, BUT: I have it wired up to a 30 amp breaker and it trips after about ten minutes of running. The heat strips are two parts rated at 5.0KW and 4.6KW, then there is the squirrel cage fan unit which runs good. I've beat my brains out doing calculations and am not sure I'm getting the correct one. Does this unit, based on the heat strips, require a "42" amp service, plus the fan? OUCH! This will mean going to at least a 50 amp breaker to run this in my shop. I do have a 150 amp service in there, but it's half full now, even using the 80% factor. Maybe I'll have to play "Green Acres" and plug in a #1 along with a #5, but not a #2.

frenchelectrican 12-30-2010 12:25 AM

Quote:

Originally Posted by Thurman (Post 559003)
I have a heat strip from a central unit HVAC. The A/C part is shot and has been removed. The heat strips and fan work just fine, BUT: I have it wired up to a 30 amp breaker and it trips after about ten minutes of running. The heat strips are two parts rated at 5.0KW and 4.6KW, then there is the squirrel cage fan unit which runs good. I've beat my brains out doing calculations and am not sure I'm getting the correct one. Does this unit, based on the heat strips, require a "42" amp service, plus the fan? OUCH! This will mean going to at least a 50 amp breaker to run this in my shop. I do have a 150 amp service in there, but it's half full now, even using the 80% factor. Maybe I'll have to play "Green Acres" and plug in a #1 along with a #5, but not a #2.

just add 5.0 and 4.6 that will result of 9.6 KW which on 240 volts you will draw at 40 amp plus what ever the motor draw will add to the figures and normally this is pretty much continous load so you will defenity need 50 amp breaker with #6 conductor otherwise there is other option you can disabled second heat bank to reduce down to 5 KW which you can get by with 30 amp breaker without issue.

So you have two options what you need to do with this unit as I describing.

Merci.
Marc

Thurman 12-30-2010 07:44 AM

Well Thank You Sir for the info. This falls into the area I had roughly figured, but was not sure on. I had not thought about using just one set of coils. That's a good thought, if this will heat the shop up any, at all. Based on what I have now--nothing, this would be an improvement. I now have options to try this two ways, and the means to do so----Safely. Thanks, David

JPraski 12-30-2010 08:30 AM

1/2 of 150 is 75, even at the 100% instead of 80%, you should probably have enough power available in the panel for a 50A breaker, shouldn't you? Like you said, it should probably be around 42A max anyhow, not the full 50 but they don't make a 42A breaker, you must go to 50A.


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