Heater load

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mstrlucky74

Senior Member
Location
NJ
We have a temp system in the jobsite are about to power up many temporary unit heaters. How would you calculate the load these will have on the system. Some suspect the service is not enough? Just curious thanks.
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I would add it up and then guesstimate what the duty cycle will likely be on these heaters to get an idea of what the average load will be. The code may not explicitly allow for this though.
And if there is a chance that all of the heaters will be turned on together at the start of the work day, they you would have to just add up all the heater wattages.
 

roger

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Location
Fl
Occupation
Retired Electrician
On a job site I would not assume any load diversity unless it is a very weather tight building.
Same here, most times heaters on job sites run wide open constantly.

Roger
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
I would never, ever, make sure my wire sizes are properly protected by the breakers and then just hook them up and see what happens. ;)
 

J.P.

Senior Member
Location
United States
Electric temp heaters?

All of the jobsite heater I have seen just need a little power for the blowers. The gas or fuel does the hard work.
 

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I agree with Bob and Roger figure all heaters running at 100% output 24/7. I would use 3 phase heaters if possible. Last winter we ran 3 10KW heaters in a drafty service room and raised the temperature about 10-15 degrees in the dead of winter.
 

mstrlucky74

Senior Member
Location
NJ
Guys thanks for the put but still don't know how to figure demand/load on service? We have a 2000a dust panel feeding a bunch of branch panels which feed the heaters. Thx
 

kwired

Electron manager
Location
NE Nebraska
Guys thanks for the put but still don't know how to figure demand/load on service? We have a 2000a dust panel feeding a bunch of branch panels which feed the heaters. Thx
How about this?

220.51 Fixed Electric Space Heating.

Fixed electric space-heating loads shall be calculated at 100 percent of the total connected load. However, in no case shall a feeder or service load current rating be less than the rating of the largest branch circuit supplied.


Exception: Where reduced loading of the conductors results from units operating on duty-cycle, intermittently, or from all units not operating at the same time, the authority having jurisdiction may grant permission for feeder and service conductors to have an ampacity less than 100 percent, provided the conductors have an ampacity for the load so determined.
 
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