resistive heat

Status
Not open for further replies.

j rae

Senior Member
I have a 19.5 kw heater 53.4 amp what size wire and breaker is needed and are there any codes about over or under sizeing the wire or breaker
 

M. D.

Senior Member
How did you come up with 53.4 amps ? What does the name plate give for information??
 

M. D.

Senior Member
Maybe that is the min branch circuit ampcity with the 125 % figured in ?? on 3 phase??
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
The numbers work together if you have a 208 volt, three phase heater. Assigning the current a value of 53.4 takes into account an extra 25% for its being considered a continuous load. Therefore, you need a wire with an ampacity of at least 53.4 amps, and need not oversize it beyond that point. So a #6 copper THHN would answer, since it has an ampacity of 65 amps. A #8 would not work, since it is rated only for 50 amps. You cannot ?undersize a wire?; it must have an ampacity at least as high as the load. Of course, if the branch circuit is a long one, over 100 feet, you might want to consider upsizing for voltage drop considerations.

The breaker need only be rated to protect the wire. A 60 amp breaker would do. Since the wire has an ampacity of 65 amps, and since that is not a standard size overcurrent protection setting, you can upsize the breaker to the next step, and use a 70 amp breaker. You can always undersize a breaker. You could protect this installation with a 15 amp breaker, if you wish. I don?t think the owner would be happy with the results (i.e., it will trip all the time), but that is not a concern of the NEC.
 

eprice

Senior Member
Location
Utah
charlie b said:
You can always undersize a breaker. You could protect this installation with a 15 amp breaker, if you wish. I don?t think the owner would be happy with the results (i.e., it will trip all the time), but that is not a concern of the NEC.

Wouldn't that be a violation of 210.20(A)?
 
Status
Not open for further replies.
Top