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Alwayslearningelec

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NJ
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Estimator
Ok I have a job I am estimating and the motors are not circuited. I refered to the schedule and found my draw(amps) based on the KW. If I have a 5kw 3 phase 208 v unit heater that draws 14amps do I need a 3pole disconnect? I am think a thermal switch as it is 14amps. My vavs show thermal switches clearly but these unit heaters show disconects.

Sidebar- how do I figure how many I can have on a circuit?

Thanks.
 
horsegoer said:
Ok I have a job I am estimating and the motors are not circuited. I refered to the schedule and found my draw(amps) based on the KW. If I have a 5kw 3 phase 208 v unit heater that draws 14amps do I need a 3pole disconnect? I am think a thermal switch as it is 14amps. My vavs show thermal switches clearly but these unit heaters show disconects.

Sidebar- how do I figure how many I can have on a circuit?

Thanks.
Click to expand...
If you have a 3 phase circuit that requires a disconnect you need a three pole disconnect. You may not need a disconnect switch as such, just something that positively disconnects all three lines.

I would not be putting more than one such heater on a circuit. Just simpler that way, although if you used fused disconnect switches you could conceivably put as many on a circuit as you wanted to. It just might end up being inconvenient to do so.

To be honest, this is somewhat of a scary question coming from a person who purportedly has at least some expertise in the electrical field.
 
Bob,
I was scratching my head trying to come up with a decent answer comparing "thermal swithces" vs disconnects etc.
You answer adressed everything I was thinking in concise manner..
Good Answer !
 
petersonra said:
If you have a 3 phase circuit that requires a disconnect you need a three pole disconnect. You may not need a disconnect switch as such, just something that positively disconnects all three lines.

I would not be putting more than one such heater on a circuit. Just simpler that way, although if you used fused disconnect switches you could conceivably put as many on a circuit as you wanted to. It just might end up being inconvenient to do so.

To be honest, this is somewhat of a scary question coming from a person who purportedly has at least some expertise in the electrical field.
Click to expand...


What difference does a unfused disconnect make?
 
horsegoer said:
What difference does a unfused disconnect make?
Click to expand...
if you have a separate circuit for each heater, the branch circuit protection can serve as the OCPD and potentially the disconnecting means as well.

if you want to have more than one heater on a circuit, you have to have some kind of downstream OCPD, such as a fused disconnect switch. you could probably put some fuses in a junction box as well, but the cost might not be a whole lot different. presumably you could still use the branch circuit breaker as the disconnecting means, but thats not real convenient.

if these are all in the same area, it might make some sense to install a new panel board and just bring one feeder in and then distribute it from the new panel board to the new heaters. But since you mentioned something about "showing disconnects" it may be the spec calls for them.
 
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