Immersion heater service factor (practical)

[Rson]

I know I have some 12kW immersion heaters coming up for a job. I don't deal with these often, and I'm just trying to find a practical service factor for these at 480VAC.

I know pure resistive loads are a SF of 1. Do I use this value for OCPD sizing or is there a more practical value to use (like 0.9 or 0.8?)

 

[T Gibbs]

Never considered a service factor on a heating element. I always just size the ocpd by watts/volts.

 

[thingstodo]

I know I have some 12kW immersion heaters coming up for a job. I don't deal with these often, and I'm just trying to find a practical service factor for these at 480VAC.

I know pure resistive loads are a SF of 1. Do I use this value for OCPD sizing or is there a more practical value to use (like 0.9 or 0.8?)

I'm not familiar with OCPD. So this answer is a bit of a guess.

To size a breaker or a cable I'd use 125% of the full load amps, moving up to the next available size.

To guess what the load of the heater is, you need to look at the process more than the heater. Heaters can be over-sized, undersized, or correctly sized. Just like anything else. An undersized heater will come on and stay on for long periods of time.

It is technically possible to use more than Full Load Amps on an immersion heater that has a high flow rate and is undersized. But i don't think that's what you are talking about

 

[lfe]

Electric heaters tend to heat up protection devices a lot and also the cables, since they usually work at 100% during long periods.

I used to use NH fuses because they are robust and have large terminals.

 

[Rson]

Never considered a service factor on a heating element. I always just size the ocpd by watts/volts.

This is what I was planning on, but I wasn't sure with three phase heaters. I know everything has some inductance so I wasn't sure if a SF of 1 was practical or if I should use something slightly smaller for real-life scenarios. I didn't want the breaker nuisance tripping on me because it was under sized.

 

[rupej]

I usually shoot for 15-20% oversized fuses and conductors feeding a heater. The heater should pull very close to rated amps, assuming you are supplying rated voltage. If you have significantly more, there is a problem.

 

[g.mccormick]

I know I have some 12kW immersion heaters coming up for a job. I don't deal with these often, and I'm just trying to find a practical service factor for these at 480VAC.

I know pure resistive loads are a SF of 1. Do I use this value for OCPD sizing or is there a more practical value to use (like 0.9 or 0.8?)

Is this a 3ph resistance heater element? With resistance elements, there is no inrush or service factor. Unlike a motor, you cannot cause it to pull more than FLA (unless voltage increases). A motor pulled down in speed past its rated speed keeps consuming higher and higher current due to more and more slip. A resistance heater, you can't cause it to eat more current than OHMs law.

For a 3ph heater, Power = V*I*sqrt(3)=V*I*1.732.

Solving for I we get I= Power/(V*1.732).

For a 12000W heater, we get I= 12000/(480*1.732) = 14.34 Amps