What's the procedure for picking heater's?
What's the procedure for picking heater's?
(OP)
Last person who called me said he picked heaters by taking the FLA of the motor and adding in the service factor.
Now that sounds find - but what about Starting Amps how does the heater compensate for that in rush and not blow?
Simple I know but a simple answer will make me more informed in the future.
Thanks
Wayne
Now that sounds find - but what about Starting Amps how does the heater compensate for that in rush and not blow?
Simple I know but a simple answer will make me more informed in the future.
Thanks
Wayne





RE: What's the procedure for picking heater's?
See NEC 430.31 through 430.44. I suspect most of your motors will be covered by NEC 430.32.
Re: "what about Starting Amps how does the heater compensate for that in rush and not blow?"
That's the whole point of the heater, it takes some time to heat up, it's got "thermal inertia". So a short-term overload won't trip it, nor will short term inrush currents. That same current, applied over a longer duration, will give it enough time to heat up and finally blow.
RE: What's the procedure for picking heater's?
http://www.geindustrial.com/cwc/library?famid=35
Scroll down to look at the following detailed document:
GET-2681L Heater selection guide
RE: What's the procedure for picking heater's?
RE: What's the procedure for picking heater's?
RE: What's the procedure for picking heater's?
RE: What's the procedure for picking heater's?
RE: What's the procedure for picking heater's?
The alloy is more or less similar to solder, it's just a metal that melts at a relatively low temperature, but also at a very predictable and repeatable temperature. It's very similar to the alloys used in the pop-up turkey thermometers. Different alloy blends give different melting points. With the turkey thermometer, the alloy holds a spring-loaded plunger in place; when it melts, the plunger is released and it pops out.
With a motor overload heater, instead of a plunger, there's a spring-loaded ratchet. The ratchet shaft sits in a pot full of the alloy. When the heater melts the alloy, the ratchet can spin, and that trips the motor stop circuit. After the alloy cools and re-hardens, you push in the reset button, which winds the ratchet up to the next notch and tensions the spring again.