Originally Posted by
Malcolm McLeod
For most circuit interrupters, already installed in the field, there are electrical test specialists with suitably specialized equipment to perform these tests. All engineers that I've met, but I have forgotten the credential requirements. They basically use current amplifier coils (and low voltage) to inject current of sufficient magnitude and duration to cause a trip. (Last one I attended was part of new install of 4160V 4000A main CB and related MCC gear, fed from a Centaur turbine generator array on a offshore platform. I was validating the CB's interface to our automation systems.) The 'trip' felt like an earthquake! OK, a small one. 3.0:eek:
The concept is exactly the same for heaters on a 240V 5Hp saw, but I'm guessing you might not want to go to this extreme ($$$).
I would only suggest to the OP that he do what he's comfortable with, but if this system were mine, I'd buy new heaters of a known size/rating. They are not adjustable. And they have a memory: the more they are tripped, the lower and lower the trip point becomes.
If I were 'in' on this machine for years to come, I'd pull the starter/overload, and replace with an IEC-format modular disconnect, starter, and adjustable O/L. To test the adjustable O/L, you drop the setting from the typical 1.4X or 1.5X FLA, down to the motor's FLA or slightly less. Then start the unit and let it run until it trips. This tests the actual safety trip function - but you still have to trust that the adjustment scale (dial) is accurate. In my experience, from a reputable supplier, their accuracy is certainly close enough to safely operate small motors (<10hp).