Adjustable Current Motor Circuit Protector, how is that used

I was looking for a motor starter with overloads and I saw a lot of Adjustable Current Motor Circuit Protectors for sale. I do not understand how they work. I understand that that the supply wires run through them and they sense current flow. If the current is to high they do something but I do not know what they do at that point. They can not, by themselves, switch off the power. Do you have to have a contactor to do the actual switching?
Do they just switch open a control voltage signal to the contactor coil? How do they get reset? Is it automatic reset or is there a switch to push?
Bill D.

Historically they are a thermally operated switch in the contactor coil feed. Usually an add on to the contactor so the same contactor can be used over a range of currents.

The actual supply current on that phase passes through the device. which, basically, bends when it warms up. How much it warms up, and therefore how much it bends, is proportional to the current passing through the device. The adjustment lets you set how much bend, and so how much current, it takes to operate the switch.

Nice thing is that it doesn't heat up instantly so inrush current on start up generally doesn't trigger the device. But it still goes off very quickly at currents large enough to do damage. It may well go off if a bit too much current is taken for long periods too.

Cheap and effective.

Some types will auto reset, some need you to open the covers and press a button, some have a switch to select auto or manual reset. Generally the switchable ones are less reliable when they get old. Good idea to squirt cleaner on them and operate the selector afew times every decade or so.

Whatever the type once the switch has triggered the beast has to be reset before the machine can be started by pushing the go bitton in the usual way.

Clive

Bill D said:

I was looking for a motor starter with overloads and I saw a lot of Adjustable Current Motor Circuit Protectors for sale. I do not understand how they work. I understand that that the supply wires run through them and they sense current flow. If the current is to high they do something but I do not know what they do at that point. They can not, by themselves, switch off the power. Do you have to have a contactor to do the actual switching?
Do they just switch open a control voltage signal to the contactor coil? How do they get reset? Is it automatic reset or is there a switch to push?
Bill D.

Click to expand...

yes you have a starter also
and you might need a 24 vdc supply to operate the thermal

this behind a contactor is an easier circuit

it's how all the machine builders do it now
gives you an easy way to kill a device for troubleshooting