Thread: 3 phase switch problems .

Here's the switch and motor details.

Cant load them yet . Pictures have stopped loading for some reason ??

The bit at the bottom is a thermal overload and protects the motor from overheating, the more you turn it to the right the hotter you are allowing the motor to get before the overload kicks in and stops it from working.The contactor should pull in the magnet, here's a video showing how the wiring should be, the NO switch is a momentary switch which when pressed energizes the magnet and pulls the contactor together making a circuit, then it falls out of the circuit just incase you have a power cut, where power may come back on and restart the machine while your not there. https://www.youtube.com/watch?v=K1q0yoym-8I

Originally Posted by Camelot

The bit at the bottom is a thermal overload and protects the motor from overheating, the more you turn it to the right the hotter you are allowing the motor to get before the overload kicks in and stops it from working.

Ah its thermal overload. I thought it was some sort of electrical overload. ( Same thing ? )How does an electrician know where to set it when hes just wired up a new switch to a machine ? Run it for a while and lower it till it trips then just go a %? higher and leave it there?

This link seems a good explanation of them. A Guide on Thermal Overload Relay Working Principle | CHINT Blog
What do the numbers stand for ? And the A? Amps?
IMG_4520a.jpg

Originally Posted by Camelot

The contactor should pull in the magnet, here's a video showing how the wiring should be, the NO switch is a momentary switch which when pressed energizes the magnet and pulls the contactor together making a circuit, then it falls out of the circuit just incase you have a power cut, where power may come back on and restart the machine while your not there. 3 Phase Contactor Wiring Diagram DOL Starter - YouTube

I cant watch that guy in the echo chamber explanation.

Its a contactor, that's right .

The motor badge and the switch badge . I think they look fine. 5.5 KW is 7.37 HP so its not an underrated switch. It is one of the the switches originally fitted to the sander.

IMG_4513.jpg IMG_4521.jpg

Problem solved.
Lines in and out were around the wrong way.

I wrote a big long explaination about Thermal Overloads but clicked close before I sent it
The abridged version...A Thermal Overload limits the current that the motor can draw, not how hot it gets. The dial on the TOL is in Amps. You should have it set to 5 as your motor draws a maximum of 4.7 at full load.

Originally Posted by NCArcher

I wrote a big long explaination about Thermal Overloads but clicked close before I sent it
The abridged version...A Thermal Overload limits the current that the motor can draw, not how hot it gets. The dial on the TOL is in Amps. You should have it set to 5 as your motor draws a maximum of 4.7 at full load.

GREAT NC! Ive always wondered about these and how they are set.

So My motor is stamped 4.7 Amps . And they stamp them as the Max they draw at full load obviously?
If the motor is under a greater load than just running not doing any work do they pull more Amps?

Rob

Basically yes. It is a 3HP motor and with efficiencies and power factor mixed in it will draw 4.7A while doing 3HP worth of work. If you overload it and try to do, say, 4 or 5HP worth of work, there is no such thing as free energy, it will draw more current and could damage the motor so the TOL is designed to shut it off and preserve the motor. You see a lot of people just connecting a motor straight to the outlet and you can usually get away with it but when something goes wrong there is no protection there for the motor. The fuse or circuit breaker back at the switchboard has one job and that is to protect the cable. Most power circuits are protected by a 20A breaker or even larger. That's 20A that could continually flow through your 4.7A designed motor. That's what lets the magic smoke out. I've got a couple of 3 phase motors in the shed that dont have a starter but they are protected by the VFD which has all sorts of overload protection.