Manually pushing in a contactor ?

[Davebones]

Had a journeyman push in a contactor manually to check a 75 hp 480v motor for rotation . I have done this before years ago but won't do it now with what I know about arc flash . Just wondered how many people still do this ? I feel this shouldn't be done by hand . He did smoke it a little when he did it ...

 

[jumper]

Your Honor I would like to invoke my Fifth Amendment rights........

Seriously, not a 75 HP motor and would not use my hands/fingers.

I may have used a pair of Kleins on smaller stuff though.....:angel:

 

[Saturn_Europa]

I still do it every now and then. Always in arc gear and never on anything that large. On Square D NEMA starters I use an insulated slotted screwdriver.

But usually there is no need unless you are checking the coil on the starter. Sometimes they get weak and won't pull in the contacts.

For rotation......I'd use the H on the H O A

 

[don_resqcapt19]

And just remember that if it is just a 3 wire start/stop control circuit and the control power is one, the contactor will stay in when you push it.

 

[Jraef]

Never do this on anything more than maybe a 25HP starter. Ever.

When contactor contacts close, there are magnetic forces in play that are attempting to push them apart. The strength of the coil must be strong enough to overcome those forces. YOU cannot exert enough force with your finger (or a screwdriver for that matter), and if you don't believe me, take apart a starter and remove the moveable contacts, wrap your fingers around the cross arm of the armature, energize the coil and see if you can hold it back. In my personal experience, I could not hold back anything more than a Size 2 armature (GE CR300 contactors are the easiest to try this on by the way).

So when you cannot exert enough force, the force you CAN exert allows the contacts to chatter. It's a tiny amount, but any amount of chattering burns through the contact material VERY fast and risks welding them

 

[meternerd]

Actually, you must have required PPE on before you open the MCC door. Even then, faults can cause bad things to happen...overriding permissive circuits for motor starts, etc. Some systems require several conditions to exist before a motor is allowed to start. Lift pump pressure is one example on very large motors. The motor shaft bearing surface is lifted off of the Babbit bearing surface with high pressure pumps before the motor is allowed to rotate. Otherwise, the metal to metal bearings will wipe each other, destroying the bearing surface. I know because a startup tech in a nuclear plant bypassed the lift pressure interlock and ruined the bearing on a 9000HP motor. $50K damage and days behind schedule.....I know...extreme example, but you get the idea.

 

[petersonra]

I do it when checking panels out to make sure that the auxiliary contact for the starter energizes the right input. no motors connected at that point.

I've also done it to bump motors in the field but only small ones. These days am more likely to bump Motors by using a PLC programming software to turn an output on and off. The older I get the more paranoid I am that I might do something to harm myself or someone else.

 

[Besoeker]

I wouldn't.

 

[Current Eddy]

Try holding the stop button in and just bump the start and you won't have to worry about the coil holding


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[ptonsparky]

Try holding the stop button in and just bump the start and you won't have to worry about the coil holding


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If that works, you have it wired wrong.

 

[jumper]

Try holding the stop button in and just bump the start and you won't have to worry about the coil holding

:happysad:

If that works, you have it wired wrong.

:happyyes:

View attachment 16498

 

[just the cowboy]

Only time I was shocked by 480 volts

Only time I was shocked by 480 volts

Before arc flash it was common. One time I was doing it to some 10 hp motors fed with 480 corner grounded system. While watching the motor to make sure it moved my finger touched the ol unit and ground. I had a hole in my finger where the voltage went in.

That was 40 years ago never again