Which Starter Contactor

Mark Whitehouse · Dec 9, 2018

Hi all I have a 3 hp single phase motor that only runs when you hold the button and stops when you release it. I am struggling to get my head around which contactor to get for it. Any help would be great.

westward10 · Dec 9, 2018

Has it only just started doing this or did it previously carry on running once the start button was released.

Mark Whitehouse · Dec 9, 2018

westward10 said:
Has it only just started doing this or did it previously carry on running once the start button was released.

No this is how it should run for safety. The whole thing got ripped out before I got to it. So starting on the back foot. I've got a new motor but need to get a starter contactor. There is a separate button to run the motor, not on the contactor.

Spoon · Dec 9, 2018

Lads on the comp so i cant check regs.
Dont you need a thermal overload for a 3hp motor?

westward10 · Dec 9, 2018

It is single phase 3hp.

Mark Whitehouse · Dec 9, 2018

westward10 said:
It is single phase 3hp.

No single phase

Mark Whitehouse · Dec 9, 2018

Sorry yes single 3hp

Spoon · Dec 9, 2018

[ElectriciansForums.net] Which Starter Contactor

Mark Whitehouse · Dec 9, 2018

Just got the paperwork out for the motor and it has an overload built in .

westward10 · Dec 9, 2018

The control contactor will need to incorporate an overload relay.

Andy-1960 · Dec 9, 2018

Mark Whitehouse said:
Just got the paperwork out for the motor and it has an overload built in .

Can you post this paperwork?
Do you have the full load current of the motor?
Also what does this motor drive as this may affect the duty rating of the contactor and also may determine if a safety circuit may need to be incorporated.

ipf · Dec 9, 2018

Andy-1960 said:
Can you post this paperwork?
Do you have the full load current of the motor?

Well you know it's 3hp....

Andy-1960 · Dec 10, 2018

ipf said:
Well you know it's 3hp....

Yes, but full load currents do vary depending on efficiency and number of poles. Always best to rate control gear from information on the motor plate.

Darkwood · Dec 10, 2018

I take it this is a deadmans operation method, you just need a suitably rated starter that you can remove the retaining link wire out of the circuit to give this operation method, the majority of motor DOL starters out there allow you to do this, as mentioned though you will need overload protection fitted, I also would like to see this paperwork for the motor, motors can come with integral thermal devices but they normally require external monitoring but this alone may not satisfy the requirements for overload detection as they are usually a secondary backup as motors can overheat without running in overload.
You are the designer of the control circuit regardless if your copying the old method therefore you should be complying to BS 60204 (2018), this falls outside of the BS7671 although you do find the odd relevant regulation that is reflected in the BS7671.