Mutiple Motor Control from one contactor

[Elekk]

Is the following a good arrangement to control three motors from one contactor?

-One main breaker at top

-Followed by one main contactor

-Followed by three sub-breakers in parallel (feeding three motors)

 

[Sidewinder]

No Elekk it is not good practice.

What sort of equipment is this on?

If you are looking to have them working together electrically interlock them on the control side.

You should also be looking at T/M overloads for the motors with these linked into the control circuits.

 

[Elekk]

Actually these motors have to run separately so a separate sub-breaker is required for each. The sub-breakers are thermal magnetic so they already have overloads. The overloads of all three sub-breakers will be interlocked to the main contactor.

 

[septiclecky]

As said very bad practice, nothing stopping you though from having smaller individual contactors for each motor controlled by the same start button.

 

[benji]

not really enough info.supplied ie.how big are the motors ,what type of installation & what method of installation.

 

[Sidewinder]

Elekk,

I thingk we need a bit more info on what you are trying to do.

I also took breaker to mean mcb, as this is generally how this term is applied, especially on this forum.

I don't think that this is unreasonable.

I don't like the idea of the way you have described things unless you can explain a little more I can't give any more input.

I don't know the type pf mpcb you are using, however if the motors must run independently then why are you not using individual contactors, I doubt that it will be cheaper to wire this way and really your panel wiring from the main circuit breaker right through the main contactor to the indicidual motor contactors needs to be sized for the main breaker.

Please be a little more descriptive and provide some more detail & info.

It also sounds like this is outside the scope of 7671, so you are now looking at a whole new set of rules to get your head around which actually have more legal standing than 7671 by the way that the new approach directives are worded.

 

[Elekk]

Actually I want to use this main contactor for under voltage protection, not for the control of motors.

The make and model of circuit breakers is Schneider NSX thermal-magnetic.

 

[Sidewinder]

Still don't follow why you want one big contactor, I would still used 3 small ones.

Not familiar with the NSX, will have to check up later but they seem OK from your description of them & your requirements.

 

[septiclecky]

You still haven't given enough info ?How big are the motors?

Using a contractor for an under voltage relay whilst acceptable is still not good practise, a better method would be an undervoltage monitor in the control circuit with the contactor or an under voltage release on the mccb

The Schneider NSX series is an mccb (moulded case circuit breaker) not a breaker (more often an mcb), ranging from 16 to 630amps with both thermal and magnetic protection.

I do think if you are asking these sort of questions you may well be out of you depth here?

Why do you need an under voltage trip and has the machine been risked assessed for safety to the relevant BS, do you need a proper safety relay, have you thought of PUWER ?

Disagree canoeboy, Even though it is an MCCB it is still known as a breaker

 

[Sidewinder]

Septic,

Yep it is still a breaker, though this term is generally used in my experience to mean mcb.

Elekk,

To guide you on this we really need a bit more info, the more I read the thread the more I think that this is not a 7671 install.

I would not use an mccb then a contactor then 3 mccb's in the way you describe at all.

I don't know if I can suggest any more without more info is this a machine is it new, is it used, is it CE marked?

Sorry.