multiple contactors on one E-stop button

[megloff11x]

Can I use multiple small contactors in lieu of one big one, if all are controlled by the same button?

The NEC (sec 430)and NFPA79 (sec 9 & 10)require an emergency stop button for a machine containing motors. The normal way is for the E-stop to open a contactor, removing power from the motors, Groups of motors that perform a common function should have a common disconnecting means.

Bottom line, if I have four 25A motors as part of a system, two 60A contactors (tied to two motors each)are cheaper than one 120A contactor (tied to all four). One stop button setup can energize both of the 60A contactor coils in parallel.

Is this within the rules, as long as each individual contactor load times 115% doesn't exceed its rating? I won't put two 60A contactors in parallel and tie all four motors to both. Two motors each.

I don't see anything that says the scheme of two 25A loads on each 60A contactor, with all contactor coils tied to one stop button, is wrong.

Am I OK here?

 

[ccha9219]

Re: multiple contactors on one E-stop button

You are useing your e-stop to drop your control circuit, yes your fine.

 

[richwaskowitz]

Re: multiple contactors on one E-stop button

Why do you believe you need additional contactors ahead of the magnetic motor starters (unless they are manual starters) to accomplish your e-stop circuit? Could you not simply open the control circuits to the motor starters with the e-stop relay as one would do with a traditional master control relay? Refer to Annex D, page 79-59 of NFPA 79 2002 edition or 79-42 of the 97 edition.

 

[oldmanriver]

Re: multiple contactors on one E-stop button

Both Rich and CCha are right. You are OK with the E-Stop using multiple contacts, but you will need additional circuitry on the start side.

Correction on your term, the E-Stop serves to "de-energize" your contactors.

Another thing to remember in motor circuits is braking. If an E-Stop is required ASME standards say that you have 10ms to stop all movement on the motors when the E-Stop is activated. That means once you install the E-Stop, activate it and the motors do not stop in the 10ms window, you will have to purchase electric brakes. The brakes work like semi-tractor brakes; off when energized on when de-energize, so when power is cut they stop the motor(s).

It's been so long since I ordered anything like that I don't know where to send you to look for them but you could start with Grainger. Since you have 4 motors you will need 4 brakes and they ain't cheap.