Motor Wiring

ShamFeen

Been a while since I've been at this type of wiring. My current ETCI rules are out of date. A friend wants a motor (rated 7A max for a cow washer) connected with a bigger motor from the same d.o.l starter. Is it possible to do this if I put a fuse in series with the smaller motor to prevent overload?? Is this allowed?

M cebee

you won't be able to protect the motors via the overload on starter if you double up

and the starting current will be high with two motors starting simultaneously

cable and fuses feeding starter would prob be unsuited

brightspark

Not to mention that the existing overload is probably going trip with the combined load.

I'm guessing what the client wants is for both motors to start together, so he doesn't have to press two buttons.

I suggest you put in a separate contactor and overload for the new motor and either put in a small timer, that brings in the second motor automatically or if the supply is adequate just parallel the contactor coils. You will also need to wire the overloads in series, so that when one trips the other contactor drops out too.

As regards the supply you will need to check fuses/cable are capable of handling the extra starting and running current, don't forget to consider the length of cable used too!

Randyleprechaun

brightspark wrote: »

I suggest you put in a separate contactor and overload for the new motor and either put in a small timer, that brings in the second motor automatically or if the supply is adequate just parallel the contactor coils. You will also need to wire the overloads in series, so that when one trips the other contactor drops out too.

As regards the supply you will need to check fuses/cable are capable of handling the extra starting and running current, don't forget to consider the length of cable used too!

Should be ok, really your two control circuits actually become one(with the overload contacts in series as poster said above) so BOTH motors will start and stop toghether whether under fault conditions or just being stopped manually etc.

Might take abit of thinking out and wiring between each DOL starter but should be easy enough I'd say

Bruthal

Randyleprechaun wrote: »

Should be ok, really your two control circuits actually become one(with the overload contacts in series as poster said above) so BOTH motors will start and stop toghether whether under fault conditions or just being stopped manually etc.

Might take abit of thinking out and wiring between each DOL starter but should be easy enough I'd say

It definitely needs a second DOL starter. How you connect them up depends of you do just want both motors to come on and off together.

The second contactor coil paralleled with the first one will work. Overloads in series will work to stop both motors together alright, which would be the best way as its easier to see when something is gone wrong with everything stopping, this can also be achieved by connecting one each contactor coil through a spare n/o contact of the other contactor (electrical interlock). And the original start/stop setup will work fine like this.

You could also use 2 start buttons - one for each motor, and 1 stop.

If you do set them up to come on with one start you will want some sort of delay to bring in the second one, even 1 second is enough, as a 7A motor will take up to 40A at instant of starting as it has full supply on a stopped motor, and add to this the other bigger motor starting at the same instant.

Is it single or 3 phase, usually anything much bigger than 7A motors are into 3 phase and this is the smaller motor in this setup.

ShamFeen

It's single phase. Thanks gents. Was just double checking, I thought I'd have to use a seperate start stop and now I will. I'll just put it next to the old one and he can press them manually. I just wasn't sure about the overloads but my hunch appears to be right.

Bruthal

ShamFeen wrote: »

It's single phase. Thanks gents. Was just double checking, I thought I'd have to use a seperate start stop and now I will. I'll just put it next to the old one and he can press them manually. I just wasn't sure about the overloads but my hunch appears to be right.

If the motors are ok for running seperately then keep each overload to its own starter, you only need to have one control circuit if you wanted both to stop together, otherwise just keep both control circuits seperate including overloads.