means of disconnect and safety

[alananddena]

I recently was at a grain elevator installing a PLC for some control and interlock solutions in a 480VAC control cabinet for various bucket elevators and drag conveyors, at first glance this cabinet looked clean and professionally wired. When I turned off the disconnect and locked it out I found that the control circuit was still energized and the cabinet sourcing all the motors did not have its own control transformer. Tracing down the control power source I found it to be five separate 20 circuits deriving from a nearby 240/120 distribution panel. I am unsure of why this cabinet was done this way because total load of the contactors coils is 7 amps if all were energized at once. I think this is a safety nightmare for there maintenance personnel, and I am looking for some standards for this in OSHA, and NEC but so far have come up with a bunch of refer to's.

 

[GoldDigger]

I am unsure of why this cabinet was done this way because total load of the contactors coils is 7 amps if all were energized at once.

Possibly under the misguided idea that it would allow the individual breakers to be used to shut down different combinations of motors?
Is there any functional association between the other loads on each breaker and the control circuits that it powers?

 

[alananddena]

not sure

not sure

There is some association but a lot of overlaps because of interlocks and gate limits so you end up with a mixture in the raceways. And it is all 3 wire start stops.

 

[petersonra]

It may have made sense at one time.

I worked on a job once that had a bunch of 20A circuits fed into a control panel that each only powered up a single relay. Eventually I figured out that years ago the 20A circuits fed 120V motors that were eventually changed to 3 phase motors but they left the controls more or less as is and just replaced the original motor starters with relays and used a contact from it to turn on the new starters.

 

[alananddena]

not in this case

not in this case

this installation is only two or three years old, leaving the cabinet I ques you could lean towards the association thing, because they are all in the same raceway for about a 125 feet. Then it splits up to individual pipe to motors and gates, sometimes the control circuit is associated with that motor and sometimes it is not.

 

[raider1]

Check out 430.75.

430.75 Disconnection.
(A) General. Motor control circuits shall be arranged so
that they will be disconnected from all sources of supply
when the disconnecting means is in the open position. The
disconnecting means shall be permitted to consist of two or
more separate devices, one of which disconnects the motor
and the controller from the source(s) of power supply for
the motor, and the other(s), the motor control circuit(s)
from its power supply. Where separate devices are used,
they shall be located immediately adjacent to each other.

Chris