Multiple Sources in a MCC Bucket

jake-icsi

Member
I've always went out of my way to design any 120 Volt circuit that is going through a MCC bucket to first be routed through a CB aux or generate from a CPT in the bucket. I've thought this was a code requirement as much as it was in my opinion a good design practice. Is there a Code reference for this situation? Thanks

Current Situation:
Ckt1 = Control Circuit for the bucket (after plant E-stop)
Ckt2 = Auxiliary LED lighting circuit on piece of equipment.
 

paulengr

Senior Member
No Code.

It is common to find external control circuits energizing an aux contact. It would be impossible to design this out.

Less common but still out there is a common control power source rather than individual transformers in every bucket.

When doing service or especially replacement it is important to always assume control wiring is energized unless you have tested and can absolutely prove otherwise. In an active plant even previously “dead” wiring can become energized as equipment changes states. As a practice I always just treat it all as energized and tape or wire nut every wire if I disconnect one. Even aside from any shock potential blowing out a breaker/fuse can have further unintended consequences. This is what makes industrial controls so much trouble to work with.
 

tom baker

First Chief Moderator
Staff member
Yes there is a code, see requirements in Art 430, Part VI motor control circuits on disconnection of motor control circuits, section 430.75. Best to review as there are some exceptions. Basically you need to be able to disconnect all sources of power.
I preferred a CPT in each bucket, but having a separate power source allows testing with main power off, but this changes the rules for control wiring from Art 725 to Art 430.
I have done several control circuits with an aux disconnect on the bucket CB, its an accessory kit that can be added, also the foreign circuits should be yellow (UL508A)
But as pointed out, test to be sure.
 

jake-icsi

Member
Yes there is a code, see requirements in Art 430, Part VI motor control circuits on disconnection of motor control circuits, section 430.75. Best to review as there are some exceptions. Basically you need to be able to disconnect all sources of power.
I preferred a CPT in each bucket, but having a separate power source allows testing with main power off, but this changes the rules for control wiring from Art 725 to Art 430.
I have done several control circuits with an aux disconnect on the bucket CB, its an accessory kit that can be added, also the foreign circuits should be yellow (UL508A)
But as pointed out, test to be sure.
Tom - Thanks for your answer. I'm questioning since the second circuit is not a "Motor Control Circuit", but instead it is lighting circuit, do you feel this code reference may not be valid?
 

tom baker

First Chief Moderator
Staff member
If its not a motor control ckt then the rules in 430 don't apply. But the hazard is the still the same. Put an aux disconnect on the main disconnect, the AB MCCs I used, this was available as an add on. Use yellow wire.
Of course we are assuming the electricians working on are testing for voltage present.
 

jake-icsi

Member
If its not a motor control ckt then the rules in 430 don't apply. But the hazard is the still the same. Put an aux disconnect on the main disconnect, the AB MCCs I used, this was available as an add on. Use yellow wire.
Of course we are assuming the electricians working on are testing for voltage present.
Thanks again Tom. I completely agree about the hazard still being present. The CB Aux is how we are disconnecting our motor control circuit and adding a second is possible with the AB MCCs we are using. My "issue" with the CB Aux is that it is on flying leads and needs to eventually be secured in place with the adhesive on it (which in my experience seems to rarely get done)...but you still end up with the energized wire being routed through the middle of bucket. At least with the 480 Volt only hitting the lineside of the breaker in the top corner, the electrician would have to work pretty hard to accidently touch it. So to claim all the power is disconnected when the bucket disconnect is thrown is technically accurate, but seems like it could provide a false sense of security.

I'd probably add that a label on the door indicating multiple power sources present is required. Would you concur?
 
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