MWBC for control panels - tie handle or not?

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lakee911

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Columbus, OH
Let's say I have two circuits feeding a control panel. One circuit is for controls (PLC, logix, instruments, etc.) and one circuit is for utility (heater, light, receptacle). If three CCC were pulled, instead of four, would I be required to install tie handle as if it were a MWBC?

Thanks,
Jason
 
What do you mean, "as if it were"? It is. The nature of the loads is irrelevant. Two ungrounded conductors (from different phases) and one grounded constitute a MWBC. So yes, it needs a handle tie, or a two-pole breaker.
 
I agree with Charlie,

Multiwire branch circuits, regardless of the load they supply, require means to simultaneously disconnect all ungrounded conductors at the point of origin of the branch circuit.

Chris
 
Does it matter that its industrial equipment? I have seen equipment that has multiple power sources without tying breaker handles together. Or, rather I guess it's a factor of common neutral and not just common disconnect...

Thanks.
 
lakee911 said:
Does it matter that its industrial equipment?
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Nope. What matters is the sharing of a neutral wire. The hazard comes from turning off one breaker (but not the other, in the absence of a handle tie), and disconnecting wires at some outlet downstream of that breaker. There are circumstances in which power from the other breaker can feed back to the outlet box that is open with wires disconnected. To prevent that hazard, both breakers have to be open, before you work on any outlet powered by either breaker.
 
lakee911 said:
Does it matter that its industrial equipment? I have seen equipment that has multiple power sources without tying breaker handles together. Or, rather I guess it's a factor of common neutral and not just common disconnect...

Thanks.
Click to expand...

In the 2005 code, the simultaneous disconnection was only required where the MWBC supplied more than one-device on the same yoke.

In the 2002 code, the simultaneous disconnection was only required where the MWBC supplied more than one-device on the same yoke in "dwelling units" only.

The 2008 code requires all MWBC to have simultaneous disconnection. So for the installations you have seen without breaker ties, it matters what code cycle it was installed under.
 
Pulling a MWBC to a control cabinet would probably be the one place I WOULDN'T DO IT. I love MWBC's, but not for something like this.

One programmer I know even likes us to use the same phase from different circuits just in case someone gets the wiring crossed up....
 
Cow said:
Pulling a MWBC to a control cabinet would probably be the one place I WOULDN'T DO IT. I love MWBC's, but not for something like this.

One programmer I know even likes us to use the same phase from different circuits just in case someone gets the wiring crossed up....
Click to expand...

You can't even do that under the new code. Don't have my book handy, but I'm pretty sure that was a change.
 
I have said this before and I'll say it again--- This is an issue with septic pumps and alarms. If you run a mwbc then the alarm goes off when the pump trips the circuit which defeats the purpose of the alarm. If you run 2 circuits to the pump then you have a violation of 225.30. I have written a proposal for the 2014 to include another special condition in 225.30(A) that hopefully will allow two circuits to the system.
 
Dennis Alwon said:
This is an issue with septic pumps and alarms. If you run a mwbc then the alarm goes off when the pump trips the circuit which defeats the purpose of the alarm.
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Dennis, do you mean by "alarm goes off" - the alarm loses power and fails to operate?

An MWBC with to separate c/b's with a handle tie wouldn't fail like this if the pump tripped. An MWBC with a common trip c/b would. It sounds more like a design issue than a code issue to me.
 
Cow said:
Pulling a MWBC to a control cabinet would probably be the one place I WOULDN'T DO IT. I love MWBC's, but not for something like this.

One programmer I know even likes us to use the same phase from different circuits just in case someone gets the wiring crossed up....
Click to expand...

We use transformers supplied from the 480 volt feed to the control cabinet to supply our 110 volt devices. So that way when you shut the disconnect you have shut everything in that control cabinet off. Also would elimate the MWBC's
 
david luchini said:
Dennis, do you mean by "alarm goes off" - the alarm loses power and fails to operate?
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yes........

An MWBC with to separate c/b's with a handle tie wouldn't fail like this if the pump tripped. An MWBC with a common trip c/b would. It sounds more like a design issue than a code issue to me.[/QUOTE]

I have seen handle ties trip the other breaker-- not always but in the case of Cutler Hammer the trip is all the way off not partial as in other brands. This can force the other circuit off.
 
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