Motor Disconnects

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augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
The job I am inspecting is under the '08 Code which I believe is important due to some changes in later Codes.
The Situation:
Multi-motor machine with coordinated controllers that drive several parts.
One control cabinet for all motors controllers with one main disconnect means
(lockable breaker) and each controller protected by a set of individual fuses
on din-rail fuse holders (rocker type)

It appears to me that Exception 2 to 430.102(A) allows the one disconnecting means to serve as the disconnect for all controllers.

However it does not appear that the one main disconnect would serve as the 430.102(B) required motor disconnect as the exception to 430.102(B)(2) calls for
"the controller disconnecting means be individually capable of being locked in the open position"

Comments appreciated...

(E/C feels the one disconnect acceptable for the controllers would also be acceptable for the motors)
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I do not have a copy of 2008 to look at so it is hard for me to comment on. It appears top me that in both 2005 and 2014 it would be OK. Maybe 2008 says something slightly different.
 

Aleman

Senior Member
Location
Southern Ca, USA
I only have the 2011 here at the house. But having worked with machines a long time I would say this is ok as described.
It is because the machine is considered a single machine or apparatus. I never even saw a local disconnect on a motor till
I started working plants where there are lots of pumps, conveyors etc. In a spread out system without line of sight local
disconnects are required. But on an RO skid for example where there might be several pumps, it only needs the main
disconnect. It is a single apparatus and the box is close to all parts of the machine. This is the way I was taught and this
is the way machines are built.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
(bump)
I brought this back with hope for additional input...
We have a situation with two schools of thought and engineers with conflicting opinions.
Again, this is governed by the '08 Code which has different wording from later Codes but is the one I am having to use.

The facility is question has a LOTO procedure. The motors in question are all controlled from a control panel with a main lockable disconnect but no individual disconnects on the motors or the individual starters in the control cabinet. The apparatus is somewhat in sight from the cabinet but 90% of the motors are not.
The opinions seem to center around the wording in 430.102(B)(2) Exception.
In particular the wording: "provided the controller disconnecting means required in 430.102(A) is individually capable of being locked"
The problem I have is that wording seems to indicate, by use of the singular word, that each of the motor controllers needs to have a lockable disconnecting means in order to use this exception.
At present, if personnel are required to work on any one portion of the machine they pull the fuses on that one controller to assure the motor can not be started,
 
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iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
If you are looking for a legal answer - I can't help. One could argue clear to the Supreme Court and the machinery would not be any better or worse.

If you are looking for a safe, reliable, engineered answer - I think you already have the answer.

If the whole machine has to be down in order to work on anyone part, then one disconnect will be just fine.

If on the other hand, individual parts can be worked and others left running, then separate disconnects are needed.

... At present, if personnel are required to work on any one portion of the machine they pull the fuses on that one controller to assure the motor can not be started,

That sounds like they only shutdown a piece at a time.

The first one that asks for a code section - remind them the minimalistic code crap they built wouldn't pass a field UL evaluation. It's time to get by that mindset - it's a loser.

Now, if you could just find a one-armed engineer :angel:

ice
 

Aleman

Senior Member
Location
Southern Ca, USA
Well, does pulling fuses out satisfy a lockout? I have been told both ways on that one. I would say it does not but I'm comfortable working that way and have done it
many times. If pulling fuses is not considered a lockout, then to work on the machine the main needs to be locked out or they need to install locals. Whether to pass
such a thing is not my call to make and I don't know the code well enough. Besides as you point out there are different ways of looking at what the code says.

Maybe the question should be can the machine run different sections independently of the others? If so then individual disconnects should be required. Otherwise the
main disconnect should be all that's needed. If this was mine I would replace the fuses with motor protectors with lockable rotary switches.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
IMHO, there are two elements of the disconnect to look at:
1. Does it clearly indicate ON and OFF?
2. Can it be locked?
So, can the door providing access to the fuse holder be locked?
And can you see the fuse sockets with the door closed.
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
In my opinion if the main controller has a lockable disconnect ahead that can be "locked in the open position" then in my opinion it's compliant and serves the intent. Based on the single cabinet concept I would venture to think adding additional lockable disconnects at various locations could only serve to confuse the individual working on the equipment and raise the level of potential confusion and hazard, thinking they have locked out one location only to not actually lock out anything...since it is all in a single cabinet...why introduce potential confusion and invoke the exceptions and item (a). Install labels to such effect and incorporate the process into the established LOTO procedure and roll with it.

Just my thoughts on it.....going from memory. I will gander at the NEC 2008 when I get home.
 

kwired

Electron manager
Location
NE Nebraska
I will say Gus' inspection is likely for compliance with NEC (2008 as he mentioned). Others have added ideas that maybe need to apply but are required by 70E or other safety reasons - they may not be bad design ideas, but Gus has his hands tied by 2008 NEC when it comes to what his responsibility is.

Can't recall which year they made changes here I was thinking it was 2005 but at one time it was acceptable to have remote disconnect that was lockable at the motor controller and no local disconnect at the motor. So if that practice was gone in 2008 then I think Gus has no option but to reject the install if the motor doesn't have a disconnect within sight, or would meet any exceptions to the rule, or apply local amendments if there are any for this rule.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
In my opinion if the main controller has a lockable disconnect ahead that can be "locked in the open position" then in my opinion it's compliant and serves the intent. Based on the single cabinet concept I would venture to think adding additional lockable disconnects at various locations could only serve to confuse the individual working on the equipment and raise the level of potential confusion and hazard, thinking they have locked out one location only to not actually lock out anything...since it is all in a single cabinet...why introduce potential confusion and invoke the exceptions and item (a). Install labels to such effect and incorporate the process into the established LOTO procedure and roll with it.

Just my thoughts on it.....going from memory. I will gander at the NEC 2008 when I get home.

Please do.
I don't want to get hung up by the NEC wording, but as kwired notes above I am duty bound to the '08 Code and, although I don't ignore intent, I can't pick & choose the words written
The '08 wording "individually capable" is the "bear" in this case.
The fact that the "main" disconnect for the equipment coupled with the fact that the machine can be operated with any one of the motors taken out of service makes me lean toward a disconnect for each motor.
 
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