I have an NFPA-79 question regarding the interlocking of a remote motor drive panel (still line of sight and only 15ft away). I have a control cabinet that has an existing remote enclosure for the interconnecting of two motors. I need to replace the motors with new motors and replace the enclosure with a slightly larger enclosure to enclose drives for the new motors. The existing enclosure requires a tool (screwdriver to turn tabs) to open and is fed by a main control cabinet just a few feet away that has a disconnect for the whole system. The disconnect is properly interlocked with the main enclosure door so you can lock it out in any door position. The new enclosure requires the same method to open as the original and I plan to add a label to the new enclosure to say it is fed by the main enclosure but am I also required to add an electrical interlock from the main enclosure disconnect? This has been a question that has come up in the past and always seems to go back and forth. I can't seem to clarify by any particular passage of the NFPA-79.
Add-on panel disconnect interlock
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See NFPA 70: 2008: 430-IX. Disconnecting Means
Compare NFPA 79: 2007: 6.2.3 Enclosure Interlocking
Compare NFPA 79: 2007: 5.3.1.4
Compare NFPA 79: 2007: 6.2.4 Enclosure Access
The motor control center is not a control enclosure. Control enclosures must be interlocked. Using a tool to access the motor panel is legitimate. Using the control enclosure disconnect for the motor disconnect is permissible provided it meets the normal requirements for a motor disconnect.
Compare NFPA 79: 2007: 6.2.3 Enclosure Interlocking
Compare NFPA 79: 2007: 5.3.1.4
Compare NFPA 79: 2007: 6.2.4 Enclosure Access
The motor control center is not a control enclosure. Control enclosures must be interlocked. Using a tool to access the motor panel is legitimate. Using the control enclosure disconnect for the motor disconnect is permissible provided it meets the normal requirements for a motor disconnect.
dbaird
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- Dayton, OH
Note:
Notice the wording none of the doors open. In your case I believe you could open the control enclosure "with a tool" with the power in the Main still on i.e. disconnect in on position. Seems to me you need to assure the disconnect is off by electrical interlock also or am I missing something?
This is the loop I always get stuck in because the term adjacent. It should really say if it is adjacent and part of the same enclosure or just in close proximity (both definitions are correct). I go back and forth between both pfalcon and dbaird's answers depending on the situation. For this one I think pfalcon is the way I will sway by means of the following logic. Thanks for your responses. It would be nice if someone from the NFPA could comment.
In regards to a disconnecting means.
5.3.1.4 Each supply circuit disconnecting means mounted
within or adjacent to the control enclosure shall be interlocked
with the control enclosure in accordance with 6.2.3.
Where the supply circuit disconnecting means is not adjacent
to the control enclosure, or where the supply disconnecting
means is an attachment plug and receptacle, the control enclosure
shall comply with 6.2.4 and a safety sign shall be provided
in accordance with Section 16.2.
So we go to .....
6.2.3 Enclosure Interlocking. When required by 5.3.1.4, each
disconnecting means mounted within or adjacent to a control
enclosure that contains live parts operating at 50 volts ac (rms
value) or 60 volts dc or more shall be mechanically or electrically
interlocked, or both, with the control enclosure doors so
that none of the doors open unless the power is disconnected.
Interlocking shall be reactivated automatically when all the
doors are closed.
This is true of the "Control Enclosure" but not the remote drive panel as it is not part of the "Control Enclosure", it is a separate enclosure so I would think we refer to 6.2.4 and 16.2
6.2.4 Enclosure Access. Where a qualified (skilled) person,
using appropriate work practices, needs to enter an enclosure
that does not have a disconnect, one of the following conditions
shall be met:
(1) The use of a key or tool shall be required for opening the
enclosure.
16.2.6 Where the disconnecting means is remote from the
control enclosure, a safety sign shall be attached to the enclosure
door or cover indicating that the power shall be disconnected
from the equipment before the enclosure is opened
and that the enclosure shall be closed before the power is
restored.
Am I correct in my logic?
In regards to a disconnecting means.
5.3.1.4 Each supply circuit disconnecting means mounted
within or adjacent to the control enclosure shall be interlocked
with the control enclosure in accordance with 6.2.3.
Where the supply circuit disconnecting means is not adjacent
to the control enclosure, or where the supply disconnecting
means is an attachment plug and receptacle, the control enclosure
shall comply with 6.2.4 and a safety sign shall be provided
in accordance with Section 16.2.
So we go to .....
6.2.3 Enclosure Interlocking. When required by 5.3.1.4, each
disconnecting means mounted within or adjacent to a control
enclosure that contains live parts operating at 50 volts ac (rms
value) or 60 volts dc or more shall be mechanically or electrically
interlocked, or both, with the control enclosure doors so
that none of the doors open unless the power is disconnected.
Interlocking shall be reactivated automatically when all the
doors are closed.
This is true of the "Control Enclosure" but not the remote drive panel as it is not part of the "Control Enclosure", it is a separate enclosure so I would think we refer to 6.2.4 and 16.2
6.2.4 Enclosure Access. Where a qualified (skilled) person,
using appropriate work practices, needs to enter an enclosure
that does not have a disconnect, one of the following conditions
shall be met:
(1) The use of a key or tool shall be required for opening the
enclosure.
16.2.6 Where the disconnecting means is remote from the
control enclosure, a safety sign shall be attached to the enclosure
door or cover indicating that the power shall be disconnected
from the equipment before the enclosure is opened
and that the enclosure shall be closed before the power is
restored.
Am I correct in my logic?
DBaird,
Correct when applied to a control enclosure.
5.3.1.4 Disconnects adjacent to the panel must be interlocked to the panel.
6.2.3 Disconnects interlocked to the panel per 5.3.1.4 must ensure the power is off before opening.
Someone stole my copy for a few days but there is another place where the NFPA79 says a key or common tool must be available to bypass the above interlock. This is to make live troubleshooting possible.
Control,
You are correct. The key is recognizing that the motor control center is not the control enclosure. Therefore mechanical and electrical interlocking is not required. The motor control center falls under the NEC disconnecting means for a motor control center.
Correct when applied to a control enclosure.
5.3.1.4 Disconnects adjacent to the panel must be interlocked to the panel.
6.2.3 Disconnects interlocked to the panel per 5.3.1.4 must ensure the power is off before opening.
Someone stole my copy for a few days but there is another place where the NFPA79 says a key or common tool must be available to bypass the above interlock. This is to make live troubleshooting possible.
Control,
You are correct. The key is recognizing that the motor control center is not the control enclosure. Therefore mechanical and electrical interlocking is not required. The motor control center falls under the NEC disconnecting means for a motor control center.
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