NFPA 79 Disconnect Question

[whiggins]

I've been reading NFPA 79, getting confused!

I have a control panel containing four VFD controllers (four motors with local disconnects located out of sight of the panel). The panel has a main disconnect handle for the 480V supply. Each VFD controller has an internal mounted disconnect.

The question is, do these VFD disconnects need to be accessible from outside the panel? Currently, you can only shut them off by disconnecting the main and opening the panel door.

 

[Gregg Harris]

I've been reading NFPA 79, getting confused!

I have a control panel containing four VFD controllers (four motors with local disconnects located out of sight of the panel). The panel has a main disconnect handle for the 480V supply. Each VFD controller has an internal mounted disconnect.

The question is, do these VFD disconnects need to be accessible from outside the panel? Currently, you can only shut them off by disconnecting the main and opening the panel door.

What is the application of the motors, and is it industrial?

 

[whiggins]

What is the application of the motors, and is it industrial?

The motors drive machinery that raises a roadway bridge. I suppose it is technically not a "machine" by code but sometimes the specifications require panels NFPA 79 compliant.

 

[Gregg Harris]

The motors drive machinery that raises a roadway bridge. I suppose it is technically not a "machine" by code but sometimes the specifications require panels NFPA 79 compliant.

Take a look at 430.102

 

[whiggins]

Take a look at 430.102

I've read that section before which is what prompted my question. My reading of 430.102 would indicate that I'd need a disconnect for each controller (you cannot see the motors or bridge equipment from this panel). It doesn't really meet exception 2.

I don't see the same controller disconnect requirements in NFPA 79. If a panel is designed to comply with NFPA 79 can the disconnects for the controllers be inside the panel? The notes to NFPA 70 section 430.102 indicates that "disconnect switches or circuit breakers that are located only behind the locked door of a panelboard or within locked rooms do not comply with the requirements of 430.102"

I've been on several movable roadway bridges that had factory assembled panels containing starters and circuit breakers feeding motors located remotely. The circuit breakers feeding the starters were not accessible without opening the control panel door. Are these code violations?

 

[GoldDigger]

I've been on several movable roadway bridges that had factory assembled panels containing starters and circuit breakers feeding motors located remotely. The circuit breakers feeding the starters were not accessible without opening the control panel door. Are these code violations?

1. If the controllers themselves are located inside the same factory-made panel, they may not be separately covered.
2. Is the door locked? That, rather than the need to open the door, seems to be the critical point.

 

[Gregg Harris]

(B) Motor. A disconnecting means shall be provided for a motor in accordance with (B)(1) or (B)(2).
(1) Separate Motor Disconnect. A disconnecting means for the motor shall be located in sight from the motor location and the driven machinery location.
(2) Controller Disconnect. The controller disconnecting means required in accordance with 430.102(A) shall be permitted to serve as the disconnecting means for the motor if it is in sight from the motor location and the driven machinery location.
Exception to (1) and (2): The disconnecting means for the motor shall not be required under either condition (a) or condition (b), provided the controller disconnecting means required in accordance with 430.102(A) is individually capable of being locked in the open position, The provision for locking or adding a lock to the controller disconnecting means shall be installed on or at the switch or circuit breaker used as the disconnecting means and shall remain in place with or without the lock installed.
(a) Where such a location of the disconnecting means for the motor is impracticable or introduces additional or increased hazards to persons or property
(b) In industrial installations, with written safety procedures, where conditions of maintenance and supervision ensure that only qualified persons service the equipment

Informational Note No. 1: Some examples of increased or additional hazards include, but are not limited to, motors rated in excess of 100 hp, multimotor equipment, submersible motors, motors associated with adjustable speed drives, and motors located in hazardous (classified) locations.

 

[whiggins]

1. If the controllers themselves are located inside the same factory-made panel, they may not be separately covered.
2. Is the door locked? That, rather than the need to open the door, seems to be the critical point.

The door is not locked, it is interlocked with the main disconnect switch. Power off to open the door. To operate the disconnect on the controller you have to open the door after shutting off power. The motors are provided with a local disconnect.

 

[Jraef]

NFPA 79 states that you must have a disconnect on the SUPPLY, so that is covered by your main disconnect (assuming you followed all the other NFPA 79 rules).

NFPA 79 then goes on to say that you must be able to isolate / disconnect the feed to a piece of equipment to allow working on it safely. If you HAVE individual disconnect devices for those that are INTENDED to be used in that manner, then they must follow ALL of the NFPA 79 requirements for disconnects, which would require that they be operable with the door open or closed.

But...

5.5.2 The supply circuit disconnecting device (see Section 5.3)
shall be permitted to fulfill this requirement where there is
no need for disconnecting individual portions of the electrical
circuit.

So if one of your VFDs going down means the rest cannot work anyway, then there is no need to have separate lockable disconnect handles on the VFD disconnects, as long as everyone knows that to LO/TO any one of them, you must LO/TO them all using the main supply disconnect.

But then again, you said that you have local disconnects within sight of each motor anyway right? Then it's all a moot point.

 

[GoldDigger]

But then again, you said that you have local disconnects within sight of each motor anyway right? Then it's all a moot point.

Not under the NEC, which requires that if you have a motor disconnect within sight of the motor, you still need to have a controller disconnect. But if your controller disconnect is within sight of the motor you may not need a separate motor disconnect.

The requirements for motor disconnect and for controller disconnect are spelled out separately.

 

[Aleman]

You should be able to get into the door without turning off the main, should be some kind of mechanical override. Since you have disconnects in the panel and also locally
I would think you are ok code wise. If it is an issue you can always add some type of door mounted disconnects for your drives, but I don't believe something like that is required.

 

[whiggins]

You should be able to get into the door without turning off the main, should be some kind of mechanical override. Since you have disconnects in the panel and also locally
I would think you are ok code wise. If it is an issue you can always add some type of door mounted disconnects for your drives, but I don't believe something like that is required.

I'm still somewhat confused with the code but I think you are right.