max cable distance btwn motor and control per NEC 2

[thekman]

Someone told me that the NEC states that the max distance between a (in this case, a 3HP 230/460v continuous duty) motor and the controls is 6 feet. I am unable to find this mentioned in the 2008 NEC (latest I have), and don't imagine it has changed since then, but don't know. Anyone happen to know off hand what this distance is if there is one? I know it's to be as short as possible..

 

[wroggent]

I don't think there is necessarily a requirement for the location for the controller. There is a requirement for the location of the motor disconnect, 430.102(B), which if 430.102(B)(2) is followed, then by proxy there would be a requirement for the location of the controller by 430.102(A) if no exceptions to 430.102(B) were applicable. Keep in mind though, the NEC treats 'motor control circuits' and 'motor controllers' as separate items. I believe start/stop buttons would fall under 'motor control circuits' and not 'motor controllers' so the requirement mentioned above wouldn't necessarily apply to the control buttons.

 

[dpc]

Not aware of any distance limitation. You also have be careful with terminology. The motor controller is the starter. The start and stop control is not the controller. Those are pilot devices.

One basic rule is that the controller must be within sight of the disconnecting means. The other basic rule is that there must be a motor disconnecting means within sight of the motor. But that is not the control - the motor disconnect must disconnect the motor power leads. There is an exception to the local motor disconnect when the disconnect at the controller can be locked opens (and subject to some additional restrictions).

But if you are talking about the ON/OFF control for the motor, it can be anywhere.

I suspect this 6 foot rule may be in reference to a specific type of equipment or other safety requirement. Possibly such as for a machine tool, conveyor, etc.

 

[jraef]

I don't think the CONTROLLER needs to be in sight of the disconnect, but the disconnect must be within sight of the MOTOR.

The 6 foot rule may be related to the maximum distance that you can run "sealtite" flexible conduit to the motor, which if it is running from the controller to the motor, indirectly creates that limit. But you can have a junction box next to the motor or use the in-sight disconnect near the motor to make that transition and the Controler can be a mile away if you like, as lng as you can afford the size of wire it will take to overcome voltage drop.

"Will work for (the memory of) salami"

 

[waross]

A six foot rule would make almost all MCCs a violation. You generally can't even get out of the electrical room with a six foot conductor limit. In some cases you may not even get out of the MCC. (Cable enters at the top left hand side of the section. Then crosses to the right hand wire-way and drops to the bottom cell. That is often more than six feet.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[thekman]

Thank you all for your input. In my case, the controller and the disconnects are in/on the same enclosure, (VFD, disconnect switch, incoming power breaker) maybe 3 feet from the motor. I believe the 6' being exceeded is due to routing of the conduit to avoid it just being draped from a to b. The complaintant referenced the NEC for this 6' limitation, but I have yet to find any such thing, at least in my 2008 copy. The enclosure is definitely in plain site. It is a flexible metal conduit with a rubber-like (not sure of exact material) watertight skin.

 

[dpc]

You can actually read the 2014 NEC on line for free if you go to the NFPA website.

But as far as general motor control provisions in Article 430, there is no reference to a 6-foot rule for the control.

Jeff - the NEC requires a disconnect within sight of the controller and a disconnect within sight of the motor. This can be the same disconnect but it may be two separate disconnects. See 430.102. Or maybe I misinterpreted your comment.

Dave

 

[jraef]

356.12 Uses Not Permitted. LFNC shall not be used as
follows:
...
(3) In lengths longer than 1.8 m (6 ft), except as permitted
by 356.10(5) or where a longer length is approved as
essential for a required degree of flexibility

So because a lot of people connect motors this way in order to facilitate the vibration, confined spaces etc., some people think it is a "rule" that the disconnect (or controller) must be within 6 ft.


dpc,
I have to admit that in all these years, I never noticed that! Of course, I have never needed to address it because I cannot think of a project where the issue came up. I have always either built the disconnect into the controller, or mounted one right next to it.

Whew... good to know I was following the rules...


"Will work for (the memory of) salami"

 

[itsmoked]

How can that be?!! How do you explain some place like a refinery or any other big plant? The motor controllers are often hundreds of feet away. Yes the disconnect is nearby, but not the controller.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

The 6 foot limit is on the flexible connection to the motor. No limit on most other wiring methods.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

Ah, the flexible conduit length - I should have thought of that.

 

[jraef]

I've had this conversation several times in the field.

"Will work for (the memory of) salami"

 

[dpc]

The motor controllers are often hundreds of feet away. Yes the disconnect is nearby, but not the controller

Keith, I'm not sure what you are questioning, but if the controller is hundreds of feet from the motor, it will need to have a disconnect within sight of the controller. There is no exception to this rule. The other requirement is a disconnect within sight of the motor. These are two separate requirements. So in this case, the basic rule would be that two separate disconnects are required. However, there are some exemptions to the local disconnect at the motor if certain requirements are satisfied.

 

[itsmoked]

Hi dpc,
Re:

I'd never heard of needing a, "disconnect within site of the controller".

So someone has a control room, with 10 computers running DCSs. The DCSs are the 'controllers'. Next door there is a control bay with twenty VFDs, dozens of motor starters, soft starters, etc, etc.

Where and even "what" would be a disconnect in this case? How would one even know which is which? With a disconnect next to the actual motor/device there is sort of a one-to-one association there is nothing like that when 50 control outputs 1/2 of them motors come out of a computer bay.

I'm just trying to understand how this could be implemented.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Keith, the NEC article he pointed to was for disconnect switches, as in "power" disconnect switches, so the use of the term "controller" in that context was regarding power devices, not something like a DCS system. So if you have a motor starter, VFD or SCR controller of some sort, and the disconnect is not part of the assembly, then that disconnect for it must be within sight, just like there must be a disconnect for the motor within sight. But if your "controller" (again, in this context) is for example a "combination starter" or an MCC cubicle where the disconnect is built in, the requirement is already satisfied. What violates it would be if you hang an out-of-the-box VFD on the wall, no internal disconnect, and the device that feeds power to it is in another room, i.e. a circuit breaker in a panelboard that is not in sight of the VFD.

Controller. A device or group of devices that serves to
govern, in some predetermined manner, the electric power
delivered to the apparatus to which it is connected.

It's one of those things that I think most of us are just inherently going to do because it makes sense. But if it became a rule in the NEC, it's likely because someone else at some time in the past cut corners and caused a fire or injury because the means to kill power to a controller that was having a problem was too far away, or someone restored power to it while someone else was working on it.

"Will work for (the memory of) salami"

 

[itsmoked]

OK! It get it now. Thanks Jeff for setting me straight. I was very puzzled. And thanks dpc for puzzling me. I like puzzles. Really I do!

Keith Cress
kcress -

http://www.flaminsystems.com