max cable distance btwn motor and control per NEC
max cable distance btwn motor and control per NEC
(OP)
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..





RE: max cable distance btwn motor and control per NEC
RE: max cable distance btwn motor and control per NEC
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.
RE: max cable distance btwn motor and control per NEC
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"
RE: max cable distance btwn motor and control per NEC
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: max cable distance btwn motor and control per NEC
RE: max cable distance btwn motor and control per NEC
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
RE: max cable distance btwn motor and control per NEC
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"
RE: max cable distance btwn motor and control per NEC
Keith Cress
kcress - http://www.flaminsystems.com
RE: max cable distance btwn motor and control per NEC
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: max cable distance btwn motor and control per NEC
RE: max cable distance btwn motor and control per NEC
"Will work for (the memory of) salami"
RE: max cable distance btwn motor and control per NEC
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.
RE: max cable distance btwn motor and control per NEC
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
RE: max cable distance btwn motor and control per NEC
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"
RE: max cable distance btwn motor and control per NEC
Keith Cress
kcress - http://www.flaminsystems.com