Flexible Cable Lengths

[murli8]

Hello
Is there any restrictions to the lengths of Flexible cables such as SO or others that one can install between the sources and loads within a complex machine. it may assumed that mechanical protection is provided and there is no issues with voltage drops. Does NEC or NFPA has any restrictions as to any max lengths that can be used for the flex cables
thanks
murli

 

[petersonra]

Inside of a machine NEC generally does not apply.

IIRC, NFPA79 contains no limit on cable lengths.

It does limit cord length to 50 feet.

I think SO is a cord and not a cable.

 

[realolman]

seems to me flexible cord oughta be used to provide flexibility... if something has to move or be moved.

I'm not sure wiring long lengths with flexible cord inside a machine isn't just laziness.

 

[petersonra]

seems to me flexible cord oughta be used to provide flexibility... if something has to move or be moved.

I'm not sure wiring long lengths with flexible cord inside a machine isn't just laziness.

How do you feel about DeviceNet? Its just a cable. No conduit at all. It is designed just for this type of application to eliminate the need to have conduit. 1000 meters maximum distance (or something like that).

Conduit takes up space and adds cost without adding value in many cases. In many machines you could not find the room to install conduit.

Most machines vibrate - quite a bit in some cases. Conduit tends to come loose in such conditions.

Many machines have oil or cutting fluids spraying all over the place. Conduit fittings are rarely really liquidtight, and even if they can be made that way, rarely stay that way. It is quite easy to make cord and cables liquidtight.

Conduit is tough to work around. Cut a few cable ties and you can easily move cords and cables to get at things.

So why would you spend extra money for a solution that provides less utilty?

The only real issue with cords and cables inside a machine is protecting them. Most of the time that ends up being fairly easy. There are of course a few hack machine builders out there that don't do a good job of this, but really, how much extra protection is required for a cable that is inside a machine surrounded by sheet metal guards?

 

[realolman]

Boy, I'm feeling spanked.:sad:

I have some experience with DeviceNet, it's not in the same ballpark as wiring stuff with SO cord.

I suppose you could wire your entire machine with S.O. if you wanted. I personally think it's sloppy.
I think it should be used where something needs to move or be moved... I also think people use way too much flexible conduit.

But hey that's just me.

 

[petersonra]

I don't like flexible conduit at all, especially the metal stuff or metal stuff with the PVC jacket. They tend to come apart under vibration and stress, and there seems to be no solution to the problem that actually works. The orange non-metallic stuff seems to work best.

Even so, I prefer cord. It can be routed where it needs to go to stay out of the way.

 

[marcb]

See 400.7 and 400.8 also 422.16

 

[muskiedog]

SO Cord

SO Cord

On thing to take in to consideration is what fluids or solvents, etc.. are used with the piece of equipment. They may effect the insultion of the cord causing deterioration. Basically when when I worked for a Printing Company the only time we wire with flexible was for equipment that needed to be moved or vibrated excessively.

 

[petersonra]

See 400.7 and 400.8 also 422.16

Those sections apply to an electrical installation. They do not apply to something part of a machine.

That is like trying to claim the internals of a toaster have to comply with the NEC. They don't because the NEC does not apply to the innards of a toaster anymore than it applies to the innards of a machine.

 

[mario]

DeviceNet ???

DeviceNet ???

what is this "DeviceNet" stuff ... never heard of it ... m

 

[petersonra]

what is this "DeviceNet" stuff ... never heard of it ... m

DeviceNet is an industrial cabling and communication system that supplies both the power and communications wiring in a single cable. It is a dream to install because you can just run the cable where you want it to go and daisy chain from device to device.

You can have such things as switches, lights, solenoid valves, drives, motor starters just about anything connected to it. A DeviceNet device, for instance a motor starter, needs no control wiring other then to bring in the DN cable. It is a HUGE time saver and reduces wiring errors by a lot.

It also allows for a fair amount of diagnostic data to be returned from the device that is ordinarily extra. Like overload and motor starter feedback, current feedback, etc. It is all built in. The motor starter costs more, but all the diagnostic stuff is already included and the wiring is much simpler.

It is especially nice along conveyor lines where you might have pushbuttons and lights dropped every 100 feet. You just run the cable from station to station, and the wiring is done. No conduit.

Better yet, even I can add a drop if needed. No skills like conduit bending needed. Just tie wraps.

 

[realolman]

Durn ya petersonra... you type too fast...

It's an open protocol system meaning anyone can use it. It's not proprietary.

Allen bradley and others have all kind of stuff for it.

In one setup you can have a Device Net slot in your PLC and a length of flat cable that has, I don't remember, 4 or 5 conductors that runs the entire length of your machine.

Then, you have special blocks that tap right into this cable by displacing the insulation when you tighten three screws, that communicate with the PLC. Those blocks might terminate 16 limit switches that plug right into the block. Another kind might be hooked into a bank of solenoids with no field wiring at all. Another kind will communicate with Variable Frequency Drives to control all the parameters you would associate with VFD's frequency, ramp on / off , start, stop,direction etc.

Your PLC read and writes to all of this stuff as if you had cords / wires from each discreet switch to the PLC. It does it in real time. it's pretty cool.

http://www.odva.org/