PLC hard wiring

Is it ever permissible to run I/O wiring in the same conduit as 480 volt 3 ph motor wiring? I have a dispute going right now.

It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

I am assuming you mean 24V? I have had it work for short runs and small horsepower motors.


If you are using 120VAC, there should be no problem.

You must use 600V insulated or better wire for all conductors.

I don't believe there is an acutal law against it here. (local codes may vary)

Contrary to what Ken says it will work and as rick says there is no law against it...Is it a good idea..... no.

Analog signals would probably not work or would work intermittently. again as rick said all wires must be rated at the same voltage to meet code..

There are some things I just don't get...

So on a totally different subject, can anyone explain the insulation level requirement that both Rick and darrenj refer to? It's OK to let a wire with 600 volt insulation lay against a grounded conduit but its NOT OK to let it lay against another wire that has 300 volt insulation. That just doesn't intuitively make sense.

Keith

Not so much to do with insulation - how about cross talk caused by inductance . Big problem on many networks , railways included - flemings right hand rule - and his left hand one as well , you are making little current transformers , all set to upset your I/O

Wire has 2 very important factors, voltage and temp. Voltage rating relates to the wall thickness and temp rating relates to the type of insulation.

Current thru parallel wires will create induction, this in turn will create heat. The idea is to have all wires rated at same voltage/temp etc to minimise the effects of the induction on the wire.

As far as wire laying against grounded conduit, the conduit should not have current flowing thru it and creating inductance.

I know I should be able to explain this better with more detailed facts but I seem to be brain locked.

I was being facietous, of course. I hope Ron Doran will chime in here, because his opinions are well rooted in both code and practice. I can only speak on experience because I don't have a background in the electrical trades.

I have experienced many installations in which 120 VAC and the output from a 480VAC variable frequency drive were run for a moderate distance (100+ feet) in the same conduit. We got a lot of induced noise on the PLC inputs from those 120VAC input points, causing false input signals. This is far less likely with "clean" 480VAC, but the longer the conduit the more likely that induced voltage will be a problem.

"Code-wise", I have only experienced problems when users get their hands on 300V insulated appliance wire. Typical "THHN" wiring that I see used in industrial applications has 600V insulation and can be installed in proximity to equally insulated conductors that are carrying 480VAC.

Ken i figured that!.and yes i have run into many situations with control and power from a drive causing problems. i have even had problems with main power and output from the drive in the same conduit cause problems...as i said it will work but is not a good idea

Ken Roach said:

I was being facietous, of course. I hope Ron Doran will chime in here, because his opinions are well rooted in both code and practice. I can only speak on experience because I don't have a background in the electrical trades.

I have experienced many installations in which 120 VAC and the output from a 480VAC variable frequency drive were run for a moderate distance (100+ feet) in the same conduit. We got a lot of induced noise on the PLC inputs from those 120VAC input points, causing false input signals. This is far less likely with "clean" 480VAC, but the longer the conduit the more likely that induced voltage will be a problem.

"Code-wise", I have only experienced problems when users get their hands on 300V insulated appliance wire. Typical "THHN" wiring that I see used in industrial applications has 600V insulation and can be installed in proximity to equally insulated conductors that are carrying 480VAC.

Click to expand...

It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

Click to expand...

I would stick with this answer. The variables to this question are many. A lot of yes`s and a lot of NO`S. The safe answer is NO the unsafe answer is yes.
My 2 pennies

:site:

I will say this, code is a guideline for installation to mostly protect the wire/component/system...ie to prevent shock, fire etc.

Can they be combined...yes. Do you want to combine them? That you have to determine. If its strictly power wiring it shouldnt matter overall but if its any form of "signal" wire then its better not to.

NOTE: PLC discrete inputs are a "signal", analog, high speed, communication, etc are all "signal", induction, harmonics or noise generated from wire and/or field devices can interfere with the signal to or from any device.

I suggest you attempt to separate high voltage, especially motor leads from control voltage and/or signal wires. In the long run it may save you a lot of headaches.

Ken Roach said:

It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

Click to expand...

actually, as long as all conductors share the same insulation, you CAN run them all together....that much is in the NEC.

In my experience, unless you are using crappy drives or analog (seen most on 4-20 mA) signaling, the noise won't affect controls operation in most 480 Volt systems as long as all wiring has the same insulation type...most 'engineers' will argue otherwise, and text-book answers back them up. But in a real-world setting, I have never encountered any problems running different voltages or AC/DC in the same panel/conduit....maybe I'm just lucky?

I think that signal wirings are best not mixed together with power wirings.

My views are on the What Ifs:

- Poor insulation. Heat generated from power cables, especially high voltage supply, may affect the functionality of signal cables.

- Crosstalk. This may apply if you are running digital signal cables with analog signal cables. I experienced it once when I was doing a prototype multi-transmission box. my displayed images are totally distorted.

- And cables with very high voltage difference.. or current difference..a no no to me... unless you have good cables with good insulation. But it's always better safe than sorry.

My rookie input.

regards
Sherine T.

Ken Roach said:

It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

Click to expand...

While Ken did comment further later on, this is still pretty much correct.

With some PLC's, operation would be very erratic. Safety wise, not a good idea, as a spike on the 480 could trigger something violent to happen.

In some local jurisdictions, that actually DO inspect, it is not accepted. It could nullify your companies insurance.

And on, and on, and on.

I have never tried this, but have had to correct problems cuased by it.

As previously stated, NOT RECOMMENDED.

regards.....casey

Ken Roach said:

It's only permissible under two conditions:

1. Nobody is looking.
2. You don't want it to work.

Click to expand...

Thanks again for helping Emir today!!!