# Analog and Discrete wiring



## HAL9000 (Feb 28, 2016)

Just wanted to get a discussion going here about how you should run the wire for analog and discrete devices, I have been in places where we run conduit for each ( one analog pipe; one discrete pipe) I have been in places where they were mixed together in pipes, some people swear they have to be separated some people say you can mix them, in all cases the discrete has been 24V and the Analog has been 4-20mA, what are the feelings out there?


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## don_resqcapt19 (Jul 18, 2010)

I always keep them in separate conduits, but if the discrete is all 24 volt, there isn't really a problem.


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## splatz (May 23, 2015)

I can't think of a reason to separate them. As far as I know the 4-20ma is nice because induced voltages aren't a problem, not that 24vdc is going to induce much voltage. Can't see any way the 4-20ma would trip up discrete.


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## MechanicalDVR (Dec 29, 2007)

The only restriction I have ever dealt with is they have to have the same insulation rating on the conductors.


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## NC Plc (Mar 24, 2014)

We mix them up but we use a lot of shielded cable.


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## don_resqcapt19 (Jul 18, 2010)

Mech Diver said:


> The only restriction I have ever dealt with is they have to have the same insulation rating on the conductors.


That is not correct....all of the conductors have to be insulated for the highest voltage circuit that is in the raceway. 
You can mix 600 volt rated discrete conductors with the 300 volt rated analog conductors and be code compliant. 


> 300.3(C)Conductors of Different Systems
> (1) 1000 Volts, Nominal, or Less. Conductors of ac and dc circuits, rated 1000 volts, nominal, or less, shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation *rating equal to at least the maximum circuit voltage applied *to any conductor within the enclosure, cable, or raceway.


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## micromind (Aug 11, 2007)

I've mixed them in a single pipe for many years and have yet to have a problem. Even very long runs, no trouble at all. 

For that matter, I've pulled 120AC and 4-20 (shielded) in the same pipe, though it was a fairly short run (40'or so) and the 120 had very little current (instrument power).


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## splatz (May 23, 2015)

micromind said:


> I've mixed them in a single pipe for many years and have yet to have a problem. Even very long runs, no trouble at all.
> 
> For that matter, I've pulled 120AC and 4-20 (shielded) in the same pipe, though it was a fairly short run (40'or so) and the 120 had very little current (instrument power).


It's my understanding that this is one of the advantages of 4-20ma over 0-5VDC sensors. Induced current would be a problem with the 0-5vdc but not with 4-20, since the sensor would still make the same current.


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## JRaef (Mar 23, 2009)

Just run shielded cable (ground the shields at ONE end only) and be done with it. Put as many in the same conduit as you can within fill limits.


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## Cow (Jan 16, 2008)

don_resqcapt19 said:


> That is not correct....all of the conductors have to be insulated for the highest voltage circuit that is in the raceway.
> You can mix 600 volt rated discrete conductors with the 300 volt rated analog conductors and be code compliant.


A guy has to be careful not to take this quote out of context. Just because the wires all have an insulation rating for the voltage present doesn't mean it's always okay. It also depends on the classification of the power supply for the circuits as well. I've had to change out a class 2 power supply for a class 1 despite having all 600v cable just to meet the requirements.


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## MechanicalDVR (Dec 29, 2007)

don_resqcapt19 said:


> That is not correct....all of the conductors have to be insulated for the highest voltage circuit that is in the raceway.
> You can mix 600 volt rated discrete conductors with the 300 volt rated analog conductors and be code compliant.



Well unless you know of some magic cat 5 cable that you an run 1000v in then the way I stated it will still hold true. But thanks for the code reference.


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## KennyW (Aug 31, 2013)

Mech Diver said:


> Well unless you know of some magic cat 5 cable that you an run 1000v in then the way I stated it will still hold true. But thanks for the code reference.


1000v or less just means cables with a rating of 1000V or less. 

It's actually pretty common in the industrial world to run tray rated 600V CAT5 in the same cable tray as 1000V rated motor cables (600v or 480v motor circuits). The cat5e and the motor cables are both shielded, of course. 

I think this rule is actually worded for exactly this sort of situation, and that particular cat5E is made specifically for this requirement. So yes, I guess it is a magic cat5e that can be run in the same raceway as 1000V cables. 

My take is the same as Jraef. Use shielded instrument/comms cables and don't worry about it.


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## MechanicalDVR (Dec 29, 2007)

KennyW said:


> 1000v or less just means cables with a rating of 1000V or less.
> 
> It's actually pretty common in the industrial world to run tray rated 600V CAT5 in the same cable tray as 1000V rated motor cables (600v or 480v motor circuits). The cat5e and the motor cables are both shielded, of course.
> 
> ...



A myopic reader, you missed the point.


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## RePhase277 (Feb 5, 2008)

splatz said:


> I can't think of a reason to separate them. As far as I know the 4-20ma is nice because induced voltages aren't a problem, not that 24vdc is going to induce much voltage. Can't see any way the 4-20ma would trip up discrete.


A minor nit to pick, but it isn't voltage that is responsible for inductance. 1 amp at 24 volts induces the same voltage in a nearby conductor as 1 amp at 480 volts. Just sayin'..


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## EC2253 (Mar 7, 2008)

If the discrete is a class 1 circuit then no see 725.136


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## HAL9000 (Feb 28, 2016)

analog are shielded and have the mylar screen as well and the discrete are single conductor #16


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## don_resqcapt19 (Jul 18, 2010)

EC2253 said:


> If the discrete is a class 1 circuit then no see 725.136


That is assuming that the analog is not Class 1 also. 
I don't think I have ever seen an industrial analog power supply that was marked as a Class 2 power supply. Just because it is 24 volts does not mean that it is Class 2


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## Cow (Jan 16, 2008)

don_resqcapt19 said:


> That is assuming that the analog is not Class 1 also.
> I don't think I have ever seen an industrial analog power supply that was marked as a Class 2 power supply. Just because it is 24 volts does not mean that it is Class 2


The Class 2 power supply we had to change out was Allen Bradley. Fortunately, they had a similar Class 1.


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