Low and high voltage in same conduit

[Arthur Soderstrom]

I know that you cannot run 12-24 vdc in the same conduit it 110 vac. I am stumped as to where in the code this is listed. I have found a reference to mey situation in 760.55 but it refers to power-limited fire alarm circuits. Any ideas where it might also be addressed in the 2005 code?

 

[iwire]

Welcome to the forum.

As with most things NEC there is no hard and fast answer.

Depending on the application and the wiring methods you may or may not mix power and lighting conductors with other types of electrical systems.

It is worth noting that the NEC does not use the terms high or low voltage and often both 12 volt and 120 wiring is considered 'low' voltage.

What is your specific application?

 

[STHOMAS]

It is important to understand power limited and non-power limited circuits....As you reference Article 760 I assume your question is regarding the installation of fire alarm and power circuits.

I do not have the 2005 Edition, but 2002 Edition,Section 760.55 states:

Separation from Electric Light, Power, Class 1, NPLFA, and Medium Power Network-Powered Broadband Communications Circuit Conductors.
(A) General. Power-limited fire alarm circuit cables and conductors shall not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power, Class 1, non?power-limited fire alarm circuits, and medium power network-powered broadband communications circuits unless permitted by 760.55(B) through (G).

The intent of this section is to prevent a a technician from working on low and high voltage circuits in the same raceway.

 

[iwire]

The intent of this section is to prevent a a technician from working on low and high voltage circuits in the same raceway.

I do not believe that is the intent of that section at all.

 

[Arthur Soderstrom]

Welcome to the forum.

What is your specific application?

We install 12 and 5 VDC access control system that also use locks powered by 24 VDC all are power limited.

I knew that running "low and high" in the same conduit was allowed at the end device but without exception all the electricians I know have said that they must be separated in different conduits at all other times. I now need to prove this for a cuatomer who wants me to use the same conduit that feeds an auto-door that I will control with card readers.

 

[raider1]

For class 2 and 3 circuits take a look at 725.136 (2008 NEC) or 725.55 (2005 NEC).

Chris

 

[tom baker]

Forget calling this low voltage. We don't know what low voltage is.
There is a proposal for the 11 NEC to call any system operating under 1000 volts "low voltage". Now what?
We need to know what type of circuit it is. See if you can find it listed in Art 725 under Class 1, 2 or 3.

 

[STHOMAS]

I do not believe that is the intent of that section at all.

I may have stated that in error....most "low volt" wiring (fire alarm data, access control data, security data) is very susceptible to 60 hz interference.

?.It was my assumption that many requirements found in the electrical code regards the safety of those working on power circuits, and that mixing different circuits of different voltages serving multiple appliances poses an inherent danger to installing and servicing technicians.

In California, fire alarm installers are limited to working on low voltage?.meaning under 100 volts. Even though we work on 120 VAC circuits all of the time (power to our panels, smoke/fire dampers, etc). In the electrical world, under 1000 volts being termed low voltage is still voltage that no fire alarm installer has any business being around.

?low volt? technicians are not properly trained to work on what we in the systems trade call high voltage. Remember 120 VAC is considered high voltage for us ?half watts? as we have been called?.

 

[Mr. Wizard]

What is the insulation rating of the LV cable you are wanting to use? If you are using a non-shielded 18/2 for power, you may consider using 18 gauge THHN. It has a 600 volt insulation rating, and it can be pulled along with 120/240 voltages.

 

[don_resqcapt19]

What is the insulation rating of the LV cable you are wanting to use? If you are using a non-shielded 18/2 for power, you may consider using 18 gauge THHN. It has a 600 volt insulation rating, and it can be pulled along with 120/240 voltages.

Not if the the "low voltage" circuit is a Class 2 or 3 circuit.

 

[danickstr]

This came up with generator install. The company said that if 600v wire was used, it was OK to pull the LV control wires in the same conduit up to 35 feet. I think the inspector was more concerned with the routing of the 3/0 through the transfer switch and the changing of the primary grounding location than the mix of 18ga and 14 ga line and low voltage, (since they are in the transfer switch logic area looping around next to each other anyway) but I would not mind knowing what was correct.

 

[Pierre C Belarge]

Not if the the "low voltage" circuit is a Class 2 or 3 circuit.

Insulation types do not absolve one of 725.55 if the source is a Class 2 source.


I believe the reason for dissallowing the two types of systems in the same raceway is to keep the power voltage from becoming imposed on the Class 2 wiring system - which has a tendency of starting fires, etc...

 

[don_resqcapt19]

Insulation types do not absolve one of 725.55 if the source is a Class 2 source.


I believe the reason for dissallowing the two types of systems in the same raceway is to keep the power voltage from becoming imposed on the Class 2 wiring system - which has a tendency of starting fires, etc...

But we can reclassify the circuit and install it that way

 

[nhfire77]

Yes you can reclassify but you must destroy the class 2 markings on all attached equipment.

 

[don_resqcapt19]

Yes you can reclassify but you must destroy the class 2 markings on all attached equipment.

My point is that taking the markings off does not change the physical installation. When you "reclassify the circuit you use Chapter 3 wiring methods. How is it any less safe if you use Chapter 3 wiring methods and don't reclassify the circuit? In either case if there is some type of fault between the reclassified circuit conductors and the power conductors you will energize the Class 2 equipment with line voltage creating a shock and fire hazard and maybe even a hazardous material incident...if the line voltage causes the mecury bulb switch in a stat to explode.

 

[tom baker]

What is the insulation rating of the LV cable you are wanting to use? If you are using a non-shielded 18/2 for power, you may consider using 18 gauge THHN. It has a 600 volt insulation rating, and it can be pulled along with 120/240 voltages.

See the FPN to 300.3(C)(1), which is what Don is stating above.
However, if your circuit is a Class 1 remote control circuit, then it can be in the same raceway, etc if functionally related, and wired with a Chapter 3 wiring method.

 

[realolman]

I'd like to be wrong ( it's usually so easy for me )

I'd like to be wrong ( it's usually so easy for me )

.... It has a 600 volt insulation rating, and it can be pulled along with 120/240 voltages.

According to 725.26 (B) (1) I believe this is incorrect unless the equipment powered is functionally related. I am not sure exactly what "functionally related" means.

I "inherited" an existing system where I need to get a 24vdc 10a. circuit from one panel to another.

There are two existing conduits... one conduit contains an ethernet cable and the existing 24vdc 10 a. circuit as two conductors in a 22 awg. 15 conductor communication cable. The other conduit contains a bunch of motor conductors.

Because of the 10a. power supply , I believe the communication cable isn't adequate, and that it makes the 24vdc circuit class 1, so it can't go with the ethernet cable either.

So I intended to run it in thhn in the same conduit as the power conductors for some motors... but because of 725.26(B) (1) I think that isn't Kosher either.

Because everything involved is part of a conveyor system, I think that I am going to claim it's all functionally related, but I think I should probably be running another conduit... which seems goofy to me, but that's what I'm getting from reading the code.

I'll be thrilled if someone will show me where I'm wrong, so I can run the 24vdc with the motor conductors (or the ethernet cable ), and I don't have to run another conduit.:smile: