24 volt AC & 120 volt AC in same conduit

[shade23]

I know that #18 THHN, 600 volt wiring used for 24 volt AC can be run in the same conduit as #12 THHN, 600 volt wiring used for 120 volts but I have always been reluctant to do so.
I have four baseball batting cages that will use 120 volts AC for operating the motors of the throwing arms. There is a 24 volt AC circuit that is being used as a switch leg that will turn on the batting cage motor (at the batting cage control box) whenever a coin is deposited (at the coin box) to start the system. Because of the appearance and limited space of :angel:multiple conduits I would like to run the 24 V and 120 V in the same conduit. I hope someone says go ahead but I have never mixed voltages and it is hard for me to do so.
Thanks for any help, it is hard to teach an old dog new tricks.

 

[oldsparky52]

It depends on the "Class" of the circuit. If the 24 volts is a Class 2 circuit then they need to be separate. I've never been strong in this. Check out article 725

 

[Dennis Alwon]

Do you know what class the wiring is for the low voltage? See 725.136(A)

 

[texie]

As others have mentioned, it depends on the class of circuit. This is almost certainly a class 2 circuit and could not be run in the same raceway as power conductors regardless of the insulation rating.
It is erroneous to believe that just because you have 600 volt insulation that you can in all cases share the same raceway.

 

[shade23]

Do you know what class the wiring is for the low voltage? See 725.136(A)

I would call it a Class 1 location. You have four pitching machines, each with it's own control box. There is a hopper with it's own control box which directs the balls back to the pitching machines. The 24 volts is simply used to close the contactor on the pitching machine which starts the motor for the pitching arm when a coin is deposited in the coin box. . When any one of the four coin boxes is fed with a coin, the hopper starts to direct balls and the batting machine associated with the coin box for that cage starts. I think it is a Class 2 because it is 24 volts on #18 thhn wire and it is only acting to start the motor contactor. The batting machines are only serviced by qualified people and are not accessible to the public. All the wiring is associated with the batting system.

 

[kwired]

I would call it a Class 1 location. You have four pitching machines, each with it's own control box. There is a hopper with it's own control box which directs the balls back to the pitching machines. The 24 volts is simply used to close the contactor on the pitching machine which starts the motor for the pitching arm when a coin is deposited in the coin box. . When any one of the four coin boxes is fed with a coin, the hopper starts to direct balls and the batting machine associated with the coin box for that cage starts. I think it is a Class 2 because it is 24 volts on #18 thhn wire and it is only acting to start the motor contactor. The batting machines are only serviced by qualified people and are not accessible to the public. All the wiring is associated with the batting system.

Is whatever is in the "coin box" rated for use only on class 2 circuits? If so then you can't reclassify your control circuit as class 1 and still connect it to this device.

 

[shade23]

Is whatever is in the "coin box" rated for use only on class 2 circuits? If so then you can't reclassify your control circuit as class 1 and still connect it to this device.

The coin box is fed with a direct buried shielded five wire cable from the pitching machine control box. The coin box is fed from the pitching machine control box which has it's own 12 volt DC transformer which only runs the coin box.. The switch leg for turning on the ball hopper is fed from the ball hopper 24 volt ac transformer. Twenty four volts is in parallel to each pitching machine and when any pitching machine is started, then the hopper starts and runs until the pitching machine times out. These are good machines but it makes it very difficult to distinguish which classes are present. I am trying to eliminate an extra conduit by running the motor voltage and 24 volts together.

 

[Dennis Alwon]

I would love to know the reason why the different classes change the compliance or why it matters

 

[kwired]

The coin box is fed with a direct buried shielded five wire cable from the pitching machine control box. The coin box is fed from the pitching machine control box which has it's own 12 volt DC transformer which only runs the coin box.. The switch leg for turning on the ball hopper is fed from the ball hopper 24 volt ac transformer. Twenty four volts is in parallel to each pitching machine and when any pitching machine is started, then the hopper starts and runs until the pitching machine times out. These are good machines but it makes it very difficult to distinguish which classes are present. I am trying to eliminate an extra conduit by running the motor voltage and 24 volts together.

So the control box needs both class 1 and class 2 circuits run to it? (presuming your 12 DC transformer must be derived from 120 volts?)

Only way you can "reclassify" to run all conductors in same raceway is to "reclassify" the entire circuit, not just the portions that are convenient for you. Might need to know more details of what you have to know if this is even possible. Take a typical heating/cooling unit with 24VAC control circuit. If you wanted to pull control wires in raceway with power circuit just to avoid two raceways, it is possible, but reclassifying the entire control circuit means you run raceway or cable that is not CL2 cable throughout the entire circuit, you replace any standard low volt thermostats with ones that are rated for line volts. That 18-2 that is convenient to just strap to the refrigerant lines at the AC condenser - must be line volt rated method. You can't pick and choose which sections you wire as class 1 and 2, it is all class 1 once you reclassify.

 

[shade23]

So the control box needs both class 1 and class 2 circuits run to it? (presuming your 12 DC transformer must be derived from 120 volts?)

Only way you can "reclassify" to run all conductors in same raceway is to "reclassify" the entire circuit, not just the portions that are convenient for you. Might need to know more details of what you have to know if this is even possible. Take a typical heating/cooling unit with 24VAC control circuit. If you wanted to pull control wires in raceway with power circuit just to avoid two raceways, it is possible, but reclassifying the entire control circuit means you run raceway or cable that is not CL2 cable throughout the entire circuit, you replace any standard low volt thermostats with ones that are rated for line volts. That 18-2 that is convenient to just strap to the refrigerant lines at the AC condenser - must be line volt rated method. You can't pick and choose which sections you wire as class 1 and 2, it is all class 1 once you reclassify.

Thanks to everyone for all the help. It looks like the NEC has made something simple into a
sophisticated mess. It would be far more simple just to say no mixed voltages. I am sure if most cases were studied almost all of them would have to be reclassified. Thank You

 

[kwired]

Thanks to everyone for all the help. It looks like the NEC has made something simple into a
sophisticated mess. It would be far more simple just to say no mixed voltages. I am sure if most cases were studied almost all of them would have to be reclassified. Thank You

It kind of makes sense though, class 2 wiring methods allow things that class 1 and power doesn't because the risk of shock is less, why would you mix those two methods and increase the shock risk, by reclassifying the class 2 circuit as class 1, you need to use all class 1 methods throughout the circuit, otherwise you still have increased shock hazards if you leave some of the class 2 only rated items in place.

 

[MAC702]

This happens all the time in the HVAC world. And we frequently find the 24V thermostat wire pulled in the same conduit as the 240V lines, especially on residential rooftop package units. They separate them below the roof penetration.

Sometimes this is done in a method that might be okay, and other times not. The roof penetration is sometimes just a sleeve of flexible liquidtight, and the wiring method is NM inside (other issues.)

Even when the roof penetration is a sleeve, the conduit from the disco to the unit is a raceway, and the stat cable and line voltage wires are often together.

Not saying it's okay or not, just that it's frequently found.