24v wiring methods

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Nolanmichaelp

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Highlands, NJ, US
Hello all, my name is Mike and I work in Northern New Jersey typically in boiler rooms. I come across this often, where I see 24 V wiring not in conduit. What is the article in the NEC, I don't even know where to look. I believe all of this wiring should be in conduit, but for whatever reason it always passes.
 
You're probably looking for articles 720 and/or 725.

Roger
 
With class 2 power supplies the risk for shock or fire hazards is much lower then for other sources, and this is a major reason for relaxed requirements for such systems. If reliability is a high priority additional protection may still be a good design decision.
 
Nolanmichaelp said:
I agree that it is always a good idea to put any cable in conduit, but my question is; is it a requirement, when is it a requirement, and why is it never enforced?
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For most class 2 circuits, NEC leaves the degree of physical protection up to the designer or AHJ. There is limited risk to life or property if the class 2 circuit gets damaged.

Specific applications or even other codes may have more protection requirements if the class 2 circuit is part of something that is protecting life or property. But often times those types of systems have "supervised" circuits and with such systems the physical protection requirements aren't always that strict either because if something happens to the cable the "supervised system" will detect that damage and give a trouble alarm to the user.
 
Nolanmichaelp said:
I agree that it is always a good idea to put any cable in conduit, but my question is; is it a requirement, when is it a requirement, and why is it never enforced?
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Hardly ever.

When subject to physical damage.

Assumes facts not in evidence. See above.

The one thing that usually is a violation is zip-tying the thermostat wire (for example) to the 120AC conduit or MC.
 
gadfly56 said:
Hardly ever.

When subject to physical damage.

Assumes facts not in evidence. See above.

The one thing that usually is a violation is zip-tying the thermostat wire (for example) to the 120AC conduit or MC.
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Class 2 wiring can't be supported by other wiring methods as a general rule. You can support it from the power supply wiring method for equipment/appliances it has an association with though. For example a raceway that supplies power to a furnace/air handler can have the class 2 control circuit for that appliance tied to it. You can not tie that thermostat cable to raceways for something like lighting or general purpose receptacles though.
 
kwired said:
Class 2 wiring can't be supported by other wiring methods as a general rule. You can support it from the power supply wiring method for equipment/appliances it has an association with though. For example a raceway that supplies power to a furnace/air handler can have the class 2 control circuit for that appliance tied to it. You can not tie that thermostat cable to raceways for something like lighting or general purpose receptacles though.
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Yes, thank you for expanding on that. It is a little subtler than I made it out to be.
 
You may want to look at 725.31

725.31 Safety-Control Equipment.
(A) Remote-Control Circuits. Remote-control circuits for
safety-control equipment shall be classified as Class 1 if the failure
of the equipment to operate introduces a direct fire or life
hazard. Room thermostats, water temperature regulating devices,
and similar controls used in conjunction with electrically
controlled household heating and air conditioning shall not be
considered safety-control equipment.
(B) Physical Protection. Where damage to remote-control
circuits of safety-control equipment would introduce a hazard,
as covered in 725.31(A), all conductors of such remote-control
circuits shall be installed in rigid metal conduit, intermediate
metal conduit, rigid nonmetallic conduit, electrical metallic
tubing, Type MI cable, or Type MC cable, or be otherwise suitably
protected from physical damage.
 
Article 725.8 is very ambiguous and highly subjective. I got sent out to get a job "through inspection". Is there a 'rule of thumb' that anyone works off of with protecting class 2 circuits? Nobody can give me a firm answer, and most inspectors don't batt an eye with most of these installations, however, this particular inspector is very savvy and actually does his job. Just looking for a little guidance. Thanks a lot guys this is much obliged.
 
Nolanmichaelp said:
Article 725.8 is very ambiguous and highly subjective. I got sent out to get a job "through inspection". Is there a 'rule of thumb' that anyone works off of with protecting class 2 circuits? Nobody can give me a firm answer, and most inspectors don't batt an eye with most of these installations, however, this particular inspector is very savvy and actually does his job. Just looking for a little guidance. Thanks a lot guys this is much obliged.
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The only time we run conduit for class 2 cables is when the job specs require it or it is within reach of the general public.
 
Nolanmichaelp said:
... Is there a 'rule of thumb' that anyone works off of with protecting class 2 circuits? Nobody can give me a firm answer, and most inspectors don't batt an eye with most of these installations, however, this particular inspector is very savvy and actually does his job. Just looking for a little guidance. Thanks a lot guys this is much obliged.
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I'll make it easy. There is no NEC requirement. That's why inspectors don't say anything- and they shouldn't.

-Hal
 
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