Ac wiring quetion

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relbas

Member
can I run control wiring 24V ac to the condenser in the sane conduit with the power circuit.
All conductors are the same insulation THNN.
24v is taken from the transformer with in the unit( evaporator).
 

iwire

Moderator
Staff member
Location
Massachusetts
can I run control wiring 24V ac to the condenser in the sane conduit with the power circuit.
All conductors are the same insulation THNN.
24v is taken from the transformer with in the unit( evaporator).

Those are class 2 conductors and cannot be run with power conductors.

You can however jump through a bunch hoops and reclassify them as Class 1 conductors and run them in the same conduit as the power wires.

If you decide to do that you would have keep those Class 1 conductors in a Chapter 3 wiring method for their entire length. All the way to the air handler, all the way to the thermostat etc.

Most folks just keep them separate.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
interesting,
I have seen many a A/C in commercial run in the same conduit, then go to a jbox and split to separate run then to the T-stat. What happens when you land those wires on a standard T-stat that is probably not listed for the instance you describe.

I have never done this. When we are hooking up a A/C unit we often find T-stat wires run through the A/C disconnect- We remove them!
 

iwire

Moderator
Staff member
Location
Massachusetts
What happens when you land those wires on a standard T-stat that is probably not listed for the instance you describe.

Darn good question and the NEC does not tell us it is possible, only that the NEC will permit it.

725.130 Wiring Methods and Materials on Load Side of
the Class 2 or Class 3 Power Source.
Class 2 and Class 3
circuits on the load side of the power source shall be permitted
to be installed using wiring methods and materials in
accordance with either 725.130(A) or (B).

(A) Class 1 Wiring Methods and Materials. Installation
shall be in accordance with 725.46.

Exception No. 1: The ampacity adjustment factors given
in 310.15(B)(3)(a) shall not apply.

Exception No. 2: Class 2 and Class 3 circuits shall be
permitted to be reclassified and installed as Class 1 circuits
if the Class 2 and Class 3 markings required in 725.124 are
eliminated and the entire circuit is installed using the wiring
methods and materials in accordance with Part II,
Class 1 circuits.





Informational Note: Class 2 and Class 3 circuits reclassified
and installed as Class 1 circuits are no longer Class 2
or Class 3 circuits, regardless of the continued connection
to a Class 2 or Class 3 power source.
 

GoldDigger

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Location
Placerville, CA, USA
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Retired PV System Designer
Darn good question and the NEC does not tell us it is possible, only that the NEC will permit it.
I would rather say that the NEC tells us that the T-stat wiring may be reclassified as Class 1, but that at that point it would not be legal to connect it to a t-stat which is rated only for Class 2 or Class 3 use.
You could use a line voltage stat if you want, although if you have a self-contained thermocouple powered millivolt circuit for heating a line voltage stat may have too much contact resistance.
 

relbas

Member
I would rather say that the NEC tells us that the T-stat wiring may be reclassified as Class 1, but that at that point it would not be legal to connect it to a t-stat which is rated only for Class 2 or Class 3 use.
You could use a line voltage stat if you want, although if you have a self-contained thermocouple powered millivolt circuit for heating a line voltage stat may have too much contact resistance.

LV power (24v) for the remote condenser (relay) is coming from the evaporator and not from the thermostat. Those are the control wires that I am referring to.
those are 2 wires that I am running up to the roof and I am planning to use 2#14 THHN conductors together with the power wiring 3 Phase 208V in the same conduit.
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
LV power (24v) for the remote condenser (relay) is coming from the evaporator and not from the thermostat. Those are the control wires that I am referring to.
those are 2 wires that I am running up to the roof and I am planning to use 2#14 THHN conductors together with the power wiring 3 Phase 208V in the same conduit.
As long as the relay is not limited to Class 2 power input you should be fine.
Although there may be some inspectors who do not agree that the relay signal is "functionally related" to the unit power. :(
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
LV power (24v) for the remote condenser (relay) is coming from the evaporator and not from the thermostat. Those are the control wires that I am referring to.
those are 2 wires that I am running up to the roof and I am planning to use 2#14 THHN conductors together with the power wiring 3 Phase 208V in the same conduit.

As mentioned you'll first need to confirm that the power supply does not say Class 2 only.
 

kwired

Electron manager
Location
NE Nebraska
LV power (24v) for the remote condenser (relay) is coming from the evaporator and not from the thermostat. Those are the control wires that I am referring to.
those are 2 wires that I am running up to the roof and I am planning to use 2#14 THHN conductors together with the power wiring 3 Phase 208V in the same conduit.
But one of those two wires likely makes a loop through the thermostat before heading out to the condensing unit. If you "reclassify" the circuit to a class 1 circuit you must do so for the entire circuit which includes the wall thermostat, outdoor temp sensors, automatic dampers, humidifier controls, etc.

If you just want one run to the AC unit to be reclassified you could provide a control relay at appropriate location and then switch your class 1 circuit with that control relay. But now you possibly need an additional pole or aux contact at the AC disconnect so that it removes all power when operated. If you had a 120 volt control circuit I think that would be required, not quite certain just yet if a class 1 circuit operating at 24 volts would need to have control circuit disconnect provisions.
 

GoldDigger

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Location
Placerville, CA, USA
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Retired PV System Designer
And what code would they cite to bring that up? :?
Maybe 725.48(B)(1) [2011]?
Just reclassifying the circuit as Class 1 by itself does not give you carte blanche to mix those Class 1 wires with power circuits.
(And, in this section, I believe power circuits include power to lighting, FWIW.)
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Maybe 725.48(B)(1) [2011]?
Just reclassifying the circuit as Class 1 by itself does not give you carte blanche to mix those Class 1 wires with power circuits.
(And, in this section, I believe power circuits include power to lighting, FWIW.)
The case of A/C controls with A/C power seems pretty clear, but at least one member has reported an inspector who ruled that the voltage sensing wires for a generator controller were not functionally associated with the power output wires from that generator. :(
Perhaps because it was a source rather than a load???
 

kwired

Electron manager
Location
NE Nebraska
Maybe 725.48(B)(1) [2011]?
Just reclassifying the circuit as Class 1 by itself does not give you carte blanche to mix those Class 1 wires with power circuits.
(And, in this section, I believe power circuits include power to lighting, FWIW.)

I would need to look it up but am pretty certain you can run class 1 control circuits with power circuits the controls are associated with. I have been doing it for many years and have looked this up a few times to make sure what I did was ok.

Example a run from a remote starter to a motor load - and you put a control switch near the motor - you can run both the motor circuit and the control circuit in same raceway instead of separate raceways if the control circuit is a class 1 circuit.
 
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