POWER AND CONTROL WIRE SEPARATION

RLMJR

Member
Location
British Indian Ocean Territory (Diego Garcia)
Occupation
Electrical Engineer
I have a project replacement of split type AC unit in a building, the condenser unit is 20 ft away from air handling unit and panel board at mechanical room, there is an existing underground conduit from condenser (outside) to mech room w/c i planned to reuse. the conduits are 2 -ea 2" pvc sch 40 wth separation of 1" apart, my plan is to use one conduit for power of condenser (8 awg) 208v 3 phase 60 hz, and the other for control wire connection of ahu to accu and other controls, question is , is this orientation allowed in the code? is there any specific distance requirement for control of acu and power? is this orientation going to affect the control signals? note the voltage is 208V 60 hz 3 phase. Is this better that putting all in one conduit? or i need to add a conduit for control far enough from the power conduit?

Thanks in advance for the answers.
 

tom baker

First Chief Moderator
Staff member
If the control ckt is a nec article 725 class 1 wiring method that circuit can be run with functionally related power. There will be no issue with interference. Often the control wiring is tray cable, s 600 volt direct bury wiring method.
 

mtnelect

HVAC Contractor
Location
Southern California
Occupation
Contractor
Section 725.136(A) - Cables and conductors of Class 2 and Class 3 circuits shall not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway or similar fittings with conductors of electric light, power ...

Jackets of listed Class 2 and Class 3 cable do not have sufficient construction specification to permit them ...
 

JEFF MILLAR

Senior Member
Separation is good engineering . Only communication cable should have a clearance from MV power cable. What you want to do sounds good to me.
 

JEFF MILLAR

Senior Member
I have no experience with thermostat cables. I lam here to learn from your collective experience.
And very grateful for this excellent forum.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
the conduits are 2 -ea 2" pvc sch 40 wth separation of 1" apart, my plan is to use one conduit for power of condenser (8 awg) 208v 3 phase 60 hz, and the other for control wire connection of ahu to accu and other controls, question is , is this orientation allowed in the code?

If I'm understanding you correctly, you plan on running power through one conduit and the control through the other. Not only is this allowed by code, but it is also required.

Generally, low voltage control cannot be run with power conductors except in special circumstances. One of those circumstances is for the control wiring to be functionally associated with the power wiring. In other words, the equipment powered by the power wiring cannot operate without the control wiring. This is up to the AHJ. In this case you might get away with it if you "reclassify" the low voltage control and use conductors that have the same 600V insulation as the power conductors.

That said for your general information, you don't have to worry about it here because you have separate conduits. Separate conduits are the preferred and 100% acceptable way to do it.

-Hal
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
If I'm understanding you correctly, you plan on running power through one conduit and the control through the other. Not only is this allowed by code, but it is also required.

Generally, low voltage control cannot be run with power conductors except in special circumstances. One of those circumstances is for the control wiring to be functionally associated with the power wiring. In other words, the equipment powered by the power wiring cannot operate without the control wiring. This is up to the AHJ. In this case you might get away with it if you "reclassify" the low voltage control and use conductors that have the same 600V insulation as the power conductors.

That said for your general information, you don't have to worry about it here because you have separate conduits. Separate conduits are the preferred and 100% acceptable way to do it.

-Hal
With a 2" conduit he could put the control wiring in a 1/2" smurf or LFNMC as long as he maintained 1/4" of separation from the power wires where they immerge. That is my interpretation anyway.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
With a 2" conduit he could put the control wiring in a 1/2" smurf or LFNMC as long as he maintained 1/4" of separation from the power wires where they immerge. That is my interpretation anyway.

Doesn't he have TWO conduit runs? Run the control in its own conduit and be done with it- or am I missing something??

-Hal
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Doesn't he have TWO conduit runs? Run the control in its own conduit and be done with it- or am I missing something??

-Hal
No, you aren't missing anything and you spelled it out comprehensively, I was merely offering another alternative and felt quoting you was the best place, as it already covers the primary method. ;)
 

RLMJR

Member
Location
British Indian Ocean Territory (Diego Garcia)
Occupation
Electrical Engineer
With a 2" conduit he could put the control wiring in a 1/2" smurf or LFNMC as long as he maintained 1/4" of separation from the power wires where they immerge. That is my interpretation anyway.
-Hi Hbiss, thank you for the clarification, yes you are correct i am using diff conduit for the power and control w/c is required in the code, however i am using an existing conduit with 1 inch apart only, thats my question really is, if that one inch separation is enough? or there is a certain distance in code requirement b/w the the two conduit?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Do we really know what type of circuit the interconnect wiring for a mini split is? Anyone ever seen this defined in a destruction manual? FWIW, none of the ones I have seen were "low voltage".
The mini spits I have looked at use a three wire system with two wires carrying the power and the third operates at line voltage and carries low voltage signals superimposed on that.
All three are insulated for full line voltage and as far as I know do not have any power limits on the signal receiving circuitry. So Class 1, 2 and 3 rules are not applicable. On top of that, of course, the control is clearly functionally related to the power. If there were conventional thermostat wiring involved, it would be a different situation.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
-Hi Hbiss, thank you for the clarification, yes you are correct i am using diff conduit for the power and control w/c is required in the code, however i am using an existing conduit with 1 inch apart only, thats my question really is, if that one inch separation is enough? or there is a certain distance in code requirement b/w the the two conduit?

It wouldn't matter if the conduits were zip tied to each other. The Code has nothing to say about the spacing either.

-Hal
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Here is an example on Class 2 with HVAC.
A good example of a conventional two piece system, and a good description of using traditional low voltage thermostats. Because of the design of the low voltage thermostat, it is not possible to re-designate it as Class 1 and combine the wiring in one conduit.

Mini splits are configured differently, since there is normally one power source, to the outside unit, with the power being fed through to the inside unit and thermostat information from the inside unit needs to be relayed to the outside unit. Line level encoded signalling has taken the place of the simple on-off low voltage thermostat.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
It wouldn't matter if the conduits were zip tied to each other. The Code has nothing to say about the spacing either.

-Hal
Confirming that hbliss is correct, the code requires separation, that can be by means of a permanent barrier of which any article 300 raceway method is, or a mere 1/4" of separation from power wiring inside of a piece of equipment where they both terminate.
 
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