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Joined: Oct 2000
Posts: 2,749
Mixing Line Voltage and Thermostat Wires in a AC Disconnect Switch.

What's the consensus? Seems to be a violation of the code?

[Linked Image from]

Joe Tedesco, NEC Consultant
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Joined: May 2004
Posts: 81
Where is the ground wire to the unit

I hate it when guys ramset boxes to a wall

Joined: Oct 2000
Posts: 2,749
It was not installed!

and ... Posted: Jul 31, 2004 8:43 AM Post subject: OK!


Dennis: OK, I think you done real good! and below see also the discussion on the question first posted in the link above:

The low voltage thermostat wires are not permitted to be run in the same cable or conduit because they do not have sufficient construction specifications to permit them to be installed with electric light, power conductors and any failure of the cable insulation due to a fault could lead to hazardous voltages being imposed on the thermostat circuit conductors.

The use of the same insulation for circuits up to 600 volts for both AC and DC is acceptable when run in the same cable or conduit, but not for this application.

It is better to see that thermostat wiring run in a separate cable or conduit, or wrapped around the cable or conduit that will supply the unit.

Joe Tedesco, NEC Consultant
Joined: Feb 2004
Posts: 62
Agreed it's not a good practice, but if the wiring is all 600v rated, is it a violation? What Code reference, so I can tell the HVAC guys next time I see this done.

Joined: Oct 2000
Posts: 2,749
300.3(C) Conductors of Different Systems.

(1) 600 Volts, Nominal, or Less.

Conductors of circuits rated 600 volts, nominal, or less, ac circuits, and dc circuits shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway.

All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.

Exception: For solar photovoltaic systems in accordance with 690.4(B).

FPN:See 725.55(A) for Class 2 and Class 3 circuit conductors.

Joe Tedesco, NEC Consultant
Joined: Jun 2003
Posts: 681
725.55 does not permit under any circumstance for Class 2 conductors to be installed in RACEWAYS with any power conductors, even associated conductors are not permitted in the same raceway.
Enclosures and other items yes, under specific restrictions, but not raceways.


Pierre Belarge
Joined: Feb 2004
Posts: 1,438
where is the T-stat wire gaining access to the electrical system here anyways??? It looks like its spliced into the #12TW's on the left? This is a strange installation from what I'm used to... [Linked Image from]


Joined: Jul 2003
Posts: 394
OK, the picture is not too clear to me. We have the heavy black and light blue conductor pairs that look like line and load. We have an orange and a blue spliced to the aux contacts on the breaker. And we have some sort of a coil of unidentified white wire that doesn't really seem to start or end anywhere. What's with the white - what is it? Where does it originate and terminate?

Joined: May 2004
Posts: 116
The blue wire on the very left of the photo comin gout of the yellow wire nut goes up and then back down ans seems to end in a spade connector that is not attached to anything. The smaller blue wire from the same yellow worenut goes almost directly to the right and ends up in the coil of white, green, red, and yellow wire. What is going on here?

Joined: Jan 2003
Posts: 4,391
No you can not run class 1 and 2 in the same raceway but you can reclassify class 2 or 3 circuits to class 1 then run them in the same conduit with other class 1 conductors [Linked Image] 725.52(A)Exception No. 2

I doubt highly that is the case of the wiring in Joe's Picture.


Bob Badger
Construction & Maintenance Electrician
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