ECN Forum Forums Code Related Discussion NEC & other Code issues 120 vac and 24vdc in same conduit

Yes in the past I have always kept them separate also.
Problem is that we are working in a plant utilizing plant electricians who were fighting me on the issue. They wanted to use 1 conduit.

The NEC2002 and NEC2005 sections are quite clear in the matter. It more or less says "thou shall not mix wires" when talking about low voltage and line voltage under both 725 for Class 2 and 3 discussions, and 800 for comms wires. LAN wiring sections and methods may also come into play as we give lighting fixtures, security, and access control devices IP addressing in the BAS. There are several exceptions that narrowly bound the field conditions where it might be OK that also require physical barriers and separation distance, and there is also an exception under 725 if Class 1 wiring methods are used, which also is quite clear about minimum wire gauge (16 or 18) and insulation rating (600) - NEC2005 clearly also says de-rating methods shall not be allowed.

Not sure what NEC2008 might have that varies the game, haven't looked yet. But then it would fall back on what version the juristicion State is currently adopting anyway.

If the plant mechanics want you to either deviate from the Code, or exploit a loop hole, I would suggest you get it in writing and signed off by a responsible party at the plant (how often would management back the loop hole in the case of safety standards or process performance "vulnerabilites" ?).

IEEE 518 and 1100 may also be helpful, along with TIA/EIA 862.

I have never seen an exterior residential condensing unit with two electrical conduits attached, they only ever have one, it would be carrying 230V and 24V conductors.

It seems that often times the low voltage control wire is simply zip tied to the insulation of the refrigerant lines?

If the low voltage relay wires are in with the power, this is probably a code violation since it is unlikely that the furnace/ac installer ran those wires in compliance with a chapter 3 wiring method and the exceptions that were in my original reply.

Around here, the installers cable tie the low voltage cable to the sealtight conduit as permitted in 300.11(B)(2)

I see a problem brewing when the Class 2 wiring is tied to the "sealtight" due to the fact that the conductors are exposed to sunlight and most of these installations are installed this way using a two conductor cable that does not have a sunlight resistant jacket.

Ann,

Most of the manufacturer's cut sheets say more or less the same thing RE field wiring.

For example:

Q

Power Supply
1 All wiring should be made in accordance with the
National Electrical Code. Consult the local power company
to determine the availability of sufficient power to
operate the unit. Check the voltage at power supply to
make sure it corresponds to the unit’s RATED VOLTAGE
REQUIREMENT. Install a branch circuit disconnect
near the rooftop, in accordance with the N.E.C.,
C.E.C. or local codes.

- and -

Hook-Up
POWER WIRING MUST BE RUN IN CONDUIT. Conduit
must be run through the connector panel below the service
cover and attached to the bottom of the control box.
If low (extra-low in Canada) voltage control wire is run in
conduit with power supply, Class I insulation is required. If
run separate, Class II is required. Low voltage wiring may be
run through the insulated bushing provided in the 7/8 " hole
in the connector panel then routed to the control box.

EQ

http://www.mcquaybiz.com/mcquaybiz/literature/lit_ch_cu/IMOM/IM909-RCS6-7Tons.pdf

What actually happens in the field may well be a different story.

Offhand, I don't know of any NEC requirement for the Class 2 conductors for the outside unit to be sunlight resistant if exposed, nor I am I aware of a requirement for a wet location listing. Can anyone post a code reference?

Maybe it is just a Florida thing but they use sunlight resistant thermostat cable around here.
I assumed it all was. A am not sure about the "wet" listing but since it doesn't have paper packing I am not sure why it wouldn't be. PVC is water tolerant.
The real issue I have heard about is "riser" and "plenum" ratings when that is appropriate.
You might have trouble if you needed plenum, wet and sunlight in one cable.

Not sure about UV ratings or wet environment applications to the example given with an AC unit, but it would seem to apply in some way. But then we could have an entire lengthy separate post / comment thread about the difference between best practice, industry standards, NEC compliance, and what really happens in the field...

With respect to this business of zip-tying Low Voltage to refrigeration lines or the power feed flexible conduit, I would think there may be issues to the whole business of Low Voltage being required to be properly fixed to the building. For example it seems Low Voltage can not be zip-tied to the exterior of conduit or suspended ceiling suppport wires inside the building, so why would it suddenly be OK outside?

We might want to follow this:

http://ecmweb.com/nec/whats_wrong_here/whats_wrong_000409/index1.html