Thread: Low Voltage routed with High Voltage

When you see the low voltage control wiring for an HVAC system routed through the furnace cabinet in the same knockout opening with the high voltage cable (same clamp), is this considered a defect? If so, could someone provide me the code that would support this.

Thank,s
Rob

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Originally Posted by RobertSmith

When you see the low voltage control wiring for an HVAC system routed through the furnace cabinet in the same knockout opening with the high voltage cable (same clamp), is this considered a defect? If so, could someone provide me the code that would support this.

Thank,s
Rob

That would fall under a manufacturers installation requirement and not a code. I don't see why it would be a problem.

Now finding low voltage in an high voltage electrical panel is different issue.

is this considered a defect?

Yes

If so, could someone provide me the code that would support this.

E4204.1 Separation from other conductors.

In cables, compartments,

enclosures, outlet boxes, device boxes, and raceways,
conductors of Class 2 circuits shall not be placed in any
cable, compartment, enclosure, outlet box, device box, race-

way, or similar fitting with conductors of electric light, power,
Class 1 and nonpower-limited fire alarm circuits.
Exceptions:
1. Where the conductors of the electric light, power,
Class 1 and nonpower-limited fire alarm circuits are
separated by a barrier from the Class 2 circuits. In
enclosures, Class 2 circuits shall be permitted to be
installed in a raceway within the enclosure to separate
them from Class 1, electric light, power and
nonpower-limited fire alarm circuits.
2. Class 2 conductors in compartments, enclosures,
device boxes, outlet boxes and similar fittings where
electric light, power, Class 1 or nonpower-limited fire
alarm circuit conductors are introduced solely to connect
to the equipment connected to the Class 2 circuits.
The electric light, power, Class 1 and
nonpower-limited fire alarm circuit conductors shall
be routed to maintain a minimum of

1/4 inch (6.4 mm)

separation from the conductors and cables of the
Class 2 circuits; or the electric light power, Class 1
and nonpower-limited fire alarm circuit conductors
operate at 150 volts or less to ground and the Class 2
circuits are installed using Types CL3, CL3R, or
CL3P or permitted substitute cables, and provided
that these Class 3 cable conductors extending beyond
their jacket are separated by a minimum of

1/4 inch

(6.4 mm) or by a nonconductive sleeve or

nonconductive barrier from all other conductors.

E4204.2 Other applications.

Conductors of Class 2 circuits

shall be separated by not less than 2 inches (51 mm) from conductors
of any electric light, power, Class 1 or nonpower-limited
fire alarm circuits except where one of the following
conditions is met:
1. All of the electric light, power, Class 1 and
nonpower-limited fire alarm circuit conductors are in
raceways or in metal-sheathed, metal-clad, nonmetallic-
sheathed or Type UF cables.
2. All of the Class 2 circuit conductors are in raceways or in
metal-sheathed, metal-clad, nonmetallic-sheathed or

Type UF cables.

E4204.1 Separation from other conductors.

In cables, compartments,

enclosures, outlet boxes, device boxes, and raceways,
conductors of Class 2 circuits shall not be placed in any
cable, compartment, enclosure, outlet box, device box, race-

way, or similar fitting with conductors of electric light, power

Then how do you place the thermostat wire into the unit if it can not be placed in the compartment or enclosure?

This is one of those code items that just does not make much sense. Or I should say it does not make much sense to me. I still say the manufacturer would be the one to go to on this and not the code.

Then how do you place the thermostat wire into the unit if it can not be placed in the compartment or enclosure?

Scott
The OP's question was about using "same knockout opening ". It is not allowed to feed the LV cable and the A/C througe the same knockout.
But the cables are allowed to share a cabiner/ enclosure in some cases.
Note the exceptions.

"High Voltage" is not permitted in a residence, & 600V and less is considered low voltage, it would be better to refer to low voltage & line voltage conductors mixed together.

"High Voltage" is not permitted in a residence, & 600V and less is considered low voltage, it would be better to refer to low voltage & line voltage conductors mixed together.

You are correct. Which is why I refered to it as " A/C", not high voltage.
It is somewhat confusing though.
I have a "Low Voltage" license. It allows me to work on 30 volts or less, but phone line voltage can be as high as 90 volts, yet I can also work on them. Go figure.

Thanks everyone.

I'm trying to convince a city inspector that 120v can not be routed through the same knockout opening with the low voltage control wiring.

Rob

Originally Posted by RobertSmith

Thanks everyone.

I'm trying to convince a city inspector that 120v can not be routed through the same knockout opening with the low voltage control wiring.

Rob

Tell him/her to look at the installation instructions - the manufacturer will show separate entries for them too - which puts it to 110.3(B) as a back up for those who do not know or understand the main code and reasons.

I often see 2 or more conductor thermo wire routed neatly thru sealtite from a j-box above into a switch and recpectacle mounted on the cabinet. From there it goes into it's seperate k/o, so what's the difference? it sure looks neater.

(bold red is mine)

Originally Posted by Mike Locurcio

I often see 2 or more conductor thermo wire routed neatly thru sealtite from a j-box above into a switch and recpectacle mounted on the cabinet. From there it goes into it's seperate k/o, so what's the difference? it sure looks neater.

And it is just as likely to cause a potential problem as having them both enter through the same opening, and NEITHER is any good, and BOTH are not acceptable.

What do you think would happen to a standard low voltage thermostat when energized with 120 volt to ground, or, worse yet, 240 volts between two of the low voltage cable conductors? Think it would survive in one non-smoldering, non-melted, still-on-the-wall piece?

What about the person who happened to be turning it on when that happened?

I simply do not get why some people will spend so much time and energy trying to defend something which is so wrong????