Of the suggestions, it looks like the one that will work is Daring
Dufas's relay in a box suggestion.
It meets all my requirements:
easy to mount as it comes in it's own box
15 amps so controlling outlet on 15 amp circuit is OK
takes 24V input
available online for $21
One remaining question. Someone mentioned isolation of the 24V
circuit from 120V circuit? I would assume that since an electrical
equipment manufacturer is making these relays and they are UL listed
they are OK and meet code for my application even though the 24V wires
obviously go into the same box as the 120V wires?
Thanks again for the suggestions
If there is not separation between line and low voltage compartments within
the enclosure, I would recommend connecting line voltage conductors to the
low voltage terminals, then run them outside the enclosure through a
knockout, where you can splice them to typical low voltage conductors.
When you have "low voltage" conductors in the same box as line voltage
the whole low voltage circuit needs to be treated as "class 1" which
means it needs to be treated the same as you would treat the line
voltage. Everything needs to be in a box, conduit or in a cable like
Romex, end to end.
When you have separation you can treat the low voltage side as "class
2" and you can take the liberties we usually have with "low voltage".
It is really a little more complicated than that but you see what the
general implications are.
On May 12, 1:28 pm, firstname.lastname@example.org wrote:
I think I may see an out here. Upon closer inspection of the
datasheet, the "relay in a box" that I want to use has what appears to
be a plastic divider inside the box that seperates the low voltage
section from the line voltage. Essentially it's like two seperate
sections. Does this make it OK to use as I intended?
Here's a pic and the datasheet:
I also looked at their app notes and they sure show a lot of
applications where similar relays are being used in end user type
installations as opposed to OEM.
On May 12, 1:28 pm, email@example.com wrote:
I wonder how it is that hvac components don't cause this issue.
Inside air handlers and outside units there is both 24vac and
110/220vac circuits. There is no specific separation of the wiring
inside the units. Low an dhigh get co-mingled all over the place
inside the units. And the 24vac wires go between units and the
thermostat without any special treatment. Does the brown jacket on
the low voltage wires count as satisfying the "class1" requirement?
Is all that is required a 2nd insulation layer like house wiring?
Because it would be easy enough to use thermostat wire for the low
side of whatever it is he is doing.
"725.136-D Associated systems within enclosures
Class 2 and 3 circuit conductors in ...boxes... shall be permitted to be
installed with electric light, power... circuits where they are
introduced solely to connect the equipment connected to Class 2 and
Class 3 circuits, and where (1) OR (2) applies:
(1) The electric light, power... circuit conductors are routed to
maintain a minimum of 0.25 in. separation from the conductors and cables
of Class 2 and Class 3 circuits."
The separation required is 1/4" between conductors. The class 2
conductors can attach to the relay in Dufas's relay box as long as they
are kept 1/4" from power wires
Using a barrier is another method (725.136-B).
There should not be a problem with using a listed relay/contactor in a
listed box (where the combination is not listed together).
The relays that gfretwell and John showed take minimal space in normal
boxes, which makes them easy to use in normal wiring (in addition to
having the low voltage wires outside the box). It is an advantage if
they are installed where exposed (like a basement) to replace the relay
in the future. Both are available as 2 wire or latched (momentary) versions.
This is generally read to say that the entire class 2 system is inside
that enclosure. You can't take a wire out of there to another place
and still call it class 2.
The handbook commentary on that section says
"Power circuit and Class 2 circuit conductors can be permitted in the
same motor-starter enclosure, where the Class 2 circuit source is the
secondary of a control transformer in the same motor-starter
enclosure. In such an installation, the Class 2 conductor insulation
is not required to have the same voltage rating as the insulation on
the power conductors in the same enclosure."
There is plenty of confusing language in 725. I think the whole thing
should be evaluated and parts totally rewritten. You really have to be
careful cherry picking out a few lines and believing that applies to
your installation. Generally speaking you really need separation
between class 2/3 and line power circuits. That is why they have class
Things that go on inside listed equipment do not necessarily apply to
things you assemble yourself. Even there, the use of barriers is
becoming the norm. The barrier itself may just be a little piece of
mylar that the installer throws away but it was there when the product
was listed. You also have to remember, cable jackets provide
separation, so if the terminations are separated, the jacketed cable
can go through the box.
That also means you CAN pull a low voltage cable and line voltage
cable in the same raceway,as long as you have separation where they
Hold your nose legal ... Pull your CAT5 and Romex through the same
conduit, extend the CAT 5 through the box and terminate it in a LV
ring next to the box. Some might argue that you need a separation
between the place where you split open the RX jacket and the exit of
the CAT 5 but if you went in and out in the back of the box with the
LV cable, stuffed in a mylar insulator and split the RX jacket on the
outside of that you comply.
A little dodgier is CAT 5 and THHN in the same pipe. Most AHJs will
not let that fly.
If the wires can't leave the box there is no particular usefulness in
being class 2 - they can be class 1.
The section quoted above says class 2 wires are "introduced solely to
connect the equipment". Reasonably read, "introduced" can mean to enter
the enclosure from the outside.
It is common practice for class 2 thermostat wires to enter a
"compartment" in a furnace/boiler where there are exposed insulated
power wires. IMHO the section I quoted allows that practice if the class
2 wires are kept separate from the power wires.
I dug out an old copy of UL913 which is for intrinsically safe
apparatus. As you are no doubt aware, intrinsically safe wiring is a lot
touchier than class 2. The standard has several methods to separate
field wiring terminals for intrinsically safe circuits from power
wiring. One of the methods is to separate the terminals by 2" (and
there are requirements for insulation rating and securing the wiring).
Intrinsically safe wiring can be in the same enclosure (like a control
panel) as the power wiring and terminate in the enclosure. The
intrinsically safe wiring is certainly intended to leave the enclosure.
Doesn't say the wires can't leave the box.
Separation? Like the 1/4" specified in the section I quoted?
725.136-A says class 2 (and 3) wires can't be in the same box,
compartment, raceway, ... with power and light wiring - *except* as
permitted by 725.136-B through I.
Several of these provisions (B, C, G) allow the combination if class 2
wiring is separated by a physical barrier. The clear intent to me is
that the barrier allows the class 2 to remain class 2. IMHO D-1, which I
quoted, similarly allows class 2 to remain class 2.
The section I quoted, 725.136-D, essentially has 3 parts (I quoted only
the first). Class 2 wires are allowed in an enclosure if it meets any
*one* of the parts
- separation of power and class 2 wires by at least 1/4"
- specified class 2 cable jacket and separation or barrier for wires
outside the jacket
- else the class 2 circuit becomes a class 1 circuit.
Becoming class 1 is a possibility, but only if one of the first 2
provisions is not met.
For listed complete products the instructions from the manufacturer,
based on UL requirements, predominate.
If I put a UL listed contactor/relay in an appropriate box, and the
installation follows the listing for the contactor/relay, I don't see
why the NEC does not apply - specifically 725.136-D-1. What is the
You have posted that previously and it seemed quite reasonable.
When I looked at 725.136, it looks like class 2 and power can be in the
same raceway *if* the power (or class 2) is wired in UF (725.136-I).
What allows class 2 and Romex? Do the jackets constitute a "barrier"
It would allow the use of a class 2 listed transformer.
Again this is a listed assembly and I bet a new one has some kind of
plastic barrier when it is shipped. It may not make it through the
installation process and electrical inspectors don't really look
inside that equipment.
It is an interesting question I will bring up with the IAEI..
You can certainly try it and see what your AHJ says but I doubt it
would fly with any inspector I know.
A lot depends on how that part is listed
BTW there are plenty of inspectors who say I am wrong about this "both
in the same pipe" thing. They are far more restrictive about how class
2 and line voltages need to be separated.
On May 13, 7:32 pm, firstname.lastname@example.org wrote:
I'll have to pay more attention next time I have one of my ac's or
heat pumps opened up. I've never noticed any plastic separators even
in a new unit. On straight AC the only 24vac is to pull the main
relay. That starts the whole thing up. On a hneat pump you have that
as well as 24vac switching the unit between airconditioning and heat.
IMHO "introduced" clearly allows external class 2 wires to enter a box
to connect to "the equipment connected to Class 2 ... circuits".
As I said in my previous post, 725.136-D has 3 options for class 2
wiring entering a box that has power wiring. Separation by at least 1/4"
is one option. Only if the first 2 options are not used does 136-D
explicitly require the class 2 wiring be class 1.
I agree that it is listed apparatus and should generally be beyond your
purview (if wired according to manufacturer instructions). But it is
compliant with what I understand is permitted by 725.136-D (class 2 and
power wires in the same "compartment").
The AHJ would be arguing with what is explicitly allowed by UL.
And, IMHO, what is allowed by 725.136-D.
But inspectors enforce the same code.......
I thought your options sounded reasonable.
IMHO 725.136-I clearly allows THHN power wires in the same raceway with
class 2 that is in UF. Now if they would just make #18 UF...
I always liked taping UF with class 2 to the power conduit for
installations like external condenser/compressors.
OMG - a virtual red tag.
No sure I was clear on what I meant. When I was installing them long ago
I used sealtite conduit for power. (Or Minneapolis allowed, and probably
preferred back then, flex.)
I suggested tying class 2, in UF, to the sealtight - which is allowed
I would rather keep the wiring away from the refer guys, but reading
your post reminded me that I tied the UF to the insulated low pressure
line - the hole the refer guys put into the house was too convenient.
I wouldn't want to run power and class 2 in the same raceway even if
=====================If I remember right, a couple people linked to your website for the
drill rig explosion/fire. Nice piece.
A "Class 2" xfmr is simply a double-insulated transformer without an earth
ground on its plug, nor a polarized plug.
A "Class 1" xfmr requires a third wire, the earth ground pin on its plug.
The "Class of xfmr is a UL/CSA et al classification which approves the xfmr
and nothing else as safety approved. Secondary ckts attached to the output
of a xfmr are not subject to UL/CSA et al safety testing unless a voltage in
it equals or is more than 42VDC or 42V ac p-p. The original spec, UL1459
(now superceded but not changed in this area) is online for those who wish
to read it. I -think- the CSA spec was CS-03.
Whatever class 1 & 2 means ckt-wise, I don't know; it's not a UL/CSA et
al type spec but might be NEC, NFPA or otherwise.
The primary characteristic of class 1, 2, and 3 power sources is that
they are power limited. There is a specified maximum voltage, current
and power you can get from the source. For a class 2 24V transformer the
max current is 8A - the maximum current you get if you short circuit the
Because the power is limited, the downstream circuit does not have to
meet the general wiring requirements of the NEC. Article 725 is used
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