DIYbanter - View Single Post - Suggestion for 24V/120V relay to control new outlet?

Bud--

wrote:
On Thu, 13 May 2010 09:43:48 -0500, bud--
wrote:

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.
"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).

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There should not be a problem with using a listed relay/contactor in a
listed box (where the combination is not listed together).

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.

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.

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."

Doesn't say the wires can't leave the box.

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
1.

Separation? Like the 1/4" specified in the section I quoted?

Cherry picking?

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.

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.

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
violation?

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
terminate.

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.

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"
(725.136-B)?

--
bud--