Armored wiring for a 24 VAC system

EdwinD

I'm configuring a Pressuretrol and Vaporstat for a 24 VAC system steam boiler.

Can I use aluminum armored wiring for a 24 VAC system? If so, what size?

Thanks

Jamie Hall

Frankly, I wouldn't use aluminium wire for anything -- 24 vac or no. Use copper wire.

ratio

I think @EdwinD means Al jacketed MC or possibly Al FMC with Cu conductors? In which case local codes might say otherwise, but other than that should be just fine. #14/2 MC is good for 15A under most conditions, a 40 VA xfrmr is good for nearly 2A; way overkill but not too hard to come by. #16 TFFN in 3/8" flex would look nearly the same but probably cost more in the end, accounting for the labor spent in sourcing it. Normal stat wire in 1/2" flex could be done from a Big Box store and might be the cheapest way to get it done.

EdwinD

@ratio @Jamie Hall Correct, jacketed is what I want. I'll go with Normal stat wire in 1/2" flex. Thanks!

HVACNUT

If you're referring to Greenfield aluminum flexible conduit, that's fine. You can sleeve regular thermostat wire or THHN through it.
You just can't sleeve 24v low volt thermostat wire in the same conduit with line volt unless they are of the same gauge, usually #14 or larger.

EdwinD

@HVACNUT Thanks! I want wire already sleeved, so I guess Greenfield aluminum flexible conduit is what I need? Whats the smallest size I can use?

ratio

Flex is empty, you have to add the wires you need. MC cable has a number of conductors in it, most common is #12 gauge solid, but it is available with #14, and stranded, conductors; likely a special order at an electrical supply house. You probably don't really want to use MC cable.

HVACNUT

Greenfield with wires already sleeved is called B/X. Residential is usually 3/8" clad. You can get up to 4 conductors with #14 wire.
14/2, 14/2 with ground wire, 14/3, 14/3 with ground, etc.
Use 1/2" straight or 90° angle connectors.
The big box stores have it packaged to length. 25'- 50' etc.
Also invest in a B/X cutter and buy a bag of "Red Heads" insulators so the metal doesn't cut into the wires.

EdwinD

Fantastic. You guys are really helpful! I'll mull my options. Thanks!

EBEBRATT-Ed

@EdwinD

I would recommend 3/8" or 1/2" flex either made of steel or aluminum. If it is aluminum you must use a "squeeze" type connector that won't damage the aluminum jacket. You can use straight or angle connectors or 45 deg connectors. It's better to use stranded connectors with crimp on sta kons. It's just a better job than solid wire.

EdwinD

@EBEBRATT-Ed Got it! Thanks for your input! Stranded connectors with crimp on is what I prefer. All appreciated.

Steamhead

HVACNUT said:

If you're referring to Greenfield aluminum flexible conduit, that's fine. You can sleeve regular thermostat wire or THHN through it.

You just can't sleeve 24v low volt thermostat wire in the same conduit with line volt unless they are of the same gauge, usually #14 or larger.

Actually, IIRC all the wire in this type of installation has to be insulated for the maximum voltage that will be encountered therein. In this case that would be 120 volts. So, even the wire carrying 24 volts must have insulation rated for at least 120 volts.

Ordinary circuit wire, as found in Romex or MC (formerly BX) cables as well as conduit installations, is rated for 600 volts. That's more than enough. However, I don't think the usual thermostat wire is rated for much more than 50 volts. If that's true, you can't put it in the same conduit or flex as 120-volt wiring.

JUGHNE

Whatever wire you use, stranded #14 with crimp connections is the most user friendly now and in the future when pigtails have to be removed. Solid wire puts some strain on the small control screws.

Steamhead, years ago I was called on running 24 volts in raceway with 240 volts. All insulation was rated for the nominal 600 volts. The issue was the class of transformer providing the 24 VAC. IIRC there are 3 classes. The class is determined by the over current protection for the transformer.
I guess the scenario could be insulation failure of both circuits inside the raceway. Feedback thru the transformer could cook the other controls in the air handler/furnace.
That is why we have that too small of a JB in outside equipment for the t-stat wire to splice. Apparently equipment manf. are allowed the distance to the compressor contactor.

Anyhow, since the red tag call I have always kept the voltages in separate raceways. (easier than studying the NEC book).
Also, there may be more than one disconnect for the sources.
Digging into a J-box when you are sure it is only 24 volts can produce some unique notches in your tools.

Steamhead

That may have been a local thing. Inspectors here are OK with it.

EdwinD

@HVACNUT @Steamhead @JUGHNE @ratio @EBEBRATT-Ed @Jamie Hall

Aluminum Cable Thhn 14 Ga (see link), is what I'm considering. I wasn't intending to sleeve wiring thru a conduit.

I'd like to pigtail existing wiring which currently doesn't travel very far (it's attached to existing Pressuretrol at the front side of unit) then pigtail to the aluminum cable and run further back to where I'm installing 1st to Probe LWCO, then travel to top back side of case, then wire Vaporstat and then to the new Pressuretrol
see attachement - blue line represents run of cable. I'll be removing the manual LWCO and old pressuretrol device

Does that make sense? Thoughts?

https://www.amazon.com/gp/product/B000BQUQLQ/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Jamie Hall

That ought to work -- just make sure that everything is properly wired in series! Also, though it doesn't affect function, the neater you can run the wiring the happier you will be...

EdwinD

Thanks @JamieHall
I totally agree about the neatness factor. I want to get it in tip top shape. I'll circle back to share how it all turned out with pics and such. Waiting on parts.

Thanks everyone!

JUGHNE

If you are doing some type of flex, I have found it simpler to mount a 4" square box on the boiler jacket and send a single flex to each device. Some controls have only a single knockout and room for 2 wires.
I use 3/8" flex conduit and run the 14 GA stranded wire inside and loop thru the J-box up to the next control, etc. Fewer splices make for easier wiring and troubleshooting.

EdwinD

@JUGHNE Great advice. I was thinking along those same lines. Thanks!

JUGHNE said:

If you are doing some type of flex, I have found it simpler to mount a 4" square box on the boiler jacket and send a single flex to each device. Some controls have only a single knockout and room for 2 wires.
I use 3/8" flex conduit and run the 14 GA stranded wire inside and loop thru the J-box up to the next control, etc. Fewer splices make for easier wiring and troubleshooting.

EBEBRATT-Ed

@JUGHNE That 24 volt thing in the same raceway with 120-600 I don't see an issue as long as all the wire is 600 volt.

But your right.

I have never understood article 800 or whatever it is nor have I ever had anyone be able to explain it to me successfully what the problem is. Maybe I am just dumb. But @Steamhead is right it depends on location as to how it's enforced, it shouldn't be, I wish the code was clearer on this because it has always been and I guess will always be an issue.

For me I try and keep it separated as much as possible. But as "much as possible" depends on how much money it will cost me and how likely I think I will be caught LOL

EdwinD

JUGHNE said:

If you are doing some type of flex, I have found it simpler to mount a 4" square box on the boiler jacket and send a single flex to each device. Some controls have only a single knockout and room for 2 wires.
I use 3/8" flex conduit and run the 14 GA stranded wire inside and loop thru the J-box up to the next control, etc. Fewer splices make for easier wiring and troubleshooting.

@JUGHNE Question:

If I run a single flex from the J-box to each device, how would this work in a series? I like your idea, just not sure how to do it.
I was planing on running a series in the following order

1) J-Box
to
2) Probe LWCO
to
3) Vaportstat
to
4) Pressuretrol
to
5) J-box

1) Connect the hot (red) from transformer to BX-cable red conductor
2) route BX cable and connect hot wire to 1st terminal in probe LWCO,
3) next connect a separate BX cable hot wire to 2nd terminal probe LWCO and route to 1st terminal on Vaportstat,
4) then hot wire 2nd terminal of Vaporstat then route and connect to first terminal of Pressuretrol
5) lastly connect neutral wire to 2nd terminal of Pressuretrol, then connect to neutral wire (white) in J-Box.

Is this correct ? Is there an easier way?

The old LWCO is being taken out.

See attached: flex cable, transformer for 24 volt wiring, and existing wiring for existing (old) pressure device.

EdwinD

EdwinD

Add'l info - vapour boiler - Weil-McClain EG-55

Probe: https://www.supplyhouse.com/Hydrolevel-SAFGARD-400-Electronic-Low-Water-Cutoff-24V-Steam
Vaportstat: https://www.supplyhouse.com/Honeywell-L408J1009-Vaporstat-Controller-Steam-0-to-16-oz-in2
Pressuretrol: https://www.supplyhouse.com/Honeywell-PA404A1033-Pressuretrol-1741000-p

hot_rod

why not just low voltage wire, like 16 ga plenum wire? Stranded copper with aluminum jacket and plastic coat? Does 24V need to be in any conduit?