Low voltage wiring

tgallagher

Recently I have had a series of boiler that failed due low voltage wire being strapped to the copper does anyone have another way to run the wire? 

Intplm.

Encase the wire in "emt" pipe. Electromechanical tubing.
I'm guessing the copper pipe is getting hot and shorting the wires?

mattmia2

What? Did it cut through or soften the insulation and cause it to creep? Unless there is something sharp on the piping or it is some sort of wire with a jacket that softens easily, it shouldn't be a problem.

Do you mean you had to repair some control in the boiler?

EBEBRATT-Ed

It shouldn't be strapped to any pipe unless it is an electrical conduit. A pipe could be too hot and melt the insulation or be too cold and sweat and the water may damage the wire. Run it in EMT (electrical Metallic tubing) or or metallic flex (greenfield) or non metallic flex (plastic seal tight)

tgallagher

It seems that in NJ inspectors don’t want any control wire strapped to the heating pipe they claim the high temps will damage the wire I have never had an issue until now it’s been on 4 boilers now 

tgallagher

I will look into the metallic flex I was thinking about non metallic but the smallest size I could find was half and I think it will look sloppy 

Jamie Hall

You really need to determine the failure, and the root cause. While wire should not be strapped to pipe, unless the pipe was insanely hot (250 plus) it shouldn't have damaged the insulation enough to cause a short to the pipe -- and almost certainly not enough to cause a wire to wire short.

Did the wire break? Did the insulation actually get cut? Or is there any possibility of a voltage spike and an arc punching the insulation? You really need to know...

tgallagher

Nothing happened to the wire it was a new installation and that’s what the inspector failed me for. 

Jamie Hall

Ah. Well, in my humble opinion the inspector was right -- strapping wire to a pipe just isn't a good idea because the insulation does wear or get cut with not so good results.

mattmia2

I would use 1/2" rigid pvc or emt. flexible conduit looks sloppy, just support it with some straps to the equipment on one end and the joists or some blocking or unistrut at the ceiling or bend a 90 in it and support it with straps to the surface of the ceiling

rick in Alaska

I have seen this problem a lot. People strap the 12-2 stat wire to the supply line, and over time, the wire gets hot enough that it actually melts the insulation off the wire on the inside, but not the outside. Typically, the outside looks blackened, but not compromised. The wires on the inside will be bare for quite a ways, and shorting out. I had one job where there where multiple wires strapped like that, and I had to replace almost all of it. Sure wish he paid me for that job.......
Rick

ChrisJ

rick in Alaska said:

I have seen this problem a lot. People strap the 12-2 stat wire to the supply line, and over time, the wire gets hot enough that it actually melts the insulation off the wire on the inside, but not the outside. Typically, the outside looks blackened, but not compromised. The wires on the inside will be bare for quite a ways, and shorting out. I had one job where there where multiple wires strapped like that, and I had to replace almost all of it. Sure wish he paid me for that job.......
Rick

You guys using 12-2 for thermostat's up there in Alaska?

mattmia2

Apparently t-stat wire is cl2 and cl2 is only 60c so a bit of a standoff with insulation or tubing or virtually anything would solve the problem but if the inspector is failing it then you need to find another route.

ChrisJ

How about some pictures of installs showing how you ran the low voltage wire to the pumps?

That may help him and others out.

I can't see running EMT etc to a pump and honestly don't recall ever seeing that at least not on residential installs.

How about some 1/2" Armaflex on the pipe and simply zip tie the low voltage wire loosely on the outside of the insulation? I come up with a surface temp of 112F worse case under those conditions.

JUGHNE

There is some means of getting the 120 to the boiler, EMT or Flex.
Often the tstat wire is cable tied to that raceway.

However, in the past, some AHJ here determined that those 1-2 cables could cause overheating of the 120 circuit inside the pipe.......common sense finally prevailed.
Apparently some cable guy tied many cables to some pipe, totally enclosing it and it did overheat.

ChrisJ

JUGHNE said:

There is some means of getting the 120 to the boiler, EMT or Flex.
Often the tstat wire is cable tied to that raceway.

However, in the past, some AHJ here determined that those 1-2 cables could cause overheating of the 120 circuit inside the pipe.......common sense finally prevailed.
Apparently some cable guy tied many cables to some pipe, totally enclosing it and it did overheat.

True,
That's how I did all of mine, it's just ziptied to the MC I ran.

But, what if you have pumps and want a nice way to run the low voltage. That's what I assumed the op is talking about. Not directly to the boiler.

pecmsg

What low voltage is going to the pumps?

ChrisJ

pecmsg said:

What low voltage is going to the pumps?

*shrug*
I assumed they used low voltage to turn the pumps on and off, or something.
I'm not a HW guy.

In that case, zone valves.

Regardless, I think it would help the OP to see some examples.

JUGHNE

You could secure a length of EMT from the ceiling with a strap and then a pair of Mini-pipe clamps bolted together to secure the other end to the copper.

Or a pair of the mini-pipe clamps to run an EMT pipe parallel to the copper and slip the control cable down the EMT. The EMT and copper would have about an inch between them. There are neat looking push on EMT bushings with low voltage in mind. One on each end.

I have seen plenty of pictures here of bad examples.....just let er hang all the over the place. To the extent you have to lift control cables up just to walk around the boiler.

ratio

When I started in the electrical trade (last century!), it was verboten to strap low voltage wire to a raceway or conduit. Got into many a pissing match with low voltage guys over that, but our inspectors wouldn't let it fly. (Actually had to cut a wire once or twice, when they kept tying it back onto the raceway.) Some time in the last code revision or two it became allowed for associated wiring to be tied on to the feeder raceway to the equipment.

rick in Alaska

"You guys using 12-2 for thermostat's up there in Alaska?" Yeah , you know it is so cold up here that the electricity won't flow unless it is a really big wire. You know, friction loss and all.
I have been so good proofreading all my posts, and the first time I missed, you had to catch it
Think I will try some of that 18-2 you guys use.
Rick

JUGHNE

For a gas furnace I would put the doorbell transformer on the furnace disconnect box. Hopefully that one extra 18-2 is permitted or overlooked.

ChrisJ

rick in Alaska said:

"You guys using 12-2 for thermostat's up there in Alaska?" Yeah , you know it is so cold up here that the electricity won't flow unless it is a really big wire. You know, friction loss and all.
I have been so good proofreading all my posts, and the first time I missed, you had to catch it
Think I will try some of that 18-2 you guys use.
Rick

Sorry, I couldn't let that one go.

Besides.............I'm sure on a 500 foot run 12-2 would be beneficial.

Zman

I wonder if you picked up a roll of wire with a low temp rating.
This product is a great way to clean up low voltage wiring. https://www.alliedelec.com/cable-management/wire-duct-raceway-tray/

EBEBRATT-Ed

For the most part strapping CL2 or 24 volt wiring on the outside of an electrical pipe is not allowed

However, the code allows it if the pipe it is strapped to and the wiring inside the pipe and the low voltage on the outside are associated with the same piece of equipment.

So a pipe going to a boiler, furnace air handler etc can have it's low voltage wiring strapped to it.

See 725.143 support of conductors &

300.11(C) (2)


from the 2017 NEC

tgallagher

For now I’m going with the strapping of the 24 wire to the outside of the high voltage EMT until I find a better way @EBEBRATT-Ed is that the most update version of the NEC cause I searched in the mechanical code and I couldn't find anything but I didn't look into the NEC which is a code book that I might have to buy 

EBEBRATT-Ed

@tgallagher

The 2020 NEC is out now but not all states have adopted it yet. MA is on the 2020, CT is on the 2017. I don't keep up with the other states some are still on 2014 and some on on older codes than that.

Depends what your state has adopted


Low voltage wiring has always been in the NEC but years ago was seldom enforced, but as usual with all the alarm and security wiring guys and cable guys making such a mess ( I have seen so much wire laying on ceiling tiles on commercial jobs you can't lift the tiles out) that they had to start enforcing stuff.


My other pet peeve is the low voltage that gets run out to a condensing unit is just strung out their through a hole in the wall. That stuff isn't weather proof. It should be in seal tight to protect it from the weed wackers

mattmia2

My mom's condenser installed in the 80's is wired with flex with something like thw in it. I don't think liquidtite existed at that time. The t-stat wire is just fine after 30 years in the sun. There are lots of parts of it that it would be inadvisable to get a weed whacker near.

ChrisJ

mattmia2 said:

My mom's condenser installed in the 80's is wired with flex with something like thw in it. I don't think liquidtite existed at that time. The t-stat wire is just fine after 30 years in the sun. There are lots of parts of it that it would be inadvisable to get a weed whacker near.

I used Belden brand wire but don't remember the exact stuff. It was 16 gauge 4 conductor and most likely PVC inner and outer insulation. I strapped it to the liquid line's armaflex and then it all got a good heavy coat of latex paint to protect from the sun.

I have many complaints about things around me but that low voltage wire isn't on the list. The outer PVC jacket covered in latex paint is more than "weather proof" in my book.

Jamie Hall

A very minor addition to @EBEBRATT-Ed 's comments. Although many of the "smart home" devices now are connected via wifi -- which brings its own little bundle of joy to the mix -- some are still connected, and the wifi is connected to the internet, with hard wiring. That hard wiring needs to be shielded from other wiring, or at least twisted pairs -- low voltage or line voltage -- to prevent problems from stray signals

ChrisJ

Jamie Hall said:

A very minor addition to @EBEBRATT-Ed 's comments. Although many of the "smart home" devices now are connected via wifi -- which brings its own little bundle of joy to the mix -- some are still connected, and the wifi is connected to the internet, with hard wiring. That hard wiring needs to be shielded from other wiring, or at least twisted pairs -- low voltage or line voltage -- to prevent problems from stray signals

We buy cable specifically made for this purpose, CAT5E and CAT6.

EBEBRATT-Ed

Just because everybody does it that way doesn't make it code compliant. There isn't any building on earth that you can't walk through that you can't find something wrong.

I just don't thing running class 2 wire outdoors is the way to go. I usually drill a hole in the house for 3/8 or 1/2 " seal tight, just stick it through the hole and put a minerlac on the seal tight on the inside so it can't be pulled out, run it over to the condensing unit with a connector on it

mattmia2

Technically if the low energy wiring's insulation is rated for the line voltage you can run it in the same raceway as the line voltage wiring if it is controlling the equipment the line voltage wiring powers(I would have to look up the exact wording of the exception).

SuperTech

pecmsg said:

What low voltage is going to the pumps?

Pumps like the Viridian VT2218 have sensors for the supply and return.  I don't see any way of them working without being strapped to the pipe.

Zman

In the commercial HVAC world, all controls wiring is shielded and in conduit. Sensors are installed in wells with J-Box to make the transition.
That being said, I have seen very few problems with t-stat wires strapped to pipes, as long as no one gets careless with a torch.
The biggest issue I see with low voltage wiring in residential jobs is line voltage interference with the new smart t-stats.