Wiring Method LV Swith

mstrlucky74

Senior Member
Is switch is recessed in gyp wall what would you use as your LV wiring from switch to ceiling? LV cable with a conduit stub up? Can't use MC cable as that's 600v, correct?
 

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blkmagik21

Senior Member
You can use MC. It's for up to 600 volts but I would do conduit and then run CL3/CL2 riser rated 16-2 or 14-2 stranded cabling.


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hbiss

EC, Westchester, New York NEC: 2014
Everything south of the "power pack" is LV CL2 wiring. Nothing says that you couldn't use MC to the switch but why would you? Thermostat wire would be fine, either dropped down the partition or in a stub up conduit from the switch box into the ceiling.

-Hal
 

mstrlucky74

Senior Member
Everything south of the "power pack" is LV CL2 wiring. Nothing says that you couldn't use MC to the switch but why would you? Thermostat wire would be fine, either dropped down the partition or in a stub up conduit from the switch box into the ceiling.

-Hal
Yes but the wire has to be protected within the wall by conduit or an armored cable like MC. Can't just run tstat wire or any other wire down the wall. So my question is why a conduit stub instead of MC cable? I think MC would be quicker.
 

gadfly56

Senior Member
Yes but the wire has to be protected within the wall by conduit or an armored cable like MC. Can't just run tstat wire or any other wire down the wall. So my question is why a conduit stub instead of MC cable? I think MC would be quicker.
Sez who? What's the diff with that and Romex?
 

hbiss

EC, Westchester, New York NEC: 2014
Yes but the wire has to be protected within the wall by conduit or an armored cable like MC.
Sez who? Not the NEC. If your job specs call for it, it's customary to run conduit from the box up into the ceiling (stub up) and pull a CL2 cable into it. What are you doing with the data and communication drops?

-Hal
 

blkmagik21

Senior Member
Why would you do conduit? Thanks.
Most commercial building require emt stub ups for low voltage. If it's not required on your project then just run 16-2 stranded CL2/CL3 Riser rated UL listed wire.

With low voltage power circuits stranded wire is always recommended as it has more throughout than solid wire of the same size. Especially in lower voltages.


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blkmagik21

Senior Member
What??

-Hal
Electricity doesn't flow through copper, it flows on the surface of copper. Therefor stranded 16 AWG wire has more surface wire on all the individual strands than a solid wire of the same size. This is called the skin effect in electrical theory books.


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gadfly56

Senior Member
Electricity doesn't flow through copper, it flows on the surface of copper. Therefor stranded 16 AWG wire has more surface wire on all the individual strands than a solid wire of the same size. This is called the skin effect in electrical theory books.


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No, stranded wire has the same issue as solid, unless it is Litz wire, plus in the same gauge size it has very slightly lower total cross sectional area. The skin effect is the result of back EMF generated by AC at the interior of the cable, solid or stranded. On yet another hand, the skin depth for copper at 60 Hz is given as 8.5 mm, so for the conductors in play here, negligible. For DC there is no skin effect. And you couldn't pay me enough to do any significant amount of wiring with stranded, it's just such a PITA.
 

GoldDigger

Moderator
Staff member
Electricity doesn't flow through copper, it flows on the surface of copper. Therefor stranded 16 AWG wire has more surface wire on all the individual strands than a solid wire of the same size. This is called the skin effect in electrical theory books.


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A gross oversimplification, as indicated in previous comment. The only place the current would flow only in the surface layer would be in the case of a superconductor. Flows *near* the surface makes for a much better statement.

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hbiss

EC, Westchester, New York NEC: 2014
It's also very much frequency dependent. At 60hz skin effect is for all practical purposes non-existent. You would have to get up into RF to see it.

-Hal
 

GoldDigger

Moderator
Staff member
It's also very much frequency dependent. At 60hz skin effect is for all practical purposes non-existent. You would have to get up into RF to see it.

-Hal
An over generalization. At 60Hz the skin depth is large (8.5mm) but as you increase conductor diameter it does become noticeable.

See http://chemandy.com/calculators/skin-effect-calculator.htm for skin depth in various materials. The higher the conductivity, the smaller the skin depth.

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hbiss

EC, Westchester, New York NEC: 2014
Ok. Here we go again. We can go probably 4 more pages with theory to try and prove a point but what purpose does it serve? The statement was that because of skin effect, 18ga stranded copper will have more conductivity than 18ga solid at 60Hz and you should use stranded for a simple LV switch setup. That's a ridiculous statement and we all know it.

-Hal
 

ActionDave

Moderator
Staff member
Ok. Here we go again. We can go probably 4 more pages with theory to try and prove a point but what purpose does it serve? The statement was that because of skin effect, 18ga stranded copper will have more conductivity than 18ga solid at 60Hz and you should use stranded for a simple LV switch setup. That's a ridiculous statement and we all know it.

-Hal
AMEN BROTHER!
 

mstrlucky74

Senior Member
Most commercial building require emt stub ups for low voltage. If it's not required on your project then just run 16-2 stranded CL2/CL3 Riser rated UL listed wire.

With low voltage power circuits stranded wire is always recommended as it has more throughout than solid wire of the same size. Especially in lower voltages.


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Thanks
 
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