wire gauge

[dustman1747]

This is the first year i started doing lightshows and i am looking to buy wire. Now normal 120V house wiring is 14Awg and my local hardware store recommended 14awg. Iv been doing research and SPT-1 and SPT-2 is alot cheaper, and i see alot of people using it. So is it safe to say that its perfectly fine to use 16 or 18 awg wire (SPT-1/SPT-2)? For the most part there is only 1 strand per channel/wire.

Thanks

[WireWrap]

This is the first year i started doing lightshows and i am looking to buy wire. Now normal 120V house wiring is 14Awg and my local hardware store recommended 14awg. Iv been doing research and SPT-1 and SPT-2 is alot cheaper, and i see alot of people using it. So is it safe to say that its perfectly fine to use 16 or 18 awg wire (SPT-1/SPT-2)? For the most part there is only 1 strand per channel/wire.

Thanks

As long as you are only using less than 1 amp, 16 or 18 gauge should be fine. 16 gauge is rated for 3.7 amps and 18 is rated for 2.3 amps. I believe that the difference between SPT1 & SPT2 is the insulation thickness, not the wire gauge. Either should be fine for light loads.


:)

[John Benedict]

This was a discussion on another board not long ago. I have quoted from that discussion:

NEC 400 deals with cord. SP-1, -2, and -3 are all the same as far as its concerned. Table 400.5(A) defines the ampacities of these cables (and they come in gauages other than 18, with SPT-1 being 18 or 20, and SP-3 being 18 to 10).

The 18ga cord has an ampacity of 7 (column A) or 10 amps (column B) depending on whether its use falls in column A or B. Column A applies to cords with 3 current carrying conductors and column B is for 2 current carrying conductors. A shared neutral, like for a range or dryer, isn't considered current carrying, so just about all residential cord uses will be column B. Christmas lights will always be column B unless you have a multi-cable twisted together so there are 3 or more conductors. If you have 4 or more conductors bundled, the ampacity needs to be derated from Column B.

Also, hopefully there is a W on the end of these cables, as that means they are rated for wet use (which Christmas lights almost always are).

It wouldn't surprise me to see GFCI's trip with the length of lights and the damp locations they are installed in. All you can do is use more receptacles with less light sets on a given GFCI

This is from 400.5(A)
Column B
18 10 amps
16 13 amps
14 18 amps
12 25 amps

And all the non-belivers said,"That almost seems counter - intuitive
So an extension cord can carry MORE amps then permanent wiring?"

No, they are not higher (and #14 cord is a little less than normal). The NEC wiring table allows premises wire of #14 at 20 amps and #12 at 25 amps (and this is at 60C). It doesn't list any values for #18 or #16 since you normally can't use wire that small. There is a separate rule limiting use to 15A breakers on #14 and 20A breakers on #12 in many cases. This rule doesn't apply to cords. If you look at the larger cords (like dryer and range cords), their ampacity is the same as house wiring.

[Photovor]

I've always found this chart/calculator very useful:

http://www.mikeholt.com/documents/freestuff/other/VoltageDropCalculator.xls

The first part of it does voltage drop calculations based on wiresize, amperage and voltage, and the other sheets in the document have information regarding ampacities for different wire sizes and such.