I'm replacing a feed-through switch on an IKEA (Canada) floor lamp. Its using an SPT 2 cable (photo attached). Both wires have the same insulation color and both are copper. Neither is ribbed (as far as I can tell to the best of my ability). However, one side has inscription embossed while the other is completely smooth.

In this case, how can I identify Live and does it matter in a 2 wire setup? I am using a Leviton 5410.

Edit: I stand corrected. I have found the ribbed side, it is the wire without the inscription. Therefore is this the neutral?

enter image description here

  • 1
    I could be mistaken, but that 'box' looks like a power-supply/transformer - in which case neither of those wires is 'live' (or neutral either) because they're carrying low-voltage and isolated form the mains.
    – brhans
    Commented Feb 12, 2018 at 20:48
  • @brhans Yes, it is a supply for a lamp cord. However, based on research it seems to have a polarized plug - not sure if this helps.
    – eszed
    Commented Feb 12, 2018 at 20:54
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    Sure - but the wires coming out the side are not connected to the plug pins - polarized or not. There's electronics and/or a transformer in between.
    – brhans
    Commented Feb 12, 2018 at 20:56
  • The ribbed side should indicate that, however use most any digital volt meter to verify. If the voltage reads positive then the red meter lead is connected to positive, if the voltage reads negative, the red meter lead is connected to negative.
    – Tyson
    Commented Feb 12, 2018 at 21:15
  • The ribbed is usually the common in dc this would be the -, after checking 1 cable I checked another and they were mixed with 2 different brands.
    – Ed Beal
    Commented Feb 13, 2018 at 0:30

1 Answer 1


That's probably an extra-low-voltage DC adapter outputting something like 12V DC.

The word "live" is generally only used for AC 120V or 240V

For low voltage DC the terms are "positive" and "negative". Which is which is sometimes marked on the connector. Alternatively there may be a rib or line marked on one side of the wire. I think that usually marks the positive. If the connector is a typical barrel-plug, they are most often centre-positive - but you can't be sure without testing.

I'd just check with a multimeter to work out polarity. A typical multimeter set to a DC voltage range will show a positive number if the red lead is connected to the positive conductor and a negative number if the red lead is connected to the negative conductor.

  • On an isolated DC supply like that, there's no reason to break a sweat trying to figure out which is positive or negative as neither one is special. Commented Feb 12, 2018 at 21:32
  • Hook them up backwards and the magic smoke comes out on the device or supply so I would say they are special nomater what voltage.
    – Ed Beal
    Commented Feb 13, 2018 at 0:33
  • @EdBeal - What is the ETA on this magic smoke after wiring? I ask because based on these wiring instructions imageshack.com/a/img924/5746/clEzN1.png I placed the ribbed in place of the 'neutral' and so far so good.
    – eszed
    Commented Feb 13, 2018 at 0:48
  • That is just a switch , not a DC supply.
    – Ed Beal
    Commented Feb 13, 2018 at 13:08

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