Led light - Identifying the hot wire

Old 10-14-20, 07:22 AM
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Led light - Identifying the hot wire

Hi DIY community,

I am looking for a double check to identify the hot wire since I need to cut and extend provided wires. Here is a picture. As far as I can see, the lined wire is the one soldered to the circuit, which makes me think the other one (with letters is the neutral).

Thank you for your help!

<img src="https://cimg8.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x948/16026852710485921990292110831748_563401611e58e810a79f30c67104ff35999b870f.jpg" width="449" height="948"/>
Old 10-14-20, 07:55 AM
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That is a DC fixture so there is no "hot" and no "neutral" like you would have with a household AC circuit. You have positive and negative.

I usually approach a problem like this from the other end. I use a multimeter to check the output of the power supply to confirm which wire is positive and which is negative. I've found that there isn't a hard & fast rule that the conductor marked with a line is + or - or even red and black so I always double check.

If you don't have a multimeter you can sorta cheat with some batteries in a dark room. I touch the wires to one 1.5 volt battery. It doen't matter if it's a AA or D. While touching the wires look for some or all of the LED's to glow dimly. If they do then you've got the polarity correct. If nothing illuminates then switch the wires (reverse the polarity) and check again. If it still doesn't light then I add another battery to bring the voltage up to 3v and repeat the test again. Only connect the wires for a second, do not leave them connected for an extended time. The idea is to start with the lowest voltage possible so if the polarity is backwards you don't fry anything and you gradually increase the voltage until you reach the threshold where the LED's will start to glow.
PJmax voted this post useful.
Old 10-14-20, 08:11 AM
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I am not sure why you want to know the polarity.
You are just adding wire.
You cannot just add one wire you need to add to both.
Old 10-14-20, 08:34 AM
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Thank you for your replies. I will try to borrow a multimeter or use the batteries method on my 12v circuit.

I plan to plug the lights to a 120-12v adapter, this is why I need to figure which one is positive and negative. On the 120 side, wire has a marker which makes it easy to identify.
Old 10-14-20, 04:29 PM
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3v button cells make excellent test batteries. The + side is marked.
Not enough current to cause any damage but enough to light the LED's.

<img src="https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/202x131/bc_71decf074edb9e7cef4a0776c29926f26fadae16.jpg" width="202" height="131"/>

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