# Positive, Negative sides



## Mike Swearingen

On two-wire wiring, the imprinted or marked side is usually the neutral (negative). The smooth side is the hot (positive).
In 110v "romex" such as 12/2-with-ground, the black is the hot (normally connected to brass screws in switches and receptacles), the white is the neutral (silver screws), and the bare is the ground (green screws).
In 220v "romex" such as 10/2wg to a water heater for instance, both the black and white insulated wires are hot (no neutral with 220v) and the bare wire is ground. 
Things can vary, but those are the "usual".
Mike
Note: I'm just a DIYer, not a professional electrician.


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## mdshunk

There is no such thing as 'positive' and 'negative' in AC household wiring. Positive and negative only relate to DC. 

What exactly are you wiring up?


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## tribe_fan

The original poster said it was for a cig lighter - I assume for a car ?

You didn't state if you were running a new wire or replacing using existing. Personally I never trust the tricks. Get a meter and set it to DC, and something above 12 v.

Put the black meter lead on on one lead, red on the other. If it reads PLUS 12 - then the wire attached to the black lead is the ground wire. If it reads Minus 12 , then it is the opposite. 

As an example - on a small charger - the black wire with the stripe is the positiive wire.


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## Speedy Petey

mdshunk said:


> There is no such thing as 'positive' and 'negative' in AC household wiring. Positive and negative only relate to DC.
> 
> What exactly are you wiring up?


I was about to post the same thing Marc, then I noticed the cigarette lighter part at the end.


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## calabashfire

it is for a warning light bar. i know this board is for more then 12v.. like 120v,220v. 
i cut the wire to hook up to a switch, and there are two of the same wires. i heard a trick you can tell on the side of the wire if its positive, or negative. on one side of one of the wires is groved, and other side on the other wire is smooth. 



> On two-wire wiring, the imprinted or marked side is usually the neutral (negative). The smooth side is the hot (positive).


i think he knows what im saying. so your saying that the groved side is negative, and the smooth side of positive?
just double checking.


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## mdshunk

Hold the phone, here. Those light bars can take an incredible amount of current. You might want to consider running a line off the battery, through a fuse, and have your dash toggle switch turn on a relay. I have an arrowstick with strobes on the one truck, and it uses nearly 10 amps. It's up to you... just a suggestion.


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## LanterDan

I would second md's caution about the high current draw of such light bars. I know my mother burned up some wiring when she first installed a double strobe light on her vehicle used for rural mail delivery. (I wasn’t living in town at the time, so I can’t tell you anything about how it was wired.) Since connecting directly to the battery she has gone through several alternators. Although the constant use of a mail route is going to harder than the intermittent use of running to a fire (as you name seems to suggest would be its use).


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## calabashfire

it used to have cig. lighter plug. now i cut the wire. i have a switch box. like the onces you see in police cars. i need to hook up the positive from the light onto one of the wires from the switch, then i need to take a negitive and hook it up as a ground. i have a few lights, so im going to run all the negitive and all run them to the same ground. this is what a few other people do in my dept. (yes it is fire) then i need to take the positive from the switch box and run it to my battery, but yes, im going to have a fuse in between the battery and positive wire.

i know how to wire all that stuff up. the only question i have is what is the positive side. is it the groved or the smooth side. im not sure if you guys know what i mean because im sure most of you are used to wiring up houses with those kind of wires.

so the only question i have is.. does the positive wire have the groves or the smooth. if you guys arent sure, i am talking about the institution. not the *WIRE* it self. im pretty sure like desk lights have this kind of wire that has the 2 prong on the end. 

thanks guys for all your help. hopefully you understand what im talking about now.


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## mdshunk

For parallel cord (type SPT) used on DC circuits, the side with the "grooves" is the DC negative. The smooth conductor is the DC positive.


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## crecore

mdshunk said:


> For parallel cord (type SPT) used on DC circuits, the side with the "grooves" is the DC negative. The smooth conductor is the DC positive.


 
SPT on AC circuits (polarized lamp cord for example) is the same... the neutral is always the "marked" wire. You also cant go by the writing, you must look for the ribs.


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