# testing wires?

Discussion in 'The Projects Forum' started by vultac, Mar 15, 2009.

1. ### vultac Thread Starter Active Member

Mar 2, 2009
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0
Hi there, I would like to ask who do i check the polarity a power cable (red,black wires)??? how do i know which 1 is negative which 1 is positive using multimeter? and the diode function in the multimeter does it has similiar property as the "buzz" we get when wires are conducting? thx

2. ### kubeek AAC Fanatic!

Sep 20, 2005
4,670
804
What about just measuring the voltage on the power cable??

I dont undenrstand the part about diode function..

3. ### vultac Thread Starter Active Member

Mar 2, 2009
142
0
how do i measure the voltage? i don have the plug, just the pin.

Diode function..cause normally we have got some sort of function which allow us to test whether the wires are conducting or not isint it? and when it is it will give a buzz sound?

4. ### ke5nnt Active Member

Mar 1, 2009
384
15
A multimeter expects a certain polarity when measuring voltage. You'll either see (for example) 12 volt reading, or -12 volt reading(in which case your leads are backwards). So...

To check polarity, set the multimeter to read voltage. If you're unsure how much voltage you're going to be reading, start with the highest setting on the meter so you don't blow it up and work down from there. Take your red multimeter lead and touch it to the red wire, put your black lead to the black wire. If you get a positive reading on the meter, red = positive, black = negative. If you get a negative reading on the meter, then red is negative and black is positive. Easy yeah?

Multimeters don't conduct, they read. There should typically not be any "buzzing" emitting from your meter. Maybe I misunderstand your question regarding the diode.

5. ### ke5nnt Active Member

Mar 1, 2009
384
15
If the wires/leads/whatever aren't conducting, you wont get any reading on voltage or current. So I don't see the issue with that, no reading = no conductance.

6. ### vultac Thread Starter Active Member

Mar 2, 2009
142
0
Basically, Im given the power as shown on the attachment and im not sure whether it is negative center or positive center

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7. ### kubeek AAC Fanatic!

Sep 20, 2005
4,670
804
You can´t measure voltage on diode-check setting. It can destroy your meter, depending on the voltage you try to measure.
In other words, what is connected to the meter on picture one?
Use the voltage setting like ke5nnt described above.

8. ### vultac Thread Starter Active Member

Mar 2, 2009
142
0
if theres no current flowing the wire, how could the multimeter be able to supply small current to check whether its conducting or not?

9. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
If you are simply checking continuity of the wire, use the Ohmmeter setting - there is a battery in your meter to supply current on this setting.

If you just want to know if your supply is center positive or not, use the Voltmeter setting.

The diode check setting is used for checking diodes. You are not checking a diode in this application, so don't use the diode check setting.

10. ### vultac Thread Starter Active Member

Mar 2, 2009
142
0
thanks for erplying, what if its for example a ribbon cable which has been stripped already at both ends could i still test it the same way? using ohmeter settings??

and for supply? how using the voltmeter could i tell it is center positive or not?

11. ### vultac Thread Starter Active Member

Mar 2, 2009
142
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because in some multimeter there hav this function with is together witht eh diode whereby u could hear a buzz sound when the positive and negative lead are put together.

May 16, 2005
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13. ### vultac Thread Starter Active Member

Mar 2, 2009
142
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pok thx for the hlp!