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Old July 9th, 2007, 11:57 PM   #1
ckchew666
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Test pen lighted when testing 24V DC?

Hi guy,

Sorry, this is not a PLC question, but it's something regarding wirings & power.

I'm checking a system which consists of many remote indicators. All indicators are 24V DC or AC supported. But the system are using 24V DC. When I test the supply at the indicator connector (2 wires), the test pen lighted up.

I taught test pen only lighted when we test on AC system? How can it be? Some other colleague also get a minor short when accidentally touched the cable (which lighted the test pen).

Any comments on this system wiring? Thank you.
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Old July 10th, 2007, 04:34 AM   #2
aikona
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Forget the test pen and use a proper digital meter

Eric
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Waar is die Biltong -
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Old July 10th, 2007, 07:40 AM   #3
TPS Reports
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Grab a Fluke meter or something similar with an actual AC/DC selector. Test pens should only be used to test if something is "hot" or not (usually 120/240 AC, etc.)
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Old July 10th, 2007, 08:55 AM   #4
rsdoran
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Quote:
Originally Posted by TPS Reports
Grab a Fluke meter or something similar with an actual AC/DC selector. Test pens should only be used to test if something is "hot" or not (usually 120/240 AC, etc.)
I do not trust these things so only believe them when they show hot. The reason they may "light" on DC is because there is some form of AC riding on the DC, this could happen if the DC common is connected to ground or errouneously combined with the neutral of a single phase ckt, there could be other reasons too.

As suggested, when you obtain a power reading when you think you should not then use a voltage meter to get more precise reasons. If still unsure may want to use an oscilloscope and check for AC on the DC ckt.
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Old July 10th, 2007, 09:17 AM   #5
ckchew666
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Hi guys,

Thanks for your replies. I'll check it with the multimeter.

One of my colleague told me that DC high amp, it'll lighted up the test pen (HOT). I taught it was true.
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Old July 10th, 2007, 09:55 AM   #6
JvdV
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Wink

Some test pens react on magnetic fields as well.

Nice to test if solenoid valves without indicators are powered. As far for testing / indicating life circuits..........it was nice knowing you, I will start ordering some flowers
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Old July 10th, 2007, 10:14 AM   #7
ckchew666
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Quote:
Originally Posted by JvdV
Some test pens react on magnetic fields as well.

Nice to test if solenoid valves without indicators are powered. As far for testing / indicating life circuits..........it was nice knowing you, I will start ordering some flowers
sorry, there is no valve, basically are all pilot lamp/indicators only.

"it was nice knowing you, I will start ordering some flowers " What do you mean by this? I don't get it
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Old July 10th, 2007, 05:42 PM   #8
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High currents produce a magnetic field als well (all currents produce a magnetic field, but big currents produce significant currents)

The flowers part, in the netherlands it's custom to send some flowers to a friends funeral. And sinds yuo work with a .........you get the idea I think.
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Old August 20th, 2009, 03:02 AM   #9
tscoffee115
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Hi there, Would a new one like me be welcome here?
Thanks so much in deed.


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Old August 20th, 2009, 10:24 AM   #10
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Yes you would be welcome

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