Test pen lighted when testing 24V DC?

ckchew666

Member
Join Date
Aug 2003
Location
Malaysia
Posts
591
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.
 
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.)
 
TPS Reports said:
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.
 
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. :(
 
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 o_O
 
JvdV said:
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 o_O

sorry, there is no valve, basically are all pilot lamp/indicators only.

"it was nice knowing you, I will start ordering some flowers o_O" What do you mean by this? I don't get it ;)
 
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.:eek:
 

Similar Topics

Hi, I am using M221 reading from 3 different sensors (modbus rs485) sharing same bus (daisy chain). I am currently using READ_VAR (in total...
Replies
0
Views
67
I am trying motor startup with pf525 drive by using wizard start over ethernet communication but during direction test it's showing control error...
Replies
3
Views
159
See code at the bottom. Hi all. For the story, this is my first complete project using a Rockwell PLC, I've been mostly working with Unity Pro...
Replies
7
Views
763
My question is regarding the number of Test outputs vs the number of inputs in a module. In the case of a 1734-IB8S card, there are 4 test...
Replies
5
Views
1,021
Hi, I have to test a control logic that required to change the input temperature as the process variable from thermocouple transmitter on the...
Replies
7
Views
574
Back
Top Bottom