Wednesday, August 29, 2012

Phantom Voltage its there but its not?

I had one of those trouble shoots the other day which can drive you nuts if you do not have the proper equipment to check it out.
One of the many buildings I take care of a building maintenance man was having problems getting the remote emergency light heads to work off the main battery packs,
in the hall ways out of frustration he called me and asked if I could check it out for him .

He had a small standard digital meter he was using and he hooked into what he thought was the correct wires as he was reading 12 volts DC  but the lights would not work. Well I hooked in my meter also and had 12 volts but it was not really there. after hooking in my own small independent tester which has a neon bulb in it and it did not light I knew I had something fishy going on. So I them put my tone tracer on the wire followed it back and found he had missed a splice point in the ceiling. I connected the wires and it worked.  Wait a minute how does a wire that is not hooked up still show voltage on it. This is a electrical phenomena known as Phantom voltage. While digital and some analog  meters will pick up and register it as a working voltage it is not really there. Because digital meters are so sensitive what is happening is the wire is receiving transient voltages thru the air from other higher power wires running thru and next to these wires and the wire which is not hooked up acts like an antenna and absorbs it  and looks like it has power. That's why I used the light bulb tester as it draws an actual small current and will tell you if the voltage is real or not. I even see this with 120 and higher voltages I have a solenoid tester meter known as a Wiggy Meter made by Square-D that does the same thing as a light bulb tester  that is very useful in these situations.
when testing motor leads and such. Phantom voltage is only getting worse particularly in office type buildings as the use of  Electronic Ballasts instead of magnetic ballasts are being used and can throw off unwanted transients as Building switch from T-12 to T 5 and T 8 bulbs .
Which is what I suspect was causing the Phantom power in this building.

Remember if you hook up something it does not work you test  and get voltage  and  you test the device and it works elsewhere suspect you may be getting Phantom Voltage. get a proper tester which actually requires  small power draw and check it out. Some time stranded wire can break and only one strand is making thru and can act like phantom power as well .

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