ECN Forum Forums Technical Discussion Electrical Theory and Applications PAT Test

Paul, the test pen was up near around the Centre of the body, away from the switch.
Like I said it lit up when the drill was not running. But once the trigger was pulled on, it went out! The switch was definately single Pole. I tried another non-contact test Pen...Same result! Tried same on 115mm Grinder...Same.

Cheers!

If it's a single-pole switch, that would explain it. With the drill off, the pen is picking up the field from the 55V hot leg which is still connected to the motor.

Once running, you've got both 55V legs (180 degrees out of phase) connected to the motor to balance out.

Thanks Paul,

could you explain how the 180* out of phase bit?

thanks

It's exactly the same principle as the standard U.S. residential supply, only at half the voltage (or thereabouts).

The center tap of the 110V secondary is grounded, which gives you 55V relative to earth at each end of the winding.

As one end of the winding starts to go positive, the other end simultaneously swings negative (both with reference to ground). On the next half cycle, the polarities are reversed. Thus the zero crossing points coincide, but the positive peak on one leg corresponds with the negative peak on the other -- 180 deg. out of phase.

The electrostatic fields in each leg will be equal and opposite due to the inverse phase relationship. So when you have the drill running, you have the electrostatic field from one 55V leg balancing out that from the other 55V leg, giving no indication.

When you open the single-pole switch, you are then registering the field from just a single 55V leg.

Have you tried putting the volt-pen along the flex feeding the drill?

Thanks Paul,
Great answer, I'll try the flex tomorrow & let you know.

I think I put the pen on the flex last time, I dont think it lit up In the on or off position, but I'll double check.

Thanks.

Paul, I tested the flex feeding the drill.
Drill on...nothing.
Drill off...nothing.

Don't forget this drill is Class 2, Double insulated (no earth). Single Pole Switch.

Switch on... nothing.
Switch Off....Pen lights up from behind chuck back down to switch.

9" Grinder Double Pole Switch... nothing all ways.

Do you think it could be anything to do with the Capacitor/suppressor joined up at the Switch?

That makes sense, because at the flex you have both 55V legs producing equal but opposing electrostatic fields at all times.


When running you have 55V opposing on the flex, at the switch, and at the motor. When off, you have two 55V opposing legs on the flex and at the switch, but only one 55V leg energized from there to the motor.


I think you'd get the same results without the suppressor. The grinder has a double-pole switch, so testing at the motor gives you either both 55V opposing legs or neither, so no indication on or off.

The key is the electrostatic (voltage) field from one or both 55V legs of the supply. If you were looking for an electromagnetic field, it would be a different story, since that will be produced only when current is flowing.



[This message has been edited by pauluk (edited 10-28-2005).]

Thanks Paul,

Have you ever thought of becoming a GP.!!
So these pens pick up both Electrostatic & Elrctro magnetic fields. Once again thanks for the explaination.

J2R