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Posted By: Uppeydog PAT Test - 04/04/05 11:07 PM
1) What's the Mininum Insulation Resistance(M Ohms)to Pass.
2) How can you check Polarity, with just a meter (not a PAT tester).In this case wanting to check if a single pole switch is on the live conductor & not the neutral, on a 240v appliance, without taking any covers off to access the "switched" conductors.
Cheers!
Posted By: pauluk Re: PAT Test - 04/13/05 11:53 AM
I already sent this link to John (who is in the U.K.) a few days ago, but for anyone else interested, the following is the IEE's current PAT requirements:
www.iee.org/Publish/WireRegs/PAT_CodeRevised.pdf

I can't think of any reliable way to check for a switch in the hot line without getting inside the unit, not that a switched neutral on a portable appliance is really a big deal.
Posted By: marcspages Re: PAT Test - 04/13/05 04:10 PM
Uppeydog,

Although I cannot claim the following to be a completely fool-proof way of testing for "polarity", it has served me well over the years. It only works on Earthed equipment (i.e. 3 wires). 'Dual Insulated' does pose more of a challenge!

The principle of operation is the so-called "risidual voltage" (whatever that is!?) that is found on an isolated cable lying next to a live one. The effect seen here is the capacitive coupling twixt the two conductors.

Using this same principle; By having the switch off, there should be more capacitive coupling between the Earth and the innards of the device under test on the Neutral than should be on the Live ('cos the switch breaks any coupling on the Live side).

The test is to Earth the device under test, and then, using any suitable multimeter (I find analogue types work best), test for this capacitive coupling by placing the multimeter between a socket Live (120/230VAC) and alternately the Neutral and Live plug pins of the device under test. Any difference in capacitive coupling will be noted as a voltage difference - the lower is more than likely the Live in the device under test.

M.
Posted By: Trumpy Re: PAT Test - 04/16/05 12:52 PM
Paul,
Quote
I can't think of any reliable way to check for a switch in the hot line without getting inside the unit, not that a switched neutral on a portable appliance is really a big deal.
I'd agree, sure, if the appliance has the Phase and Neutral transposed at the plug, this could cause the same effect.
But, one thing has to be mentioned, is the fact that all of the wiring inside the appliance will be live, up to the switch.
This wouldn't normally be a real problem, unless you are the sort of person that likes to repair appliances with them plugged in. [Linked Image]
Uppeydog,
I can't think of any common technique that can be used to test polarity without opening the appliance up.
That's what test equipment is for. [Linked Image]
Posted By: Uppeydog Re: PAT Test - 08/10/05 07:22 PM
Thanks Guys,
Marc..great idea for Class 1 appliances!
Now rack your brain for Class 2 (double Insulated...no earth wire)
Cheers!
Posted By: chipmunk Re: PAT Test - 08/10/05 09:49 PM
Quote
Now rack your brain for Class 2 (double Insulated...no earth wire)

Non contact voltage detector pen. These can usually detect even as low as 100v through several cm of insulation/appliance casing. (A double pole changeover switch securely mounted to a short extension cord or 'power strip', labelled "FOR TEST USE ONLY" and reversing phase/neutral is very useful for this kind of test, to compare results, I have one I made years ago, with a 15 amp toggle switch mounted in a 20mm conduit knockout on a double outlet. It's also been added to with a momentary 15amp pushbutton 'start' type switch, to prevent any but momentary use.)

If the class II appliance is metal cased, (unusual) the reaction will usually be unequivocal, if it's plastic (more usual) you'll have to go poking around with the detector pen, but you can usually tell which line is switched.

As Paul said, a reversed phase/neutral is no big deal in an appliance that's class II anyway, but it's nice to get it 'right' [Linked Image]
Posted By: Uppeydog Re: PAT Test - 10/08/05 10:16 PM
Chipmunk....Yo! Thats great! I carry 2 of those in my pocket. So simple yet so effective. Where I work lots of grindng goes on (The Angle Grinder Type...so don't get excited!!)I've had Grinders, Drills & Welding plants full of Carborundum, tracking power to metal parts, even on Class 2 gear.

Cheers. J2R
Posted By: pauluk Re: PAT Test - 10/13/05 02:32 PM
Quote
As Paul said, a reversed phase/neutral is no big deal in an appliance that's class II anyway, but it's nice to get it 'right'

Sometimes even the manufacturers don't worry about it. I've seen a lot of Moulinex kitchen appliances (made in France) from the 1970s with the switch in the blue wire. Of course, in their native country they'd have been used with reversible plugs anyway.
Posted By: Uppeydog Re: PAT Test - 10/17/05 07:20 PM
Good one Paul, good to look at different angles, very interesting.

110V Class2 Drill. Plugged into 240/110v Tranny. Put none contact voltage Pen on case.

Drill Off.... Pen Comes On.
Drill On......Pen Goes Off.

Would I be right in saying...
Drill Off...110V.
Drill On....55V.
Posted By: pauluk Re: PAT Test - 10/18/05 11:15 AM
Hmm.... That's a good one.

For the benefit of non-UK readers, let's just point out that the low-voltage building site tools we use here are generally fed from a transformer which has a 110V secondary with a grounded center-tap.

Whereabouts on the case was the pen to give these readings? If it's a single-pole switch, then when turned off the motor will just be hot at 55V from one side of the supply (although no current flowing, obviously).

Most of the newer drills have double-pole switching though.
Posted By: Uppeydog Re: PAT Test - 10/18/05 04:28 PM
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!
Posted By: pauluk Re: PAT Test - 10/19/05 11:50 AM
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.
Posted By: Uppeydog Re: PAT Test - 10/24/05 06:57 PM
Thanks Paul,

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

thanks
Posted By: pauluk Re: PAT Test - 10/25/05 09:00 AM
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?
Posted By: Uppeydog Re: PAT Test - 10/25/05 06:27 PM
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.
Posted By: Uppeydog Re: PAT Test - 10/26/05 10:58 PM
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?
Posted By: pauluk Re: PAT Test - 10/28/05 12:48 PM
Quote
I tested the flex feeding the drill.
Drill on...nothing.
Drill off...nothing.

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

Quote
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.

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.

Quote
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?

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).]
Posted By: Uppeydog Re: PAT Test - 10/28/05 06:33 PM
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
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