ECN Forum Forums Technical Discussion Electrical Theory and Applications PAT Test

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!

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.

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.

Paul,
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.
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.

Thanks Guys,
Marc..great idea for Class 1 appliances!
Now rack your brain for Class 2 (double Insulated...no earth wire)
Cheers!

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'

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

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.

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.

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.