Failed PAT

[ericmark]

At @RandomGrinch has hit the nail on the head, it was always a problem. The one I had was the fig 8 lead set, in the office not a problem, but on the factory floor too easy for it to be dropped in water. So the same item would have a pass in the office and a fail on the factory floor.

The same with RCD protected sockets in one part of building and not in others, the

will all pass where the socket is RCD protected, but fail if not. Today all sockets in commercial premises should be RCD protected, I know BS7671 is not retrospective but HSE rules are. So there is a problem with not having RCD protected sockets today.

OK I know where I work many sockets are not RCD protected, in theory they should only supply step down transformers, as to if RCD protection is required with reduced low voltage not sure, I think it is, but non of our transformers have RCD protection.

 

[RandomGrinch]

That list causes so many arguements when a brand newpurchase from one of these
View attachment 249437
is failed on pat before ever being put into service.

It also leads to crazy daisy chains along with all of the stress and strain placed on additional plugs and sockets.

...the other problem with RCD extensions... They latch on, only when powered.
When PAT'ting, the insulation resistance test will test up to the RCD and that's it.
A separate test we used was a polarity and continuity check (surprisingly useful!).
Again this would be invalid.
The only useable test for an RCD extension lead is the earth bond test (and of course, the visual inspection ).

 

[plugwash]

You could do an IR test from the socket end, though there may be safety implications to doing that and I think you would need extra test leads/adapters that don't come with most PAT testers.

You could also presumably do a "run test" to determine leakage and possibly polarity.

 

[RandomGrinch]

You could do an IR test from the socket end, though there may be safety implications to doing that and I think you would need extra test leads/adapters that don't come with most PAT testers.

Thanks yes - a plug to plug lead would be very interesting if it got into the wrong hands!

You could also presumably do a "run test" to determine leakage and possibly polarity

Good point, I hadn't thought of that.

 

[Harry Bloomfield]

is failed on pat before ever being put into service.

It also leads to crazy daisy chains along with all of the stress and strain placed on additional plugs and sockets.

A bit of a safety warning about using extension sockets on reels, or coiled up cables - which it is easy for even the most knowledgeable of us to forget.....

An extension lead, like any flex or cable needs an air flow to keep it cool and from over-heating, when used near its current capacity. The reason has nothing at all to do with inductance, as many seem to think - rather it is entirely due to the heating effect as a result of the resistance of the cable. On holiday, away with the caravan, I often see the orange EHU cables neatly coiled up on reels and supplying up to 16amps to the caravan or motorhome. It's not long before the cables on the reel begin to melt and I have witnessed the result a number of times.

 

[plugwash]

Thanks yes - a plug to plug lead would be very interesting if it got into the wrong hands!

I would suggest rather than making up a permanent 13A plug to plug lead, using a combination of test leads and adapters to make the connection.

 

[Lectrician]

ISAT Testing? Don’t ya love it?

 

[SUNRAY]

A bit of a safety warning about using extension sockets on reels, or coiled up cables - which it is easy for even the most knowledgeable of us to forget.....

An extension lead, like any flex or cable needs an air flow to keep it cool and from over-heating, when used near its current capacity. The reason has nothing at all to do with inductance, as many seem to think - rather it is entirely due to the heating effect as a result of the resistance of the cable. On holiday, away with the caravan, I often see the orange EHU cables neatly coiled up on reels and supplying up to 16amps to the caravan or motorhome. It's not long before the cables on the reel begin to melt and I have witnessed the result a number of times.

The inductance does have a little effect and I stress LITTLE. If the cable is wound in a non inductive way it makes a 'just measurable' difference.

The main problem at you say is lack of ventilation and bunching, one only has to look at derating factors in the regs to see what difference it makes.

A little nugget I tell hails back to when colour televisions were just becoming popular and still being full of valves consummed a few hundred watts, I visited one of my colleagues and entering the lounge noticed the unmistakeable tang of warm pvc. I mentioned it and he said it was the new TV, I wasn't convinced and looking over the back of the stand found the cat curled up. He mentioned the cat had started laying there on the coil of extension lead.

Knowing where the cable had come from (work) I knew it was 0.5mm² and as it was the same lead he used to hoover the car it had to be near 20m long, with all but a metre or two in a 200-250mm coil.

The cat didn't like being moved but the coil was very warm to the touch, as we uncoiled it some of the cable was positively triangular in shape.

It didn't take him long to shorten it to just the straight part and bin the rest.

 

[JohnW2]

The inductance does have a little effect and I stress LITTLE. If the cable is wound in a non inductive way it makes a 'just measurable' difference.

I must say that I would be surprised if it were 'measurable' at all at 50Hz, particularly given that (for that frequency) we are talking about a very modest 'coil'

Kind Regards, John

 

[crystal ball]

A bit of a safety warning about using extension sockets on reels, or coiled up cables - which it is easy for even the most knowledgeable of us to forget.....

An extension lead, like any flex or cable needs an air flow to keep it cool and from over-heating, when used near its current capacity. The reason has nothing at all to do with inductance, as many seem to think - rather it is entirely due to the heating effect as a result of the resistance of the cable. On holiday, away with the caravan, I often see the orange EHU cables neatly coiled up on reels and supplying up to 16amps to the caravan or motorhome. It's not long before the cables on the reel begin to melt and I have witnessed the result a number of times.

Yes especially in winter, heating, hot water, microwave all powered off a coiled extension despite all the warnings issued by various caravanning organisations

 

[AdrianUK]

I must say that I would be surprised if it were 'measurable' at all at 50Hz, particularly given that (for that frequency) we are talking about a very modest 'coil'

Kind Regards, John

But, since the coil contains no 'net turns' (ie. it contains both the line & neutral conductors, carrying exactly the same current but in opposite directions) does it even have ANY inductance?

 

[SUNRAY]

But, since the coil contains no 'net turns' (ie. it contains both the line & neutral conductors, carrying exactly the same current but in opposite directions) does it even have ANY inductance?

The inductance is there regardless, the effect of the inductance will be tiny anyway (but measurable) at such low a frequency and as you say it will be reduced even further by being balanced.

 

[JohnW2]

But, since the coil contains no 'net turns' (ie. it contains both the line & neutral conductors, carrying exactly the same current but in opposite directions) does it even have ANY inductance?

Good point - that would certainly make it 'unmeasurable'

Kind Regards, John

 

[JohnW2]

The inductance is there regardless, the effect of the inductance will be tiny anyway (but measurable) at such low a frequency and as you say it will be reduced even further by being balanced.

I'm not sure what you mean by 'regardless' - as Adrian has pointed out, if the situation is perfectly 'balanced' (and 'mutual inductance' 100% - i.e. 'perfectly magnetic coupled' conductors) then there will be no net inductance (hence net inductive reactance) at all, will there?

Kind Regards, John

 

[SUNRAY]

I'm not sure what you mean by 'regardless' - as Adrian has pointed out, if the situation is perfectly 'balanced' (and 'mutual inductance' 100% - i.e. 'perfectly magnetic coupled' conductors) then there will be no net inductance (hence net inductive reactance) at all, will there?

Kind Regards, John

In theory no. In practice?

I'll draw a comparison; plug an equivalent coiled cable into a balanced amplifier input and turn the volume up, then unroll it.

That's why the stage multicore cables (the fat cable running between the stage and sound desk for microphones) will usually be stored in a tank (Flight case) rather than on a reel, that way one only has to pull out enough cable rather than have to find a way of unrolling the whole thing.