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Topic Title: Leakage PAT Test on Hoover
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Created On: 14 November 2013 10:31 PM
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 14 November 2013 10:31 PM
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maidstonevacs

Posts: 3
Joined: 14 November 2013

Hi,

I PAT test a Dyson today and it passed insulation test and leakage test but before the leakage test ran it came up with the following message.

Resistance too Low L-N 14.3 Ohms.

I can understand how it may be too high if there is a loose connection or even a open circuit, but what could cause this message ?

Can i pass the vacuum cleaner as safe to use.

Thanks
 14 November 2013 10:41 PM
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impvan

Posts: 922
Joined: 07 September 2005

So it's telling you there's a resistance between L and N - isn't that what you'd expect from a vac with the switch 'on' ???
 14 November 2013 10:49 PM
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maidstonevacs

Posts: 3
Joined: 14 November 2013

Thanks for reply

Correct , but according to the manual for the PAT tester if it gives you that message it states this

"Resistance is lower than 20 ohm, if the resistance is lower than 20 ohms then the current might be higher than 16 amps check the appliance". But it still passed !!
 15 November 2013 01:06 AM
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Legh

Posts: 4427
Joined: 17 December 2004

Ok,
This is basically telling you that the loading is greater than 3kW and that anything that is supplied by a BS 1362 plug does not have the capacity to cope with anything more than 13A.
You need to apply your knowledge and understanding of what might be expected by the appliance here. and it becomes a game of 'cat and mouse'
I often have to convince my PAT that its wrong because its limited intelligence is flawed in a particular case.
The good thing about 'lying' to the PAT is that it just acquiesces.

Legh

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http://www.leghrichardson.co.uk

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 15 November 2013 09:02 AM
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broadgage

Posts: 3170
Joined: 07 August 2007

The appliance is probably fine.
Some automatic PAT testers measure the resistance between the live and neutral wires connected to to the appliance, and from this attempt to calculate the current that would be used in normall operation.

A resistance of less than about 20 ohms is presumed to suggest a running current of more than 13 amps, which is a "fail" for an appliance with a 13 amp plug.
This works fairly well for resistance heating appliances but is very misleading for motors such as those in vaccuum cleaners.
The resistance of a motor is much lower than would be expected from the running current and the resistance test between live and neutral is therefore worthless with such appliances.

Very high power filament lamps, as might be used for theatrical or photographic purposes also have a lower resistance than would be expected from the running current.
 15 November 2013 09:14 AM
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Legh

Posts: 4427
Joined: 17 December 2004

This works fairly well for resistance heating appliances but is very misleading for motors such as those in vaccuum cleaners.
The resistance of a motor is much lower than would be expected from the running current and the resistance test between live and neutral is therefore worthless with such appliances.


I think you summed that up quite nicely. However, the load leakage test through the PAT will confirm this. But it does require a mains connected PAT as opposed to the hand held 'executive' types.

Legh

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http://www.leghrichardson.co.uk

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 15 November 2013 09:21 AM
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perspicacious

Posts: 8055
Joined: 18 April 2006

Back emf theory anyone?

Regards

BOD
 15 November 2013 10:12 AM
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Legh

Posts: 4427
Joined: 17 December 2004

Originally posted by: perspicacious

Back emf theory anyone?

Regards

BOD


Yes BOD, it goes backwards....

But I suspect that was not the answer you were looking for.

You've probably got a net voltage across the coils of 40V.
Then apply Ohms Law
or alternatively,
knowing the resistance and reactance of the coil by measuring both the DC and AC current flowing (experimental) you could then apply the other equation.
Now, that's what I would expect something like the Robin 5500 to do on a load test.

Legh

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http://www.leghrichardson.co.uk

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 15 November 2013 01:23 PM
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maidstonevacs

Posts: 3
Joined: 14 November 2013

Thanks all...ill pass it then. I did another one today and it came up with the same message, only 17.3 ohms.

Obviously it's nothing to concern myself with. As the PAT still passed it !!

Thanks again
 15 November 2013 04:00 PM
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daveparry1

Posts: 8020
Joined: 04 July 2007

I'd guess this is a class 2 device? if so there's little point in PA testing it anyway, just a visual inspection is all that's required,

Dave.
 15 November 2013 07:09 PM
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westfield6

Posts: 210
Joined: 12 October 2007

So what has this got to do with Hoover who are a manufacturer of vacuum cleaners, washing machines etc? Yours was a Dyson.
 15 November 2013 07:13 PM
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daveparry1

Posts: 8020
Joined: 04 July 2007

Good point Westfield!
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