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SimplyPats Portable Appliance Testing Software
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 Post subject: Help!
PostPosted: Tue Jul 10, 2012 8:23 pm 
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Joined: Tue Jul 10, 2012 6:48 pm
Posts: 7
Hi All,

Today I had a bit of an accident and managed to rip the wires out of my earth bond lead at the point were it joins the crocodile clip. Any one got any ideas as in how to rewire it? As in what goes were?



Regards

TC :?:


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 Post subject: Re: Help!
PostPosted: Tue Jul 10, 2012 8:31 pm 
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Joined: Wed Jan 23, 2008 11:47 pm
Posts: 1077
Location: Cornwall
Hi Tc

What pat tester is it for? I beleive the Earth Continuity it is a single wire for most PAT testers as it has a banana plug or spade on one end and a croc clip on the other.

Richard


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 Post subject: Re: Help!
PostPosted: Tue Jul 10, 2012 8:34 pm 
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Hi

Metrel Beta PAT , it has 3 wires at end earth live and neutral but only two connectors on clip, so which two go together? AT the croc end btw.


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 Post subject: Re: Help!
PostPosted: Tue Jul 10, 2012 8:39 pm 
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Joined: Wed Jan 23, 2008 11:47 pm
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Location: Cornwall
Unfortunately am not at work at the moment so cannot look at the Metrel BetaPat earth wander lead that I have until tomorow.

I know there are 3 pins at the pat tester end (same design as the Seaward Europa Supernova) however there is only 1 crock clip.

I'll do some quick research but can only bell out our cable tomorow.

Richard


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 Post subject: Re: Help!
PostPosted: Tue Jul 10, 2012 9:06 pm 
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Joined: Tue Jul 10, 2012 6:48 pm
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Yeah that correct Richard, Its at the crocodile clip end, do i join the nuteral and live in one terminal and the earth in another or what combination.


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 Post subject: Re: Help!
PostPosted: Tue Jul 10, 2012 9:22 pm 
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 Post subject: Re: Help!
PostPosted: Wed Jul 11, 2012 2:27 pm 
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Joined: Wed Sep 08, 2010 2:47 pm
Posts: 117
Location: Cornwall
Hi TC

Below is a picture of a lead we dissected earlier. You can see that the three cores are all connected to the croc-clip with a link between the two connection points on the clip.


Attachment:
Earth-Wander-Lead.jpg
Earth-Wander-Lead.jpg [ 80.96 KiB | Viewed 1823 times ]



We would recommend that you replace your earth probe lead as the link is missing and it looks as though someone has tried to fix it using odd parts (the spade) – poor connections will give poor readings.

I’m not sure why an XLR plug is used (all the conductors are tied at the croc-clip) although it is possible that this is for redundancy or to ensure better connectivity at the PAT end. You will have to ask the manufacturers.

Regards,
Lorna


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 Post subject: Re: Help!
PostPosted: Wed Jul 11, 2012 3:50 pm 
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Joined: Tue Jul 10, 2012 6:48 pm
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Hi Lorna

Thanks for that will , just have to bite the bullet and order a new one. :)

Thanks again everyone for your help.

Regards

TC


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 Post subject: Re: Help!
PostPosted: Thu Jul 12, 2012 10:48 am 
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Joined: Sat Nov 20, 2010 10:08 pm
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All three wires need connecting to the croc clip.
I don't think the link wire on the clip is too important. Clips on some of these type of lead have it, some don't. Mine certainly don't.

Support wrote:
I’m not sure why an XLR plug is used (all the conductors are tied at the croc-clip) although it is possible that this is for redundancy or to ensure better connectivity at the PAT end. You will have to ask the manufacturers.


There are 2 methods that PAT testers use to disregard the resistance of the test lead from earth bond measurements.

Some testers have a single-core test lead, that connects to the tester via a banana plug (as mentioned above).
On these testers, the user must perform an operation to null the lead. The tester will then automatically ignore the resistance of the test lead in any earth bond measurement. If a different lead, of different length etc., is used, the user must perform this 'lead null' operation again.

Other testers use what is known as the Kelvin or 4-wire method.
A much better explanation than I can give can be found here: http://www.allaboutcircuits.com/vol_1/chpt_8/9.html

Sooooo.... if you take the Kelvin circuit from that link, and imagine how it's used in a PAT tester:
Internally, both the current-carrying wire and the voltage wire from one side of the circuit are connected to the earth pin of the 13A socket on the tester.
On the other side of the circuit, the current-carrying wire is connected to 2 of the pins on the XLR socket, the voltage wire connected to the remaining pin.
The test lead takes these, and then brings them all together at the croc clip.
So there are your 2 measuring points, the earth pin of the appliance's 13A plug, and wherever you attach the croc clip.
Doesn't matter how long the test lead is, as long as all the wires from the XLR are connected to the croc clip, the tester ignores the test lead, and only gives you a resistance reading between the plug earth pin and the croc clip attachment point.
I imagine that 2 conductors are used for the current-carrying part, so as to reduce any potential overheating in the test lead.

Hope that's made the method a little clearer!

PS. don't get too hung up on the description of the special Kelvin clips in the web-link. These are used for extreme accuracy, so you wouldn't really expect to see them on a PAT test lead!

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Last edited by Grizzly on Fri Jul 20, 2012 8:27 pm, edited 1 time in total.

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 Post subject: Re: Help!
PostPosted: Thu Jul 12, 2012 3:33 pm 
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Joined: Wed Jan 23, 2008 11:47 pm
Posts: 1077
Location: Cornwall
Hi Grizzly

Many thanks for your comprehensive post explaining the use of the 3 wires in the earth probe. It explains the clever design. I wonder why some manufacturers have moved away from this design and back to a single core.

Quote:
I imagine that 2 conductors are used for the current-carrying part, so as to reduce any potential overheating in the test lead.


yes I had wondered if that was the reason for the multiple conductors before you explained the ignoring of the resistance of the test lead.

Many thanks for explaining.


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 Post subject: Re: Help!
PostPosted: Fri Jul 20, 2012 12:16 am 
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Joined: Tue Jul 10, 2012 6:48 pm
Posts: 7
Again thank you to all and admin, ... WoW Grizzly you know your stuff :)


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