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Idea for a new tester...........

………….which helps work out where a buried wiring fault is? 

Having watched a youtube video

 

 where the electrician finds a short in a cable by measurement and calculation rather than stripping out the whole infrastructure I have been thinking that something like the process employed in the video could be turned into a test meter but I have no idea how to go about achieving it. 

Basically, what I had in mind was something the size of a multimeter with a display which would give a read-out in centimeters. The scale could be made seletable for whole metres too.

You program in the tabulated resistance value in miliohms for each cable size given in the OSG /  regs book onto some kind of chip. 

you make this a selectable range option with a dial on the meter, say 2.5mm/1.5mm for example. 

The range would go from 0.75mm to 10.00mm for the common cable sizes, so 1.00mm/1.00mm, 1.5 mm/1.00mm, 2.5mm/1.5mm, 4.00mm/1.5mm, 6.00mm/2.5mm, 10.00mm/6.mm. 

These are the common twin and earth sizes but an option could be included for cables with cores of the same cross sectional area such armoured or round flex e.g. 2.5mm/2.5mm etc. 

Selecting this would set the internal chip to the correct miliohms range value for that size cable. 

You then measure the ends of the cable - one measurement taken from each end (fault somewhere in the middle) and each measurement result would be displayed in centimeters. 

It would then be a simple case of getting the tape measure out and marking the wall or floor with the values given in centimeters by the test meter. 

Why make something like this? Well, it would speed up fault finding on site by not having to disturb vast amounts of building materials, floor coverings, cosmetic finishes etc. You would only need to focus upon a small area for remedial repairs and it would automate the calculation process to give a distance measurement rather than an electrical one. 

Achievable? If so, how? Being something of an old buffer who is a contacts and relays man rather than 0's & 1' I know nothing about silicon chips and programming etc. 

Going by gut instinct and not mkt research here, but if such an item were available I think I'd buy one. 

Do you think the idea has legs?

Your thoughts? 
 

Parents
  • Given that the kind of thing David Savery is describing in his video is just measuring R1+R2 (where the short is the link between L + E) then dividing it by by the (R1+R2)/m value for copper looked up in table L1 of the OSG, having that function as a dedicated meter seems a bit of an overkill. Even if you don't have the OSG to hand, the value from the table is just (18.1 / 2.5 + 18.1 / 1.5)

    Of course as Mike points out, using a dedicated low-impedance meter will give you a more accurate result.

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  • Given that the kind of thing David Savery is describing in his video is just measuring R1+R2 (where the short is the link between L + E) then dividing it by by the (R1+R2)/m value for copper looked up in table L1 of the OSG, having that function as a dedicated meter seems a bit of an overkill. Even if you don't have the OSG to hand, the value from the table is just (18.1 / 2.5 + 18.1 / 1.5)

    Of course as Mike points out, using a dedicated low-impedance meter will give you a more accurate result.

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