Commissioning a ring circuit

[Clive Summerfield]

For single phase a.c.

Live (was red) will now be brown Neutral (was black) will now be blue Earth (green or bare copper) will now be green and yellow

Cheers Clive

[Bob Eager]

For insulation/continuity, what do people think about this, at 89 quid from TLC?

[Chris Oates]

[Bob Eager]

was showing an inexpensive way to check earth loop impedance. The item I mentioned is complementary, not a replacement - the other major part of the equation.

I've not seen anything else at this price, so opinions are welcome.

[stefek.zaba]

For insulation, it's useful, I s'pose; but the more significant problems on domestic circuits are likely to need low-ohms metering rather than hi-ohms (you want to tell the difference between a solid and a partial screw connection; to tell the difference between the two legs of a ring; and so on). The kit you mention doesn't seem to do that - though the much pricier 255-quid-plus-VAT thing below does. All-in-one meters with low-ohms ranges are a bit thin on the ground, but Fluke do a mid-price one (same sort of price as the insulation tester you mention) which does a reasonable 20-ohms-full-scale, 0.01 nominal resolution, as do Wavetek (T120B - or at least they did ;-) For Regs-conformant-final-testing a

200mA test current is needed; I don't think these multis do that, but they're cheaper than the Robins/Seaward and so on things.

(Pauses to flick through RS catalogue) Hmm, not many cheaper "low ohms" meters to be found here, in fact a dearth. For those with a bit of electrickal skill, making up a Wheatstone bridge with a decade or binary box of low-value reference resistors might be a more affordable way of doing Low Ohmage, as might the more direct route of creating a

200mA constant-current source (hey, may as well use the current the Regs tell us to!) capable of developing, say, 10V, then use the "normal" low-voltage sensitivity of even a cheapie multimeter (2V full scale, nominal 1mV sensitivity) to measure the voltage dropped: each 200mV means 1 ohm, thus allowing quite reasonable sensitivity. Absolute accuracy will be poor, granted; but you'd certainly be able to do the ring-resistance tests with such a rig, and you can calibrate with a decent 0.5ohm wirewound or similar...

Stefek, rambling on.

[Bob Eager]

I agree. The spec sheet (downloadable via link in corner) says there are four ranges, the fourth being:

OHMS: Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 Ohms Resolution . . . . . . . . . . . . . . . . . . . . . . . . . .0.01 Ohms (ñ1%) Max open circuit voltage . . . . . . . . . . . . . . . . . . . . . . . .4.2V Short circuit current . . . . . . . . . . . . . . . .>=200mA @ 2 Ohms

(or am I misunderstanding this spec)

[BigWallop]

LOL

Especially from regulars I would imagine. :-))

[Chris Oates]

No - I think Stefak missed that bit

[Dave Plowman]

Trouble is, don't such things have to have a calibration certificate to pass regs? And getting a one off checked would likely cost more than buying a commercial version. Unless self certification is allowed...

[PoP]

Hmm, I think I've worked on some of your installations previously ;)

PoP

[stefek.zaba]

D'oh! I certainly did miss that - I'd say you've hit on an excellent cheapie; not a day-in day-out commissioning tool, but a non-ludicrously priced conscientious DIY'ers tool. Nice!

Stefek

[stefek.zaba]

I expect they do. It's all about why we're wanting to "pass regs". If it's to get a bit of paper to keep the H&S mafia or the buyer's solicitor off our backs, a test cert for the whole installation from someone who does the job for a living and has paid the right baksheesh, I mean trade association membership fee, is what you need.

If, however, you're wanting to be regs-conformant so that the work you perform is safe to your own satisfaction and so that you can with a clear conscience assert that your d-i-y work is at least as competent as that normally done by a practising professional, while still keeping your spend on use-once-a-year test gear down to sensible proportions, then knocking up something with which to confirm you didn't fall victim to a short bout of narcolepsy while thinking you'd tightened up one of the screws in your new sockets is an eminently reasonabubble use of resources...

Stefek

[John Greenwood]

Hello Dave,

I recently added a new ring crircuit for my kitchen and tested it with one of these:

am quite staisfied with this minimal testing and sleep easy at nights. When I come to sell my house I plan to deny doing any work on it at all.

John

[David W.E. Roberts]

That looks scarily like my trusty rusty multimeter.

More sophisticated than a wet thumb and a nose for the smell of burning insulation :-)

Cheers Dave R

P.S. there is a scary lack of demand for the lynching of top posters - has the newsgroup gone soft?

[Bob Eager]

I've got one of those!

But I've also ordered the insulation/continuity tester from TLC - let's see what it's like.

No, we just send the hitmen round these days...!

[Dave Plowman]

Agreed. In The Good Old Days, Maplin would have had a kit for one. I've got a few bits of Maplin kit test gear I still use.

An alternative, of course, is secondhand from Ebay.