Continuity tester

[Brian]

If you've been following my saga, you'll know that I'm trying to join some T&E cable.

This afternoon I went to B&Q to get some junction boxes. My plan is, like Andrew Gabriel, to both solder the joints and screw them down in a box.

While there, I also bought a simple continuity tester. With the power off, I tested the continuity between both live and ground, and neutral and ground.

To my surprise, the continuity tester "chirped" - beeped briefly - and its LED flashed briefly, before remaining silent. Continuity is normally indicated by a steady beep and a lit LED.

Now I presume that this is normal - some kind of side effect of the RCD, or something like that? Has anybody else used one of these devices and had a similar result?

(ps Also bought a Power Detector, which can detect current within a wire; to cut a long story short, I found out that my ring main was incomplete and traced the wire to a socket box in the kitchen, where a N wire was out; this socket box had been fitted by "professional" kitchen fitters as supplied by MFI. In the past I've also had to fix their plumbing and, frankly, I'm considering getting somebody in to check out the gas hob they fitted.)

[Tim Morley]

Does the continuity tester still work? There is continuity between neutral and earth. You said with power off, just cct breaker off, or main switch?

[Andy Pandy]

With the mcb off there should be no connection between L and E whatsoever.

The N and E will be connected and it will depend on the resistance to the looping point and the tolerance of your tester, as to whether or not it beeps continuously.

As for your soldering, strip 2 cms bare and clean the surface by scraping to remove any oxidation. Immediately tin the single wire, knocking off any excess solder. Repeat for 2nd wire.

Twist firmly together and solder up. The solder should flow easily and look neat and smooth. Don't apply any more than necessary.

HTH Andy

[Stefek Zaba]

There's plenty of ways to account for your 'chirp'. L-to-E first: any appliances still plugged in to the ring with interference suppressors will have capacitors placed L-to-E (and N-to-E, too). There'll be a brief current flow as these charge up on testing. There's natural cable capacitance too - those L and E conductors run next to each other with nobbut a mil or of PVC between 'em for tens of metres, don't they...

N-to-E not only has those capacitances, but they're actually bonded together in the UK. That bond may be close as the supplier's side of your fusebox if you have a TN-C-S (wot we old farts call PME) installation, or as far away as the local substation for TN-S or TT. Since you only got a chirp, you prolly don't have PME, and have the 'usual' small voltage offset between your N and local E.

The scare quotes seem entirely appropriate; just because you pay more than peanuts doesn't mean you don't get monkeys (who themselves may well see only peanuts - after all, someone's got to pay for the salesdroid's new Jag. D-i-y by a conscientious householder is notably safer than a tradesman who just 'turns their hands to a bit of leccy work'...

Stefek

[Jason Judge]

Sounds like there is a capacitor in the circuit. That would conduct briefly, until it was charged up. If you swap the leads over and test the continuity, it is likely to chirp again, and again when you swap them back over. Capacitors are used, amoung other places, across switches to suppress RFI.

-- Jason