Power cable dead or alive conundrum

[Dabop]

Does that happen a lot in Oz, then? Loss of a neutral is a very bad circumstance but, fortunately, doesn't happen often here.

Not often, but there's other ways you can get a bad 'safe' reading from a tester (its required testing procedure in the UK as well for electricians- has been since 1989 there!!!)

2.30 long from the UK

Another possibility is some only bother checking Active/Neutral- but an O/C Neutral can give a false 'dead' reading if only that test is done- hence the 'check A/N, A/E then N/E triple check'- never just rely on the A/N check alone... (and why many testers now include both 'non contact' and 'dual contact' detection circuits in the one unit...)

 

[Sideways]

If you work 3 phase, you learn the ten test for safe isolation.
Checking the voltage between every possible pairing from L1, 2, 3, N and E
10 measurements in all to prove dead, plus the checks of the tester before and after.
The principle holds good for single phase work too. L against both N and E, and check N to E as well. Then you know.

You simply can't make a test like that with a pen type detector, but they do have their uses for faultfinding, especially where you detect live and then follow it until you lose it , e.g. to locate a cable break in flex. If you are toggling a switch and the voltage detector is going on and off at the same time, it's a handy indication, but doesn't prove live continuity or dead.

 

[Spectric]

What catches many DIY'ers out is the fact a neutral can be live and lethal, just a basic understanding of ohms law would often save the day.

 

[Scruples]

Not often, but there's other ways you can get a bad 'safe' reading from a tester (its required testing procedure in the UK as well for electricians- has been since 1989 there!!!)

2.30 long from the UK

Another possibility is some only bother checking Active/Neutral- but an O/C Neutral can give a false 'dead' reading if only that test is done- hence the 'check A/N, A/E then N/E triple check'- never just rely on the A/N check alone... (and why many testers now include both 'non contact' and 'dual contact' detection circuits in the one unit...)

Quite right...

 

[Scruples]

Yes, and that's one reason I'm not that keen on rings really. Never used them in industry, (although I'm sure they do get used) only domestic really. I believe they were first used to combat the shortage of copper after WWII, at least I think that's what we were told.

Hmm...I've heard that story about the reason for ring mains many times but I have never read any credible evidence. A ring main is a good way distributing power in houses or in offices. In factories single sub circuits (radials) are the rule to remove downtime to more than one machine.

In my time as an electrician we removed radial circuits with rings because it was a less expensive to distribute power to many sockets. Prior to that era, 15A sockets were sparsely installed throughout houses.

 

[paulrbarnard]

Yes the good old MICC but not as common now since you can get cables like Prysmian FP200 for your fire alarm circuits.

I hated MICC. I had to work with it during training as an apprentice and always found it a complete faff. Getting all the curve radius right and the lengths to the junction boxes and the fiddly little core spacers and fittings. Arrghh. Life is better today.

 

[Limey Lurker]

It is unusual for sockets to be fed via the roof space. They are nomally fed from under the floor on the lower level. What you might have detected is switchline feed in the roof on its way between a switch and an upstairs light. It would be live, as detected by your 'non-contact' device but wouldn't supply 240V because it doesn't have a neutral, it has a return live from the switch.
As there probably won't be a ring main cable in the roof space, you should look to getting a spur from the floor below.

Solid ground floored dwellings are normally fed from above.

 

[Scruples]

Solid ground floored dwellings are normally fed from above.

From new, solid ground floor dwellings were/are mostly fed via steel comduit embedded in the concrete. But there are always exceptions. I've done a fair bit of that in my time. The biggest problem was the concrete pourers who run the risk of knocking the pipework and rnd boxes out of position.

 

[Dabop]

From new, solid ground floor dwellings were/are mostly fed via steel comduit embedded in the concrete. But there are always exceptions. I've done a fair bit of that in my time. The biggest problem was the concrete pourers who run the risk of knocking the pipework and rnd boxes out of position.

Never seen that- expensive to install and makes repairs bloody expensive....
(something the 'cookie cutter' builders avoid to the max lol)

All the 'concrete pad' ones I've seen/worked on had nothing in the pad except drainage pipes- hot and cold water, electricity (power and lights) it was all in the roof and walls... (the only exception (sometimes) was 'islands' in some kitchens where a feed conduit was put in place from a wall to the island for power etc)

Even then, the feeds were often put in after the pour by slotting the new concrete and fitting a cover over the slot... (I was never quite sure if that was a case of it being cheaper to do it that way- or cheap builders simply forgetting that you need services to the island LOL)

 

[Scruples]

Never seen that- expensive to install and makes repairs bloody expensive....
(something the 'cookie cutter' builders avoid to the max lol)

All the 'concrete pad' ones I've seen/worked on had nothing in the pad except drainage pipes- hot and cold water, electricity (power and lights) it was all in the roof and walls... (the only exception (sometimes) was 'islands' in some kitchens where a feed conduit was put in place from a wall to the island for power etc)

Even then, the feeds were often put in after the pour by slotting the new concrete and fitting a cover over the slot... (I was never quite sure if that was a case of it being cheaper to do it that way- or cheap builders simply forgetting that you need services to the island LOL)

Perhaps I was talking about a time when these things were done differently, and on a bigger scale than just a few houses. I remember assisting an electricity board inspector (those were the days) on a prefabricated high-rise block of flats. That was interesting... (back in the early 70s).

 

[Dabop]

Perhaps I was talking about a time when these things were done differently, and on a bigger scale than just a few houses. I remember assisting an electricity board inspector (those were the days) on a prefabricated high-rise block of flats. That was interesting... (back in the early 70s).

I was talking about detached houses ie your standard 'cookie cutter' suburbs, much more recently (1990's onwards)...
Where a 'builder' (company) constructs an entire estate of 'detached' (lol nominally anyway) houses, all identical (hence cookie cutter) and made as cheap as possible...

Always good for repair work afterwards- built down to a price, uninterested builders in repairing anything afterwards (often the company is dissolved after a suburb is finished, and a 'new' company builds the next one... grrr), and often some seriously 'dodgy' stuff done where the inspectors can't see...

What could possibly go wrong with that combination....
(got a mate that lives in one- I know 'his' house- red front door- otherwise identical to every other one in the street...)