Anyone ever had a false positive testing for dead with...

[sebmaster]

...the back of your hand?

Refurbishing basement today and removing the ceiling; being an old house there is alot of wiring that is disconnected and can be safely removed, so one of my tasks was to pick apart the installation and find out which of the 50 year old cables I could take out.

One in particular I track back and see it dissappears behind a couple of CUs, one of which is a 12hr switched one for storage heaters (of which we only have one left - about 2m from the CU) and the other the main one for the house.

In my cable there is a junction box joining the two halves: follow usual procedure to test the cable: each core + earth to each other with the meter - 3v or so, induced current, fine - next with the back of the forefinger to make sure - dead as expected.

Must be connected to the heater CU which I isolated earlier.
So I leave the junction box open and proceed with ripping down the rest of the ceiling.

Later on in my wiring investigation I see that the aforementioned cable could not be connected to the heater CU. So I follow it back and check a second junction box in it and sure enough 230v. It is connected to the CU below the heater - I have found the supply for my immersion heater.

Somewhat concerned I dart back to the original junction box, jam the probes in tight and yes 230v that all three tests failed to spot first time round .

I can only assume that the ends and my hands were so dirty and dry the resistance was just too high, either that or I should give up working on electrics since I literally cannot touch a cable right.



Two more finds from today:

One was a ring circuit for the storage heaters - sure, fine, except if I am not mistaken in a ring circuit the phase at the end of the ring is meant to go into the same fuse as the start, not the one next to it...

Also if you ever run out of junction boxes remember two cables can be joined with a ceiling rose... and if that ceiling rose should only have three blocks of connectors instead of the four required no problem, just connect all the commons together, it'll be fine

 

[PrenticeBoyofDerry]

What was you using as your test instrument?
And remember
Junction boxes should only be used if easily accessible for later inspection and testing and should not be left in ceiling voids with no access to them!

 

[sebmaster]

My multimeter was my test instrument (my nice one aswell!)

I remember that unfortunately whoever installed it didnt (it was long ago judging by the cable to be fair to them ); well, at least it isn't in a ceiling void anymore.

Not that that helps a great deal when the cable from the CU is grey T&E, going to a junction box that connects to two lengths of black T&E (with insulation so old you can pull it off (before scoring with the cutters!)) connected by the aforementioned junction box.
Now, between here and the heater I am not quite sure what happens but I do know the cable to the heater is white... and looking under the floorboards far back enough I see another lonesome grey one....

The joys of old houses! (And this is a good day with this house)

PS. you wouldn't know approximately the year that t&e was commonly sheathed with a soft metal as opposed to plastic? (I don't mean for special installations this was, as far as I can tell, a lighting circuit)

 

[Monkeh]

Lead and VIR insulated cables? That place needs a rewire.

 

[Geps]

The house I'm working on now has the same as well as some "newer" cables from a partial rewire. The empty cable drums stashed in the voids suggest the rewire happened in 1960s...so the old cables have got to be originals...(1930s!)

 

[1john]

The black crumbly cable is rubber sheathed cable and the metal one is lead! This house needs a re-wire, if PVC has been connected to either of these then you will need a re-wire 9.5 times out of ten. Dont bother moncing aboiut with it any more, get a sparky in to do a periodic inspection report and see how much is dangerous with the installation. I expect you will be missing main equipotential bonding conductors, RCD protection, insulation resistance readings will be poor at least.

 

[sebmaster]

Don't I know it! Unfortunately this is my parents house and they will not consider a rewire.

Its not the money, its because its a beautiful old Victorian house that they've kept perfectly in character; original features and antique fixtures in fittings in every room, everything custom built and perfectly finished. That is acctually why I enjoy working on this house so much, its like working with an especially nice material.

But it means there is no way they are going to rip it all up for a rewire.

"The 1930s wiring was dangerous in our parents house when they moved in!"

I am trying to explain the difference between 'simply behind the regs' and 'acctually dangerous', and to at least have a PIR done so they know which part of the installation belongs to which but "there is no point"

At the very least half the house was done when the loft was converted and the kitchen redone. There is no RCD protection on the old CU but I have made sure all the sizing and earthing checks out and its bonded properly; and since every accessory has been replaced over the years there are no nasty surprises behind those (apart from the one in the utility with just two conductors disappearing into the brick wall). In fact I'd thought had thought I had found all the quirks until yesterday.

BTW, anyone here consider it worth it to sell old cable to a scrap metal dealer? How much do you usually need to make a trip worthwhile?

 

[sterowley]

It'll be smoldering wreck before long if they dont get it sorted. Proberly with them insider it.

Crumbleing Rubber insulation IS acutally dangerous.

 

[Donkmeister]

PS. you wouldn't know approximately the year that t&e was commonly sheathed with a soft metal as opposed to plastic? (I don't mean for special installations this was, as far as I can tell, a lighting circuit)

Well, my house was fully-rewired in 1998 according to the lying g*ts I bought it from, and much of the under-floor wiring is lead-sheathed. So, I'd say your cables must be about 13 years old

However, when I did some research I found two groups of loonies, one thinks lead-sheathed VIR was only produced up to 1948, the other thinks 1951. Are you sure yours is T&E though? In my house it only has phase and neutral.

 

[sebmaster]

Oh dear, I hope they didn't leave a forwarding address!

Now that you mention it I am having trouble remembering. I know that in the junction box I removed them from there was a load of CPCs all twisted together but these may have been from the rubber sheathed cables; I do remember pulling out a lead shethed length with only two cores.

I have also managed since then to use a still in use rubber sheath cable to convince my parents to have a PIR done - my years worth of warnings meant absolutely nothing but apparently one look at the scoring the CPC has left on the conductors (seriously it looks like someone was sawing at it ) is enough to convince them maybe the installation might need a little work.

 

[Hipokondriak]

Has anyone seen that old comedy film where they buy a cottage and they rewire it and "daddy" puts oversize amperage fuses in the CU and the cottage goes up in smoke?

Show the parents that film and casually mention that they used rubber sheathed wires in that house too...

 

[sparkwright]

Has anyone seen that old comedy film where they buy a cottage and they rewire it and "daddy" puts oversize amperage fuses in the CU and the cottage goes up in smoke?

Show the parents that film and casually mention that they used rubber sheathed wires in that house too...

Father Came Too.

 

[bhm1712]

a multimeter should NOT be used to prove a circuit is live or dead.

 

[Taylortwocities]

a multimeter should NOT be used to prove a circuit is live or dead.

Because?

 

[Alarm]

a multimeter should NOT be used to prove a circuit is live or dead.

A nice calibrated one?

Why not?