What happens when Copper gets damp?

[Martin Angove]

Piece of T&E behind a hardboard facing on a damp wall of an old stone-built ex-barn, socket slightly damp too. Lots of green stuff all over the Copper. Obviously the screw terminations are a bit iffy so the faceplate gets replaced, but what about the cable? Insulation tests L-N are fine, N-E is ok, L-E is slightly lower than expected.

The green stuff is only on the bare ends of the L & N wires - i.e. only as far as the insulation, but tracks about 2ft up the bare earth (I took out a 4ft section to see).

So for the chemists here (I'm sure there must be some) what is happening to the Copper? What is the green stuff? How does green stuff manage to reduce the insulation test readings? On a similar bit of cable without the reduction in insulation resistance readings would sandpapering the green stuff off and re-terminating be ok?

This green stuff seems very similar to the usual sort of thing which happens to Copper if left outside / in the damp, but its electrical properties don't really matter on water pipes or roof ornaments :-)

Oh, and as to the original cause, stopping the damp is going to be mighty difficult - the wall in question is stone/rubble-built, questionable mortar, and underground :-)

Hwyl!

M.

[Wheelbarrowbob]

All metals when exposed to the atmosphere react and start to corode. Alliminium reacts almost instantly and over time a white dust appears and this is alliminum hydroxide. copper reacts the same but turns green, cant remember wether the green stuff is copper oxide ot hydroxide. the insulation test you did , did you put put 500V through the conductors ? On a digital ohm meter you should expect a reading of greater than 999 Mohms or infinity on an analougue meter. yes , emery cloth and clean and re terminate. I work on the 400KV grid OHLines and when we get hot joints ( high resistance , which is what your green terminations are ) we break the joints , file them shiny clean apply a thin layer of grease and re make the joints then mega them again.

[tony sayer]

In article , Wheelbarrowbob writes

That somehow sounds amusing "we megger them"

Any piccys of your day job on a website Bob?...

[Colin Wilson]

I`m more interested in the kit they use to megger them...

Would I be right in thinking you use a ducter rather than a megger to check the resistance of the joint, as you would on breakers ?

(I used to work on ground mounted 11kv & 33kv plant)

[PoP]

Sounds interesting. I've heard of a megger but not a ducter. What is a ducter please?

PoP

[Wheelbarrowbob]

A ducter is a digital ohm meter made by megger and is 10 inches by 5 inches and

10 inches deep with 4 test leads about 30ft long all incased in a big orange plastic box with a carry strap so a donkey like me can carry it 200 ft up a tower and measure the resistance of the joints on an earth wire ( single wire at top of transmission tower )

[The Natural Philosopher]

Its copper carbonate. Its sort of potects the copper from further corrision. If there is any sign of blackening tho, you may be in trouble. Do a google on Black Wire Syndrome. That doesn't stop until the wire breaks, and then loss of connectivity is far preferable to a nice arc and a fire..

[The Natural Philosopher]

Except noble metals like gold and platinum.

To form a highly impervious oxide layer.

But this generally takes a weak acid to form.

Neither. Copper oxide is black. Its usally copper carbonate from the carbonic acid in rainwater. Most houses are full of carbpon dioxide as well ...tends to be a by product of any rainwater and cements.

I can't remember, but ISTR copper hydroxide is more pale bluish. Not as blue as the sulphate...

[N. Thornton]

If cable insulation value is reduced by water presence I wouldnt be comfortable reusing it. At what voltage did you test this R? Thats an important question.

PVC cable is impervious to water so to prevent rewetting all one need do is keep the cut end dry. Mounting your electrics on standoffs helps greatly to keep the damp from a damp wall away from the lectrickery. Also vent holes in the underside of the boxes - must be kids finger proof - can help.

Regards, NT

[Andy Hall]

Wow. I realised that those things were pretty big, but had not realised that they were that high.

Eaves level on the house is my limit and I'm not comfortable then.

I hope that you're well rewarded for this work.....

.andy

To email, substitute .nospam with .gl

[PoP]

Interesting story time.....

About 8 years ago I worked for Lanier in Wokingham, and our office was on the top floor. This was the 2nd floor, and the floors were quite high.

We were sitting in the office one summer day and this ladder appears at the window - just over the sill, not all the way up. And the ladder started shaking as it does when someone is climbing up it. This ladder must've been extended to about 40 feet, and when we looked out this ladder must have been whipping back and forth a good couple of feet in the central section as the guy climbed up/down.

A few seconds later this guy reaches the top rung - and carries on climbing! I'm not kidding when I say he stood on the last rung but one to reach up and clean the windows - his knees were at the top of the ladder. He was just balanced very precariously at the top of this shaky wooden ladder.

Unbelievable that someone could do that without falling off.

PoP

[Gary Cavie]

I have no problem with going to any height on a ladder, and working from it, but get vertigo if I go on a tower, or flat roof. Pitched roofs, even on a bungalow with eaves 7' from the ground, and I'm petrified. My shed roof is about 6' up, flat, and 20' x 10'. If I have to go up there to fiddle with the aerials, I can't look down.

Is this a weird combination, or is anybody else the same?

Gary

[tony sayer]

In article , Gary Cavie writes

Well I've been up a TV transmitting mast on a windy day to 770 feet and after the first couple of hundred you don't really notice much difference, except the swaying motion gets worse the higher you go!..

[Richard Savage]

Brother-in-law has had a bad fear of heights since childhood, as have both his sisters and mother (guess where the children get the fear from? Thanks Mum). Anyway, they were much amused that he more or less cured his fear by becoming a roofer. He can now do all those frightening things roofers do, like walk along ridges. But he cannot go near the edges of flat roofs.

Rgd sRichard

[Mary Fisher]

I'm the same.

I suspect it's because on a ladder I don't look down. On a roof I cling to what's most central. On a cathedral roof I sit in the middle and whimper ...

Mary

[Martin Angove]

Good point, having thought about it most of the "insulation breakdown" I was measuring was probably at the terminations rather than in the length of cable, but it made sense to replace 4ft anyway as it was relatively easy. Yes, I did it properly using the right kit and 500V :-)

Hwyl!

M.

[Mary Fisher]

I've been reading this thread carefully and while I can't comment on the technical electrical stuff I used to be a chemist so, because I haven't seen any correct response to this specific question I'll tell you.

It's almost certainly copper carbonate (cupric carbonate-hydoxide), a pale green powder as opposed to a crystalline salt. Copper in the presence of atmospheric moisture and carbon dioxide produces copper carbonate. Cupric oxide is black by the way, cuprous oxide is red.

That's because it's the same stuff.

Mary

[N. Thornton]

Thats a relief! I was imagining someone measuring breakdown at 3v then putting it into service. eek!

Regards, NT

[Martin Angove]

[...]

Brilliant, thanks for this. I'm happy with what I have done electrically (you should have seen the circuit's readings before I started!) I was just trying to satiate my curiosity about the physical process involved. If I may ask a cheeky follow-on question...

...the screw terminals in the socket are... ummm... brass I should think. Some sockets seem to be all brass, or maybe brass and copper, others have brass terminals riveted (in the case of the Earth which can be seen) onto steel.

Damp (plus unknown contaminants) plus copper plus brass plus pressure equals ?

Yes, I have seen very blackened exposed copper in this combination, but usually cutting back an inch or so reveals something approaching shiny :-)

Hwyl!

M.

[Wheelbarrowbob]

Yep, all the water I can drink for free