Domestic Wiring - the Green Goo

[DTR]

Morning all,

Our house was built in 1957, and a single-story flat-roofed extension was added at the back some time in the 60s (if memory serves. We have only lived here for 3 1/2 years). For what it's worth, the extension contains the kitchen and is roughly 9' x 10'. A few years ago we had the house rewired, all except the extension. The reason the extension was not done is because there is no access to the wiring. To access the lighting circuit would mean either bringing down the ceiling or taking up the flat roof. Similarly, the kitchen ring is all concealed behind the tiles and kitchen units. With my permission, the sparkies replaced as much as they could up to the point of no access.

The kitchen adjoins the dining room, which is lit by two pendants (new pendants installed by the sparkies). Today I was going to replace the pendants, but (you've guessed it) one of the pendants contained the green goo. Sure enough, this pendant is the point at which the old, stranded T&E joins to feed the kitchen light.

From what I've read online, the general consensus is that any affected T&E should be replaced. Of course, if it was as easy as that it would have been done already. I have two concerns here: One; the risk that the green goo is creating resistance and therefore heat. And two; what I've read suggests that the green goo only forms when the wiring is already running hot.

What are your suggestions?

Thanks

 

[mjcann]

Just a thought, but could the extension have been wired in the early 70s, if so it may have aluminium conductors, (there was a copper shortage), and what you are seeing is reaction between ali and new copper.

 

[CHJ]

If the extension wiring was installed somewhere in between 1965 and 1971 or shortly thereafter and indeed you have Green Goo from plasticiser leaching out of the PVC then it would be wise to get the extension wiring insulation checked (meggered) at least to prove that the insulation is still adequate.

I'm surprised that you are getting the reaction on a lighting circuit, I've only ever heard of the reaction happening where the circuit is heavily loaded and the wiring is running near its temperature limit.

Does the existing lamp fitting heat up the rose and associated local wiring?

I have seen localised leaching in someones house where they had a heavily loaded twin socket with old plugs in it that was over heating.

Here's hoping you only have a localised problem and don't have to go for the worst case scenario.

 

[DTR]

This is definite goo rather than staining from a reaction between metals

I'm surprised that you are getting the reaction on a lighting circuit, I've only ever heard of the reaction happening where the circuit is heavily loaded and the wiring is running near its temperature limit.

Does the existing lamp fitting heat up the rose and associated local wiring?.

That's what concerned me apart from the goo itself. I just added up the wattage and the circuit should only be drawing an amp at most. I'll leave the lights on for a few hours and see if that fitting warms up.

 

[mjcann]

Having seen Pics, I tend to agree with previous post, its leaching from pvc, there were some really dire products at that time, unable to seperate sheath or strip conductors etc

 

[MMUK]

If there's sufficient air space in the ceiling void, you may be able to use the old cable as a drawstring to pull a new 1.5mm T+E through

 

[DTR]

If there's sufficient air space in the ceiling void, you may be able to use the old cable as a drawstring to pull a new 1.5mm T+E through

I was thinking about that, but with my luck they'd come apart half way through

 

[dickm]

If there's sufficient air space in the ceiling void, you may be able to use the old cable as a drawstring to pull a new 1.5mm T+E through

I was thinking about that, but with my luck they'd come apart half way through

Solder them together with lead based solder!

 

[MMUK]

Or connect them with butt splice crimps.

 

[RogerS]

Both solutions doomed to failure if the cable goes through any tight holes or round bends.

 

[kostello]

I'd be tempted to use a Tesla coil and transmit the power through the air instead of down wires........

 

[Dee J]

I'm puzzled... all I can see there are blue and brown wires... which dates that wiring to post 2004. Up to that time fixed wiring was black and red. Can't deny the green goo, but never seen it on wiring that new! Get the insulation resistance checked to decide if more work is needed.
Dee

 

[RogerS]

could it be corrosion from a water leak?

 

[CHJ]

I'm puzzled... all I can see there are blue and brown wires... which dates that wiring to post 2004. Up to that time fixed wiring was black and red. Can't deny the green goo, but never seen it on wiring that new! Get the insulation resistance checked to decide if more work is needed.
Dee

Re-Read the OP, he has old (possibly 1960's ?) wire interfaced with a new rewire at that ceiling rose.

 

[mjcann]

If you look closely you can see red and black, they have brown/blue sleaving on them,
martin

 

[tomatwark]

deleted

 

[ChrisR]

Morning all,

Our house was built in 1957, and a single-story flat-roofed extension was added at the back some time in the 60s (if memory serves. We have only lived here for 3 1/2 years). For what it's worth, the extension contains the kitchen and is roughly 9' x 10'. A few years ago we had the house rewired, all except the extension. The reason the extension was not done is because there is no access to the wiring. To access the lighting circuit would mean either bringing down the ceiling or taking up the flat roof. Similarly, the kitchen ring is all concealed behind the tiles and kitchen units. With my permission, the sparkies replaced as much as they could up to the point of no access.

The kitchen adjoins the dining room, which is lit by two pendants (new pendants installed by the sparkies). Today I was going to replace the pendants, but (you've guessed it) one of the pendants contained the green goo. Sure enough, this pendant is the point at which the old, stranded T&E joins to feed the kitchen light.

From what I've read online, the general consensus is that any affected T&E should be replaced. Of course, if it was as easy as that it would have been done already. I have two concerns here: One; the risk that the green goo is creating resistance and therefore heat. And two; what I've read suggests that the green goo only forms when the wiring is already running hot.

What are your suggestions?

Thanks

This is due to a manufacturing defect, can’t remember which cable manufacturer it was, but there was a lot of comment in the electrical trade journals at the time (late 1950-1960‘s), but as far as I know there was no action taken other than to withdraw that cable batch from sale, but I suspect most of it had been used, by that time.

I have this cable throughout my house, and it would be a major job to replace, but will have to be done at some stage.

If you look at the cable closely you can see that it is the copper earth conductor, interacting with the outer pvc sheath that causes the problem (green goo), the live and neutral conductors have there own red & black sheath, so are not in contact with the outer pvc sheath and are not effected.

This in its self will not cause the cable to run hot, (assuming correct sizing of cables), but a problem does occur in socket outlets, if the goo gets around the L & N female parts of the socket the plug top pins may not make a good contact, this will then generate heat. It will also cause the generation of heat in the socket if the switch is not making a good contact due to the ingress of goo, likewise with light switches.

I have replaced all of the socket outlets and the light switches in my house, a number of the sockets more than once, and keeping a close eye on same, as I said above at some stage the whole house will have to be rewired.

Take care.

Chris R.

 

[CHJ]

Electrical Safety council comment on the subject (2.3mb PDF)

 

[MMUK]

If you look closely you can see red and black, they have brown/blue sleaving on them,
martin

I would imagine that the previous sparks sleeved the old colours to prevent confusion when he fitted the pendants. It's what I generally do in that situation. However, most times when I'm fitting lighting circuits, I put all the connections into a JB in the ceiling void and just drop a single pair into the fitting, much neater and less confusing should the customer ever decide to change the light fitting.

 

[ChrisR]

Electrical Safety council comment on the subject (2.3mb PDF)

As my comments in my previous post on green goo, if not word by word.

But the (Electrical Safety Council), have not commented on the possibility of generating heat from poor contact between socket and plug top or switch contacts if the green goo was to ingress into these areas.
In my opinion a significant omission from their paper on the subject.

They mention having a insulation test of the wiring, I have never been involved in domestic wiring other than my own property, as my whole working live was in industrial electrical engineering, and any circuit showing signs of green goo, would have failed on the initial visual inspection, any further tests would not take place, however I never came across green goo when working, as T&E cable does not tend to be used in industrial electrical engineering.

I would assume that any electrician called in to inspect/test a domestic installation and found green goo, would fail the installation without the need for further testing, other than to confirm or otherwise if the installation should be disconnected from the supply immediately of if it could continue in service on a temporary biases, until a rewire could be carried out.

I have insulation tested my home installation, and found it to be sound at the time of testing, I am however keeping a close check on it.

I did not advise in my previous post, that anyone finding green goo, should call in an electrician asap, as it is not my place to tell anyone else what they should or should not do.

Take care.

Chris R.