Green Neutral Insulation

[chloebear]

Hi All
Anyone come across cable where the BLUE insulation on the neutral turns GREEN after a while??

Visited a site yesterday to carry out some testing and noticed that the insulation on the neutral of the 10mm Twin/earth cable had turned green at the shower and at the isolator, but still remained blue at the CU.

The main reason for asking is that these rooms were refurbished only 4 years ago, and they have had a few problems recently with electric showers overheating.

 

[polo1]

Overheating was my first thought; not come across any cable where the colour has changed for any other reason!

 

[chloebear]

I was thinking along the same lines, but on the face of it the shower is 8.5Kw and cable is 10mm with all terminations tightened ok.

two things crossed my mind 1. Faulty shower units, but to have 3 fail out of 5 or cause overheating and in one case burn out completely seems strange.
or 2. poor quality cable!!!!!!!!!!!

 

[Guest77]

Why don't you test the circuit with instruments, disconnect all cores so nothing is connected to the board or shower, firstly confirm continuity of all conductors and ensure there is no short circuit between cores, then whack a 1000 volts down the cores and then do the usual live tests, have a visual inspection of the pull cord switch and terminals, mcb terminal and actual shower terminals to see if green or black coal type dust is on or around terminals which may be hidden whilst cables are connected, whilst disconnecting you will also see if any connections were loose you know the usual school boy checks we train apprentices to look for as the standard testing routine.

 

[DRG]

Never seen it turn completely green but have seen slight discolouration due to overheating etc. Im aware of 'greening' of older cables where an ingredient in the pvc insulation reacts to the copper and gives off a green residue but if this was done 4 years ago this shoukd not be the case.

Just carry out the test mdj suggests and it should flag anything up but seems strange if its happened to 3 out of 5 shower circuits. Maybe fault coil of cable used on those 3 premises?

 

[guest119]

Must be Doncaster cable from CEF!

Boydy

 

[Electric Yo]

Why don't you test the circuit with instruments, disconnect all cores so nothing is connected to the board or shower, firstly confirm continuity of all conductors and ensure there is no short circuit between cores, then whack a 1000 volts down the cores and then do the usual live tests, have a visual inspection of the pull cord switch and terminals, mcb terminal and actual shower terminals to see if green or black coal type dust is on or around terminals which may be hidden whilst cables are connected, whilst disconnecting you will also see if any connections were loose you know the usual school boy checks we train apprentices to look for as the standard testing routine.

I agree, but why do a 1000V ins res test?? In my opinion a 500V ins res would give more realistic results. I don't even know in what situations you would use the 1000V ins res test.

To the OP, I've have never seen a conductor change colour like this. So can't give any suggestions. Heat would be the most logical reason I guess.

 

[Marvo]

I can only thing that either excessive heat or maybe chemical action unless the PVC insulation was a poor quality batch.

 

[Guest77]

I agree, but why do a 1000V ins res test?? In my opinion a 500V ins res would give more realistic results. I don't even know in what situations you would use the 1000V ins res test.

To the OP, I've have never seen a conductor change colour like this. So can't give any suggestions. Heat would be the most logical reason I guess.

yes possibly true, crack on then, we have made progress.

 

[Knobhead]

I agree, but why do a 1000V ins res test?? In my opinion a 500V ins res would give more realistic results. I don't even know in what situations you would use the 1000V ins res test.

To the OP, I've have never seen a conductor change colour like this. So can't give any suggestions. Heat would be the most logical reason I guess.

Spoken like a true wanabe.

The cable if it is rated 600/1000 even 1000V DC is to low to prove a cable is to specification. This test is for the cable only not the circuit.

Re the OP:
Chlorine and copper can give a blue/green residue.

 

[Electric Yo]

Spoken like a true wanabe.

The cable if it is rated 600/1000 even 1000V DC is to low to prove a cable is to specification. This test is for the cable only not the circuit.

Re the OP:
Chlorine and copper can give a blue/green residue.

No need to be so hostile dude, chill.

Yes the cable is rated up to 1000v, but that just tells you limit of the insulations properties, right?

My thinking is that if the circuit operates at 325v max, then 500v is closer to that voltage than 1000v, therefore would give a more realistic reading. I'm sure that even regs recommend 500V ins res test for T&E cables. I'm not here to argue, just wanna know people thoughts, so don't be so hostile. I enjoy the constructive feedback. =) If their is a reason why you would choose 1000v over 500v I would be interested too know. A nit picky subject to be honest.

However I think the chlorine copper reaction seems unlikely to be the cause.

 

[Knobhead]

Care to enlighten me to what 600/1000 alludes to?

 

[Electric Yo]

Care to enlighten me to what 600/1000 alludes to?

That the cable has a maximun rating of 600V between Live/Earth and 1000v between Live conductors. What's your point? No need for sarcasm.

 

[Guest77]

That the cable has a maximun rating of 600V between Live/Earth and 1000v between Live conductors. What's your point? No need for sarcasm.

Calm down, all that cider down there is effecting you.

 

[Electric Yo]

Calm down, all that cider down there is effecting you.

Tis true, cider is plentiful here =). Sry I just get a bit pi**ed when people act like a douche for no reason.

 

[Knobhead]

That the cable has a maximun rating of 600V between Live/Earth and 1000v between Live conductors. What's your point? No need for sarcasm.

OK so far so good.

What is the minimum test voltage to prove a cable?

Don't look in BS7671

 

[Knobhead]

BTW I’ve been drinking Melomel cider all afternoon.

 

[Richard Burns]

The higher the voltage you test at the more likely it is that small imperfections would show up as a lower IR reading and give you an indication of an incipient fault earlier than a lower test voltage.

If blue insulation is over heated then it can cause changes in the colours used to impregnate the insulation as chemical reactions including oxidation will occur much more rapidly, reduction in the number of double and triple bonds in a coloured organic material can stop the material being coloured. If the blue is made up of a mixture that includes green to get the shading right and the blue colour is decolourised then green will remain.

 

[Electric Yo]

OK so far so good.

What is the minimum test voltage to prove a cable?

Don't look in BS7671

Well for a 230V circuit, 500V.

Ol Bristolian is my favourite =)

 

[Silly Sausage]

BTW I’ve been drinking Melomel cider all afternoon.

Aaahhh...that reminds me, 3 days of free real cider coming up soon!
I work the Cider Bar at a Beerfest every year.