Cable getting discoloured / lifespan of cables

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noddy997

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What causes a cable to get discoloured?

I have a heating/hot water issue however the cable that comes from the boiler to the pump gets discolored on one side (on the side that connects to the pump). The discoloration can take a few weeks.

This then causes a delay for the heating/water to come on and eventually the heating won't come on. As soon as I strip a bit more fresh copper it works fine.

The cable is 24 years, 4 core blue, yellow, red type.

What is the cause of discoloration? I'm assuming heat?

What is the lifespan of cables.
 

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Looks like oxidation of the copper. Is it a damp area? Are the other conductors in that area also affected? If you clean the copper with a bit of wire wool or fine emery paper does that fix the problem?
 
pcaouolte said:
Looks like oxidation of the copper. Is it a damp area? Are the other conductors in that area also affected? If you clean the copper with a bit of wire wool or fine emery paper does that fix the problem?
Click to expand...
It's in the loft, other conductors perfectly fine. The conductor is in one of the terminals of the wago junction box.

I haven't tried cleaning it as you mentioned but instead strip the cable.
 
noddy997 said:
I have a heating/hot water issue however the cable that comes from the boiler to the pump gets discolored on one side (on the side that connects to the pump). The discoloration can take a few weeks.
Click to expand...
How far away is the pump from the boiler?
 
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When you cut back the wire did you also replace the terminal?

If a wire keeps failing in the same terminal, while other wires nearby are fine, then the most likely conclusion is that the terminal is to blame.
 
plugwash said:
When you cut back the wire did you also replace the terminal?

If a wire keeps failing in the same terminal, while other wires nearby are fine, then the most likely conclusion is that the terminal is to blame.
Click to expand...
This is a new wago junction box. Previously it did the same thing in an ancient wiring centre which had terminal blocks. That was in place for 24 years
 
plugwash said:
When you cut back the wire did you also replace the terminal?

If a wire keeps failing in the same terminal, while other wires nearby are fine, then the most likely conclusion is that the terminal is to blame.
Click to expand...
This is a new wago junction box. Previously it did the same thing in an ancient wiring centre which had terminal blocks. That was in place for 24 ye
jurassic sparkk said:
How far away is the pump from the boiler?
Click to expand...
Boiler is in garage, pump in loft. 15-20 meters of wiring I'd say
 
noddy997 said:
This is a new wago junction box. Previously it did the same thing in an ancient wiring centre which had terminal blocks. That was in place for 24 years
Click to expand...
The ancient wiring centre with screw down terminal blocks probably made a better connection to the wire than the new wago.
 
That's a strange one. The discolouration, as pointed out, is oxidation which is usually caused by the presence of moisture or heat.

I'm surprised stranded cable has been used over such a long run. It will have a lower current carrying capacity but unless the pump is a beast, I wouldn't have thought that's the issue.

If it's an older pump with no soft start, perhaps the inrush current as it starts might warm the junction briefly? If you have access to a thermal camera...

Are any of the other wires in that block effected? Is the boiler end of the cable oxidising? Does the problem persist if the cable is inserted into a different position in the connector?

There's nothing more permanent than a temporary fix so I'd be inclined to add a ferrule to the stranded wire and reinspect after a few months. Ideally though, you may want to consider replacing that cable with a beefier solid core one.
 
It might be that there is a fault on the other side of the connector.

The fault is usually heat.

If the connection is poor, it heats up and the copper softens, causing it to deform away from the pressure of the terminal screw, making the connection worse and the heat greater. I think it is called annealing, and is permanent unless the copper is re-hardened. The terminal expands and contracts with heat when it is turned on and off, enabling it to loosen.

If the heat travels down the wire, the softness will be present on the next bit you try to use.

This is most often seen on the switch terminals for electric showers, which carry a continuous heavy curre t, but I have also seen it in main switches.

Because copper is a soft metal, it crushes to shape after you tighten the s rew, and it is best to retighten it after a couple of weeks, as it will creep even if it does not overheat, and this can make it loose. It seems to be worse in stranded cables. If you fit a larger, solid-core wire, or if you have ratchet crimps and can add a bootlace ferrule, as suggested, you will probably cure the problem. Also examine or replace the terminal screw and the terminal mounting.

I have special ratchet pliers for bootlace ferrules, I don't know if ordinary ones are adequate.
 
DIYWell said:
That's a strange one. The discolouration, as pointed out, is oxidation which is usually caused by the presence of moisture or heat.

I'm surprised stranded cable has been used over such a long run. It will have a lower current carrying capacity but unless the pump is a beast, I wouldn't have thought that's the issue.

If it's an older pump with no soft start, perhaps the inrush current as it starts might warm the junction briefly? If you have access to a thermal camera...

Are any of the other wires in that block effected? Is the boiler end of the cable oxidising? Does the problem persist if the cable is inserted into a different position in the connector?

There's nothing more permanent than a temporary fix so I'd be inclined to add a ferrule to the stranded wire and reinspect after a few months. Ideally though, you may want to consider replacing that cable with a beefier solid core one.
Click to expand...
It is solid core. That's the issue no other cables are affected.

The boiler end wasn't affected. However back in December one of the other cables in the programmer was silver?

What bigger size would you recommend?
 
JohnD said:
Then the fault might be the terminal. Or excessive load.
Click to expand...
The connector is new installed Dec 23. It can't be both connectors were bad despite the terminal block box was 24 years old.

It will still be 240v to the boiler end. The cable that connects from boiler to the red wire at boiler end is fine and doesn't change colour.

The cable that connects to the pump is also fine it's just this one.
 
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