Fuse blown and neutral wire sheathing melted.

[Jimmy Jones 1234]

Hi guys, hope you can try to shed some light on what might be the problem. Basically nothing is new, all been the same for 3 years since we moved in but over the past few days when the dishwasher was on (or anything plugged into a socket in the kitchen) I noticed a burning plastic smell. Couldn't figure out what it was until a fuse tripped the other day (popped actually - I thought a lamp bulb had blown), I opened up the fuse box panel in the gypsum wall and saw the melted plastic fuse box cover, took that off and saw melted plastic on the wires. The fuse on the right is what tripped but it only has the kitchen sockets on it, nothing big on here only a fridge and the dishwasher, from time to time the toaster and kettle. The one in the middle serves the bathroom lights and on the power to the corridor. There aren't any big loads here at all. I can't figure out why the plastic would melt like this. I tested it again and when I plug anything for long term (like the dishwasher) the fuse gets warm and then eventually hot and I'm guessing will trip again.

I will call an electrician obviously, but when the 'Corona virus' is over, not now - I'm staying home and not inviting strangers to my home either. I have kept the fuse off for now and using an extension lead for the appliances from another socket in the next room.

Attached is a picture.

 

[pc1966]

Yes, a good point there that you do not want any joints in a CNE if at all possible.

My thought was for a separate run in parallel from one of the unused holes in the Wago set back to the incoming supply. Though without having a good idea of where it could be safely attached at the incoming board (I think there was a photo, but all have gone now).

If it had to be joined then yes, a line-tap 'oрехи' would be the way, but I would have hoped for a spare screw terminal on a strip at the board. I.e try to have any single point of failure for the CNE.

 

[Jimmy Jones 1234]

It is fairly common to have the neutral thinner than the line (phase) conductors in a 3-phase system as usually there is some cancellation of the currents where the 3 loads join the neutral. With 3 identical (linear) loads you get zero neutral current back to the source, but that is the ideal case.

Still if it is aluminium wire it has all sorts of additional issues to maintain a reliable connection as it tends to compress more, has greater risk of galvanic corrosion, etc.

The spring loaded Wago style is a good start as they tend to maintain constant pressure. Other advice is to keep the joint dry (or use jointing compound) to reduce any tendency to corrosion. Still, I think Wagos are rated for Al wire (at least I seem to remember on a USA page).

For peace of mind I would check in a few days the connections are still sound (more so screw terminals on MCBs), obviously with power off! Don't over-tighten them, but make sure the are not loose. I know that is hardly a useful description but short of getting a torque screwdriver its the best I could do!

Thanks - very helpful. I saw this syringe in the shop when I went and wondered what it was, I'll certainly pick one up and do this as you suggest. But, do I use it only on the neutral wire or the also the 3 wires going into the fuses? They also look silver but are much more rigid, are they likely to be aluminium too if the neutral is?

 

[pc1966]

They will also be aluminium and I would put paste on all of them just to be sure.

 

[Jimmy Jones 1234]

That looks good! I would definitely use aluminium jointing paste on the incoming cable though, Wagos are suitable for aluminium provided you do so. Their product is called 'Alu-plus', it prevents corrosion and electrolysis and will reduce the chances of it going high-resistance and overheating. It comes in a syringe that you use to fill the entry hole of the connector. After cleaning the end of the cable, insert it into the connector immediately, before the oxide layer builds up. You'll only use 1% of the tube of paste but I think it's worth it and the joint should then last the remaining life of the cable.

One other subtlety to do with the neutral bar, you might choose to rework or ignore...

I think the bar is made up of three 5-way connectors linked togther. At the moment, because of the layout of the outgoing neutrals and earths, the top link adds two joints and therefore points of failure to the CNE. I appreciate it's probably the most reliable connection in the box, but if it were to fail (perhaps due to heating from the aluminium connection) two of the earths might remain connected to the earthed incoming cable while the other two are connected to floating neutrals which will become live, creating a significant shock risk between different appliances in the home.

What I would do is put all four earths in the top block, all four neutrals in the bottom, and the incoming cable in the middle. That way the two joints formed by each link only carry neutral or earth, not both. If heating from the aluminium cable joint caused a failure of the middle contact block, even if the earths become disconnected from earth, at least they remain connected together. Another advantage of placing the aluminium incoming cable in one of the three middle entry points of a Wago is that there is twice the cross-sectional area of metal inside to conduct heat away from it, helping to reduce the rate of deterioration if it runs warm.

Thanks for this, very helpful - yes I will remake the neutral bar as you suggest, it makes absolute sense as you describe it. Also will get the paste too. Quick question (probably a dumb one) the cables going into the Wago bar just push in, how do I get them out - they are very well fixed and no obvious way to release them. Or I get a new one and cut/ strip the cables.
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They will also be aluminium and I would put paste on all of them just to be sure.

Okay, will do.

 

[pc1966]

Typically you pull hard and wiggle the connector. But you may find the wire is damaged where it was clamped (as aluminium is quite soft) so needs trimmed back a bit, But not as much as simply cutting the exposed cable.

If you have any spare Wago I would be inclined to use a new one for the incoming neutral joint - you really do not want any risk of it opening.

 

[Jimmy Jones 1234]

I like to scrub the end of the conductor with paste and then wipe most of it off, so that the surface doesn't get a chance to oxidise before the connection is made as it is always covered in paste. This is normal practice for jointing ali busbars.

Bauhaus also have it
Alu-plus at Bauhaus

This is not advice or a recommendation to the OP but personally what I would do is to rearrange for the CNE to be one of the larger conductors, and to make two separate joints to the conductor without cutting it. I'd strip off some insulation and pass it through a clamp to which I could connect the earth, then continue the run into a second terminal for the neutral. That way although the conductor is serving as a CNE, the joints (which are much more likely to fail than the cable run) are not. I'd make a similar double-joint at the supply end, although those would be part of the CNE.

The Soviet / Russian equivalent of the European line tap is the «ореx» (orekh) meaning 'nut'. Not as in a thing you screw on like a wirenut, but as in something inside two half-shells that split apart. I rather like them. You can make a connection to an unbroken conductor which, unlike a line tap, is clamped separately to the tap so the two can be different metals. So when you have an ali CNE running up your riser, you can pass it through two oрехи, one to tap off a copper neutral and another for the earth, and in each case have the security of four clamping screws applying strong, even pressure onto the ali conductor.

Scroll down this link for pics:
Russian 'nut' tap connectors

Yes, will take the advice with the paste. I would also do as you suggest in the rest of your description, but I can't imagine how to do that, it's like rocket science to me, sounds very complicated and I wouldn't know where or how to start.

 

[Jimmy Jones 1234]

Typically you pull hard and wiggle the connector. But you may find the wire is damaged where it was clamped (as aluminium is quite soft) so needs trimmed back a bit, But not as much as simply cutting the exposed cable.

If you have any spare Wago I would be inclined to use a new one for the incoming neutral joint - you really do not want any risk of it opening.

They are cheap enough, I'll get a new one to be sure when I get the paste later today.

 

[Lucien Nunes]

In case my description was too garbled...

 

[Jimmy Jones 1234]

In case my description was too garbled...
View attachment 60971

No - this was absolutely clear, I will do this tomorrow, I got the new terminal and alu contact paste today. So I'll redo this as you said, makes perfect sense. The bit that was rocket science to me was this:

This is not advice or a recommendation to the OP but personally what I would do is to rearrange for the CNE to be one of the larger conductors, and to make two separate joints to the conductor without cutting it. I'd strip off some insulation and pass it through a clamp to which I could connect the earth, then continue the run into a second terminal for the neutral. That way although the conductor is serving as a CNE, the joints (which are much more likely to fail than the cable run) are not. I'd make a similar double-joint at the supply end, although those would be part of the CNE.

The Soviet / Russian equivalent of the European line tap is the «ореx» (orekh) meaning 'nut'. Not as in a thing you screw on like a wirenut, but as in something inside two half-shells that split apart. I rather like them. You can make a connection to an unbroken conductor which, unlike a line tap, is clamped separately to the tap so the two can be different metals. So when you have an ali CNE running up your riser, you can pass it through two oрехи, one to tap off a copper neutral and another for the earth, and in each case have the security of four clamping screws applying strong, even pressure onto the ali conductor.

 

[pc1966]

The bit that was rocket science to me was this

Basically what was discussed was a "fancy" way of implementing the diagram that Lucian posted, but instead of the central Wago block there are two line-tap "nuts" to take off two copper (I presume) wires, one to feed the top E block and one for the bottom N block. (Plus a few other improvements along the same lines).

But it is not something you ought to try - what you have done so far looks professional and is as good as I would expect if you had got someone in.

 

[Lucien Nunes]

It was just me musing on how I would do it with my own hands in my own house. The key idea is that one does not want the neutrals and earths connected together but not connected to the incoming CNE. Any break will tend to occur at a joint, not in the middle of a cable run, so if the common earth connection is attached part way along the unbroken incoming CNE cable, which continues through to a separate neutral bar, then either joint can fail without causing this undeisrable situation. The earth joint won't burn out because it never normally carries current, and even if the neutral joint does, and completely destroys the end of the cable, the earths will still be connected to it.
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[pc1966]

Still, given the rubbery nature of the cable and its age, if doing anything fancy I would replace it with 5 core and make the system TN-C-S!

But again, not something to try yourself.