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.

 

[Lucien Nunes]

it's not 3 phase.

Oh yes it is. 3-phase 400/230V 25A incomer, 3-phase meter, standard Soviet 3-phase colours (I was right about that 4-core cable) yellow, green, red phases, blue / grey / black as PEN, even a standard Soviet 3-phase socket. Remember you have 400 volts between breakers in there and between the circuits in the house, and it is very important that the blue / black / grey PEN cables are never disconnected or make bad contact as you can get all sorts of damage through overvoltage, as well as the possibility of equipment casings becoming live.

Is that an exposed live conductor on the circular fuse (next the the single breaker, top left)?!

Yes. A lot of DIAZED fuseholders have lost their covers over time, or never had them in the first place. E2A: That might be the cover lying loose on the bottom right of the cabinet.

 

[Jimmy Jones 1234]

WTF! Is that an exposed live conductor on the circular fuse (next the the single breaker, top left)?!

It all has a bit of a three phase feel to it though, 3 fuses middle left, three breakers in box top right, what looks like a 4 or 5 pin power socket bottom left...

I have no idea, should I touch it and see.. Luckily I keep my hands to myself in there.

Everything in the house is 230 volts (237 actually when I measured) so it can't be 3 phase can it?

 

[pc1966]

Oh yes it is. 3-phase 400/230V 25A incomer, 3-phase meter, standard Soviet 3-phase colours (I was right about that 4-core cable) yellow, green, red phases, blue / grey / black as PEN, even a standard Soviet 3-phase socket. Remember you have 400 volts between breakers in there and between the circuits in the house, and it is very important that the blue / black / grey PEN cables are never disconnected or make bad contact as you can get all sorts of damage through overvoltage, as well as the possibility of equipment casings becoming live.

Nasty. I guess one reason for not having TN-C here, etc. Presumably having a 4-pole RCD and TT arrangement is not common?

Yes. Pretty normal. A lot of DIAZED fuseholders have lost their covers over time, or never had them in the first place.

Good grief! And we end up in long debates/arguments about if its OK to change a CU when old lights never had a CPC!

What is the equivalent of the IET regs over there?
[automerge]1585412029[/automerge]

I have no idea, should I touch it and see.. Luckily I keep my hands to myself in there.

Everything in the house is 230 volts (237 actually when I measured) so it can't be 3 phase can it?

3-phase is typically 230V Live-Neutral and 400V Live-Live.

If you measure any one socket you see 230V, but if you were able/foolish to measure between sockets on different phases you would see 400V. Please don't!

At least not without checking your meter is CAT-III rated to 400V or similar first, AND you are absolutely clear it is not on ohms or amps before you probe...

 

[Jimmy Jones 1234]

Oh yes it is. 3-phase 400/230V 25A incomer, 3-phase meter, standard Soviet 3-phase colours (I was right about that 4-core cable) yellow, green, red phases, blue / grey / black as PEN, even a standard Soviet 3-phase socket. Remember you have 400 volts between breakers in there and between the circuits in the house, and it is very important that the blue / black / grey PEN cables are never disconnected or make bad contact as you can get all sorts of damage through overvoltage, as well as the possibility of equipment casings becoming live.



Yes. Pretty normal. A lot of DIAZED fuseholders have lost their covers over time, or never had them in the first place.

Okay, the 3 phase thing isn't written in the old photocopied electrical plans I have at home. Interesting. I never knew that.

As for the rest of what you wrote I have no idea what any of that means - is it good or bad, or helps with my problem in any way?

 

[pc1966]

Three phase has the additional hazard that if the neutral is open you can get voltages of up to the 400V appearing on stuff that expected only 230V, you can guess how that is going to end...

Looking at your original burned out picture, is that wire aluminium by any chance? It looks suspiciously silver to me.

 

[Jimmy Jones 1234]

I can read some text on the breakers. I would not be surprised if they were B16s. Is there really nothing visible?

Hears a pic of the breakers, the two on the left say 16A when I zoom in on the picture but I can't make anything out on the one on the right. I'm guessing they're all the same. Basically they used to be exposed in the kitchen with the previous house owner (to fat/ grease etc near the cooker) but when I moved in I covered this with drywall to keep them covered.

 

[pc1966]

Also the green wire to breaker 'I' on the left looks as if it is exposed coming out of the main wire, is it really an unsheathed earth that has been sleeved and put in to use as live?!

Or has the insulation perished and broken at that point exposing the conductor?

 

[Jimmy Jones 1234]

Three phase has the additional hazard that if the neutral is open you can get voltages of up to the 400V appearing on stuff that expected only 230V, you can guess how that is going to end...

Looking at your original burned out picture, is that wire aluminium by any chance? It looks suspiciously silver to me.

Do you mean the blue wire top left coming in? It is silver looking up close actually rather than copper but it is a really rigid wire, not soft or flexible at all like I would expect from aluminium, aluminium wires - is that even possible?

 

[pc1966]

Do you mean the blue wire top left coming in? It is silver looking up close actually rather than copper but it is a really rigid wire, not soft or flexible at all like I would expect from aluminium, aluminium wires - is that even possible?

You can get harder alloys of aluminium with a small amount of copper added, used for things like rally car under shields, etc, but possibly here.

That could explain the overheating, if you have aluminium against brass or copper it tends to corrode with any humidity at all and eventually you get thermal runaway, etc. It is very rare in the UK to see aluminium wire (outside of armoured cables above 50mm, and even then it is more of a thing in power networks than factories, etc) but more common in the USA.

If using aluminium conductors it is very important to take steps to avoid corrosion, typically by putting on contact grease to keep moisture out.

 

[Jimmy Jones 1234]

Also the green wire to breaker 'I' on the left looks as if it is exposed coming out of the main wire, is it really an unsheathed earth that has been sleeved and put in to use as live?!

Or has the insulation perished and broken at that point exposing the conductor?

I checked it now, I don't see any exposed wire anywhere on it. It's green sheathing but no idea if that is normal with soviet stuff. Lucien Nunes is more clued up on that I think.

 

[Lucien Nunes]

is that wire aluminium by any chance

It does have that sheen to it. Aluminium cables are common in some places (e.g. USA) and occasionally found elsewhere. If it's stiff it probably isn't Al, they are as soft as you imagine they would be, prone to making bad connections and overheating. They are not normally used for domestic wiring now due to these problems.

Also the green wire to breaker 'I' on the left looks as if it is exposed coming out of the main wire, is it really an unsheathed earth that has been sleeved and put in to use as live?!

I think it's a trick of the light. These cables did not normally have uninsulated cores, that's mainly a UK / USA thing. The cable is made to the traditional colour code for 3-phase during the Soviet era with green, yellow and red phases.

True TN-C seems very odd to us in the UK but much more common in older European and European-derived systems. There are a couple of reasons for that, including possibly the prevalence of 3-phase domestic and light commercial supplies that started out as 3-phase delta, and the later adoption of earthing as a protective measure in place of all-insulated construction. Sometimes only submains, sometimes all the way through the finals. I remember connecting the metal casing of fluorescent lights to the neutral of a 2-core lighting circuit in a German house in the 1980s and thinking it was the craziest thing ever, but got used to it.

 

[Jimmy Jones 1234]

It does have that sheen to it. Aluminium cables are common in some places (e.g. USA) and occasionally found elsewhere. If it's stiff it probably isn't Al, they are as soft as you imagine they would be, prone to making bad connections and overheating. They are not normally used for domestic wiring now due to these problems.



I think it's a trick of the light. These cables did not normally have uninsulated cores, that's mainly a UK / USA thing. The cable is made to old Russky standards with green, yellow and red phases.

Yes, it's really rigid. I tried to tighten the top screw in the terminal on the left just in case but I guess I overdid it and it didn't 'screw' anymore so I had to put the cable in the next hole down and it was a bugger to get in there with my big fingers with it being so tough a cable to bend. But when I shine a torch in there it is quite silvery looking and not like the other cables.

 

[pc1966]

Some info (or propaganda, take your pick) on aluminium wire if anyone is interested:

Aluminum Electrical Wire Information | The Aluminum Association

www.aluminum.org

Example of jointing compound:

Bicon X1 Electrical Joint Compound

Bicon X1 electrical joint compound by Prysmian is designed to prevent galvanic corrosion and to enhance connection in electrical joints. Get yours today online from Jointing Tech

www.jointingtech.co.uk

[automerge]1585413752[/automerge]

Yes, it's really rigid. I tried to tighten the top screw in the terminal on the left just in case but I guess I overdid it and it didn't 'screw' anymore so I had to put the cable in the next hole down and it was a bugger to get in there with my big fingers with it being so tough a cable to bend. But when I shine a torch in there it is quite silvery looking and not like the other cables.

It could be tinned (i.e. plated) copper wire then.

Not usually seen for domestic wiring but quite common for equipment wire, etc.

 

[Lucien Nunes]

Not usually seen for domestic wiring

Not these days, but historically most copper cable was tinned. With natural rubber insulation it stops the sulphur reacting with the copper, as well as improving connections generally.

 

[Jimmy Jones 1234]

Not these days, but historically most copper cable was tinned. With natural rubber insulation it stops the sulphur reacting with the copper, as well as improving connections generally.

Actually, the sheathing is very rubbery, so I think you are right. Your knowledge is pretty impressive, and your help very much appreciated. Not sure what my next step is now after cleaning up the wires, guess I just have to wait and see if anything happens again. When I tested earlier with everything on and plugged in and working that I could think of in the kitchen nothing got hot (or even warm) so I'm not much wiser, unfortunately. Hopefully, the cleaning up of the wires will do the trick but not sure I want to be doing this maintenance on a regular basis.