Worcester Bosch wires melting

[redd]

Hi

about an hour ago all the lights in my house tripped out. I went to the fuseboard and one switch was down. Flicked it back and it tripped out immediately.

few moments later theres and acrid smell and a little smoke in the room

tracked the smell down to the boiler, took the cover off and was met with this (see photo)😳

have got someone coming out tonight to look at it. In the meantime have turned the power off.

Any idea what would cause this earth wire to melt?

It’s a Worcester Bosch junior 28, has been in about 8 years without any problems

 

[centralheatking]

Go to the white box adjacent to the boiler, it will have a fuse access panel. Turn the switch off take out the fuse. I may have a red monitor light as well which will go out. You have been very lucky.
centralheatking

 

[redd]

Go to the white box adjacent to the boiler, it will have a fuse access panel. Turn the switch off take out the fuse. I may have a red monitor light as well which will go out. You have been very lucky.
centralheatking

cheers, have just done that

When you say ‘very lucky’, I’m guessing we were close to a big bang or fire?

Any idea what would cause this? I’ve had a good look and it’s just that earth wire that’s melted and scorched the plastic casing.

Also, the powers now isolated for the circuit it’s on. Presumably I can keep the gas and water on? (Engineer coming later on)

 

[SJB060685]

Looks like a ground fault somewhere, do as said above and have your guy look at it.

Note your RCD has done its job and the fuse may not have blown

 

[Chuck]

Any idea what would cause this earth wire to melt?

Tens, if not hundreds of amps flowing as a result of an uninterrupted fault. The boiler should have been protected by small fuse, typically 3 amp, in its mains supply, which would have prevented this. My guess is the boiler was wired into an unfused, or incorrectly fused, junction box.

You're lucky you still have a house and any occupants are alive. Get Bosch to repair the Boiler and a properly qualified electrician to check its supply. (It would be prudent to get them to check the whole house while their at it.)

 

[centralheatking]

As Chuck stated if your boiler does not have a white box adjacent with a 3 amp red fuse then your trip has done its job, picked up high demand and saved you. Take this very serously indeed that earth wire has melted due to heat the source of the problem needs tracking down. chking

 

[redd]

Thanks all, That’s quite frightening 😳

I’ve taken a look and you can see where the earth wire has melted into the adjacent grey wire (see pic). You can see the scorch marks on the casing too.

no other wires in the boiler seem to be affected

 

[Murdoch]

Interesting that the "earth" cable seems to be damaged - unusual to say the least.

Looking at the photo I wonder if the connections to the blue item "connected" to the earth cable and created a dead short - in this case I would have expected the 3A fuse in the boiler supply to fail - was the switch down the MCB or RCD?

 

[redd]

Tens, if not hundreds of amps flowing as a result of an uninterrupted fault. The boiler should have been protected by small fuse, typically 3 amp, in its mains supply, which would have prevented this. My guess is the boiler was wired into an unfused, or incorrectly fused, junction box.

You're lucky you still have a house and any occupants are alive. Get Bosch to repair the Boiler and a properly qualified electrician to check its supply. (It would be prudent to get them to check the whole house while their at it.)

I’m thinking the adjacent fuse box has been bypassed. As I turned it off on one of my attempts to get the mains power back on, yet it all tripped out regardless.
[automerge]1578314630[/automerge]

Interesting that the "earth" cable seems to be damaged - unusual to say the least.

Looking at the photo I wonder if the connections to the blue item "connected" to the earth cable and created a dead short - in this case I would have expected the 3A fuse in the boiler supply to fail - was the switch down the MCB or RCD?

Switch was down on the RCD

 

[ShaunCorbs]

Interesting that the "earth" cable seems to be damaged - unusual to say the least.

Looking at the photo I wonder if the connections to the blue item "connected" to the earth cable and created a dead short - in this case I would have expected the 3A fuse in the boiler supply to fail - was the switch down the MCB or RCD?

sparker so probably the the high voltage wire had a bit of the insulation missing so arc across

 

[SJB060685]

As these guys have said there should be a 3 amp fuse on incoming live to boiler system. Like I said though IF you have a bank of MCB's protected by an RCD this will have tripped before the fuse in the event of an imbalance most probably. If your fuse board hasn't got RCD's then the MCB will have tripped do to the ground fault overload

 

[Murdoch]

In the case of a dead short, whether the 3A blows, the MCB in the fuseboard or RCD trips is never consistent - sometimes its the RCD and the fuse or MCB...

Often see such faults in back boxes where the box isn't deep enough and the cables are crushed together - then its a matter of time before the sleeving fails ........ then the bang and the black scorch mark

 

[centralheatking]

cheers, have just done that

When you say ‘very lucky’, I’m guessing we were close to a big bang or fire?

Any idea what would cause this? I’ve had a good look and it’s just that earth wire that’s melted and scorched the plastic casing.

Also, the powers now isolated for the circuit it’s on. Presumably I can keep the gas and water on? (Engineer coming later on)

Well done you are ok now, sit back ...cuppa tea and wait for experienced electrician...do let us know what he says as we like feedback it helps us to learn more. centralheatking

 

[SJB060685]

To answer your question redd yes fires can be caused from faults like this, however the fuse and MCB should protect the system from this. RCD's protect people from a shock and work by detecting an imbalance between phase and neutral current, ie when theres an earth fault like you've just experienced

 

[bacon_sandwich]

yep, leave the breaker off. Burnt out earth wires can be a sign of another fault not related to the boiler.

 

[centralheatking]

yep, leave the breaker off. Burnt out earth wires can be a sign of another fault not related to the boiler.

It would appear that PF can do electrics ....well done all...just goes to show We are the Senior Trade
always knew this anyway did we not ! ? ....centralheatking Is there an Electricians Forum ? yes its under a stone
somewhere but nobody knows where ....chking

 

[SJB060685]

I have a very good understanding of electrics, I like to study it in my spare time but I'm not an electrician and I certainly wouldn't argue with Murdoch or any other qualified person 😂

 

[centralheatking]

I have a very good understanding of electrics, I like to study it in my spare time but I'm not an electrician and I certainly wouldn't argue with Murdoch or any other qualified person 😂

Its always important to know ones limitations ...I do. chking

 

[redd]

Thanks for all your help chaps

will report back with the diagnosis later

 

[bacon_sandwich]

Have a degree in electrical engineering and do frequent the other forum, lol
I tend to only look at ops that are either pure gas or electrical, my best friend is plumber 😛