Hagar rcbo’s in three phase board

[Daz7h]

Has anyone had this issue before ? Was working on a three phase board, when I took the cover off I noticed a black spot on one of the rcbo’s. it happened to be smouldering and started to catch a light. I noticed another rcbo smouldering too. I instantly turned off the main switch as one of the rcbo’s was tripped and still smoking. After investigation I found that the neutral tail had dropped out of its terminal. Is there a deeper problem here or should rcbo’s catch alight when dropping a neutral ?

 

[snowhead]

Was that the Circuit Neutral dropping out of the RCBO or the Main Neutral dropping out of the Neutral bar?

What was the reason you went to the DB and needed to remove the cover.?

 

[Daz7h]

Was that the Circuit Neutral dropping out of the RCBO or the Main Neutral dropping out of the Neutral bar?

What was the reason you went to the DB and needed to remove the cover.?

The main neutral into the main switch.
Reason to be in the DB was installing new circuits.

 

[pc1966]

Sounds a bit like a fault causing high N current that is not isolated by the RCBO tripping. Very odd!

 

[ipf]

Seems a bit fortunate.....installing new circuits and coming across such a serious problem!

Any evidence it's been ongoing?

 

[Daz7h]

Sounds a bit like a fault causing high N current that is not isolated by the RCBO tripping. Very odd!

Thing is there was literally 5 sockets and 4 led high bays on the DB at the time and one of the rcbo’s was off

 

[Daz7h]

Seems a bit fortunate.....installing new circuits and coming across such a serious problem!

Any evidence it's been ongoing?

It hasn’t been ongoing, was pulling in singles in trunking around the bottom of the DB must have pulled on the neutral tail. But that isn’t the issue. Regardless of how the neutral dropping out of the terminal, the rcbo’s shouldn’t combust when losing the neutral. If the electricity suppliers dropped a neutral off the pole would the house just go up in smoke because of it ?

 

[James]

Loss of neutral to a property is a very real and dangerous thing.
And yes, things can go up in smoke.

Highlights the importance of safe isolation and testing before re energising

 

[suffolkspark]

Interested.... any photos

 

[James]

It is quite possible that you have dameaged many single phase appliances
Without the N they can have 400v across them.

 

[Daz7h]

It is quite possible that you have dameaged many single phase appliances
Without the N they can have 400v across them.

No damage to appliances only led high bays connected.

 

[Daz7h]

Loss of neutral to a property is a very real and dangerous thing.
And yes, things can go up in smoke.

Highlights the importance of safe isolation and testing before re energising

Safe isolation and testing wouldn’t work if the neutral fell from a power suppliers pole

 

[James]

Safe isolation and testing wouldn’t work if the neutral fell from a power suppliers pole

It happens quite often in rural locations, the local scrap metal thieves steal the N cable and the farm or farms end up with a fair amount of damaged equipment.

And in many situations, a loss of N would be picked up before re energising.
If I saw 3 to 4 hundred volts phase to N I would not be turning on the big red switch!

 

[Daz7h]

We weren’t re en

It happens quite often in rural locations, the local scrap metal thieves steal the N cable and the farm or farms end up with a fair amount of damaged equipment.

And in many situations, a loss of N would be picked up before re energising.
If I saw 3 to 4 hundred volts phase to N I would not be turning on the big red switch

It happens quite often in rural locations, the local scrap metal thieves steal the N cable and the farm or farms end up with a fair amount of damaged equipment.

And in many situations, a loss of N would be picked up before re energising.
If I saw 3 to 4 hundred volts phase to N I would not be turning on the big red switch!

This is in an islolated building, nothing was isolated as the only thing energised was led lighting which never failed. They stayed on so until finding the burning rcbo’s we never knew there was any fault.

 

[pc1966]

There is another thread like this when testing and things went "bang".

Wonder if the FE arrangement is partly to blame, but that is not what I understood them to do and when I IR tested some by mistake they survived 500V DC (without smoke) showning only a few hundred kOhm (from memory).