3 phase problem after spark did 5 year safety inspection

jimthegent · Dec 23, 2023

Hi lads 5 year safety inspection the spark put the tails back and later line 2 of the 3 phase blew blowing the box off the wall and taking out the main fuse on the same line into the building can you all just say quickly what you think the spark may have done wrong ?
Cheers

[ElectriciansForums.net] 3 phase problem after spark did 5 year safety inspection

suffolkspark · Dec 26, 2023

DefyG said:
I still maintain its nothing to do with a balanced or unbalanced 3phase load.
I do not think it is an overload (you dont get flash/bangs like that and molten copper from an overload)
IMHO Its a L - E or N 'Dead Short'

I think we all agree on that, but as it was running when the inspector left, something happened in between, the live side of the main switch has a significantly larger hole in the top compared to the neutral, so id say its sat there loose with 50A running through it getting mighty hot followed by a bit of arcy action first before it truly ---- itself

jimthegent · Dec 26, 2023

DefyG said:
I still maintain its nothing to do with a balanced or unbalanced 3phase load.
I do not think it is an overload (you dont get flash/bangs like that and molten copper from an overload)
IMHO Its a L - E or N 'Dead Short'

Yeah and there's a lot of breakers on our system theres breakers in the pdu there are breakers on the main board surely it would just stop working with too much power drawn

DefyG · Jan 2, 2024

This was what is left of a RCD that had been in service for years without being touched (even during an EICR a few months prior).
It was from an installation in a community hall which would have been drawing less than 20A at the time.
The 'Dead Short' caused the cutout fuse (100A) to 'blow'.
We concluded it was an internal failure of the RCD and not caused by recent activity (as there wasn't any) but why? Who knows, one of those things!

HappyHippyDad · Jan 2, 2024

snowhead said:
Looks like the Red clamp has squashed the cable and split the insulation.
That's allowed the copper core to touch the earthed metal backplate and or the screw holding the clamp.

If it was the cable lose in the terminal or wrong side of termianl clamp it would have fizzled and overheated for a while before ultimately failing.

As Westwood, it looks like a dead short, especially with the ball of copper

Good spot! It looks exactly that.

freddo · Jan 2, 2024

There have been several reports of Hager RCCBs detonating when the test button is pushed which then blows the cutout fuse, it also happened to me a few years back, really loud.

MJPD29 · Jan 2, 2024

freddo said:
There have been several reports of Hager RCCBs detonating when the test button is pushed which then blows the cutout fuse, it also happened to me a few years back, really loud.

Had it happen with a square d rcbo once. All further test buttons were pressed with eyes closed and touching cloth.

jimthegent · Jan 4, 2024

MJPD29 said:
Had it happen with a square d rcbo once. All further test buttons were pressed with eyes closed and touching cloth.

Further to all that we had surge protection fitted but it still managed to turn pdu into molten plastic and circuit boards in scrap would surge protection be useless in this situation