Can anyone suggest why the Cut out fuse has gone twice?

[oharaf]

Right guys.

Have completed the re-wire, carried out all the tests.

Continuity - fine

Ins. Resistance - fine

Polarity - fine

Ze - fine

Zs - fine

RCD Test - fine

First power up main fuse went!!! turned out pre built split load board was a duffer.

Replaced that, and got a new fuse, Re-tested all exactly the same.

Powered up, everything working AOK for hours, set off home customer phones, no power, RCD not tripped

Arrive main fuse gone AGAIN.

Carry out all the checks whilst waiting for YEDL, still all fine.

Just phoned customer, all still fine

Suggestions please!!!!

 

[RF Lighting]

There must be something very wrong in the CU, or maybe even the meter (but this is pretty unlikely)

I've only know one cutout fail in ten years that was not due to overload, and this was due to a severed submains cable and a bit of bad discrimination.

Can we have a photo?

You haven't done something daft like let the busbar touch the neutral screw on the RCD have you?

On a side note, can we have our new forum yet?

 

[oharaf]

Mmm, the problem with the CU originally was that who ever put it in the box HAD put the Neutral of the RCD on the busbar, so suprise that did take out the main.

The new one however, I checked very carefully for any stupid direct shorts and there are none!!!

Stranger and stranger

Remind me RF what was the new Forum going to be?

 

[Spark123]

What do you want another forum for when you have one here:
http://forums.rlfans.com/viewforum.php?f=17

 

[TicklyT]

I wonder if it was just the elves at work on the service fuse?

ELF = Early Life Failure, the replacement service fuse just wasn't up to specification, and prematurely failed after a few hours rather than the expected life measured in years.

We've all found some parts at some time that just shouldn't have got past QC at the factory, so why not fuses as well?

I'm still picking up the repercussions of a faulty batch of equipment from one of our suppliers. One poor customer had one unit replaced three times before the batch fault was identified.

 

[sm1thson]

On a side note, can we have our new forum yet?

is that in reference to this topic not been typical DIY? because i think its a good topic to leave on the normal boards, walking into B&Q and seeing the CUs stacked up leads many people to believe its a simple swap, this post indicates all the reading and testing that must be done and that even then it can and does still go wrong.

 

[JohnD]

it might be interesting to put a clamp meter on one of the tails

 

[sm1thson]

Another thought. there was a fault with the first CU which caused the fuse to blow the massive current may have damaged the meter or something causing a new fault (that is only a complete guess and tainted by the fact theres a current post asking about the condition of his leaking service head)

 

[oharaf]

John D, will try that tomorrow, the house is v old and might have some issues, not that i've seen any, apart from the ones i've mentioned

 

[jason1958]

> First power up main fuse went!!!
> turned out pre built split load board was a duffer.

Not sure how a board blows the main fuse.
BS1361 63-80-100A fuse takes 800-1200A to blow instantly.
During which time you are treated to a a large flash & pop.

Could be a bad termination in the cutout, overheating the old fuse, making it weak and susceptible to failure. The new fuse could be defective or the termination is running hot enough when loaded to cause the fuse to fail, however that seems unlikely (you would smell it).

Could be the polarity was reversed on the old installation, and thus what you think it Neutral is actually Live and pumping current down your MEB so blowing the main fuse. That is very unlikely - DNO get the living daylights kicked out of them if they do not check polarity at the cutout & meter.

Await the DNO.

BS88 may have different trip characteristic, but is commonly used for higher breaking capacity where your EFLI is extremely low (short run from the trans).

I assume it is a modern black plastic cutout and not some old metal thing with "Noah Woz Ere" written on the side

 

[oharaf]

Hi Jason

what you describe is true, but no flash nothing!!!!!

Just both gone... Anyway replaced now and working.

I thought may be the meter was buggered, polarity is / was fine

Mystery to me.


Love to the home country, if you're in Sligo have one in McGuinness' for me

 

[jason1958]

Very strange.

Quality control on electrical stuff is pretty poor these days.
The cause of failure of old-fuse & new-fuse may be quite unrelated.