Protecting 16mm tails

NickD · Mar 26, 2015

Got a domestic install with client requesting CU upgrade. Tails are 16mm, EC 10mm, and buried in structure between meter and fusebox. Rating of DNO cutout fuse not known. Ordinarily I would upgrade the tails & EC to 25/16 as a matter of course (domestic load includes an outdoor hot tub as well as the usual sockets/cooker/immersion type stuff, don't recall if electric shower present) but routing them through the existing route of the 16mm tails looks like a non starter and I can't see a practical alternative route. The meter box is small and absolutely chocker with no space in there to add a separate fused cutout. Adding a fused cutout next to the replacement CU (in downstairs cloakroom) would probably be doable but cluttered/messy.

Installing a 63A MCB in the new CU, suitably labelled, immediately downstream of the main switch and feeding all RCDs/final circuits...good/stupid idea?

telectrix · Mar 27, 2015

trev said:
Nick the DNO fuse is there to protect their kit so if a 40/60/80 amp fuse has been quietly getting on with the task and not bothering anyone what possible motivation could they have for changing it? I've got a 16 amp RCBO on a radial circuit in my house, it's been doing what it does for about 6 years now, think I should change it for a 20?

of course you should change that 16A for a 20A. what about when you add the 10kW shower to that radial?

NickD · Mar 27, 2015

trev said:
Nick the DNO fuse is there to protect their kit so if a 40/60/80 amp fuse has been quietly getting on with the task and not bothering anyone what possible motivation could they have for changing it? I've got a 16 amp RCBO on a radial circuit in my house, it's been doing what it does for about 6 years now, think I should change it for a 20 just for the hell of it?
I don't think you're pretentious by the way, wrong, misinformed, ill advised perhaps but not pretentious

I can't think of a reason, but that doesn't mean there isn't one. Big organisations move in mysterious ways. I would be happier with some kind of assurance that I am perfectly within my rights to rely on the DNO fuse to protect the tails.

20 is a rounder number than 16 if you tend to think in decimal?

Are you sure you're not ill advised when you advise me that I'm being ill advised?

trev · Mar 27, 2015

It's already got one Tel, the 2.5 feeding it doubles as a heater

Leesparkykent · Mar 27, 2015

telectrix said:
of course you should change that 16A for a 20A. what about when you add the 10kW shower to that radial?

Thats when you remove the circuit from the rcbo due to nuisance tripping and dab it in with the tails lol.

Knobhead · Mar 27, 2015

As an experiment I ran my flat on a 16A MCB for two months. Never tripped once.

If you look for the diversity figures UKPN use they’re unbelievably low.

trev · Mar 27, 2015

Leesparkykent said:
Thats when you remove the circuit from the rcbo due to nuisance tripping and dab it in with the tails lol.

Funny you should mention that, I did an EICR on a dog grooming place the other week, 8.5k shower fed in 4mm, no MCB, supply to it shoved in with the tails then through an 80 amp RCD

NickD · Mar 27, 2015

Why do you need a shower? You've got us.

Knobhead · Mar 27, 2015

Nick, just admit, you’re milking this job by adding totally unnecessary work.

Someone had to say it, it may as well be a grumpy git like me.

Leesparkykent · Mar 27, 2015

trev said:
Funny you should mention that, I did an EICR on a dog grooming place the other week, 8.5k shower fed in 4mm, no MCB, supply to it shoved in with the tails then through an 80 amp RCD

I see something similar in a kebab shop for the fryers once, ironically the place was called blaze kebabs lol.

NickD · Mar 27, 2015

Tony said:
Nick, just admit, you’re milking this job by adding totally unnecessary work.

Someone had to say it, it may as well be a grumpy git like me.

If I was going to milk the job, I would have just got on and milked it without asking about it. Actually I just want to do an engineeringly-correct job, if that's a word. If it suits you to believe that milking it is my motivation then that's your prerogative. I could think of a darn sight more lucrative ways to milk this job than bunging in an OCPD, if that was my inclination.

Knobhead · Mar 27, 2015

Non of your arguments have any credence yet you persist in them.

Why?

Octopus · Mar 27, 2015

Tony said:
Non of your arguments have any credence yet you persist in them.

Why?

Because the OSG has a pretty picture showing tails to be 25mm

NickD · Mar 27, 2015

Client at a job the other day had agreed a board change in order to extend the socket ring circuit. However with the fusebox cover off it became apparent that the standalone RCD next to it was protecting the socket circuit in question, not the shower circuit as advised. RCD was in good order and so was the socket ring circuit. Did I milk it by proceeding with the board change? No.

NickD · Mar 27, 2015

Tony said:
Non of your arguments have any credence yet you persist in them.

Why?

Forget any arguments you think I'm making then and please just answer my question; do you consider it is entirely justified and good engineering practice to rely on the present rating of the DNO's fuse to protect the consumer's tails?

Octopus · Mar 27, 2015

NickD said:
Forget any arguments you think I'm making then and please just answer my question; do you consider it is entirely justified and good engineering practice to rely on the present rating of the DNO's fuse to protect the consumer's tails?

and common sense applied.