New Consumer Unit - not sure on configuration

[plugwash]

if PVC cable is dying after only 25 years then either it was probablly either a bad batch to begin with or it was abused. PVC cable run within it's ratings should last a very long time.

also adding RCD protection does provide an extra layer of safety regardless of the state of the existing installation.

 

[Space cat]

Working on the meter side of a CU is more dangerous than you might think. The voltage is the same but your only overload protection is the 100 amp service fuse.

Round one: You apply your screwdriver to the incoming live terminal block and find yourself embedded in the opposite wall. OK, you're not that stupid.

Round one: With your thick rubber gloves and insulated screwdriver you remove the incoming live wire from the terminal block and pull it out down the back of the CU. There's a bright flash of light from somewhere behind the CU and the service fuse goes off with a bang. I imagine it will be a very big bang. Well done; you just put a dead short across the supply. It is Friday night. You are completely without power until Monday (how long will your freezer stay cold?) and, when the nice man from the electricity board comes to replace the fuse, you'll have some explaining to do.

Round two: The live wire can be lifted clear of the terminal block and placed carefully to one side. Or maybe you cut it with your insulated cutters. You get on with removing the neutral. Did you nudge that live wire of did it just slip - or sag under its own weight? The bare end comes down on a copper pipe. There is a blinding flash and a very big bang and --- the cupboard is engulfed in a fireball. You just blew a hole in a gas pipe! If you live to tell the tale - which is unlikely - you'll have a lot of explaining to do.

Round three: You have your new Henley block already wired up to the new CU. You take the live wire out of the old CU and put it straight into the Henley. Smart move that but don't congratulate yourself yet. You repeat this with the neutral wire. Flash! Bang! Wrong terminal block? OK, you're not that stupid but there was a short on your new CU you didn't know about.

Round four: You've tested your new Henley and CU with a temporary supply from a small breaker in the old CU and nothing nasty happened. You've successfully transferred the meter tails into the Henley block and the old wiring across to the new CU. With a sigh of relief you switch on and --- Bang! What the ---- happened? There was a pre-existing neutral to earth short on the old wiring that you never knew about. You might never have found out either except that you managed to cross the meter tails over!

Round five: Over to you.

 

[plugwash]

yeah pulling the fuse is much safer than dealing with live cables.

 

[comms]

Firstly Jimbo I apologise if my second post caused offence or upset, it was meant as a small wake up call as to why sparks charge what they do for a cu change & I did include what testing is required (so not a totaly unhelpful post).

Anyway if you do go ahead and undertake the work at least go down the route of notification to building control then it will (or should) be tested & certificated upon completion for you.

As for doing the work, as I said in my earlier post check that the main bonding to the gas/water/oil (what ever you have) service are bonded with 10mm green/yellow earth conductor.
Check that the meter phase/neutral tails are 25mm & main earth is 16mm.
And get your mate (or the seal fairy) to pull the service cutout fuse before changing the cu, it's not advisable to work with live tails.

 

[Jimbo]

Okay, well my setup is TNCS and I intend to pull the master fuse before I start.

If I start. Believe it or not, I have taken on board everything you've all said. While I like to save money where possible, and believe that there is a large part of this work that I'm capable of doing, I'm not a fool and I don't want to put anyone's life at risk.

I'll talk to my mate and ask him the questions you've posed, and if I'm not satisfied he knows what he's doing I'll go the pro route. I know that won't satisfy some of you, but I thank you all for your comments and if I survive, I'll let you know how it went

 

[securespark]

As for the 17th...don't RCD the whole circuit - that is contrary to regs. Just take the loop to an RCD spur @3A and feed the bathroom from that.

 

[viewer]

As you're going ahead and pulling the fuse, can I repeat advice given on this forum several times:-
Write a plan of action and tick off as you go along.
Check torch batteries and tools. Check everything to go inside the CU will do so and that it can be fixed where you want in (cable entry etc)
Make sure everyone in the house knows what you're doing and that they have been fed and watered. Have a cup of tea. Allow plenty of time and start in the morning so you're not in a rush to finish before it gets dark.
Ensure all circuits are isolated
Check the fuse holder condition. If it doesn't look perfect then don't touch it. Wear rubber gloves and shoes, but not a watch. Put empty fuse holder back.
Make a sketch of existing connections and MCB (etc) connections before you disconnect anything.
As you remove each wire, label it.
Test as you can (see above)
When reconnecting ensure all circuits off and start by switching RCD on, then RCD protected circuits one by one before doing same with any not on RCD side.
Best of luck
V

 

[bernardgreen]

but I thank you all for your comments and if I survive, I'll let you know how it went

Make notes as you go along. Write down each action before you do it. or dictate to a tape recorder. Then if you don't survive we will know what not to do ...... Oh no...... that is for bomb disposal work...........:

 

[Space cat]

Write down each action before you do it. or dictate to a tape recorder.

If you do survive, remember to obliterate all evidence of breaking the seal on the service fuse.

 

[Anteaus]

Oh no...... that is for bomb disposal work...........:

Many a true word... The principle is the same, a procedure that keeps you right when you simply cannot afford a mistake will suit either job.

The biggest hazard in any high-current or live work is distractions. Turn off/unplug phones and make others in the building aware of what you are doing, and that you should not be spoken-to without good reason.

Other point to note is that tails need to be very securely tightened, especially at the CU end. A loose tail will oxidise and start burning, and then you have a fire on your hands. Double-check, or better, triple-check them, waggling slightly to settle them in between tightenings.

 

[plugwash]

Other point to note is that tails need to be very securely tightened, especially at the CU end. A loose tail will oxidise and start burning, and then you have a fire on your hands.

Unlikely, modern electrical kit is made of self extinguishing plastics, they will smoulder like hell giving off nasty smoke but they are designed not to actually catch light.

 

[Anteaus]

Unlikely, modern electrical kit is made of self extinguishing plastics, they will smoulder like hell giving off nasty smoke but they are designed not to actually catch light.

In Theory.

"Self-extinguishing" only applies when there is no external source of heat-input, e.g match applied then taken away once alight.

What actually happens is that the isolator-switch or whatever plastic part carbonizes. Carbon is a conductor, thus starts to pass current. Heats up. Starts burning. Heats adjacent plastic. And so on. Domino effect. If you're lucky the supply-fuse goes before the heat-output becomes sufficient to ignite adjacent wood.

Those 1930's metal CU's with porcelain insulators were inherently a much safer design from a fire point of view. Though, I would guess, a prohibitively expensive method of construction if used for modern equipment.

 

[RF Lighting]

Severely overloaded peice of 'self extinguishing' cable