rcbo neutral and earth tails

I've just finished tidying up the CU so there is space to fit RCBOs in place of MCBs, and it looks quite neat. But then there is a pile of blue and white spaghetti from the few RCBOs that I have already fitted. What is the best way to treat the neutral and earth tails from the RCBOs ? Can they be cut ? Should they be rolled up ? Of course its fine strand wire, so I suppose ferrules would be needed ... Simon.

Reply to
sm_jamieson
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I trimmed mine and used ferrules and the appropriate crimp tool (not expensive) from RS.

Reply to
Tim Watts

and then derated?

:)

Reply to
Robin

They must be cut down to size (esp the neutrals)

I would not bother with ferrules for the neutrals.

The last one I did I put all the earth leads together.

Photo here of part finished job.

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Reply to
ARW

I was never that convinced with the need to put ferrules on all finely stranded cables to be honest. I get the point of it though. I would be inclined to twist such cable to reduce the change of it spreading away from the screw. I tinning then end with solder considered any use in place of ferrules ? What is the actual legal requirement/regulation for them ?

So in fact you didn't put ferrules on any of the cut tails ? The earth ones I know are only a reference point for the RCBOs anyway - thats why they are so thin !

So if I twist together a whole lot of FE tails and put in one earth terminal that will be OK ?

Simon.

Reply to
sm_jamieson

I always thought that putting lots of earth wires into a single screw terminal in a cu was bad practice.

If a screw works loose, you could potentially lose several earth connections in one go.

In the case of the functional earths, that means quite a few rcbos will then trip upon loss of functional earth.

You effectively have the behaviour of a split load cu rather than a high integrity and high availability cu.

I would personally use no more than two earth wires in one screw terminal so that you only loose one rcbo circuit plus one circuits earth should it work loose.

Reply to
stephenten

Soldering the ends then screwing them is a big no. Solder is soft & creeps, so a tight screw becomes a completely loose screw over time.

NT

Reply to
tabbypurr

Rather too much visible copper above some of the terminals for some tastes.

Reply to
Roger Hayter

I saw that too.....

When I wire up, I always try to have the bare wire be the same length as the terminal hole depth and the shoulder of the insulation butt up against the terminal block.

Anything that helps to protect against accidental brush contact by fingers or pointy metal tools can only be a good thing in my book.

Reply to
stephenten

And a mismatched main switch so the board fails type approval?

Owain

Reply to
spuorgelgoog

Does that matter?

I thought the only extra thing with type approval was assurance that it was good for 16kA PFC whereas individual components were only for 6 kA.

Of course if the manufacturer's instructions so you *must* not mix that might make a difference - though in the 17th all that was required was to "take account of manufacturers' instructions" (510.2). And I'd doubt a court would look kindly on a manufacturer whose component failed causing the house to burn down if they argued "it doesn't matter that our bit was faulty, it wasn't all our kit so you can't touch us".

Reply to
Robin

I did say unfinished job:-)

That was a bit of a rushed job. I only had a couple of hours to do it and I had a sore head that day - been out for drinks with Geoff CETLtd the night before.

Reply to
ARW

Is that generally considered an issue? I like to see at least some so I know i've got decent purchase.

Reply to
R D S

So you were drunk in charge and had a lethal weapon in your right hand playing russian roulette with a fully loaded & energised CU!

?
Reply to
stephenten

Actually thats a good reason for not putting both ends of a ring circuit into the same earth terminal.

Reply to
sm_jamieson

And that's why I use double sockets that have two earth terminals. So one earth loops into one terminal and the other earth loops out of the other terminal.

I believe this is referred to as high integrity earthing and is recommended practice for IT equipment/server rooms/racks given that switch mode power supplies are common

Reply to
stephenten

Yes doubling the number of terminals is a good way of avoiding faults.

Its also not easy to detect the fault as a simple test will show an earth when one side could be disconnected.

Its like rings, they are only safer if you test them a lot more frequently than the time a fault might develop.

Its why when designing System X processors you tested the redundant bits, its not much use having a failsafe thats broken.

Reply to
invalid

Yes you are correct that if one screw terminal fails, a simple earth test at the socket will not reveal this.

The only way to test is to physically unscrew a socket, disconnect one of the earth wires and do a earth loop resistance test. Put it all back together if the test results is satisfactory.

Having said that, I still prefer sockets with two earth terminals as even if one terminal fails in socket, you still have an earth connection to all sockets until an island of unearthed sockets occurs with a second earth terminal failure.

In this case the islanded sockets lack of earth is easier to test for and hopefully these are also still protected by an rcbo with 30mA leakage threshold.....

Reply to
stephenten

I believe that the functional earth of a RCBO there is so that it will still work if the neutral is lost. I do not believe that the loss of an earth will cause the RCBO to trip.

Reply to
ARW

On 01/02/2019 19:10, snipped-for-privacy@tesco.net wrote: ... snipped

... snippedA sudden terminal failure is unlikely; what failure mode are you concerned about?

Reply to
nothanks

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