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Few CU upgrade related questions


sellers

Question

Ok, so done a CU upgrade today, I'm not part of a scheme but i'm going to be using this for my assesment so i want it to be spot on.

Am I right in saying the main earth of the DB has to be no less than half the csa of the tails?

Do you guys generally upgrade the MET or leave it if its ok. Its one of those where you wind the conductors around a bolt and tighten it up about 4 bolts in total.

Is doubling up circuits a big no no, or just not good practice. I bought a 10 way cu as its only a small semi but as I was putting it all together i realised there are 11 circuits. I can get away with modifying 2 sockets that are to the left and right of db on their own circuits but do i really need to for regs?

Can you put limitations on the test results? The customer says his washing machines are pluged in behind them and they are built into the kitchen cupboards. Thus IR tests are out.

Is it correct that I can add ze + (r1+r2) to get zs as my loop tester still trips the b6 mcb even on no trip.

Cheers folks

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main earth should be upgraded, but your not supposed to touch the clamp on a TNS system, so you can only upgrade between a henley or similar and CU. main earthing conductor should be no less than half neutral, so 16mm

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With Live/neutral shorted to earth is my result LIM for L-N IR as in limited, and I note it down in limitations of testing.

Also I was getting 3.05meg for L-E and N-E on the same circuit. Could this be something electronic that I haven't spotted to unplug.

How far can you go with Limitations, Can you limit L-N on most cicuits for ease of testing or is it bad practice?

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Ok, so done a CU upgrade today, I'm not part of a scheme but i'm going to be using this for my assesment so i want it to be spot on.

.... I bought a 10 way cu as its only a small semi but as I was putting it all together i realised there are 11 circuits.

Whenever possible I think it's also good practice to leave a few spare ways when you've changed a CU (for future additions). So for an installation with 11 circuits I would probably get a new CU big enough to leave at least 3 spare ways.

Is it correct that I can add ze + (r1+r2) to get zs as my loop tester still trips the b6 mcb even on no trip.

When a B6 trips for me I usually get a temporary link with a connector block on the end and connect that 6A circuit to one of the higher rated MCB's just to get the Zs.

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With Live/neutral shorted to earth is my result LIM for L-N IR as in limited, and I note it down in limitations of testing.

Also I was getting 3.05meg for L-E and N-E on the same circuit. Could this be something electronic that I haven't spotted to unplug.

How far can you go with Limitations, Can you limit L-N on most cicuits for ease of testing or is it bad practice?

do a continuity test before the insulation, if u get open circuit should get a decent IR result, if u get a reading on continuity theres something on circuit and not bad insulation. should really be getting >1000 meg ohms with new cable

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The MET you describe should be upgraded, use an earth block 4 ways are normally enough for a domestic.

I sometimes connect all earths to this, leaving just the 16mm to the main cu.

All bonding connected to this earth block can be removed far more easily for testing.

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sellers you need to read ur osg, the inspecotr will ask every possible question under the sun and more, my first nic inspector was with me 5 hrs (afternoon cancelled so i had him all day) i did every test imaginable totally stripped a cu and did full periodic, full range of tests and a bus load of questions also filled a couple of certs in for him .. read read and read more.

Bet that was a nightmare JL , having the assessor on your back all day !!

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sellers you need to read ur osg, the inspecotr will ask every possible question under the sun and more, my first nic inspector was with me 5 hrs (afternoon cancelled so i had him all day) i did every test imaginable totally stripped a cu and did full periodic, full range of tests and a bus load of questions also filled a couple of certs in for him .. read read and read more.

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Hi sellars.

You say " Can you put limitations on the test results?"

If you are changing a C.U then you will be completing an EIC. There is no facility on there for Limitations as there is on a P.I.R.

Your best bet is to make mention of the hidden sockets on the section marked " Comments on Existing Installation."and hope the assesor accepts this.

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Hi sellars.

You say " Can you put limitations on the test results?"

If you are changing a C.U then you will be completing an EIC. There is no facility on there for Limitations as there is on a P.I.R.

Your best bet is to make mention of the hidden sockets on the section marked " Comments on Existing Installation."and hope the assesor accepts this.

I suspect that those hidden sockets should also be declared on the EIC as a departure from BS7671 as they seem to fall short on the regulations covering Emergency Switching (537.4). It is normally expected that such sockets are wired through a double pole switch which is above counter height so that in the event of a fire etc the appliance can be isolated quickly and safely.

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So when you change a cu you fill out an eic not a pir? but I can still have a limitation at they fall short of the regs. But I can't have limitations on say a kitchen full of downlighters, I'd have to take all the lamps out to do L - N insulation resistance.

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So when you change a cu you fill out an eic not a pir? but I can still have a limitation at they fall short of the regs. But I can't have limitations on say a kitchen full of downlighters, I'd have to take all the lamps out to do L - N insulation resistance.

Yes a consumer unit replacement is classed as An alteration to the whole installation and thus an EIC is necessary (check page 29, Inspection, Testing and Certification, 5th edition, for more info -- or get the book if you have'nt got it already). If the work is in a domestic dwelling then it is likely a DEIC will be necessary (chapter 3, Inspection, Testing and Certification).

You cannot do full IR tests with those appliances plugged in so, as mentioned earlier, there is no limitations section on a DEIC but you can mention this under "Comments On Exisiting Installation".

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Sellers you haven't stated if there are FCU's for the appliances that are built in?

If there are, then you can test up to this point (if radial) and note on the comments on existing installation that you have tested up to this point only (for that circuit) and that the sockets supplying the accessories you mention are inaccessible. At least if the circuit is a ring you can drop the feed out for the appliance (and by pass any neons) and cover the ring tests?

I would also make a recommendation that the customer arranges for a further inspection to the accessories that are built in (i.e. the ball is with the customer for arranging the movement of the appliances for you to check) and you have covered you back if they decide that they don't want to do it.

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Another question- its a dual split rcd board, do I need to test the rcd trip times with every circuit or just once for each side of the board and thats my result for all.

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test each RCD once, and same result for all circuits it protects.

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test each RCD once, and same result for all circuits it protects.

Would agree, as you are testing the actual trip time of the RCD. Same would apply for each RCBO in place.

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Sellars.

It would have been a good idea if you enrolled yourself on a suitable 17th edition course prior to arranging your assesment..you need to be confident in your abilities when undergoing the assesment,by the questions you have asked I dont think that is the case do you? This forum is here to help you with problems and enquiries etc, whenever you request it, but it wont be able to help at the assesment...no offence intended just trying to save you any grief.

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