Upgrade tails on CU replacement?

[andrew8902]

Hi. I have my NAPIT first assessment soon and I replaced a CU in a house which has 16mm2 consumer tails in place. I did not upgrade the tails to 25mm2, so my question is should I have upgraded them or am I allowed to leave the existing tails in place?
I do not know the rating of the DNO cut-out fuse
Yes the cut-out does have 100A stamped on the fuse carrier but that means nothing
Installation is 25 years old

Thanks
[automerge]1600593380[/automerge]

Hi. I have my NAPIT first assessment soon and I replaced a CU in a house which has 16mm2 consumer tails in place. I did not upgrade the tails to 25mm2, so my question is should I have upgraded them or am I allowed to leave the existing tails in place?
I do not know the rating of the DNO cut-out fuse
Yes the cut-out does have 100A stamped on the fuse carrier but that means nothing
Installation is 25 years old

Thanks

Also it was a Lewden RCBO board and I brought the cables through the knockout in the rear, am I required to use fire sealant in the rear section?

 

[telectrix]

16mm tails will be fine as long as they're not supplying a pot farm. mention to inspector that you've calculated the max load (allowing for diversity) at <80A.

no need for fire sealant unless you have broached a fire barrier.

 

[Dustydazzler]

I was generally under the impression that tails need to be updated to 25 on a 100a cut-out , but as tel says 16mm is fine in 99% of domestic situations and imo I would only ever use 16mm if the regs allowed it in all situations

as for fire foam , no you don’t unless it’s a ruddy great big hole in the wall

 

[ChrisElectrical88]

Be prepared to explain the reasons why they are 16mm tails and if you do what Tel says have your diversity calculations ready.
Hole in the back will be ok.
Might be asked if the RCBOs are Type AC or Type A and the reason for the selection.
Did you check all main bonding?

 

[Dustydazzler]

Be prepared to explain the reasons why they are 16mm tails and if you do what Tel says have your diversity calculations ready.
Hole in the back will be ok.
Might be asked if the RCBOs are Type AC or Type A and the reason for the selection.
Did you check all main bonding?

out of curiosity what are the fundamental differences between ac & a type rcbos

I believe only some manufacturers make both varieties

 

[buzzlightyear]

some times it's better to up grade to 25mm
Just in case they up grade more loading.
Car charger gear juccuci gear ect.. Ect.

 

[ChrisElectrical88]

Type A will do all of that of a type AC plus detect DC residual currents up to 6mA.
After watching a Sparky Ninga video earlier in the year I haven’t fitted a Type AC device since.

 

[pc1966]

The problem with the 'type AC' RCD is the current sensing transformer can be saturated quite easily by some DC component and it becomes blind to the AC part. I think some MFT used to use that trick for "no trip" Zs measurements.

Type A should have a bigger transformer and/or different magnetic core type so a "pulsed DC" waveform (i.e. AC & DC combined, say rectified mains) still produces enough of a measurement to fire the RCD trip mechanism. Cost should not be much more than type AC to make this.

I think that 'type B' RCD use a hall-effect sensor instead of a transformer's secondary winding so they can detect a smooth DC fault (as well as AC/pulsed DC), say leakage from a EV battery pack. Unfortunately the cost for parts here is significantly more than A/AC approach, but probably not as much as the catalogue price would suggest, that might be partly due to much lower demand, etc.

 

[ChrisElectrical88]

The problem with the 'type AC' RCD is the current sensing transformer can be saturated quite easily by some DC component and it becomes blind to the AC part. I think some MFT used to use that trick for "no trip" Zs measurements.

Type A should have a bigger transformer and/or different magnetic core type so a "pulsed DC" waveform (i.e. AC & DC combined, say rectified mains) still produces enough of a measurement to fire the RCD trip mechanism. Cost should not be much more than type AC to make this.

I think that 'type B' RCD use a hall-effect sensor instead of a transformer's secondary winding so they can detect a smooth DC fault (as well as AC/pulsed DC), say leakage from a EV battery pack. Unfortunately the cost for parts here is significantly more than A/AC approach, but probably not as much as the catalogue price would suggest, that might be partly due to much lower demand, etc.

Think your pretty spot on with your summery there. Although the price of A Types is now pretty low. Fusebox for example there about 4 quid more for the type A RCBOs. Type Bs are still expensive, up to £200 in some manufacturers.

 

[pc1966]

I suspect type AC will go fairly soon, as I don't think they are permitted in many EU places now, so no point in making two versions for any new design.

I don't really expect type B to drop massively though as they will only ever be used for things like EV chargers or PV supplies, which at best is going to be something like 10% or less of all applications. Fundamentally they are going to be more complex as well.

 

[ChrisElectrical88]

I don’t believe ACs are used in Europe in many country’s now, they were phased out over the last years for Types As. Frustrates me still when I ask for Type As in wholesalers and they ask me why I fit them when everyone else just sticks ACs in.

 

[AJshep]

I suspect type AC will go fairly soon, as I don't think they are permitted in many EU places now, so no point in making two versions for any new design.

I think your right! I did see a snippet of A2 (which is due to go to DPC soon) which Sparkninja put on his instagram, I expect you saw it too!
The wording was something along the lines of,"Type AC rcds can only be used to serve fixed equipment, where it is known the load contains no DC components(see note4)

Examples in note 4 being simple filament lighting and basic electric heating.

 

[pc1966]

I don’t believe ACs are used in Europe in many country’s now, they were phased out over the last years for Types As. Frustrates me still when I ask for Type As in wholesalers and they ask me why I fit them when everyone else just sticks ACs in.

Indeed.

But while AC are a couple of quid cheaper they will still be chosen by folks who don't know (or care) about the difference.

Though as said before, I suspect the real risk is small, but growing as more things have DC derived directly from mains used (e.g. washing machine motors).

 

[Mike Johnson]

I never understood the use of the AC type in France, when the A type was only a couple of € more, but the AC type is still available, I just wonder if its old stock being run down or they are still being manufactured.

 

[ChrisElectrical88]

Think we accidentally hijacked OPs post with this one ?.

 

[Mike Johnson]

All of my posts get hijacked why not this one as well.

 

[Vortigern]

I usually upgrade them, for one reason, I don't know what the main fuse is. And the cost is so little it ensures it is future proof as well. I also think belt and braces approach making sure everything can take whats thrown at it and a bit more besides.

 

[pc1966]

Wrangling the 19-strand 25mm seems easier than 7-strand 16mm, so less strain inside the CU as well. But in most cases no real need to change as free-air 16mm is easily able to cope.

E.g. Table 4D1A has 25mm vertical one-spaced method F (column 12) at 130A, and though it does not list 16mm for same conditions, applying the sort of ratio seen for method A (column 2) gives 99A

 

[nicebutdim]

Frustrates me still when I ask for Type As in wholesalers and they ask me why I fit them when everyone else just sticks ACs in.

You could politely suggest they stick to their job of selling stuff and leave specification to those qualified and well enough informed to decide what should be fitted.

 

[Dartlec]

Hi. I have my NAPIT first assessment soon and I replaced a CU in a house which has 16mm2 consumer tails in place. I did not upgrade the tails to 25mm2, so my question is should I have upgraded them or am I allowed to leave the existing tails in place?
I do not know the rating of the DNO cut-out fuse
Yes the cut-out does have 100A stamped on the fuse carrier but that means nothing
Installation is 25 years old

Another think to consider - Did you upgrade the main earth conductor from the MET?
It was/is common for 16mm tails to have a 10mm earth, but for PME I believe the regs state it must be 16mm.

If it's TN-S then maybe have the calculation ready if you are asked - or say that you've done it, with a confident look!
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I don’t believe ACs are used in Europe in many country’s now, they were phased out over the last years for Types As. Frustrates me still when I ask for Type As in wholesalers and they ask me why I fit them when everyone else just sticks ACs in.

Wonder how long it will be before all the Screwfix £70 Dual RCD boards will be Type A?