17th Edition - RCD requirements and concealled cables

[Spark123]

SWA comes under part (i), the conduit comes under part (ii) of the regulation.

 

[Spark123]

maybe the european style switching (auto alimentation???) with elv switch drops will become more common?
or pull cords?

Suprisingly ELV doesn't appear to have been considered when writing the regulation on concealled cables.

 

[ban-all-sheds]

SWA comes under part (i), the conduit comes under part (ii) of the regulation.

Indeed.

And 522.6.6(i) says that the armour or metal sheath must be suitable for use as a protective conductor, so of the likely domestic sizes, including the one I missed before, the following do not have armour suitable for use as a cpc:

10mm², 16mm², 25mm² 2-core

16mm² 3-core.

 

[Spark123]

They may not pass table 54.7 (was 54G) but if they pass the adiabatic they can still be used.

 

[NotHimAgain]

It may be of interest to know that the RCD requirement was added very late in the day. The skilled and instructed person clauses were added even later.

Not the best bit of work in BS 7671 //www.diynot.com/forums/:cry:

 

[ban-all-sheds]

They may not pass table 54.7 (was 54G) but if they pass the adiabatic they can still be used.

That's a lot of work - hand on heart, and pen about to sign to say that to the best of your knowledge and belief you've exercised reasonable skill and judgement, would you actually do the calculation for (and this seems the likeliest) SWA used to extend meter tails?

 

[Spark123]

Probably not, as long as the PFC is low enough and efli low enough etc then I'd let it pass.
At the end of the day, how many people do the adiabatic equation for flat twin and earth?

 

[ban-all-sheds]

Probably not, as long as the PFC is low enough and efli low enough etc then I'd let it pass.

PFC and EFLI tend in opposite directions....

At the end of the day, how many people do the adiabatic equation for flat twin and earth?

Not Johnny Foreigner...

'tis true about T/E, but I've always assumed (ha!) that the published tables of EFLI limits for different devices are based on the let-through of the devices, and therefore make undersized cpcs work.

Who wants to bet that if the SWA armour spreadsheet is reworked with the armour expected to be equivalent to the cpc of 10/16mm² T/E the red areas go away....

 

[Spark123]

The max efli is more to do with getting the protective device to disconnect in the specified time for the given supply voltage, for the 16th ed the figures in chapter 41 were based on 240v (Uoc) but for the 17th ed it has dropped to 230v hence now all the max EFLI figures are lower.

 

[ban-all-sheds]

What I meant was that as EFLI rises, PFC falls, as per the predictions of Herr Ohm.

And the same concern about protective devices applies to the BS1361 protecting the SWA used to extend the tails, and what it's let-through is, as it does any other circuit and device, surely?

 

[333rocky333]

Anyone know the name of the metal stuff shown in use, within the PE mag

While they claim is is metal conduit it looks to me more like american style armoured cable.

I thought that , we see similar in Krispy Kreme on there stuff brought in from the US

 

[Spark123]

What I meant was that as EFLI rises, PFC falls, as per the predictions of Herr Ohm.

Yup, so we need to ensure that theres enough fault current flowing but no too much.

And the same concern about protective devices applies to the BS1361 protecting the SWA used to extend the tails, and what it's let-through is, as it does any other circuit and device, surely?

Good thing with fuses, as the fault current increases the time decreases. The same cannot be said for the tabulated values for MCBs
Taking your example for a piece of SWA used to extend the meter tails. For a 100A circuit- 25mm selected from table 4D4A, assuming no derating factors etc, is rated 118A.
2 core 70ºC SWA has an armour CSA of 60mm².
Your BS1361 100A fuse disconnects at 0.1s for 1800A and at 5s for 630A.
The minimum size of armour when the disconnection time is 0.1s is given by sqrt(1800A² x 0.1s)/51 = 11mm²
When the disconnection time is 5s the minimum size of armour is 27mm².

Using table 4E4A for 90ºC SWA
16mm² is rated at 110A and has an armour SWA 42mm²
sqrt(1800A² x 0.1s)/ 46 = 12mm²
sqrt(630A² x 5s)/ 46 = 30mm²

So using either would be OK, otherwise the fuse selection wouldn't be!!

 

[pdcelec]

Well good luck, if that's all you know.

That is all I know at the moment. That is the reason for doing the course. If I knew all about it then there would be no reason to attend.

And why do you regard Europe as something separate from us?

I am not going into politics here or anywhere else. I have my view to which I believe I am entitled.

 

[ban-all-sheds]

From the horses' mouths (note plural) it is not envisage that a domestic installation could ever effectively be deemed to be under the supervision of a skilled or instructed person.

Well mine is.

I am a skilled person, and my installation is under my supervision.

 

[Spark123]

But the question is what would happen should something happen to yourself? Is there any system in place for the continued supervision of the installation?
In a factory for example where I work we have electricians who need to be nominated. Above them there are area engineers in charge of that area of plant. Above them there is a site engineer in charge of everything. The installations in this instance are constantly supervised. Should one electrician become ill or pass away the system is in place for it to remain supervised. Also saves on doing PIRs .