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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> New Wire https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1245105055 Message started by oldspark on Jun 15^th, 2009, 11:30pm

Title: New Wire
Post by oldspark on Jun 15^th, 2009, 11:30pm

Hi guys, doing a new wire for inlaws not done one for a while,(industrial spark)some big changes in 17th edition I see.
Unsure what dist board layout to use ie split board 1 30mA rcd or individual rcbo's (costly)or just mcb's with rcd cover. I have 16th and 2391 inspect and test certs back in 2005. Got to confirm if TT or TN-CS. There is an earth rod outside front door. The circuits are as follows:-power up RMain, power down RMain, power kitchen RMain, LT up, LT down, LT kitchen, LT outside.2 smoke alarms linked. 6mm feed to garage.
4mm radial feed to outside socket IP rated.Sorry for being long winded. I'am up to speed with the requirments of equiportential bonding but Iam uncertain of what board layout to use. I will be doing the relevant tests to comply.Thanks

Title: Re: New Wire
Post by Lectrician on Jun 16^th, 2009, 6:09am

Sounds pretty standard.

If you cannot afford (as most can't) RCBO's for al circuit, just use a new 17th edition DUAL split load consumer unit.

You can also get some of these which have a few unprotected ways which are good for the submain to the garage for example, aslong as the cable is routed correctly to negate the need for RCD protection.

DO NOT use a single 30mA RCD to cover the entire install - this is not compliant.

If you do have TT, I strongly recommend having it converted to TN-C-S. Depending on your DNO, this could cost as little as £18.

Title: Re: New Wire
Post by oldspark on Jun 16^th, 2009, 8:47pm

If I go for cheaper option dual split board ,you mentioned don't use 30mA RCD to cover all inst, is this because of too sensitive. what do you recommend.Also garage feed I've made sure run in ok and safe, what boards available for this sub connection ? I don't want to instal an additional isolator at main distribution for garage I'd rather come off board you mentioned.Also I will be installing a small sub consumers unit in garage fed from said board with its own RCD protection is that ok (powering up 2 double sockets + lighting in garage). Also should I run in 10mm earth with the 6mm garage supply.

Title: Re: New Wire
Post by Lectrician on Jun 16^th, 2009, 8:56pm

A dual split load board is used to satisfy the regulations in terms of convenience and safety.

Safety - not in the sence of protection, but in the sence that if there is a fault you only loose half of your power (lights). You should have wired your property with a couple lighting circuits and a couple socket circuits (ideally a couple per floor). You then place the socket circuit serving one area on one RCD and the lighting circuit serving that same area on the other RCD. This way, if an RCD fails you still have power available to most parts of an installation.

If the cable to the shed/garage is SWA or routed so as not to require RCD protection (no burried in a wall less than 2" etc) then you do not need to RCD protect it at the origin, you can supply it from a non RCD protected way (some dual split loads have a few non RCD ways). You could then use a consumer unit with RCD incomer in the shed/garage. No need for a dual split out there.

You do not need to supplement the earth to your shed unless there is main equipotential bonding that needs to be done out there?

Title: Re: New Wire
Post by wozzy on Jun 16^th, 2009, 9:45pm

If it does turn out to be TNCS there will be issues to connsider of exporting this to the shed/garage.

I can talk most customers into having a RCBO board but in this case it may be a bit too costly. Depends how much the inlaws want to spend.

Title: Re: New Wire
Post by oldspark on Jun 16^th, 2009, 9:49pm

Thanks again. The new wire first fix is not yet complete . I'm open to sujestions , with the dual boards we've talked about, am i right in saying both sides can be protected with individual RCD'S.
Last board I've done years ago half on RCD half not (with mcb's)
Would you protect all circuits via an RCD?

Title: Re: New Wire
Post by oldspark on Jun 16^th, 2009, 9:54pm

What issues might I have if turns out to be TN-CS?

Title: Re: New Wire
Post by Lectrician on Jun 16^th, 2009, 9:55pm

All circuits need MCBs or fuses as they always do. The RCD does a different supplementary job.

17th edition DUAL Split Load (with a couple non RCD protected ways.
[gallery]Lectrician/1245185685.jpg[/gallery]

16th edition 'traditional' Split Load
[gallery]Lectrician/1245185686.jpg[/gallery]

Not my choice of brand, but it's what google found :-)

Title: Re: New Wire
Post by wozzy on Jun 16^th, 2009, 10:02pm

not my choice either lec but reasonably priced, and readily avaliable :)

Title: Re: New Wire
Post by oldspark on Jun 16^th, 2009, 10:14pm

This is brill .Thanks for pics. Not your choice of board though. what would brand name be of your choice? or do you mean RCBO'S board? is prefrence to you.

What do you think is the biggest significant change in the 17th edition?

Title: Re: New Wire
Post by wozzy on Jun 16^th, 2009, 10:57pm

brand preference was being refered to, i like hager boards for the money, but its a personal choice.
Other will say they prefer others personal choice really. Just dont buy cheap unbranded not BS standard boards which you will see for cheap on a internet aution site.
If you can persaude them to have a RCBO board i would go for crabtree.

Title: Re: New Wire
Post by wozzy on Jun 16^th, 2009, 10:59pm

you may find this good reading

http://www.esc.org.uk/forum/index.html

Title: Re: New Wire
Post by Lectrician on Jun 17^th, 2009, 7:56am

I would always go for MEM, but these are premium prices.

Title: Re: New Wire
Post by Y3 on Jun 17^th, 2009, 12:05pm

wrote on Jun 16^th, 2009, 9:54pm:

What issues might I have if turns out to be TN-CS?

There is the issue of a loss of supply neutral which could make your earth, any exposed and extraneous conductive parts connected to it, become 230v. If you have extraneous conductive parts in the garage, then you would need to export the equipotential zone from within the house, to it, using 10mm earth. There are mixed opinions on this, and the prefered option if you do have PME is not to export it at all and TT the garage, earthing the armour in the house CU, but not in the garage. If you have extraneous conductive parts in the garage, i.e water, then bond these to the MET of the small consumer unit, where the TT's earth is also connected. A single 30mA rcd main switch will be ok in this instance, because its a couple circuits in a garage, it wont affect the house install in anyway.

Title: Re: New Wire
Post by CWatters on Jun 17^th, 2009, 5:35pm

While on the subject... Should there be some sort of residual current device (RCD or RCBO) protecting a cooker radial?

In my CU I appear to have an incoming isolation switch feeding a group of MCB (one per each lighting circuit) and a group of RCBO (one per each power circuit)... but I noticed the cooker just has a B40 MCB.

In the kitchen there is a cooker switch (only a switch, no socket) feeding a cooker connection unit hard wired to oven.

Installation is about 3 years old.

Title: Re: New Wire
Post by Y3 on Jun 17^th, 2009, 5:39pm

If the wiring to the cooker switch and cooker isnt buried, i.e, surface trunking, then no it doesnt need an RCD protecting it. If the cable is buried less than 50mm in the wall, then it does. If this is an existing install of which your doing a PIR, then a code 4 would be applied to the buried cable scenario I just mentioned.

Title: Re: New Wire
Post by Zambezi on Jun 17^th, 2009, 6:53pm

CWatters
If your install is 3 years old then it was done to the 16th ed, no need for RCD.
If it was a new install to the 17th ed then follow Y3's post above.

Title: Re: New Wire
Post by oldspark on Jun 18^th, 2009, 7:07pm

Lec. am I right in saying if you would use dual RCD would you separate lighting and power so as to not be totally out of power or lighting if one RCD should trip? One last question on this issue,
what mA RCD'S, two the same 30mA's or different.

Title: Re: New Wire
Post by oldspark on Jun 18^th, 2009, 7:57pm

Smoke alarms , I intend to feed direct from consumers unit on its own circuit , would it be ok to connect on non rcd side of dual board?

Title: Re: New Wire
Post by Y3 on Jun 18^th, 2009, 8:21pm

wrote on Jun 18^th, 2009, 7:57pm:

Smoke alarms , I intend to feed direct from consumers unit on its own circuit , would it be ok to connect on non rcd side of dual board?

Depends if your going to bury the cable less than 50mm in the fabric of the building or not, without some form of earthed metallic covering?

Title: Re: New Wire
Post by Y3 on Jun 18^th, 2009, 8:35pm

wrote on Jun 18^th, 2009, 7:07pm:

You will have two 30mA rcd's that will come with your dual rcd, split load cu, as well as a main isolator.

Title: Re: New Wire
Post by oldspark on Jun 18^th, 2009, 9:34pm

Garage feed 6mm T&E from consumers unit to sub main rcd protected @ garage will be buried in less than 50mm in wall at some stage of the run , if i sheath well can I run from main consumers unit from 40a mcb non RCD side of dual board?

Title: Re: New Wire
Post by Y3 on Jun 18^th, 2009, 10:41pm

wrote on Jun 18^th, 2009, 9:34pm:

If the 6mm t&e is enclosed in some kind of earthed metallic covering when buried less than 50mm in the wall, then the 40a mcb on the unprotected side will be ok, not sure how you will adequately earth steel conduit or capping if its only going to be installed for part of the run?

You could just use SWA and export the equipotential zone if there are extraneous conductive parts out in the garage. A supplimentary 10mm earth could be attached to the SWA to provide the bonding, or you can select a suitably sized SWA to act both as an Earth and Bonding conductor (I dont know how large this would have to be, as I dont have the regs to hand)

Title: Re: New Wire
Post by supra59 on Jul 27^th, 2009, 8:15pm

its good practice to put the smoke detection on with the lighting circuit as if it trips its easy to see as the lighting will also be off, where as if seperate fuse this would not be the case hope this helps