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New 17th Edition Regs, a few questions....

Postby goose » Fri May 30, 2008 7:40 pm

I have to rewire my house and install a new consumer unit. I'm not 'electrical' as it were, but work in IT and have some idea of cables. Also my mate who is an electrician is going to give a hand.

I've spoken with building control and was told I need to comply with the 17th ed regs.

I bought an MK consumer unit back in december ready for the work, its a sentry 12way split load. I've been getting prepared to do the chasing. But have noticed a few changes in the 17th. The 'safe' zones now need to have protection or be 50mm under surface or have an RCB on the curcuit.

if Ive understood the regs, basically every circuit in the house now needs to be on an RCB.

Right the questions.

1. The 50mm depth, say I'm using 20mm conduit, is the 50mm to the top of the conduit?? so then the chase would need to be 70mm deep!!! or can the chase be 50mm deep with the conduit inside?
(using round 20mm PVC channel), or do I now need to go an buy metal?

2. Is my new unsued consumer unit now obsolete or can I use it?? my worry is that if every chased circuit needs to be on an RCB (assuming less than 50mm) then even when I light bulb blows I'm going to completely loose power.

3. Can I use RCBO's with my consumer unit?? (they close to £25ea) Or is it worth just giving up on that one (the unit fully loaded cost me £60) and buying one of the currently advertised 17th ed compliant units.

Many thanks for advice
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Simply Build It

Postby ericmark » Fri May 30, 2008 8:55 pm

Even the electricians are not in agreement on exactly what is required but I will try.
1) In real terms the 50mm is not obtainable as there are limits to size of chase in building regulations I wouldn’t even try.
2) The use of cable to BS 5467, BS 6346. BS 6724, BS 7846, BS EN 60702-1 or BS 8436 will allow you not to use RCD protection for the cable.
3) Since all sockets and bathroom lights will need RCD protection anyway even if you use the cables to British standard above you will still need at least two RCD’s
4) Depending on make of consumer unit most can be reconfigured to take two RCD’s and/or use RCBO’s in the non protected side.
5) There are issues as to if some of the boards offered as 17th Edition compliant really are. The issue is although in one house they may be accepted in another they may not comply.
6) It is quite explicit “314.1 (iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuitâ€

Postby goose » Fri May 30, 2008 10:22 pm

thanks ericmark for the reply. I think I going to have to print it out to try and take everything in!

As you say 50mm is almost impossible to achieve - plater coat of 15mm still means a chase of 35mm into the wall.

The regs mention mechanically protected circuits would be exempt from requiring the RCD - would glav steel capping count as a mechanically protected circuit?

The Consumer unit I bought came with a RCD 80A 30mA, as its a split way unit- I presume that another RCD could be used on the other side of the split? So giving two seperate protected sections?

They do seem to be making things very difficult for people.
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Postby ericmark » Sat May 31, 2008 1:14 am

The capping is only to assist plastering and is not one of the options given. If some circuits could be wired with flexishield downstairs lights, cooker, immersion heater that would reduce the number of RCBO's required one for upstairs lights (since also bathroom lights) as to if any others required would depend on what you have.
It seems that when the 16th referred to splitting into circuits it did mean RCD as well as MCB protection and the interpretation most electricians gave the regulations was wrong.
The real problem is know one as yet really knows how close building control etc will expect one to follow the regulations.
Put yourself in there position and you have an inspector with very limited knowledge who must pass or fail something that will latter be rechecked by someone who does know the regulations if in 10 years time not so bad but if house is sold it may be only a few months time. In which case the inspectors report goes directly to a solicitors desk leaving him very open to ending up in court explaining why he passed it so it is hardly surprising they follow things to the letter. The electrician who is self certifying however has a balance between cost and following the regulations and is far more able to argue his case anyway.
There are also things like the Part P refers to BS7671:2001 not just BS7671 and until it goes through parliament or some case law is made it is still not clear as to the validity of Part P referring to obsolete regulations which are no longer available. I think it was a mistake referring to BS7671:2001 but on the other hand to refer to regulations which they don't control would also be a mistake.
This is why it is important to be building control to agree to what you intend to do. We can debate what should happen until the cows come home but last word is with building control and you will need to completion certificate when you sell.
Have you considered how you will complete the installation certificate? There are three sections Design, Installation and Testing and often you need qualifications in order to sign these forms.
And some people get some odd ideas I inquired with JIB about getting a card and was told I would have to get a labour's card and this is with a degree in electrical and electronic engineering and 30 odd years in the trade. I am sure you can work out my comments.

Postby goose » Sat May 31, 2008 7:46 am

thanks again for teh quick reply.

I interperated the following - Where mechanically protected as specified in Regulation 522.6 (iv) - that the Galvanised Steel channeling would meet this requirement. But as I'm reading it again - I wonder if it means the [i]actual[/i] cable be protected (like SWA) or as you've mentioned cable to BS 5467, BS 6346. BS 6724, BS 7846, BS EN 60702-1 or BS 8436 - are they SWA?

I'll have to speak with Building control again, they didnt mention submitting any plans, I collected a form which I have to complete and return (with a cheque) and they'll come out and inspect and certify (or not) the work after first fix and then on completion of the work. I will check about submitting plans.

I've only done data cabling in the past, so this is a real nightmare!
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Postby goose » Sat May 31, 2008 8:02 am

I've been trying to find BS number on the cable- but I wondering if this cable counts as mechanically protected?? Its 4x the price of std 2.5 cable - no wonder they want you to use it, its extortion!

SY Protected - Mulit-Flex

2.5mm 3 Core

Used extensively in construction,
food processing, heating and air conditioning installations.

Triple protection which enables the cable to resist even the most hostile of environments.
The transparent PVC outer sheath and tinned steel wire braid not only provides a high degree of mechanical protection and effective screening, but also gives the cable exceptional flexibility.
Used extensively in construction, food processing, heating and air conditioning installations.
Conductors Fine wire strands of plain copper.
Insulation: PVC, laying up: Cores twisted together in layers
Protection: Steel wire braid
Colour: Sheath - Clear
Core Colours - Blue, Brown and Green / Yellow.
Current Rating: 24 Amps
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Postby ericmark » Sat May 31, 2008 1:34 pm

I use Batt cables web site to work out what cable is what. I have found SY but no BS number except for fire BS6425 and BS EN 50266-1:2001 so although one would think it should be OK without that BS number can’t see how you can use it. Have you looked at Flexishield cable? I wonder why it says “Important Note: SY cables are not suitable for direct connection to the Public main supplyâ€

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