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#146254 - 11/21/06 05:53 AM IEE/BS7671, 17th edition
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Notes on planned changes for the 17th edition of the IEE Wiring Regs., due to be issued January 2008 and come into effect June 2008:
http://www.iee.org/Publish/WireRegs/DPC/DPC_Introduction.pdf

One of the main changes seems to be for the much greater use of RCDs than at present:

 Quote:
Chapter 41 now requires {.....} additional protection by means of a residual current device with a rated residual operating current (IΔn) not exceeding 30 mA {.....} for socket-outlets with a rated current not exceeding 20 A that are for use by ordinary persons and are intended for general use


There are a few exceptions, but this effectively means that all 13A outlets for general-purpose use will require RCD protection, not just those likely to be be used for equipment outdoors as it presently the case.

I'm not happy about this change:
 Quote:
It is now permitted to protect cables concealed in a wall or partition by a 30 mA RCD if the normal methods of protection including use of cables with an earthed metallic covering, mechanical protection or the use of the safe zones cannot be employed.

It seems to me that the RCD is being used as the answer to just about everything, including the poor installation/protection of cables which leads to their damage.

In my book, the RCD should be viewed as an extra safeguard, not the primary means of protection.

Bathrooms are in for a few changes:

 Quote:
Zone 3 is no longer defined.

Each circuit in the special location must have 30 mA RCD protection.

Supplementary bonding is no longer required providing the installation has main bonding in accordance with Chapter 41.


I'm not sure that forcing the bathroom lighting onto an RCD-protected circuit is necessarily a good move, certainly not where the RCD tripping would take out all the other nearby lights too. That's no worse than existing TT installations where a single RCD feeds the whole house, but I'm still not convinced it's necessary.

The removal of supplementary bonding requirements seems to be raising a few eyebrows already. I noticed a couple of people on the IEE forum asking how they can now justify failing a PIR for no supplementary bonding given that it may soon not be a requirement. Someone even jokingly suggested a "Code 5" PIR report: "Does not comply at present, but will in a future revision."

Still in bathrooms:

 Quote:
This section now allows socket-outlets (other than SELV and shaver supply units to BS EN 60742) to be installed in locations containing a bath or shower 3m horizontally beyond the boundary of zone 1.


At last! Given the size of many British bathrooms though, it will be impossible to get outside the specified distance, so it will still be "no sockets" for many.

And finally for this post, a point which probably will not be of such impact for many but is of particular interest in a coastal holiday area such as this:
 Quote:
Electrical installations in caravan/camping parks and similar locations now includes the requirement that each socket-outlet must be provided individually with overcurrent and RCD protection.

Looks like there will be a big demand for 16A RCBOs in 2008!


[This message has been edited by pauluk (edited 11-21-2006).]

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#146255 - 11/21/06 12:20 PM Re: IEE/BS7671, 17th edition
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
 Quote:
In my book, the RCD should be viewed as an extra safeguard, not the primary means of protection.


I must say I always thought the RCD was defined as supplimentary protection, not the primary or only means of protection. Lessening the requirements on new installs just because there is an RCD appears very strange.

Having said that, I can see the point of making an ad-hoc solution like the Americans with the exemption for "fake" grounded outlets with GFCI for old existing wiring with only two wires.

I can also see the point of requiring RCDs as a general rule in bathrooms. I would view this as replacing a marginal protection in the form of supplementary bonding by a better protection in the form of an RCD.

I don't see why protecting the light would be a problem: If the lightbulb fails, which happens every so often, you are left in the dark. The number of times the RCD will trip in comparison is, what, one to one thousand?

[This message has been edited by C-H (edited 11-21-2006).]

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#146256 - 11/22/06 12:18 AM Re: IEE/BS7671, 17th edition
Kenbo Offline
Member

Registered: 04/07/06
Posts: 234
Loc: Scotland
Thanks for the link

My understanding of the document is that it says

"additional protection by means of a residual current device............be provided for sockets with a rated current not exceading 20A"

To me that says MCBs re still to be used and an RCD added as extra protection.

I understand the terms SELV, PELV but FELV?

Part 7....will this now include portable generator sets that are so popular with caravans
_________________________
der Gro├čvater

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#146257 - 11/22/06 04:45 AM Re: IEE/BS7671, 17th edition
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
 Quote:
I don't see why protecting the light would be a problem: If the lightbulb fails, which happens every so often, you are left in the dark.

True, but at least in that case you have the chance of being able to get some light from the hallway or an adjacent room.

Given the present cost of an RCBO and the way that most homes are wired, I see the answer to this in most case being to just transfer the whole lighting circuit which includes the bathroom light onto the RCD side of a split-load board. That will also increase the chances of the whole lighting circuit being taken out by an earth fault on a different circuit.

As I said, we already have many rural homes on TT with a main RCD anyway, which is even worse, but I guess I'm just not in favor of seeing yet more branch circuits dumped onto a main RCD unnecessarily.

 Quote:
To me that says MCBs re still to be used and an RCD added as extra protection.

Again, unless the price of a combination RCBO starts to fall dramatically so that installers start fitting one RCBO per circuit, I just see all circuits which feed 13A outlets being transferred to the RCD side of a split-load board. Or perhaps in some cases we'll just see a single-bus board and a main RCD fitted to protect everything, even on TN-S and TN-C-S systems.

 Quote:
I understand the terms SELV, PELV but FELV?

Functional Extra-Low Voltage. Basically any extra-low voltage circuit which does not meet the requirements to be classified as SELV or PELV.

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#146258 - 11/24/06 02:50 AM Re: IEE/BS7671, 17th edition
djk Offline
Member

Registered: 12/26/02
Posts: 1269
Loc: Ireland
Situation we have in Ireland is that ALL socket outlets under 32A must be connected to a 30mA RCD.
Means things like the "cooker connection unit" socket is not allowed.

There have been some changes to the regs here too with regard to bathrooms.

We've a new draft of our wiring regulations in the process of being finalised at the moment by the ETCI.


-----

How about 2 RCDs on the board with the circuits split 50:50 between them. So that you never get all the lights out simultaniously, only every second circuit.

------
ETCI website info on RCDs :

The operating current level of RCDs depends on the application of the RCD. If the RCD is intended primarily for electric shock protection, the operating level will typically be 10mA or 30mA. RCDs can also provide some protection against electric fires caused by larger current flows to earth. These RCDs typically have an operating current of 100mA or 300mA. It is important to note that 100mA and 300mA RCDs are not suitable for personal protection against electric shock because the operating current would exceed the let-go and heart fibrillation current levels.

[This message has been edited by djk (edited 11-24-2006).]

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#146259 - 02/08/07 01:19 PM Re: IEE/BS7671, 17th edition
Kenbo Offline
Member

Registered: 04/07/06
Posts: 234
Loc: Scotland
Just been checking out the IEE web site and found a link to the full 17th regs (draft version)
IEE 17th regulations draft

Full doc will only be live untill 28 feb 07 but you can download it now an save it.

Kenny

Kenny
_________________________
der Gro├čvater

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#168703 - 09/13/07 05:50 AM Re: IEE/BS7671, 17th edition [Re: Kenbo]
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Just been reading the article about the 17th edition changes in the autumn issue of "Wiring Matters." There are a few more points in addition to those we've discussed above.

Apparently the 17th edition is to introduce the concept of a "skilled person" versus an "instructed person" for certain things:

 Quote:
Skilled person: A person with technical knowledge or sufficient experience to enable him/her to avoid dangers which electricity may create.

Instructed person: A person adequately advised or supervised by skilled persons to enable him/her to avoid dangers which electricity may create.


The definitions seem to be about as vague as the present one for a "competent" person.

Anyway.....

The RCD requirement for sockets rated under 20A is now shown as being where those sockets are to be used by "ordinary" persons, which means anyone who is neither "skilled" nor "instructed." An exemption exists for specific outlets intended and clearly labeled for a particular item of equipment, such as an under-counter freezer.

However, we now have the additional requirement that all cables concealed in a wall at a depth of less than 50mm must be protected by a 30mA RCD where the installation is not to be under the supervision of a "skilled" or an "instructed" person. This extends to all cables no matter what the depth where the building structure is metallic.

As I read this, it means that many homes with blockwork construction will be required to have RCD protection for just about all circuits, since at some point the cables will be run on the blockwork to sockets and switches less than 2 in. below the surface.

There's a further change to the existing 0.4 and 5-second disconnection times. All final circuits not exceeding 32A will now be required to have a disconnection time <0.4s for TN, and <0.2s for TT. I can only assume the more stringent requirement for TT is on the assumption that during the life of the installation the loop impedance may rise due to corroded earth rods, etc. Or???

Another odd change is to permitted voltage drop. The existing 4% rule is to go, replaced by a maximum allowable drop of 3% for lighting circuits and 5% for other circuits when power comes from the public supply. As if that's not peculiar enough, these figures are to increase to 6% and 8% respectively for an installation powered from a private supply. Good luck trying to figure out the logic behind that.

There are the changes to camping pitch supplies mentioned before, plus some other changes to swimming pool zones.

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#168760 - 09/14/07 03:08 AM Re: IEE/BS7671, 17th edition [Re: pauluk]
Texas_Ranger Offline
Member

Registered: 12/17/01
Posts: 2343
Loc: Vienna, Austria
Yikes, that's a lot of voltage drop!
Here it is 1% from the utility connection point to the meter and 3% to the last device.

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#168767 - 09/14/07 07:54 AM Re: IEE/BS7671, 17th edition [Re: Texas_Ranger]
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
The present rule here is a maximum 4% voltage drop from main supply terminals at the meter to farthest point, so the allowance is going down for lighting but up for everything else.

The existing 4% is an example of the rules getting laxer rather than stricter. Go back to the 14th edition (in effect 1966 through 1981) and the limit was 2.5%.

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#168789 - 09/15/07 01:29 AM Re: IEE/BS7671, 17th edition [Re: pauluk]
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
 Originally Posted By: pauluk


There's a further change to the existing 0.4 and 5-second disconnection times. All final circuits not exceeding 32A will now be required to have a disconnection time <0.4s for TN, and <0.2s for TT. I can only assume the more stringent requirement for TT is on the assumption that during the life of the installation the loop impedance may rise due to corroded earth rods, etc. Or???


Could it be they assume the TT supply to result in a higher touch voltage during fault?

If you short line to earth on a TT supply, I suppose the PE conductor will have a potential of almost the mains voltage. The current is limited by the earth rod, and therefore there is no significant voltage drop in the line conductor.

If you short a line to earth on a TN supply, the voltage potential is about half of the mains voltage. (In this case: Voltage drop in line + voltage drop in PE = mains voltage)

???

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