Outside Light Regs Interpretation - Bit Long Sorry

Hi Guys

I'm hoping someone will be able to help with the following (what to me is) grey area. Unfortunately I don't have the On Site Guide to hand, but I was looking at this last night and the subject of a direct wired outside light was under discussion.

Can't remember page references, think the clause was 3.5.2. An illustration at the back of the guide shows an outside light, actually illustrated as outside a remote shed rather than a house, and then refers back to a clause (maybe 3.5.2).

This clause covers portable equipment etc, but the last entry is an outside light and the general heading of the clause concerns items which need RCD protection with a disconnect time of 0.4 ms. The clause also mentions light fittings where conductive parts are accessible.

My questions are:

If I am fitting an outside light where one has previously been fitted (i e a ciruit already existed to supply this) do I need add RCD protection? The outside light is part of a re-fit of a rear extension in which additional circuits are not being added, but some damaged cabling is being replaced and a return to the CU added for the power circuit (formerly run radially!). The principle cable routing is not changing, so, in my opinion the work does not fall under the remit of part P. However I will have building inspectors around for other works, so comments welcome on the Part P implications! Does a light which is fixed direct to an outside wall, with a cable going straight in from the back qualify for this protection, or is this really aimed at remote lights, such as those used to illuminate pathways? There is also a rider on this clause about the light being outside the equipotential zone. Does this wall mounted fitting fall into this category if the fitting is earthed back via the lighting to the CU? If I fit a double insulated fitting will the requirement for RCD still hold? (Not sure I would get away with a plastic fitting with SWMBO!) If possible can respondents please include references to any answers given, as I would like to have all amunition necessary in case this work is questioned?

Thanks to anyone who's managed to get this far and more to anyone who can shed light!

TIA

Phil

Reply to
thescullster
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[outside light with ref. to sec 3.5.2 in the OSG]

I can't see any explicit mention of light fittings, but the paragraph does refer to any equipment with "exposed-conductive-parts" which will include most metal-cased light fittings. It refers to regulation

471-08-03 in BS7671.

The requirement is *not* for 0.4mS disconnection, it is for 0.4S disconnection (i.e. 400mS). The implication is that with correctly specified circuits and protective devices it is possible to reach this disconnection time without the use of an RCD. For example, with a fault current of 30A or more flowing a 6A MCB will meet this requirement (fig. 3.4 in BS7671). 30A is an earth fault loop impedance of about 7.5 Ohms or less which should be very easy to achieve if you have TN-S or TN-C-S earthing. If you have an earth rod (TT system) then you will need to use an RCD to meet this requirement.

If the light is connected via a fused spur to the sockets circuit with a

5A BS1361 fuse, a 22A current will do the trick (fig. 3.1 in BS7671).

If your circuits are protected by rewireable fuses to BS3036 then you might have a bit more trouble meeting the disconnection times.

See above. If the earth-fault loop impedance is low enough then probably not.

You can download Part P from the ODPM website. It has the list of exempt works in it.

It seems to me to be aimed at all outside lights, but the 0.4S disconnection time is a good thing to aim for for *all* electrical equipment in the home, and most of it requires this timing.

[snip the rest, sorry]

I find it odd that you posted on the 30th and no-one has yet replied. Hopefully this will have answered some questions, and if there are any glaring errors I'm sure someone will pick them up.

If you are at all worried about Part P or similar then I'd suggest mentioning it "in passing" to the Building Inspector when he visits to look at other work, but before you've actually done anything to the light. I'd suspect he'd be happy that you're replacing an old/damaged/worn out fitting, but it rather depends how "jobsworth" he's feeling that morning and whether his department has completed (or even started) its Part P training yet.

Hwyl!

M.

Reply to
Martin Angove

Martin

Thanks for response - yes I think others may have been put off by the essay!

No, in the paragraph, light fittings are not referred to, but I arrived at these clauses as they are indicated as applicable to an outside light (admittedly attached to a remote shed) in a diagram at the back of the On Site Guide.

Sorry that was a typo!

From what you are saying I believe that an outside light fitting, even a metal one, would be OK. The feed to this light and internal lighting to the single room extension is taken from a shared 6A type B MCB (this MCB also supplies the upstairs lighting circuit for the main house).

My house has TN-C-S earthing.

As a matter of interest, the approvals recently received from building control for the general structural alterations include in the conditions of approval "means of compliance with Part P". Examining the ODPM web site, I am confident, even though I am adding sockets and reducing numbers of light fittings, that this phase of the work does not fall into Part P - no additional circuits etc! Replacement of fittings is specifically mentioned as NOT being elligible - see below link top right hand note on affected areas

formatting link
intend to declare this with my response to their conditions.

Phil

Reply to
TheScullster

But not for a 5 A lighting circuit. BS 7671 Fig. 3.2A gives the min. current to clear a 5 A fuse in < 0.4 s as only 24 A - IOW the Zs only needs to be < 9.5 ohm (8 ohms measured on a cold test - OSG Table 2A). That would imply a heck of a length of cable - over 200 m of 1 mm^2 T&E!

- and probable non-compliance on voltage drop.

[RCD required?]

Definitely not, IMHO (other than in TT-earthed installations, obviously).

As has been mentioned a few times now, the current issue of the IEE publication /Wiring Matters/ gives guidance that installation of a light fitting on an outside wall of a house is not notifiable under Part P, provided that the supply is taken from an existing circuit and the connection is not made in a kitchen or special location.

And of course in the age of MCB protection everything gets it. BTW the unit symbol for seconds is "s" (lower case), not "S" which refers to the SI unit of conductance, the siemens (formerly known as the 'mho').

Reply to
Andy Wade

Good point. Fired off the phrase without bothering to flip the page and check :-)

Been absent from the ng for a while so have missed most of the Part P debate (semi deliberately). That is an interesting interpretation of the rules. Has it been tested in a court yet?

OK. I used to have a reason for usion capital S for seconds, but I can't remember it and given what you've said, I'll change :-)

Hwyl!

M.

Reply to
Martin Angove
[light on outside wall not Part P notifiable]

Yes, but appearing in an IEE publication, who are we to argue? The advice, as an answer in a series of Qs & As, starts "The general view of the ODPM is that it is not notifiable."

Another somewhat surprising one is:

"Q. If I replace an existing electric shower with a new electric shower connected to an existing shower circuit is this notifiable work?

"A. No, providing the shower is a like for like replacement."

("The old shower was 4 kW and the new one's 10 kW and the existing circuit is wired in bell wire - but that's near enough like-for-like innit?...")

I very much doubt it.

Reply to
Andy Wade

How likely is a like-for-like replacement anyway? Shower designs change very regularly so unless you're buying a new one just 12 months after installing the original...

And as you say, an existing shower in need of replacement is likely to be a low-ish power device, 7kW or so whereas most low-end electric showers these days start at 8.5kW. 8.5kW through a 30A rewireable is an interesting exercise, and I've seen it done in lots of places.

Will it ever be, one wonders?

Hwyl!

M.

Reply to
Martin Angove

4kW - bloody 'ell - I thought my 7kW a few years ago was bad enough!

I thought that part P was to do with wiring rather than appliances, so the actual appliance, be it a 4 kW or a 10 kW shower is irrelevant..

Still, things "may" change as a result of changes in the next 24 hours...

Reply to
Frank Erskine

I recall using one of the original (c. 1970) instant electric showers -

3 kW! People who think today's 8, 9 or 10 kW jobs are poor should try one of those...

I suspect that was tongue-in-cheek but, FAOD, the suitability and rating of the supply to fixed equipment is surely within the scope of Part P, as is the work involved in making connection to same, in certain cases.

FSVO "may" with a probability of something less than ever if there were to be a change of gov't, which won't happen either...

Reply to
Andy Wade

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