Apologies to anyone who's read this under another thread.
--
The downstairs light ring is in 'theory' overloaded, so the outside light
will have to powered by the upstairs light circuit ring but with the switch
downstairs! Is this a problem?

Also I noticed a lot of 30amp juction boxes on my 5 amp light circuit - is
this also a problem? (they were done before we moved as part of a garage
conversion and have been working fine for 10 years or so).

Thank you

On Sun, 23 Jan 2005 11:08:58 -0000, "MP"
strung together this:

Apologies to anyone who's read this under another thread.

You'd be better off apologising for sticking a sig seperator in the
middle of your post.

The downstairs light ring is in 'theory' overloaded, so the outside light
will have to powered by the upstairs light circuit ring but with the switch
downstairs! Is this a problem?

The lighting circuit will be a radial, not a ring so there aren't
tecnically any spurs on the circuit, as such, IYSWIM.

There's also the thing of diversity, which says you won't have all the
lights on at once so you can effectively go 33% over what you think
your maximum circuit current is limted to.

Also I noticed a lot of 30amp juction boxes on my 5 amp light circuit - is
this also a problem?

No, unless they're all badly terminated.
--

SJW
Please reply to group or use 'usenet' in email subject

"Lurch" wrote
| There's also the thing of diversity, which says you won't have all the
| lights on at once so you can effectively go 33% over what you think
| your maximum circuit current is limted to.

Surely there is *no* diversity allowed on a lighting circuit - precisely
because it is quite likely that all lights will be on at once - especially
in the bog-standard one-light-in-the-middle-of-the-ceiling per room types of
installation?

Owain

On Sun, 23 Jan 2005 23:38:38 -0000, "Owain"
strung together this:

"Lurch" wrote
| There's also the thing of diversity, which says you won't have all the
| lights on at once so you can effectively go 33% over what you think
| your maximum circuit current is limted to.

Surely there is *no* diversity allowed on a lighting circuit

There is, it was 66%, I don't think it's changed.

- precisely
because it is quite likely that all lights will be on at once - especially
in the bog-standard one-light-in-the-middle-of-the-ceiling per room types of
installation?

Well, can't say as I've ever overloaded a lighting circuit personally,
even with going over 6A on a few occasions. In an ideal situation you
would leave the diversity out of it rather than loading all the
circuits up to the max.
--

SJW
Please reply to group or use 'usenet' in email subject

Lurch wrote:


Surely there is *no* diversity allowed on a lighting circuit


There is, it was 66%, I don't think it's changed.

AFAICU from a quick read of the OSG, there's no 'diversity' allowed in
the design of the lighting circuit itself: its Table 1A shows 'current
demand to be assumed' as 'current equivalent to the connected load, with
a minimum of 100W per lampholder' (the latter methinks will get updated
Real Soon Now to take account of non-BC low-energy fittings - 2D, 4-pin,
and the like, where it's pretty reasonable to claim that there's little
likelihood of the 10-25W loomin' air being replaced with a
100W-tungsten-capable BC lampholder). So 14 lampholders is your lot,
roughly speaking...

However, you *are* then OK to assume diversity in calculating the load
each lighting circuit contributes to the whole installation - and that's
where you remember the 66% figure from (that's for an individual
household install, with higher proportions for commercial (90%) and
small-hotels-boarding-houses-and-similar (75%)). As with all
applications of diversity, it's not always a get-out-of-jail-free card -
if there are particular circumstances on a given circuit, e.g. 500W of
kitchen downlighters switched as one, that's already half of the 960W
with 66% of the 6A nominal represents...

"Stefek Zaba" wrote in message
...
Lurch wrote:


Surely there is *no* diversity allowed on a lighting circuit


There is, it was 66%, I don't think it's changed.

AFAICU from a quick read of the OSG, there's no 'diversity' allowed in
the design of the lighting circuit itself: its Table 1A shows 'current
demand to be assumed' as 'current equivalent to the connected load, with
a minimum of 100W per lampholder' (the latter methinks will get updated
Real Soon Now to take account of non-BC low-energy fittings - 2D, 4-pin,
and the like, where it's pretty reasonable to claim that there's little
likelihood of the 10-25W loomin' air being replaced with a
100W-tungsten-capable BC lampholder). So 14 lampholders is your lot,
roughly speaking...

However, you *are* then OK to assume diversity in calculating the load
each lighting circuit contributes to the whole installation - and that's
where you remember the 66% figure from (that's for an individual
household install, with higher proportions for commercial (90%) and
small-hotels-boarding-houses-and-similar (75%)). As with all
applications of diversity, it's not always a get-out-of-jail-free card -
if there are particular circumstances on a given circuit, e.g. 500W of
kitchen downlighters switched as one, that's already half of the 960W
with 66% of the 6A nominal represents...

I just got lost here :-(
Surely diversity allows an increase in the total loading as it assumes not
all will be turned on ? So a 6A nominal current gives about 1500W which is
then multiplied by 1/0.66 to give 2250 as the maximum lighting on the
circuit.

Mike wrote:


I just got lost here :-(
Surely diversity allows an increase in the total loading as it assumes not
all will be turned on ? So a 6A nominal current gives about 1500W which is
then multiplied by 1/0.66 to give 2250 as the maximum lighting on the
circuit.

No.

The circuit itself should be designed for running under full load, and
the protective device must be chosen so its nominal rating is greater
than that full load will draw, while being less than the rating for the
cable selected (derated by all relevant factors). You do *not* design in
an 'overload' on the individual lighting (or other) circuit.

You *do*, though, get to recognise that full load on the lighting
circuit will be 'rare' - so although the circuit itself must be safe
under its full load, the contribution to the total *installation* load
which this circuit makes is taken, in normal circumstances, to be a mere
66% of its total current demand.

Stefek Zaba wrote:

No.

The circuit itself should be designed for running under full load, and
the protective device must be chosen so its nominal rating is greater
than that full load will draw, while being less than the rating for the
cable selected (derated by all relevant factors). You do *not* design in
an 'overload' on the individual lighting (or other) circuit.
.. ^^^^^^^^

Delete "or other". Diversity /is/ allowed within many other types of
circuit - e.g. the standard (OSG Appendix 8) circuits are based on a
maximum floor area served, not on a full 13 A at each socket! The
'rules' for diversity within individual circuits are set out in Table 1A
of the OSG, together with its footnotes. Another example is that that a
domestic cooker circuit does not have to be designed for the full load
current (FLC) of the appliance(s) connected - a design current of 10 A
plus 30% of the remaining FLC[*] is allowed.
[*] FAOD this means Ib = 10 + 0.3 * (FLC - 10) amps, where Ib is the
design current.

You *do*, though, get to recognise that full load on the lighting
circuit will be 'rare' - so although the circuit itself must be safe
under its full load, the contribution to the total *installation* load
which this circuit makes is taken, in normal circumstances, to be a mere
66% of its total current demand.

The point is not so much that full load on the lighting circuit will be
rare, but that it will rarely coincide with simultaneous full load on
several other circuits. The 66%, BTW only applies for domestic
installations, higher figures are stipulated for non-domestic
situations. Diversity /between/ circuits at a consumer unit or
dis-board is dealt with by Table 1B in the OSG.

It's a common mistake to confuse the two diversity tables, and the cause
of similar thread topics here in the past.

--
Andy

Andy Wade wrote:
.................................................. ......... You do *not*
design in an 'overload' on the individual lighting (or other) circuit.

. ^^^^^^^^

Delete "or other". Diversity /is/ allowed within many other types of
circuit - e.g. the standard (OSG Appendix 8) circuits are based on a
maximum floor area served, not on a full 13 A at each socket!

Thanks for the correction, Andy!

It's a common mistake to confuse the two diversity tables, and the cause
of similar thread topics here in the past.

Aye - off to wrap head in cold wet towel (and turn on the Golf's
sidelights just to watch *both* numberplate lights being on - today's
d-i-y 'triumph'!)...