Interesting...

http://www.esc.org.uk/fileadmin/user...n-Issue-19.pdf

pp.18-19.

--
Andy

100A 80A or 60A supply is protected by a DNO cutout fuse which permits
considerably more to be drawn continually and intermittently. Likewise
the supply cable is designed usually with this in mind (135A nomimal
real capacity, although the dreadful farm growers may have disproved
that at some poor devils expense?).

Not considering the real world fuse characteristics is why we can
"meltdown" a 4-way strip adapter and "do a right number" on a BS1363
plug supplying a 2-way adapter with twin 2kW fan heaters.

Interesting how far they derate the 32A ring final tho, but I find
derating an electric shower final circuit quite bizarre.

John Rumm wrote:
On 16/02/2011 12:44, Andy Wade wrote:
Interesting...

http://www.esc.org.uk/fileadmin/user...n-Issue-19.pdf

They seem to have lifted that from NICEIC Connectons Mag Issue 160,
Pg 51
(which was what I used as a source for the last section we added to
the wiki on the judgemental approach ;-) )

http://wiki.diyfaq.org.uk/index.php?...ental_approach


I see that the ESC version managed to get the correct figures into the
chart!

--
Adam

On 16/02/2011 14:07, John Rumm wrote:

They seem to have lifted that from NICEIC Connectons Mag Issue 160, Pg 51

That figures. The ESC is the campaigning charitable wing of the NICEIC.
Is /connections/ mag still on-line anywhere? I can't find it anywhere
at niceic.com and my downloaded copies stop at no. 156.

--
Andy

On 16/02/2011 13:34, js.b1 wrote:

Interesting how far they derate the 32A ring final tho, but I find
derating an electric shower final circuit quite bizarre.

They're not suggesting that you derate the final circuit. The 80%
diversity factor is applied to the circuit feeding the distribution
board - in this case the domestic CU. The argument rests on the longer
thermal time constant in the supply wiring (DNO's works) giving an
averaging effect. This won't necessarily hold true for the final
circuit, especially if someone's used 6 where they should have used 10...

Mind you I think they've miscalculated. The equivalent continuous
current giving the same dissipation in the cables as a load with a duty
cycle of 12/15 is sqrt(12/15), not 12/15. Therefore shouldn't the
diversity factor be 89.4%, not 80%? Make it 90% say.

The other thing I don't quite buy is their use of a 40% factor for both
ring ccts. The circuit supplying sockets for kitchen appliances surely
needs a higher factor.

--
Andy

Andy Wade wrote:
On 16/02/2011 14:07, John Rumm wrote:

They seem to have lifted that from NICEIC Connectons Mag Issue 160,
Pg 51

That figures. The ESC is the campaigning charitable wing of the
NICEIC. Is /connections/ mag still on-line anywhere? I can't find
it anywhere at niceic.com and my downloaded copies stop at no. 156.

http://www.electrics-home.co.uk/downconnections.php

Now the later mags were some Flash based horror story. I sent John details
of how to access them, maybe he still has that link.
--
Adam

Andy Wade wrote:
On 16/02/2011 13:34, js.b1 wrote:

The other thing I don't quite buy is their use of a 40% factor for
both ring ccts. The circuit supplying sockets for kitchen appliances
surely needs a higher factor.

You could probably reduce non kitchen circuits to well below 40%. Especially
if you have upstairs, downstairs and kitchen rings.

--
Adam

On 16 Feb,
Andy Wade wrote:

The other thing I don't quite buy is their use of a 40% factor for both
ring ccts. The circuit supplying sockets for kitchen appliances surely
needs a higher factor.

Why? Most kitchen appliances are used very intermittently and/or are of low
rating. A ring serving several othr rooms could have a fan heater on in each
room for consifderable times in poorly insulated houses.

--
B Thumbs
Change lycos to yahoo to reply

John Rumm wrote:
On 16/02/2011 16:38, ARWadsworth wrote:
Andy wrote:
On 16/02/2011 14:07, John Rumm wrote:

They seem to have lifted that from NICEIC Connectons Mag Issue 160,
Pg 51

That figures. The ESC is the campaigning charitable wing of the
NICEIC. Is /connections/ mag still on-line anywhere? I can't find
it anywhere at niceic.com and my downloaded copies stop at no. 156.

http://www.electrics-home.co.uk/downconnections.php

Now the later mags were some Flash based horror story. I sent John
details of how to access them, maybe he still has that link.

Any use:

http://issuu.com/redactive/docs/nic_july_10_cropped/2

(clicking on the other publications link at the top yields more)


That's the one.
Ta.
--
Adam

) wibbled on Wednesday 16 February 2011
17:17:

On 16 Feb,
Andy Wade wrote:

The other thing I don't quite buy is their use of a 40% factor for both
ring ccts. The circuit supplying sockets for kitchen appliances surely
needs a higher factor.

Why? Most kitchen appliances are used very intermittently and/or are of
low rating. A ring serving several othr rooms could have a fan heater on
in each room for consifderable times in poorly insulated houses.


Also, a washing machine and dishwasher may be plate-rated at 3kW but the
heater will come on for a small fraction of the time - same with the kettle.



--
Tim Watts

On 16/02/2011 17:17, wrote:

Why? Most kitchen appliances are used very intermittently and/or are of low
rating. A ring serving several othr rooms could have a fan heater on in each
room for consifderable times in poorly insulated houses.

Fair point, although what we're concerned with is estimating the likely
total maximum loading across all socket outlets, so it doesn't matter
which particular circuit sees most load. Mention of kitchen appliances
is natural because washing m/c + tumble drier + dishwasher could
represent a significant sustained load, whereas widespread use of
portable heaters is not so common nowadays. Extensive permanently
installed electric space and/or water heating should of course be on its
own circuits, with no diversity allowed.

--
Andy

On 16 Feb,
Andy Wade wrote:

Fair point, although what we're concerned with is estimating the likely
total maximum loading across all socket outlets, so it doesn't matter
which particular circuit sees most load. Mention of kitchen appliances
is natural because washing m/c + tumble drier + dishwasher could
represent a significant sustained load

Dish washer and washing machine unlikely to be on full load for more than 15
minutes, and unlikely to be on simultaniously om full load. Tumble drier
perhaps, but 3kw for that, and 1½kw (averaged over an hour) for the others
only amounts to 18A.

--
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Change lycos to yahoo to reply