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New kitchen rewire isolators/ring mains and 13A sockets

Postby wahwahboy » Mon Aug 02, 2010 11:33 pm

Hi all, I need some advice urgently before a costly mistake occurs this week.

Kitchen is being rewired for us at the moment.

All sockets on a one new ring main:
2x double sockets under counter for 3xappliances and 1xhob
4x double sockets above counter,
1x single fused spur for fridge,
2x double sockets at low level

1: 2 appliances - washing m/c and dryer are intended for a double skt - this seems wrong to me due to a possible 20A if both are running at max power, 13A skt rating exceeded - should be in singles? I will make sure this is modified.

2: Currently no isolation forany under counter appliances: this is OK as long as these are pull out types and not built-in? (in 17th edition) but not ideal for future proofing as someone might want an integrated dryer in future...

3. Double sockets for the under counter appliances are on the ring main but are wired with the first socket on the main ring (down/back) then 2 sets of wire feeding horizontally to next socket (like a spur with 2 cables) - is this correct? So we have 2 cables drop down to socket 1 and then 2 cables over to socket 2 so it feeds back to socket 1 and back on the ring - is this normal?

4. What mcb should this ring have?- 32A seems a bit low to me (considering a washer, dryer, dishwasher, fridge/freezer, chest freezer (these are very often all on) and possible kettle, microwave etc..) - 2KW+2kW+1.5kW+0.5kW+0.5kW+1kW+1kW=8.5kW/

8500/230V=36A - I know diversity applies in these cases but I am thinking this circuit must have at least 40A.

Thanks for the help - point 3 is my main concern - Cheers all.
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Simply Build It

Postby ericmark » Tue Aug 03, 2010 7:28 pm

1) The washing machine should the weights ever come lose can wreck a kitchen and always should have an isolator so it can be turned off without touching the washing machine itself. Not in rule book just common sense.
2) Most isolating switches are ratted at 20 amp so only one socket per switch no doubles.
3) 2.5mm cable used with ring mains has a special dispensation and without any special calculations, you can use a 32 amp MCB to power it. If you want more than 32A then you need another supply, you can’t just use larger MCB to supply ring.
4) Any fixed appliance over 2000W should have it’s own dedicated supply. There is some debate as to if a washing machine or tumble drier are fixed but oven and hob are classed as fixed, and so would have dedicated supply.
5) Most hobs use well over 3000W and can’t be supplied from a socket outlet.
This should answer most questions. Having the washing machine and tumble drier on the same supply is common if you look at the curve for a B32 MCB it will deliver 45A for over 10,000 seconds so unlikely to trip out with kettle as it is on for too short of a time. Even modern washing machine does not use heat for very long around 14 minutes so unlikely to trip a B32 MCB. It would take 160 amp to trip a 32A MCB in 10 seconds or less.
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Postby sparx » Tue Aug 03, 2010 8:55 pm

not sure how to answer this one?
Presume person doing rewire is part p registered leckie, therefore should know how to wire a domestic ring circuit!

1: 13A per outlet not per double is rating.

2: Who spec'ed the work? will cost more to put isolators above when not needed/requested so could lose the company the whole jobon price.

3: if one cable goes straight through firstt socket to second one then yes both will be on ring with only one vertical chase good working practice.

4: All circuits must be 'designed', the standard A1 ring parameters are :
floor area =/less than 100M2 per ring , 2.5mm" conductors, 32A max protective device rating, no immersion water/comprehensive space heaters or cookers ovens or hobs totaling over 2kW to be connected to ring.

Make sure you get test certs, and job registered with LABC, let leckie know you want them, if being done as part of refurb. from kitchen company talk to their rep. ASAP
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Postby wahwahboy » Tue Aug 03, 2010 10:44 pm

Cheers for the reply. Had a chat this morning and yes he is part p etc and I will get a cert.

Tells me it is a ring - I understand exactly what you mean with the run through - it my case here it looks like a parallel socket , a spur with two cables but even a spur here would be OK as we are straight off the ring as I see it. Anyhow, it's getting the full test this week and I know a fair bit so I'm on it.

Thanks for putting me straight on the 13A thing. That explains how you can get 3 gang 13A sockets..
Not that concerned now tbh - believe me, the state of the wiring last week was enough to give most leckies sleepless nights (small voltages present on 'off' sockets, missing earths, lighting circuits from the early 60s) so I will sleep a lot easer with my 17th ed board..

Should be a law to force routine checks (every 20 years at least) by the electricity boards/local government. Seems our lives are shrouded by H&S except where most accidents occur, guess we can't sue ourselves can we? (Steps down from soapbox)...
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Postby jimmy_one_ball » Tue Aug 03, 2010 11:35 pm

Yes mate, all sounds OK to me, your concern about point 3, sounds like all those socket outlets are part of the ring, which is good, maybe could have spurred using one cable but would have saved like 50 pence. Better that they are on the ring final circuit.

Point 1 also is fine on one double socket outlet. Diversity also accounts for thermostats, where you might have all sorts switched on but not actually drawing current so your heating element in the dryer might be off where the cooker element might be on and the fridge matrix will be off as well, you know what I mean. Its all passing through the same MCB the worst case is that if by some fluke everything is on together for a few mins then the 32A MCB might 'nuisance trip' but I doubt it as the regs will always err on the side of caution.

Point 2 is unlikely and if such a regulation does appear in the future then it will only apply to new builds, so not your concern really.

Point 4 Don't be tempted to replace the 32A MCB with a 40A MCB as the conductors could happily overheat and start a fire.

Legal stuff: You MUST be given an Electrical Installation Certificate signed by the designer, installer and tester (may be one person) and it MUST be acoompanied by a Shedule of Inspections and Schedule of Test Results, both signed. The local council must be informed of the work before it starts, either by the NICEIC or similar (if he's a member) or by himself if he's not.

Hope this puts your mind at rest, if in doubt check him out.

All the best
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Postby sparx » Wed Aug 04, 2010 3:51 pm

just for the record, not wishing to be pedantic but j-o-b comment about LABC not quite correct.
DIY or unregistered leckie must inform LA before starting and pay a fee
£150+ for them to inspect.
However Part P registered leckies do not have to notify first, as we self certify our work, so notify through our trade bodies (Napit,Niccy, Elecsa,Bre) At the END of the job.
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