I need to get supplies to a dishwasher and a washing machine in a kitchen. Max total load would be 4.6kW for the two (according to the books - seems rather high to me!)
I've a socket nearby on the ring main. I can't run an unfused spur to both appliances since I need a seperate socket for each (either side under the sink) and only one socket per unfused spur allowed (Appendix B, OSG). A fused spur, would I think be allowed, but would have to be fused at 13A.
Options
Assume divesity of 65% and install a 13A fused spur to two sockets - one for each appliance. Would probably work most of the time.
Install seperate non-fused spurs from the same point on the ring to a socket for each appliance (is this allowed?)
Extend the ring, taking a loop around the two new sockets needed. Would work, but I did want a switch above counter to turn off the appliances
Suggestions and comments welcome.
The house has only one ring main (small terrace, re-wired about 20 yrs ago) which is a real pain. No spare ways in the CU - major job to sort out.. and we're moving next year!
1) Install two separate spurs - one for each appliance. Since they will only be feeding one socket each you do not need the spurs to be fused since the maximum load is limited to one socket load (13A). Having said that, there is no harm is using Fused Connection Units at the origin of the spur anyway.
2) Extend the ring - but *not* to the new sockets - but to the two switch positions above the worktop. Use 20A double pole plate switches at each switch position (I would go for the ones that include a neon indicator), and then run a single spur cable from each switch down below the worktop to a socket for each appliance.
It is possible to extend the ring circuit from two existing socket positions to incorporate one 45 amp Double Pole or two 20 amp Double Pole switches that are used to remotely switch sockets that are below the worktop.
If you can find the cabling that joins two of the existing sockets and break into it, then it is just a case of running new cabling to any new appliances you are thinking of installing.
If you want to hide the sockets under the worktop, then it is good practice to use remote switching above the worktop which control unswitched sockets under it.
If you are thinking of using two switch and socket combinations, then you can use 2.5 mm T&E Cable to all parts of the new circuits. But you could use one 45 amp Double Pole switch to run the two remote sockets, but the cabling to the sockets from the switch would have to be 4 or 6 mm T&E to allow them to take the load safely.
You could take two unswitched spurs from the socket on the ring if you can get four cables into each terminal on the socket. What you cannot do is take a spur from a spur or have more spurs than there are points on the ring. In theory you could have 10 sockets on a ring with 10 spurs from one socket
It is also not good practice to have washers etc on a spur due to their high load,but if you are moving and prepared to lose the cost of a rewire on the value of your house (expecteded on a 20 year old installation) then do not worry.
Why would you expect a 20 yr old install to need rewiring? Or a 30 yr old install? Is this consumerism again? Maybe I'm missing something here, but I can't imagine what.
Good question... I can only give one example at the moment. My parents' house is 36(ish) years old and hasn't been rewired in their time there (31 years). Presumably it wasn't in the first years of its life either.
The *cabling* is ok, being copper and PVC, BUT it could probably do with a rewire because:
they are seriously under-supplied in the sockets department (one per room), and house has only one ring (all sockets up, down & kitchen)
light switches when replaced (recently fitted a dimmer to one room) prove to be on the verge of failing - e.g. showers of metal filings falling out.
well-used sockets are also failing.
earthing is very suspect, though I haven't actually tried to check it. It seems to be earthed via the incoming water pipe with no separate earth rod, no RCD and no TN system.
consumer unit is rewireable fuses.
there is no main bonding or crossbonding.
So maybe not in dire need of a *complete* rewire, but certainly in need of an extensive update which *may* be better done by performing a complete rewire.
Food for thought...
...actually, I *can* think of another example. My mother-in-law's house was "rewired" some years ago (no-one knows for sure, but it seems to have been between 20 and 25 years ago). Again, cabling is ok, but the circuit layouts and suchlike are very suspect (sockets on lighting circuits, circuits connected at CU end but not feeding anything and "lost" beneath floorboards etc.). I have started a partial re-wire on this one, but am rapidly approaching the conclusion that the simplest course of action (but one which will unfortunately result in some very recent re-decoration having to be re-done) is to start from scratch. It doesn't help that she's 150 miles away :-)
I'd agree with you on this one, 35 years is about what I guesstimated. And of course it will vary from one case to another too.
As long as your incoming water pipe is bare metal, the result is the same as a large earth rod. But...
If you rely on an earth rod then you do need an RCD. An earth rod plus
30A wire fuses makes an earth system I wouldn't be very confident in. Wire fuses are not quick blowing, you'd need several times 30A to blow one within a few seconds.
Nothing wrong with that in itself.
ok if you have all metal supply pipes, since each will be thoroughly earthed.
Given the whole picture though, I quite agree with your conclusion.
Nonsense: an incoming metal water pipe could change to plastic only a very short distance underground.
At least two RCDs for a house installation to current standards.
This reveals the fact that you haven't understood the principle of equipotential bonding at all. Electrical 'earth' conductors have finite impedance. Under earth fault (i.e. short-circuit) conditions, the current flowing through 'earth' conductors causes a large voltage drop across their length - often more than half the mains voltage because the 'earth' conductors tend to be smaller than the live (load current carrying) conductors. That's why 'earths' are now properly called protective conductors - when they're doing their job they ain't necessarily at earth potential at all.
In a TN system your incoming 'earth' could rise to a dangerous voltage (relative to earth) due to a fault outside your installation (a fault on someone else's service cable would be an example). Such faults can take several seconds to clear, during which time the voltage between your "thoroughly earthed" pipes [1] and the metalwork of an earthed electrical appliance is dangerous - possibly lethal in a wet situation. In the TN-C-S (PME) system there is an even worse case to consider and that's where the neutral connection to the mains comes adrift (o/c) on your service connection. Your house earth wiring is now connected to the 'live' side of the mains through the impedance of all the appliances that you happen to have switched on at the time. In the context of its ability to limit shock current to a safe value that impedance is negligibly low and you're exposed to full mains voltage between your earthing and your plumbing.
Or rather you would be, if it wasn't for the bonding. The whole point of the main bonding is not to 'earth things' so much as to tie all the incoming services together and to the electrical 'earth' with a suitably low impedance. Then under fault conditions everything rises to a similar potential and safety is restored. The concept creates an 'equipotential zone' in which the voltage between simultaneously accessible metalwork stays safe. Local supplementary bonding in the bathroom (etc.) creates a local 'inner zone' in areas where there is greater risk of shock; this extra protection is principally against fault-induced voltage drops on the circuit protective conductors in your own installation.
So your argument that bonding doesn't matter if the pipes are well earthed is tosh. The better earthed they are the greater the danger!
[1] Actually the gas pipe is likely to have an insulating insert just before the meter.
A 20 year old house will not be up to the 16th edition (actually not a problem in itself), but you usually find DIY bodges to the electrics done over the years that need correcting. There are usually too few sockets for a modern lifestyle and in this case just one ring main. There will also probably "only be one lighting circuit, no RCD protection and the CU will be a Wylex fuse board."
Very much not allowed. If it is a TT supply get a rod fitted.
Agreed, but they are shit.
There is no guarantee the mains bonding is a good earth. You need your own as any utility could change the incoming supply.
It can be as cheap to rewire as mess about trying to correct and test old circuits, especially if you are going to DIY. And you know the installation will be good for another 20-30 years.
Since most buyers only opt for a basic "valuation survey" there is only a small chance that it would be commented on. Even if they go for a home buyers report the most they normally commit to is:
"We had a look, it looked OK - what we saw of it - only most of it was burried". So unless the wiring looks like a death trap the surveyor is unlikely to recomend a full electrical survey.
[a load of stuff with dodgy attributions - not all his fault :-) ]
Just a quick note to anyone seeing this message in isolation, or Googling... please read back to the early stages of the thread to see who said what and why! By now it has become very confused :-)
That's fine. She's such a technophobe that she is now having trouble communicating with her other daughter (the one I'm not married to) who is profoundly deaf (hence can't use a telephone) and has all-but ditched the Minicom in favour of SMS/fax/email/MSN so I doubt she'll ever get around to investigating usenet :-)
On the other hand, since I brought it up, you can blame my own mother too.
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