house buying and electrics

[masamune]

I am buying a 3 bed property which is a little dated, but I took my electrician around to have a look and said that overall the electrics have been kept well. We need to add RCDs and earth a couple of things.

The owner said that he changed some of the wiring back in 2005 and the fuse box was also changed. Nothing was certified though. I believe the wiring is mostly white PVC around the house which the electrician said is a little older than the 2005 standard (grey?) but it's fine.

About the RCDs, the sparky suggested two ways of updating, either fit an separate RCD unit before the consumer board if the board is not changed (wiring to be tested for tripping) at £250 + ~£140 for certification, or fit a new consumer board with dual RCDs, £550 with certification. He thinks it's very unlikely to have problems with the wiring in case of tripping after testing the sockets around.

I don't understand a lot about layout etc and me thinks this is the time where I have to decide about any switches moving, lighting etc. I am also wondering whether I should fit installation for an alarm or buy a wireless one.

Any suggestions for what to look out for and prepare in advance would be appreciated.

Thanks

 

[ericmark]

OK 2005 means it could have been planned before Part P came in so maybe there was no need to have informed council (LABC) should have still had a installation or minor works certificate but at that time it was common for electricians not to issue where there were worries about tax man using them to prove work on the side so not too worried about not being there.

As to RCD’s then one would expect any electrician today to issue an installation certificate without extra cost but with a scheme member electrician the guy could not do anything else but register the work with his scheme provider but with non scheme member then the LABC will charge and £140 seems about right but it can be done by you or the electrician and since it’s a minimum charge if any other work is being done at same time then better if all lumped together.

As to fittings RCD’s before the consumer units well that is exactly what I have done. However note I say consumer units not unit and to fit a single RCD would likely not comply with BS7671:2008 314.1 (i) (iii) and (iv) and as such it may be a problem getting the LABC issuing a completion certificate.

There are many ways of adding RCD protection but the most common is either using a special consumer unit split into two so at least two RCD’s are fitted or to fit RCBO’s instead of MCB’s which are a RCD and MCB combined the latter is considered the better method.

However a RCBO is one longer than a MCB so can not be fitted into all boards and two costs around £35 each rather than £5 each so can become expensive.

There is however no need to up-grade you could continue with no RCD protection as until 2008 it was only required for electric showers and sockets likely to be used with items used outdoors.

There was one exception that’s where the supply is TT that’s it uses an earth rod. With that it would have before 2008 have been fitted with a 100ma RCD not a 30ma RCD as used today.

So you need to find out supply type either TN or TT. You need to decide if you want RCD protection now. And it would be better to say where in UK the rules change between England, Scotland and Wales.

You also need to be aware that due to LABC charges likely it will be cheaper to use a scheme member electrician for this type of work.

Personally I time an alarm is a waste of money although fitting an empty bell box may be an idea.

The rules to have an alarm monitored mean you have to use registered alarm companies and pay an annual fee for the monitoring. Normally fitting is not that expensive as the firms make the money on the maintenance contract and monitoring fee.

I don’t know of any wireless alarm which is accepted by the Police to allow them to be directly called out without the monitoring station calling a private firm to check first so by time the police arrive there is not chance of them being caught on the job.

 

[JohnW2]

There was one exception that’s where the supply is TT that’s it uses an earth rod. With that it would have before 2008 have been fitted with a 100ma RCD not a 30ma RCD as used today.

I don't think that is necessarily true. Yes, if all final circuits are protected by 30mA RCDs, then that, alone is usually adequate in a TT installation (unless there are complications like metal CUs or isolators). However, if there are any final circuits which are not RCD protected, then it will be necessary to have an up-front RCD, which, AFAIAA, even in 2014, is still likely to be a 100 mA (time-delayed) one.

Kind Regards, John

 

[ericmark]

Yes I agree John but it seems odd that anyone would suggest a single RCD of 30 mA to protect all circuits and since there is no need to add a RCD to an existing system I just had that niggle maybe the RCD was not for personal protection but because it had a TT earth and maybe an old ELCB-v fitted?

 

[JohnW2]

Yes I agree John but it seems odd that anyone would suggest a single RCD of 30 mA to protect all circuits and since there is no need to add a RCD to an existing system I just had that niggle maybe the RCD was not for personal protection but because it had a TT earth and maybe an old ELCB-v fitted?

Indeed. I suppose that for those who 'believe in' RCDs (as savers of lives and limbs), to put a single 30mA one in front of an existing non-RCD CU (in a TN installation) is a step in the right direction, safety-wise, even though most people would probably say that the lack of 'separation of circuits' meant that it was not compliant with current regs.

If we were talking common sense, rather than (most people's interpretation of) the regulations, I suppose one would make a judgement as to which, on balance, was more important to safety - having 30mA RCD protection or avoiding a situation in which one fault could take out the entire installation (as, of course, can a 'power cut', operation of the DNO's fuse!).

Kind Regards, John

 

[ban-all-sheds]

I don't understand a lot about layout etc and me thinks this is the time where I have to decide about any switches moving, lighting etc.

It's a quandary. On the one hand if (and this may not be the case) the house is vacant then that sort of work becomes easier and faster, and therefore cheaper - no moving furniture about, no need (possibly) for scrupulous dust avoidance, no need to keep some power available etc.

Even if that doesn't apply, it's still best to do the work before you do any decorating, floor or carpet laying and so on.

On the other it's harder to decide where you want accessories if you've not lived there for a bit.

• Upstairs sockets
• Downstairs sockets (or a L/R or front/rear split)
• Kitchen sockets
• Circuit for appliances
• Cooker circuit
• Non-RCD circuit for F/F
• Non-RCD circuit for CH boiler
• Dedicated circuit for hifi
• Dedicated circuit for IT equipment
• Upstairs lights
• Downstairs lights
• Lighting circuits with switches in the usual places but with 2A/5A round pin sockets at low level.
• Immersion heater
• Loft lights
• Shower
• Bathroom circuit
• Alarms
• Supply for outside lights
• Supply for garden electrics
• Supply for shed/garage

Plus any peculiarities brought about by your house layout & construction - e.g. in mine because of solid floors and where the socket circuits run, I have a radial just for a socket in the hall, the doorbell and the porch lights.

RCBOs have come down in price to the point where it's quite realiastic to use them throughout, but if not the CU should have at least 3 sections, 2 on RCDs and one not into which you can install a mix of RCBOs and MCBs.

It can be a good idea to put all wiring in conduit for ease of future changes. And if you specify metal conduit for switch drops, or BS 8436 cable it removes the need to have RCDs on lighting circuits (apart from bathrooms).

If you live somewhere where supplies are dodgy in the winter, have the lights, the boiler supply, and a socket in each room wired to a separate CU, or a separate section in a large one, that can be supplied by an emergency generator - lights, heating, TV and a kettle/microwave make life a lot more bearable.

Flood-wiring with Cat 5e, Cat6 or Cat6a cable is worth thinking about. Do not listen to people who tell you that wireless is a perfectly good alternative to wired networks - it isn't.

I am also wondering whether I should fit installation for an alarm or buy a wireless one.

Check on the Alarms forum. Personally I don't like anything wireless if there's a realistic wired alternative, but I may be unduly pessimistic.

 

[masamune]

Thank you all for such good advice, I will discuss the layout with the electrician.

I agree about the conduits, although I may not be rewiring the entire house if not necessary, just to keep costs down.

Any idea of the cost for flood-wiring in a three bed house?

 

[ban-all-sheds]

Sorry, no.

 

[masamune]

There is a potential for the skirting boards to be removed to fit flooring and replaced.

Is this a good opportunity to run flood wiring?

Two questions, what about wiring for speakers in i.e living room

and can I accommodate phone lines and network and alarm wiring with the Cat6? Is this a job for an electrician or do I need to find a specialist?

Thanks again.

 

[DaftPunk]

A good electrician should be able to do the wiring for you. Cat6 is good for phones, computer network, CCTV, HDTV, and all sorts of other things, but the alarm should be wired in proper alarm cable.

The speakers will probably work on cat6 but would be best using proper speaker cable.

 

[ban-all-sheds]

You can use Cat 6 cable to make speaker cables with.

http://www.tnt-audio.com/clinica/diycables.html

 

[masamune]

Thank you, yes I was planning for the speakers to have their own cable (something like thick multicore copper).

Just worried I am adding too many things in the way but it's probably the best opportunity to add all of this wiring before decoration.

I have to decide where sockets will go and where it all ends up for my switch/routing etc probably at the hallway where I plan to build a small cupboard. I may also ask the electrician to move the CB from under the staircase there, depends on the cost.

 

[masamune]

Unfortunately part of the plan does not work the way I had hoped. The wires are all good and modern. But, there is no budget for complete rewiring and the house has a few rings, with one of them as the sockets of the ground floor. Kitchen inclusive!

The radial MCB is 32A on 2.5mm cable, he said that I should not use an oven of more than 3kW and that should be fine. My problem is that the electrician insists not to install a separate cable for the oven alone. However all the ovens I am interested in buying are rated 3.5+kW e.g Neff

Is he right? What is the best option here and what are the potential problems?

 

[ban-all-sheds]

The radial MCB is 32A on 2.5mm cable,

Not good at all - 2.5mm² is rated at 27A at best.

Needs to be at least 4mm² for a 32A radial.

My problem is that the electrician insists not to install a separate cable for the oven alone.

Why on earth would he insist on not installing a circuit for the oven?

Is he right?

I don't like the way he's happy with a 2.5mm² 32A radial.

What is the best option here and what are the potential problems?

Get him to change the breaker to a 16 or 20A one.

 

[ericmark]

I seem to remember you saying white twin and earth which may mean it is thermal setting not thermal plastic cable and thermal setting is rated 90°C not 70°C so reference method C for 2.5mm² is 33A table 4E2A.

Personally unless marked on the cable I would assume it to be thermal plastic and use BAS list but what I am pointing out your electrician could be correct without seeing how installed and having a bit of the cable to inspect or test I would certainly question 32A with 2.5mm² but would still accept it once shown it is thermal setting cable.

Appendix 15 states:-

The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers). This can generally be achieved by:
(i) locating socket-outlets to provide reasonable sharing of the load around the ring
(ii) not supplying immersion heaters, comprehensive electric space heating or loads of a similar profile frog the ring circuit
(iii) connecting cookers, ovens and hobs with a rated power exceeding 2 kW on their own dedicated radial circuit
(iv) taking account of the total floor area being served. (Historically, limit of 100 m² has been adopted.)

From that most electricians would say oven and immersion heater needs a dedicated circuit however it would also mean washing machine, tumble drier, and dish washer all over 2kW and over the weight limit to be considered as portable should also have a dedicated circuit however it is rare to provide them.

The kitchen grid switch with two 2.5mm² feeds and radials to non portable equipment like fridge, freezer, washing machine, dish washer and tumble drier is not really a ring final but conductors in parallel so slight change in the rules.

Personally I would consider as a ring final which means you can't have a 3.5kW oven but technically since just conductors in parallel one could fit a 32A socket or a cooker connection unit. I think it is wrong but as long as only the grid switch is connected to the pair of 2.5mm² feeds it would be hard to fail with an inspection.

I would agree with BAS that his methods are questionable but I would not condemn them without seeing the house.

Personally I would always feed an oven with a dedicated supply and would be wary with cable rated 90°C as often the units supplying and terminating the cable are not also rated at 90°C. Not all white twin and earth is thermal setting but much of it is so although as I say it's right to question I would not say he is wrong.