Electrics Upgrade Advice

[mysearch]

Hi, I was hoping I might get some advice on a number of issues. My son recently bought a 25 year old 3-bedroom detached house and now wants me to help him to fit a new kitchen/utility area. While I have done a lot of DIY stuff over the years, I realise that build regs now restrict the DIYer from certain jobs, although this apparently did not stop the last owner doing some ‘cowboy’ installations. Anyway, getting to the issues:

Issue-1: Consumer Unit & RCDs
Currently the house only has a fuse box with the following circuits (2*5A, 2*30A, 2*15A), which I assume are upstairs & downstairs lights, upstairs & downstairs mains. I am not really sure what both 15A circuits power, e.g. immersion heater & ???. However, I believe it would be sensible to replace the fuse box with 17th consumer unit (CU) with 2 RCD’s plus up to 10 MCB circuits.

Q: Can RCD be problematic when fitted to older wiring installations?
Q: Would people recommend Wylex products from Wickes?
http://www.wickes.co.uk/Products/El...al/Wylex-Consumer-Units+Accessories/c/1000054

Issue-2: Consumer Unit & MCBs
In order to handle the kitchen and utility requirements I was thinking of getting a 10 MCB CU fitted (professionally+cert) with the following sizes:

2*6A, 2*32A, 2*16A: covers the original circuits +
1*6A, 1*32A: covers a new light and mains circuit in the garage/utility area
2*32A: radial 10mm cable radial circuits for electric oven and hob

I thought it might be sensible to have the utility room in the garage on its own circuits. Looking at the specs for electric oven and hobs, it seems that many would either push or exceed the sensible current loading of a mains ring, even ignoring anything else on the circuit. Therefore, I thought that it might be easier to have the oven and hobs on separate circuits with individual double pole isolation switches.
http://www.wickes.co.uk/Wickes-45A-Double-Pole-Switch-With-Neon/p/710029

Q: Is this proposal sensible?

Issue-3: 10mm Radial circuits
The CU would replace the fuse box in the garage and barring the concern about RCD problems with old wiring, this should be a straightforward job, which I am assuming might cost £100 for CU+MCBs and £300-£400 installation. I was assuming that the electrician could also wire up the new light and mains MCBs to appropriate rated junction boxes to which the new circuits in the utility area could be connected at a later date. However, the 10mm radial wiring would have to be run from the CU to the kitchen and I am not sure of the restriction regarding installing this type of cable. For example, the total length of these cables would be ~12m, the first 5m inside the garage attic area, which could then be drilled though to the kitchen. Inside the kitchen, I was hoping that these cables could be embedded in the wall running horizontally near the ceiling, if suitably protected with a metal conduit.
http://www.wickes.co.uk/Wickes-Galvanised-Steel-Channelling-25mmx2m/p/195132

Q: Is this possible?

Realise that this may be too many questions for one post, but would really appreciate any knowledgeable help on any of the issues raised. Many Thanks[/i]

 

[EFLImpudence]

I shall just deal with the cooking appliances.

A 32A circuit is what is normally fitted.

With the cable installation method you mention, i.e. not running through thermal insulation nor conduit then 4mm² is satisfactory (conduit is not required for cables buried in the wall in the recommended areas (vertical from accessory or within 150mm. of the ceiling)).
It will be RCD protected if you have a new CU.

Most people will install 6mm² because that is what was always done as required with 30A rewireable fuses.
If 6mm² is used then, if you want, you can have a 40A MCB.
This will be more than adequate for any oven and hob in a domestic situation.


Just to add - a lot of flats have 10mm² for their whole supply.
Also, just looked at the link. That is not conduit. It is called capping and does no more than hold the cable in place. It may be used if you wish.

 

[securespark]

The other 15A circuit could be anything: sometimes you find a disused circuit for a stairlift, maybe a circuit for a garage or outhouse or additional sockets elsewhere.

Yes, RCD's can be problematic in older installations in that you need to get the wiring thoroughly tested for insulation resistance before you fit the new CU. In fact, get the wiring scoped out so that you know EXACTLY what's what before it is reconnected to the new unit.

Best advice here is that Hager or MEM are a better brand than Wylex.

Before you just assume there are 6 circuits in your house because there are 6 fuses, you need to get the cover off and thorough testing and scoping out.

You may find 2 or more circuits attached to some fuseways, so it is best to segregate wherever possible to minimise disruption in the event of a fault.

This may lead to a bigger board than 10 way.

Plus you need to leave space for future expansion.

You can use diversity to put the oven and hob on one circuit, but yes, by all means have the oven and hob on separate circuits. If you use a split board, put one on each side. Similarly put upstairs sockets and downstairs lights on one side and downstairs sockets and upstairs lights on the other. Again, this will minimise disruption and increase safety lighting-wise if there is a fault.

Have a look at safe zones in the wiki. The diagram will tell you you can run cables within 6" of the ceiling in the safe zone:

//www.diynot.com/wiki/Electrics:walls

You do not need capping, galvanised or otherwise, however from my experience it is prudent to fit it to protect the cable from damage during plastering. It does not give protection against penetration or mechanical damage.

Hope this helps.

 

[JohnW2]

The other 15A circuit could be anything: sometimes you find a disused circuit for a stairlift, maybe a circuit for a garage or outhouse or additional sockets elsewhere.

... or it may always have been an unused 'spare'.

Kind Regards, John

 

[mysearch]

Many thanks for both replies, which were very helpful.

With the cable installation method you mention, i.e. not running through thermal insulation nor conduit then 4mm² is satisfactory (conduit is not required for cables buried in the wall in the recommended areas (vertical from accessory or within 150mm. of the ceiling)). It will be RCD protected if you have a new CU. Most people will install 6mm² because that is what was always done as required with 30A rewireable fuses. If 6mm² is used then, if you want, you can have a 40A MCB. This will be more than adequate for any oven and hob in a domestic situation.

Yes, it would seem that 10mm cable is an overkill. For the type of oven and hob that will be fitted, now and in the future, I think 6mm cable on 32A MCB is probably a reasonable match to the requirements.

The other 15A circuit could be anything: sometimes you find a disused circuit for a stairlift, maybe a circuit for a garage or outhouse or additional sockets elsewhere. Before you just assume there are 6 circuits in your house because there are 6 fuses, you need to get the cover off and thorough testing and scoping out. You may find 2 or more circuits attached to some fuseways, so it is best to segregate wherever possible to minimise disruption in the event of a fault. This may lead to a bigger board than 10 way. Plus you need to leave space for future expansion. Yes, RCD's can be problematic in older installations in that you need to get the wiring thoroughly tested for insulation resistance before you fit the new CU. In fact, get the wiring scoped out so that you know EXACTLY what's what before it is reconnected to the new unit.

Very good advice. Would this ‘testing and scoping out’ be something that a DIYer can do or something a qualified electrician would do prior to fitting the RCDs? For example, would you normally disconnect all equipment to the ring mains and switch of all lights etc. If so, what would you measure prior to installing the RCD, e.g. resistance? I am also assuming that this might become an unknown cost factor if problems are found???

Best advice here is that Hager or MEM are a better brand than Wylex.

Thanks, will check out these units.

You can use diversity to put the oven and hob on one circuit, but yes, by all means have the oven and hob on separate circuits. If you use a split board, put one on each side. Similarly put upstairs sockets and downstairs lights on one side and downstairs sockets and upstairs lights on the other. Again, this will minimise disruption and increase safety lighting-wise if there is a fault.

I think I would prefer to use 2*32A MCBs with 6mm cable for the oven and hob on separate isolation switches. When you talk of a ‘split board’ do you mean the CU split into 2 RCD sections? Would you expect the electrician to layout the CU as you suggest or should I double check as it seems a good idea?

Have a look at safe zones in the wiki. The diagram will tell you can run cables within 6" of the ceiling in the safe zone:
//www.diynot.com/wiki/Electrics:walls
You do not need capping, galvanised or otherwise, however from my experience it is prudent to fit it to protect the cable from damage during plastering. It does not give protection against penetration or mechanical damage.

Your advice seems to be in-line with that above. As such, I am assuming that both 6mm cable runs could be buried in the wall within the 150mm safe zone from the ceiling. While the capping might be a useful optional extra to hold the cables in place prior to plastering, although there might be better/easier ways to do this.

Hope this helps.

Very much so. Thanks again for both replies.

 

[PrenticeBoyofDerry]

Issue-1: Consumer Unit & RCDs
Q: Can RCD be problematic when fitted to older wiring installations?
Q: Would people recommend Wylex products from Wickes?
http://www.wickes.co.uk/Products/El...-Consumer-Units+Accessories/c/1000054[/QUOTE]
Yes, I would recommend an electrical installation condition report, prior to any swap over to RCD units.
A: There are many consummer units available at varying prices and quality. Hager are championed by most, I don't mind using Wylex, Crabtree and British General units. Tend to stay away from the MK boards.

Issue-2: Consumer Unit & MCBs
In order to handle the kitchen and utility requirements I was thinking of getting a 10 MCB CU fitted (professionally+cert) with the following sizes:

2*6A, 2*32A, 2*16A: covers the original circuits +
1*6A, 1*32A: covers a new light and mains circuit in the garage/utility area
2*32A: radial 10mm cable radial circuits for electric oven and hob

Q: Is this proposal sensible?

It is sensible to divide loads up, I am not against having the hob and oven on separate circuits, this often depends on load size and positioning of these appliances. But rule of thumb allows 15kW of output on a 32A circuit and this can generally be supplied on a 6.00mm radial circuit, but correction factors my require the cable to be that of a higher CSA.
It would also be recommended that the CCU were at least 32A in most cases, the neon is not really required as long as the switch is engraved/identified with the on/off logo.

Issue-3: 10mm Radial circuits

Q: Is this possible?

Anything is possible, and providing cable is installed within the prescribed safe zones, they will require no additional against mechanical damage. But this and all the above would be best discussed with the electrician you decide to employ.

 

[securespark]

The other 15A circuit could be anything: sometimes you find a disused circuit for a stairlift, maybe a circuit for a garage or outhouse or additional sockets elsewhere.

... or it may always have been an unused 'spare'.

Kind Regards, John

Hence the later advice:

Before you just assume there are 6 circuits in your house because there are 6 fuses, you need to get the cover off and thorough testing and scoping out.

 

[JohnW2]

Yes, it would seem that 10mm cable is an overkill. For the type of oven and hob that will be fitted, now and in the future, I think 6mm cable on 32A MCB is probably a reasonable match to the requirements.

As EFLI said, with the installation method described, even 6mm² cable is really overkill - and there's certainly not much point in using 6mm² if you are going to have a 32A MCB (which is fine). That is even more true given that you favour having separate circuits for oven and hob - a single 4mm² circuit with a 32A MCB would be more than adequate to supply both, so it would certainly seem unnecessary to go beyond 4mm² if you are to have two separate circuits. However, as has been had, there's nothing wrong with having 'unnecessarily large' cable - it's simply not necessary.

Kind Regards, John

 

[mysearch]

As EFLI said, with the installation method described, even 6mm² cable is really overkill - and there's certainly not much point in using 6mm² if you are going to have a 32A MCB (which is fine). That is even more true given that you favour having separate circuits for oven and hob - a single 4mm² circuit with a 32A MCB would be more than adequate to supply both, so it would certainly seem unnecessary to go beyond 4mm² if you are to have two separate circuits. However, as has been had, there's nothing wrong with having 'unnecessarily large' cable - it's simply not necessary.

John, the following link supports what you are stating for method C being used. I will give it some thought. I guess I was considering whether the 6mm would allow some flexibility to up-rate the MCB to a higher current should the wattage of some of these multi-ovens and induction hobs go even higher in the future. Other than extra cost, is there any downside to using 6mm? Thanks
http://www.lightwiring.co.uk/lighti...-cables/twin-and-earth-cable-current-ratings/

Yes, I would recommend an electrical installation condition report, prior to any swap over to RCD units.
A: There are many consummer units available at varying prices and quality. Hager are championed by most, I don't mind using Wylex, Crabtree and British General units. Tend to stay away from the MK boards.

I need to look into the issue of an ‘electrical installation condition report’ as this might be in-line with the other previous sensible advice prior to fitting RCDs. Does anybody known how much this might cost and are there any cheaper option specific to RCD compatibility? Thanks

 

[securespark]

For an IR test, yes, you would disconnect all loads on a socket circuit and remove lamps on lighting and with two way switches conduct tests with switches in both positions.

You do need special equipment and knowledge to do the insulation resistance testing: it's not something you can do with a multimeter.

There are other tests as well. If you are not comfortable using a multimeter it may be best to get your chosen electrician to test and inspect your installation prior to your proposed electrical alterations.
There would indeed be extra costs involved if anything was wrong with the installation, which is why these checks are a good investment.

Afterwards you will have a full picture of what the situation is: what is right and wrong with the installation and what needs to be done to make it safe.

Yes, when I say "split-board" I mean a unit with two banks of circuits each protected by its own RCD.

I would indeed believe any spark worth their salt would arrange circuits as I have described. In this way, if either RCD goes off, there will still be a supply to the sockets on that floor for table lamps.

You could also consider fitting cooker control units so that if the sockets downstairs went off, you would still have a supply (fed from the other RCD) to either the oven or hob circuit.

The best situation however, is RCBO's. Each circuit has its own RCD and MCB combined so that, in the event of a fault, only that circuit goes down. But this is much more costly.

 

[mysearch]

For an IR test, yes, you would disconnect all loads on a socket circuit and remove lamps on lighting and with two way switches conduct tests with switches in both positions. You do need special equipment and knowledge to do the insulation resistance testing: it's not something you can do with a multimeter. There are other tests as well. If you are not comfortable using a multimeter it may be best to get your chosen electrician to test and inspect your installation prior to your proposed electrical alterations. There would indeed be extra costs involved if anything was wrong with the installation, which is why these checks are a good investment. Afterwards you will have a full picture of what the situation is: what is right and wrong with the installation and what needs to be done to make it safe. Yes, when I say "split-board" I mean a unit with two banks of circuits each protected by its own RCD. I would indeed believe any spark worth their salt would arrange circuits as I have described. In this way, if either RCD goes off, there will still be a supply to the sockets on that floor for table lamps. You could also consider fitting cooker control units so that if the sockets downstairs went off, you would still have a supply (fed from the other RCD) to either the oven or hob circuit. The best situation however, is RCBO's. Each circuit has its own RCD and MCB combined so that, in the event of a fault, only that circuit goes down. But this is much more costly.

I think I am quickly coming to the conclusion, based on good advice, that I need to get these checks done upfront. Clearly if the RCD trip, they presumably suggest a problem that needs to be fixed which has gone undetected by a simple fuse box. How did we all survive all those years ago before these regs appear. Maybe we all didn’t.

Quick footnotes:
Any rough idea of costs.
My son’s house has RF light switches which are active components – would they be problematic for RCDs?
http://www.lightwaverf.co.uk/Home-Automation-Wireless-Lighting-dimmer-switches-bulbs/

 

[JohnW2]

John, the following link supports what you are stating for method C being used. I will give it some thought. I guess I was considering whether the 6mm would allow some flexibility to up-rate the MCB to a higher current should the wattage of some of these multi-ovens and induction hobs go even higher in the future. Other than extra cost, is there any downside to using 6mm?

No, no particular downside. However, provided it's Method C, a 4mm² cable is fine on a 32A MCB and, given the concept of diversity, a 32A circuit can serve up to about 19 kW of cooking load. I seriously doubt that (even if only because of 'eco' considerations!) we are ever going to see things evolving that far!

... and don't forget that I would be saying exactly the same if you were proposing to (as most people do) feed both oven and hob from a single 32A circuit. Given that you are talking about separate circuits, I think you can be confident that no oven, and no hob, is ever (alone) going to get even close to that 19 kW limit!

Kind Regards, John

 

[mysearch]

No, no particular downside. However, provided it's Method C, a 4mm² cable is fine on a 32A MCB and, given the concept of diversity, a 32A circuit can serve up to about 19 kW of cooking load. I seriously doubt that (even if only because of 'eco' considerations!) we are ever going to see things evolving that far! Given that you are talking about separate circuits, I think you can be confident that no oven, and no hob, is ever (alone) going to get even close to that 19 kW limit!

Thank, I think I am now reasonably clear on the basic layout. It is the fitting of the CU and potential problems with the RCDs that I now need to get clear in my mind.

However, there is one other issue that somebody might be able to confirm regarding who is allowed to connect to an existing CU+RCD+MCB installation? For example, if the CU+RCD+MCB is fitted by a qualified electrician, can a ‘competent person’ connect a radial circuit to an installed MCB?

 

[JohnW2]

However, there is one other issue that somebody might be able to confirm regarding who is allowed to connect to an existing CU+RCD+MCB installation? For example, if the CU+RCD+MCB is fitted by a qualified electrician, can a ‘competent person’ connect a radial circuit to an installed MCB?

Anyone competent (in the everyday sense) can undertake any electrical work, provided they do it is compliance with Part P of the Building Regulations (which is just one sentence, essentially requiring that the work should be done safely).

The main difference is in relation to requirements for 'notification' to the local authority's building control department. Since April 2013, very few things remain notifiable in England (although many more things are notifiable in Wales) - essentially just replacement of a CU, installation of new circuits (not extensions to existing ones) and some work within the prescribed 'zones' of a bathroom. If you undertook any notifiable work yourself, you would have to notify it, and pay the appropriate fee (which can sometimes be 'a few hundred pounds' - varies between authorities). If a registered self-certifying electrician does such work, (s)he does the notification, at minimal cost.

Even for a DIYer who is competent to design and undertake electrical work (whether notifiable or not), the main issue usually relates to the testing which should be undertaken, since many/most DIYers do not have the equipment and/or knowledge to undertake the required testing. Having said that, a lot of DIY electrical work is undertaken, so I leave you to draw your own conclusions from that!

Kind Regards, John
Edit: typo corrected!

 

[ericmark]

Time and relative dimensions in space in space may allow you to see into 2103 but for most of us we have to limit it to 2014.

As to what you can and can't do it's down to how you want to read the Part P regulations no one seems to agree at the limits.

I have fitted RCD's and found they don't comply. I have simply slackened off the terminals and tightened again and on re-test everything has passed. There is only one way to know if what you have installed is safe and that is to test and inspect and this is where the whole idea of DIY fails.

In the main DIY means breaking the rules and what you have to decide is how far to go breaking the rules. I have from time to time done a risk assessment and not followed rules to the letter. But experience tells me what that risk is. As a DIY guy it's everything forward and trust to the Lord.

If you want to be sure then do it all and then get an EICR done to highlight any faults.

Forget Part P and BS7671 it does not really matter what the rules say it's down to if it's safe for you and your family. I fitted RCD protection back in 1994 well before any laws required it as I wanted to protect my family.