Interesting Conundrum 1.5 power

[Dustydazzler]

So...

A mate just moved into his new house and wants a few extra sockets added for wall mounted TVs etc
No problem you would think as house it fairly modern, I would say less than 10 years old...
Popped round on my way home this evening and looked at the consumer unit , looked okay dual rcd split board so rcd present and correct.
Here comes the kicker , I noticed all the circuits labelled sockets were on 16a MCBs , no rings at all.. So one would assume all socket were wired in 2.5 radials... NOPE. Dropped 2 double socket fronts down and all the power is run in 1.5.

My initially thinking is to extend the circuits in 2.5 but then I got thinking while driving home would anyone think it was badger rough to extend the circuit in 1.5 keeping the cable size the same through-out

Thoughts please

 

[littlespark]

Is 16A suitable OCPD for 1.5mm which is no doubt run in insulation part of its route...

Is this ALL power? including kitchen appliances?

 

[Dustydazzler]

Is 16A suitable OCPD for 1.5mm which is no doubt run in insulation part of its route...

Is this ALL power? including kitchen appliances?

I dropped the cover of the board and everything back at the board is 1.5 orn16amp mcbs for socket circuits ( 3 circuits total for sockets) , dropped a double off in the kitchen was 1.5 and double off in the lounge and it was 1.5

I can honestly say its been a good while since I have seen a new build with 1.5 used to wire all the sockets

 

[pc1966]

That is astonishingly cheap and disappointing.

It might be OK for most light electronics use, but hardly good for a kitchen of high power stuff or even form some vacuum cleaners, etc, with a big switch-on surge. It also more or less guarantees that a blown fuse will always take out the MCB as well, so rubbish selectivity.

 

[Dustydazzler]

That is astonishingly cheap and disappointing.

It might be OK for most light electronics use, but hardly good for a kitchen of high power stuff or even form some vacuum cleaners, etc, with a big switch-on surge. It also more or less guarantees that a blown fuse will always take out the MCB as well, so rubbish selectivity.

I remember when these houses were thrown up and everything went to the cheapest bidder, the cheapest of everything was used and it shows in the finish. all the cables are plastered in , no capping used , everything is wonky as ----.
My mate just paid top top money for the house so there is no way I can tell him to re-wire all the sockets , he has already had some plumbing and drainage issues he has had to fork out nearly a grand to fix.

 

[swaRRR]

1.5mm and 16a for sockets is fine. Yes, even in kitchens. Lots of countries on the continent do this but with the caveat that there is usually a socket limit per radial.

 

[pc1966]

1.5mm and 16a for sockets is fine. Yes, even in kitchens. Lots of countries on the continent do this but with the caveat that there is usually a socket limit per radial.

They also have lots of circuits to make up for it, and usually kitchen appliances are on dedicated radials.

But as they don't have fused plugs like we do, they have to balance MCB rating against appliance cable adiabatic limit which is why 0.5mm flex is not seen.

 

[Dustydazzler]

I am going to extend the socket circuits in 1.5 and keep the same size cable through-out , just seems a bit strange wiring sockets in 1.5 but with the price of cable these days maybe 1.5 socket radials will become all the fashion like on the continent

 

[pc1966]

I am going to extend the socket circuits in 1.5 and keep the same size cable through-out , just seems a bit strange wiring sockets in 1.5 but with the price of cable these days maybe 1.5 socket radials will become all the fashion like on the continent

Well for the same capacity you need twice as many circuits (more really, due to poorer diversity) so comparing 2*N 16A radials on 1.5mm versus N 32A RFCs on 2.5mm I doubt it is cheaper.

Of course if no one can afford to use the power, then telling them it is basically an indoor camping supply might work!

 

[mattg4321]

What are the chances it was wired by foreign sparks?

 

[Dustydazzler]

What are the chances it was wired by foreign sparks?

Highly likely as there is some writing on the cables in the consumer unit and it ain't English

 

[timhoward]

This really beggars belief. I'd be livid if it were my house.

1.5mm and 16a for sockets is fine. Yes, even in kitchens. Lots of countries on the continent do this but with the caveat that there is usually a socket limit per radial.

It can meet the regs but it depends how the cable is run. Unclipped in an insulated wall or in loft under insulation and there's an issue.

My mate just paid top top money for the house so there is no way I can tell him to re-wire all the sockets

I honestly think this is worth a complaint. NHBC Section 8.1.7 says that the electrical installation should comply with BS7671.

If they've skimped and used 1.5sq mm I'd bet there are cables loose in insulation somewhere. It's also worth a shot saying they they haven't used standard circuits as per appendix 15 (I know they are not obliged to!).

 

[littlespark]

The only way 1.5mm c.c.c is above 16A is if its clipped direct in open air. Bury it in a wall, or run it through insulation and youre down to 14 approx.

I would be wary if i found a house wired like this.

1.5 off a 13A fused spur... but not from 16A breaker

You certain it is 1.5, and not some weird inbetweeny size


If you dont say anything... and theres a fire down to melted cables... youll kick yourself.
Mention it to him. Tell him its not how you would have done it. Leave the responsibility up to him to have it changed if he wants to.
If he values your opinion, he might do something. (dropping 16A to 10 might be a start)

 

[Dustydazzler]

The only way 1.5mm c.c.c is above 16A is if its clipped direct in open air. Bury it in a wall, or run it through insulation and youre down to 14 approx.

I would be wary if i found a house wired like this.

1.5 off a 13A fused spur... but not from 16A breaker

You certain it is 1.5, and not some weird inbetweeny size


If you dont say anything... and theres a fire down to melted cables... youll kick yourself.
Mention it to him. Tell him its not how you would have done it. Leave the responsibility up to him to have it changed if he wants to.
If he values your opinion, he might do something. (dropping 16A to 10 might be a start)

Defiantly 1.5 cable , and all on 16amp circuits. Feels very much European

I didn't have time to add up all the sockets but I would suspect that there is around 6 or 7 sockets on each 16amp radial , possibly 1 circuit for upstairs , 1 for downstairs and 1 for the kitchen , but this would require further investigation

Certainly not how I would have wired a brand new house but an interesting way to wire a house never the less

Trying to convince him to rewire all the circuits in a finished house less than 10 years old is going to be a tough conversation , there is no way he will want all the walls chased out

 

[littlespark]

At 10 years old, you would think the builder is still trading.

All you can do is give the owner your opinion. You dont have to convince him.... if he knows the likelyhood of danger, he'll make his own decision.
It could be perfectly ok, if they never overload the cable... and there will be some safety margin built into the c.c.c.

What code would you give, if it were to have an EICR? C2 or C3? Potentially dangerous or improvement recommended

 

[Dustydazzler]

At 10 years old, you would think the builder is still trading.

All you can do is give the owner your opinion. You dont have to convince him.... if he knows the likelyhood of danger, he'll make his own decision.
It could be perfectly ok, if they never overload the cable... and there will be some safety margin built into the c.c.c.

What code would you give, if it were to have an EICR? C2 or C3? Potentially dangerous or improvement recommended

Certainly not a C2 and there is no real danger risk as the 16amp Mcb would trip before the cables became loaded

C3 as 16amps is a bit restrictive and could cause nuisance tripping if you turn several things on at the same time

If the 16amp circuit only fed a couple designated sockets for say a small room or study office then I probably wouldn't bother coding it at all

 

[littlespark]

I take it everything else is ok? RCD protecting etc?

Its very unlikely that they will be pulling exactly 15A for long durations... enough to melt the cable and burn something before the conductors touched as a fault, but not trip the OCPD as an overload

It just doesn't seem to sit right.

 

[UNG]

1.5mm and 16a for sockets is fine. Yes, even in kitchens.

Based on what

Lots of countries on the continent do this but with the caveat that there is usually a socket limit per radial.

A lot of the continental countries electrical systems are a law unto themselves I dread to think how many C2's you would find if they were inspected to BS7671

 

[timhoward]

Certainly not a C2 and there is no real danger risk as the 16amp Mcb would trip before the cables became loaded

If I could see for sure that the cable route / installation method reduced the CCC to under 16A then I'd feel I had to C2 it.
As unlikely as it is to actually cause a problem I wouldn't want to state things are satisfactory if it's not right.
The design of T+E requires some talented misdirected DIY to cause a L-N fault but nothing is fool-proof for a sufficiently talented fool!

Its very unlikely that they will be pulling exactly 15A for long durations

It could in fact pull 32 amps for approx 10 seconds without tripping. It would take rather a lot of arranging though!

I think I might pass on this job, there's easier money to be made with less thinking!

 

[Dustydazzler]

If I could see for sure that the cable route / installation method reduced the CCC to under 16A then I'd feel I had to C2 it.
As unlikely as it is to actually cause a problem I wouldn't want to state things are satisfactory if it's not right.
The design of T+E requires some talented misdirected DIY to cause a L-N fault but nothing is fool-proof for a sufficiently talented fool!

It could in fact pull 32 amps for approx 10 seconds without tripping. It would take rather a lot of arranging though!

I think I might pass on this job, there's easier money to be made with less thinking!

That is the frustrating thing , this on the face of it should be a piece of cake job to add 2 or 3 new sockets to a new build with dot and dab walls just chop in some flush boxes spur off a nearby socket etc. A lovely days work.
Now I am faced with non conventional circuits in a house less than 10 years old, and to think this is a small estate of around 18-20 houses and if the same sparks wired them all then they will all be like this.
Very annoying

 

[SJD]

Are you quite sure these socket circuits are radials, and not 16A ring final circuits? (Yes yes, I know that would be rather non standard ...)

 

[Dustydazzler]

Are you quite sure these socket circuits are radials, and not 16A ring final circuits? (Yes yes, I know that would be rather non standard ...)

One cable at the board coming from each 16a mcb

unless they have ringed the socket all together ( which is possible )and then taken just one cable back to the board in a lolli-pop circuit

 

[UNG]

I suppose on the face of it you have to question the design criteria if the builder gave a brief directive of a working electrical installation with X number of sockets then it could be argued it meets the design brief whether it is compliant with the regs is a totally different matter, while any number of sockets can be wired on a 16A radial the size of the cable has to be considered, 1.5mm² may work but one consideration that may have been overlooked is volt drop and it can be very easy to lose 25m or more of cable on a radial and you start to creep over maximum allowed volt drop

You hear a lot about the east European's who move from site to site one week they are brickie's the next week on a different site they are joiners the next week they become ???? I think you get the idea

Faced with this job my only solution short of a rewire would be to install a whole new circuit for the extra sockets

 

[Pretty Mouth]

Carp design for sure, but I'd be surprised if this was dangerous, or even non compliant, all other things being correct.

Most recently built houses that I have worked on tend to have the cables for socket circuits run in the floor void between floors, dropping or rising to the sockets. There's not usually any need to run the cables through any significant insulation.

 

[UNG]

Carp design for sure, but I'd be surprised if this was dangerous, or even non compliant, all other things being correct.

Your clearly being very optimistic with that comment on compliance

Most recently built houses that I have worked on tend to have the cables for socket circuits run in the floor void between floors, dropping or rising to the sockets. There's not usually any need to run the cables through any significant insulation.

If there is any insulation does it really matter if it is significant or not for me you always calculate on the worst possible.
If a cable is running in a floor void is that in free air or is it a duct and given that you can also have heating pipework running in the same void how do you assess the thermal effects of that on the cable

 

[swaRRR]

Defiantly 1.5 cable , and all on 16amp circuits. Feels very much European

I didn't have time to add up all the sockets but I would suspect that there is around 6 or 7 sockets on each 16amp radial , possibly 1 circuit for upstairs , 1 for downstairs and 1 for the kitchen , but this would require further investigation

That's completely fine electrically speaking. It's literally what French regs specify. 8 sockets max on a 16a radial in 1.5mm.

Normally over there they have freezer, washing machine, dryer, and dishwasher on their own runs but kitchen countertop sockets used to be fine on 16a, i think they now have to be on 20a.

 

[littlespark]

That's completely fine electrically speaking. It's literally what French regs specify. 8 sockets max on a 16a radial in 1.5mm.

Normally over there they have freezer, washing machine, dryer, and dishwasher on their own runs but kitchen countertop sockets used to be fine on 16a, i think they now have to be on 20a.

But this house isn’t in France.

We have to work to BS7671, and have to design circuits with estimated load, installation method, current carrying capacity, length of circuit…..
If none of it mattered, it wouldn’t be there in the regs.

 

[UNG]

That's completely fine electrically speaking. It's literally what French regs specify. 8 sockets max on a 16a radial in 1.5mm.

Normally over there they have freezer, washing machine, dryer, and dishwasher on their own runs but kitchen countertop sockets used to be fine on 16a, i think they now have to be on 20a.

Connect all the wires up and it can be fine electrically speaking whether it is compliant in the UK is a different matter and that is the pertinent point of this thread

Clearly it isn't what the french regs say when you then qualify your comment in paragraph 2 with a load of separate circuits

 

[Pretty Mouth]

Your clearly being very optimistic with that comment on compliance

If there is any insulation does it really matter if it is significant or not for me you always calculate on the worst possible.
If a cable is running in a floor void is that in free air or is it a duct and given that you can also have heating pipework running in the same void how do you assess the thermal effects of that on the cable

The bulk of the insulation will be in external walls, under the ground floor slab, and in the loft/roof. With a couple of exceptions, there's no reason that cables for socket circuits would need to come into contact with these insulated spaces. One exception being bungalows where cables would be run in the loft and would indeed find themselves under a lot of insulation.

Otherwise, the worse that is likely to be encountered is insulation for sound proofing stud walls between some rooms, or in external walls of some timber frame housing. Method 102: In a stud wall with thermal insulation with cable touching the wall, giving us 16A for 1.5mm T+E.

In a building void is method B, so 16.5A. I take your point about the cables sharing a void with heating pipes, but this would apply to many circuits in centrally heated homes. I'll be honest, I don't give it a lot of thought.

I think VD is, as you mentioned earlier, where it may fail. We're probably starting at 240V rather than 230, so perhaps not a big deal real world, but still.

 

[swaRRR]

But this house isn’t in France.

We have to work to BS7671, and have to design circuits with estimated load, installation method, current carrying capacity, length of circuit…..
If none of it mattered, it wouldn’t be there in the regs.

Where in BS7671 does it say you can't use 1.5mm cable with 16a breakers?

Anyway my point was it's electrically sound and if it doesn't break a reg then it shouldn't be coded anything surely?

 

[UNG]

I think VD is, as you mentioned earlier, where it may fail. We're probably starting at 240V rather than 230, so perhaps not a big deal real world, but still.

What does it matter whether you start at 240v or 230v, ok at 240v you have an extra 0.5v before you hit maximum allowed volt drop within the installation but if you are on the limit then potentially you are running equipment possibly below it's optimum voltage

 

[swaRRR]

The only way 1.5mm c.c.c is above 16A is if its clipped direct in open air. Bury it in a wall, or run it through insulation and youre down to 14 approx.

2.5mm ran in a wall is only rated at ~18.5a yet everyone puts them on 20a breakers when doing a radial. Shouldn't your advice to the homeowner then apply to basically every building in Britain with a radial in it for sockets?

In fact even ring final's buried in walls are rated at less than 32a too. Why does nobody contest this? I'm genuinely curious. Technically if you're going to bury cable in walls then radials should be done in 6mm shouldn't they? Or am i missing something?

 

[littlespark]

I generally put 2.5mm radials on a 16A UNLESS the install method allows a 20A

I really should have the BBB at hand to check my CCC but 2.5 on an rfc has a combined ccc of 52A. 26A on both legs. Much more than the 32A ocpd.

32A will just cover a 4mm radial… depending on method… but 6mm would be fine on 32A.

 

[Pretty Mouth]

What does it matter whether you start at 240v or 230v, ok at 240v you have an extra 0.5v before you hit maximum allowed volt drop within the installation but if you are on the limit then potentially you are running equipment possibly below it's optimum voltage

I did say real world rather than regulations world.

If you calculate 5% of nominal 230V, you have a voltage drop limit of 11.5V. This will give you 218.5V at the furthest point of use, and is deemed to be the lower limit of acceptable.

However, typically the supply voltage is actually 240V, and often higher still. At 240V, you have to drop 21.5V to reach the same acceptable limit. That's an extra 10 volts to drop, not 0.5. A very significant buffer, no?

For that reason, I find it difficult to take voltage drop in domestic installations tremendously seriously for the most part.

 

[Pretty Mouth]

2.5mm ran in a wall is only rated at ~18.5a

Which table/ref method are you taking this from?

 

[swaRRR]

Which table/ref method are you taking this from?

Cable Ratings dot co dot uk i think

Some NIC site i've just been looking at states 'For a single cable likely to be totally surrounded by thermally insulating material for a length of 0.5 m or more, the current-carrying capacity must be taken as 0.5 times the current-carrying capacity for that cable clipped direct to a surface (Reference Method C).'

So ring finals should be only able to carry the 'normal' clipped current of a single 2.5mm cable at ~27a.

I just want to know why 16a + 1.5mm is apparently borderline dangerous but 32a + 2.5mm isn't? Eager to learn.

 

[Pretty Mouth]

Cable Ratings dot co dot uk i think

Some NIC site i've just been looking at states 'For a single cable likely to be totally surrounded by thermally insulating material for a length of 0.5 m or more, the current-carrying capacity must be taken as 0.5 times the current-carrying capacity for that cable clipped direct to a surface (Reference Method C).'

So ring finals should be only able to carry the 'normal' clipped current of a single 2.5mm cable at ~27a.

I just want to know why 16a + 1.5mm is apparently borderline dangerous but 32a + 2.5mm isn't? Eager to learn.

It's better you take this info from the tables in the regs. The statement from NIC is true, but it's only part of the picture, there's a lot in between.

1.5mm T+E has a rating of 16A when installed in a stud wall with insulation, so long as it not completely surrounded by the insulation, and is touching the plasterboard. Installed this way, it would be adequately protected against overload by a 16A breaker, so not dangerous at all.

Ring finals are an unusual circuit. Invented after WW2, they were a pragmatic solution to reduce the amount of copper needed to wire a house.

Each point on the ring has 2 paths back to the fusebox. The current is shared proportionally between the paths, more of it taking the shorter route. Fully loaded at 32A, it's unlikely that either leg will carry more than 20A, and if overloaded, the cable should be protected by the 32A breaker, even though the cable rating as installed may be only 20A.

In theory, you can overload one leg of a ring by putting lots of heavy loads a short distance along one leg from the fusebox, but I've yet to see this happen in the real world. After 80 years of them being in use, if this was really a problem we would know about it by now.

 

[timhoward]

I just want to know why 16a + 1.5mm is apparently borderline dangerous

I don’t think anyone said exactly that. The speculation is about whether it passes through insulation.
If the 1.5mm is in insulation in a wall the table in the regs (table 4D5) says it’s current carrying capacity is only 10 amps.
That would rate it at less than it’s over protective device which contravenes the regs.

If on the other hand it’s all touching the surface it’s rated at 16A as @Pretty Mouth explains above.

It feels like a poor design to plan from the outset for circuits to be this heavily loaded, especially in the kitchen / utility room.

 

[Dustydazzler]

Do other countries have similar de-rating factors for cables touching insulation ?
1.5 clipped is 19 amps but our regs then say if it passes through insulation you effectively have to reduce its ccc by half , which imo does seem a bit OTT

 

[pc1966]

For that reason, I find it difficult to take voltage drop in domestic installations tremendously seriously for the most part.

Like many rules and regulations, there has to be a defined point for acceptable or not. Our regs happen to say 5% drop (3% lights but that is another debate...) from the nominal 230V for calculation and if it less then OK, if not then you need to alter the design (usually thicker cable, as typically load is fixed and route has no shorter paths).

What you can get away with in practice is a lot more, but that is not really the point of compliant design!

 

[swaRRR]

Do other countries have similar de-rating factors for cables touching insulation ?
1.5 clipped is 19 amps but our regs then say if it passes through insulation you effectively have to reduce its ccc by half , which imo does seem a bit OTT

Literally every lighting circuit i've ever seen upstairs in a loft has been cocooned in the stuff

 

[7029 dave]

Nope I would not even touch it.
New circuit for the additional sockets with 2.5mm T&E

 

[Pretty Mouth]

Like many rules and regulations, there has to be a defined point for acceptable or not. Our regs happen to say 5% drop (3% lights but that is another debate...) from the nominal 230V for calculation and if it less then OK, if not then you need to alter the design (usually thicker cable, as typically load is fixed and route has no shorter paths).

What you can get away with in practice is a lot more, but that is not really the point of compliant design!

Most of my work is additions and alterations to existing circuits in occupied houses, often to installations of not a very high standard. I find that 100% compliance isn't always feasible, and sometimes I have to take a pragmatic approach.

An example being using RCD spurs to provide additional protection while working to 18th edition and 1st amendment - it wasn't compliant, but it provided the protection without me having the change the fusebox, so why not?

Same with voltage drop. If a circuit length already exceeds the theroretical VD limit (fairly common for ring finals in older houses), but the owner wants a new socket installed (usually in a place where they're running an extension lead to anyway), I just go ahead and fit it. I know it's going to be fine regarding VD.

The OP's situation is the sort of thing I would encounter, and I would try to find a way to make it work for the customer if I could, as long as I was happy that there was no danger in it.

 

[Dustydazzler]

So...

Been discussing this job with my mate and long and short is he now wants it all done properly so we are going to re-wire all the socket circuits from scratch

I have done him a mates rates quote of £75 per point as long as he helps me do all the labouring and fortunately he is a painter decorator so will do all the making good of chases

 

[7029 dave]

Best solution all round .

 

[UNG]

So...

Been discussing this job with my mate and long and short is he now wants it all done properly so we are going to re-wire all the socket circuits from scratch

I have done him a mates rates quote of £75 per point as long as he helps me do all the labouring and fortunately he is a painter decorator so will do all the making good of chase

Panic what panic

It makes sense and your mate has obviously taken your concerns onboard at least you have the fishwires already in place

 

[pc1966]

Most of my work is additions and alterations to existing circuits in occupied houses, often to installations of not a very high standard. I find that 100% compliance isn't always feasible, and sometimes I have to take a pragmatic approach.

An example being using RCD spurs to provide additional protection while working to 18th edition and 1st amendment - it wasn't compliant, but it provided the protection without me having the change the fusebox, so why not?

Indeed, why not? Many asked that question of the IET/BSI over their removal in the 18th and all they got was a weaselly-worded statement that they were not to such-and-such standard, not why they were now deemed to be unsuitable.

Thankfully they seem to have made a return in AM2 so some sanity!

Same with voltage drop. If a circuit length already exceeds the theoretical VD limit (fairly common for ring finals in older houses), but the owner wants a new socket installed (usually in a place where they're running an extension lead to anyway), I just go ahead and fit it. I know it's going to be fine regarding VD.

The OP's situation is the sort of thing I would encounter, and I would try to find a way to make it work for the customer if I could, as long as I was happy that there was no danger in it.

In many cases that is the sensible approach.

Here the discussion is kind of over now they are getting them rewired but the debate was down to "acceptable or not?" and my view is they were marginal. Probably safe but poor practice for the UK due to the normal assumptions of loading/area covered on a socket circuit where they are normally expected to be 32A RFC or 20A radials.

 

[Dustydazzler]

So

I actually started the job today and to make matters even worse there are JBs under the floors and hidden in the stud walls where I assume cables were either too short or sockets moved during the 1st fix stage and rather than pull in some new cable the electrician just cut the cable and added a bit never to be seen again once boarded over

So not only were the sockets wired in 1.5 , there are JBs hidden all over the place NICE

 

[pc1966]

So not only were the sockets wired in 1.5 , there are JBs hidden all over the place NICE

That is the thing about seeing Muppetery, usually the face value is only the beginning of it...

 

[UNG]

So

I actually started the job today and to make matters even worse there are JBs under the floors and hidden in the stud walls where I assume cables were either too short or sockets moved during the 1st fix stage and rather than pull in some new cable the electrician just cut the cable and added a bit never to be seen again once boarded over

So not only were the sockets wired in 1.5 , there are JBs hidden all over the place NICE

If this is one house that is badly wired in a relatively new estate what are the rest of the houses in the estate like