Another Garage to shed wiring question

[SUNRAY]

FGS - am I the only one who read the OP?

His proposed design was 2.5mm² SWA on a 32A breaker supplying a CU with 1 x 16A and 6 x 6A breakers in it.

Its totally permissable to fit a dsso on a 2.5 spur on a ring final and as I have mentioned before its common practice to make this provision for a washing machine and dishwasher for example.

Spurring off a ring final does not absolve you from considering the current carrying capacity of the 2.5mm² cable as installed. Method C is 27A, which is less than 2 x 13A.

You cannot blindly shove in a 2.5mm² spur and rely on the downstream protection of plug fuses to prevent overload if the CCC of your cable as installed is less than 26A.

Much of this sort of appliance coming in from abroad with CE markings and moulded 13A plugs is rated at 3KW or even 3.2KW at 220V. Doing the sums 3200/220=14.55A, So thats wrong.

So stop there.

It's wrong.

Don't do it.

It contravenes the wiring regulations and therefore cannot be used as a justification for other, related, designs which also contravene them.

220/14.55=15.2ohms and 240V/15.2=15.7A or 3.7KW. and there is 2 of those plugged into a DSSO so thats wrong too

Ditto.

as the 2.5mm is running at peaks of 31A on a cable rated at 28A tops and yet it still complies with the regs

No it does not.

and works ok till the cable gets too hot and fails.

Or until the socket overheats and fails, because 31A is in excess of the current that BS 1363 sockets are rated at.

I know I am making reference to unrelated regs but that does not change the fact that in some circumstances it is permissible to inadequately protect a 2.5mm cable with a 32A device, knowing that the following protection is inadequate too.

No it is not.

It may be done in practice by the ignorant and incompetent, and it may even be fairly widespread and not responsible for many problems but that does not make it permissible.

Hi BAS

I'm on your side here, I say the practice of using a 2.5 spur on a ring final is wrong despite the fact that it is well documented within the regs and associated 'official' publications

The simple fact is that as it is acceptable, it is done and frequently, I know its wrong and you know its wrong but its still in the regs. I have corrected too many such installations to be able to count them, fortunately its usually the socket or termination that fails open circuit before a fire starts.

Its also a fact that many goods come into the country with CE markings and moulded 13A plugs which blatantly require more than 13A, and yes I have measured the current of these machines. In one Bosch washing machine the heater alone was measured in excess of 14A and it still had its working, melted, moulded plug in place. If the manufacturers and the qualified sparks are getting this so wrong what chance does Joe Public have?

Again apologies for raising this subject in an unrelated thread. BUT to my mind the 2.5mm feed on a 32A breaker was probably the worst error in the proposed works, most of the other errors were just wrong but not particularly dangerous.

 

[SUNRAY]

You cannot blindly shove in a 2.5mm² spur and rely on the downstream protection of plug fuses to prevent overload if the CCC of your cable as installed is less than 26A.

I agree but it is permissible to install a SSSO or DSSO on a 2.5mm as a spur and rely on the fuse(s) in the householder appliance plug(s) for its protection if its rating as fitted is over 26A.

Then the householder plugs in 2 machines running at 15A apiece

 

[ban-all-sheds]

Hi BAS

I'm on your side here, I say the practice of using a 2.5 spur on a ring final is wrong despite the fact that it is well documented within the regs and associated 'official' publications

It is not wrong as long as the cable is not overloaded.

If the cable is installed such that it is rated at 27A, and if you don't put more than 27A on it then it will be fine.

But if either of those conditions does not apply then it is not fine, and the regulations do not permit it.

That's what I was taking issue with - "the 2.5mm is running at peaks of 31A on a cable rated at 28A tops and yet it still complies with the regs" - it doesn't comply. Whether you agree with unfused 2.5mm² spurs or not when they do comply is irrelevant - your example does not comply.

Its also a fact that many goods come into the country with CE markings and moulded 13A plugs which blatantly require more than 13A,

Which is wrong, and probably illegal.

If the manufacturers and the qualified sparks are getting this so wrong what chance does Joe Public have?

A fair bit, actually. Ohm's law, Ib ≤ In ≤ Iz, the concept that cables need to be able to shed heat etc are hardly rocket science, and anybody who can read without moving their lips should be able to grasp it.

The cost of the Wiring Regulations, a decent guide to them, and the OSG is not huge - people will happily spend more than the minimum on holidays, cars, clothes, TVs, golf clubs, bikes, eating out etc etc in order to get a superior result, so why not, if they want to do DIY electrical work, spend a bit in order to do a better job there?

I agree but it is permissible to install a SSSO or DSSO on a 2.5mm as a spur and rely on the fuse(s) in the householder appliance plug(s) for its protection if its rating as fitted is over 26A.

Yes, that is permissible.

Then the householder plugs in 2 machines running at 15A apiece

And that is not.

 

[SUNRAY]

Hi BAS

I'm on your side here, I say the practice of using a 2.5 spur on a ring final is wrong despite the fact that it is well documented within the regs and associated 'official' publications

It is not wrong as long as the cable is not overloaded.

If the cable is installed such that it is rated at 27A, and if you don't put more than 27A on it then it will be fine.

But if either of those conditions does not apply then it is not fine, and the regulations do not permit it.

That's what I was taking issue with - "the 2.5mm is running at peaks of 31A on a cable rated at 28A tops and yet it still complies with the regs" - it doesn't comply. Whether you agree with unfused 2.5mm² spurs or not when they do comply is irrelevant - your example does not comply.

Its also a fact that many goods come into the country with CE markings and moulded 13A plugs which blatantly require more than 13A,

Which is wrong, and probably illegal.

If the manufacturers and the qualified sparks are getting this so wrong what chance does Joe Public have?

A fair bit, actually. Ohm's law, Ib ≤ In ≤ Iz, the concept that cables need to be able to shed heat etc are hardly rocket science, and anybody who can read without moving their lips should be able to grasp it.

The cost of the Wiring Regulations, a decent guide to them, and the OSG is not huge - people will happily spend more than the minimum on holidays, cars, clothes, TVs, golf clubs, bikes, eating out etc etc in order to get a superior result, so why not, if they want to do DIY electrical work, spend a bit in order to do a better job there?

I'm not aiming my comments at DIYers particularly, if anything I am addressing kitchen fitters as thats were I find this problem most prevalent BUT I'm not making that accusation.

I agree but it is permissible to install a SSSO or DSSO on a 2.5mm as a spur and rely on the fuse(s) in the householder appliance plug(s) for its protection if its rating as fitted is over 26A.

Yes, that is permissible.

Then the householder plugs in 2 machines running at 15A apiece

And that is not.

So Mrs Smiths 20 year old washing machine which is rated at, lets say, 3KW at 240V packs up [12.5A]. She trundles along to Currmets and chooses a nice bright shiny replacement which is rated at 3.2KW at 230V [13.9A]. Mr Smith struggles to get it in the family hatch back and then into the kitchen and fits it where the old one was and of course all the connexions are the same except that this new machine only has cold fill.
Mr Smith is not an electrician and has not the faintest idea but 'it is CE marked and it has a 13A plug so of course its fine darling'. In reality the Smiths supply is 245V and the recalculated current is 14.8A or 3.63KW.
Who has got this wrong? surely not Mr Smiths error? it cant be, he's a lovely man and never done a wrong thing in his life.

 

[ban-all-sheds]

The fault, as in who has responsibilities towards the lovely Mr (and, I'm sure, Mrs) Smith, is with Comeys - they should not be selling appliances with a plug fused at less than the load of the appliance.

Legally the importer is also at fault, and, I would think, the manufacturer, but I'm not 100% sure on the latter.

Maybe the regulations should be amended to allow 16A radials with Schuko/Hybrid-F sockets......

 

[cymru001]

To everyone, I would like to thank you for you input and especially thank Ban all Sheds for his links.

I would, however, like to say a few things in defence of my original design.

When I had the house re-wired, the spark asked me what I would be using in the garage. I told him about the welder. He loooked at the garage installation, he looked at the cable supplying it and then HE installed a 40a MCB into the house CU.

I thought I was being safe by using an MCB rated slightly lower than the one in the house. I now think 20a should've been the proposed option!!

In my mind, I thought I was being over cautious with all the RCD's and MCB's which, as I said originally, I hoped was belt and braces. I didn't realise the quickest RCD would trip irrespective of its location.

I also have to admit to not thinking specifically of the loads in the shed being supplied with the 2.5 SWA. I did think about the house rings which have all sorts of appliances running at the same time. I know its a fuzzy logic but I thought if my kitchen can have a dishwasher, fridge, washing machine and tumble drier potentially all working at the same time while I boil the kettle using 2.5 T&E on a 32a MCB, then a similar MCB to run the odd battery charger, my lawn mower and strimmer should not pose a problem. These items would be running during the day and the lighting would be running at night (obviously!!). Also, no thought given to 230v equipment being fed with 240+ volts.

I simply thought by having each 'zone' protected via an RCD within a CU and each circuit within the CU protected by an MCB was the safest and neatest way of doing it.

I know I could've just opted for an FCU spurred off the garage ring, but felt this was just adding to the existing load potential and increasing the risk to the garage.

I accept this is a job for a spark, but please credit it me with the intelligence to come to a forum like this, read through existing posts and then create one of my own when I did not get the answers to my specific questions. I still feel I am capable of installing the cabling, sockets, lights etc, but know it has to be under the direction of an electrician.

I would never attempt to do something I do not understand and wonder how many people are dull enough to do so and get hurt in the process. I also wonder how much higher that figure would be if it weren't for forums like this where people like you inform people like me????

 

[ban-all-sheds]

I did think about the house rings which have all sorts of appliances running at the same time..

Rings.

That's why you can have a 2.5mm² on a 32A breaker - the current drawn at each socket is shared between two cable runs from the CU.

http://www.tlc-direct.co.uk/Book/6.3.2.htm

 

[SUNRAY]

What you have designed would probably work, and could well be compliant, however it is a complete waste of materials and time.

Another method:

Add a metalclad 13A FCU to the garage socket ring.
Fix a 3A metalclad FCU in the shed.
Connect the two FCUs with a length of 2.5mm SWA.

In the shed, connect the socket to the supply side of the 3A FCU.
Connect the shed light and the outside light control box to the load side of the 3A FCU.
Fix a single large metal box to connect all of the outside light SWA cables into.

Flog the rest of the gear on eBay.

I thought that would be a simple way of doing it, I was just worried about the loading of it all and making sure it was safe!! Plus, had I thought of that a couple of years ago, I would've saved a lot of time in stock piling all I thought I needed!!

I guess I need to come here first when I get my next bright idea

Seems like a sensible solution.
As you have the 5 way CU, I'd be tempted to put that in place of the 2 way in the garage, with a 20A or 16A MCB instead of the 13A FCU.