(Debate) Using 1.5mm wire for external double socket:

[mainline]

Hi all,

I've got a 1.5mm wire running from the consumer unit to the outside which was previously a light. I've done away with the lights and want to repurpose the wire for a couple of plug in cameras.

Appendix 15 of BS 7671:2018 says it is acceptable to use a 1.5mm cable for a socket as long as there is a fused spur first as the cable can handle up to 15 amps and the spur will limit it to 13A anyway.

However, my question is;

As this cable goes straight from the CU, with no other lights or demand, does it still need a fused spur or can it go directly without one?

Many thanks!

If this is a socket which is outside, then it should be RCD protected.

 

[SPECIAL LOCATION]

If this is a socket which is outside, then it should be RCD protected.

If this is a socket inside it would also need RCD protection anyway!

 

[mainline]

If this is a socket inside it would also need RCD protection anyway!

Yes, but the OP is on about putting one outside.
Your post #4 suggested that an MCB would be fine.

 

[7029 Dave]

IMO a radial circuit suppling socket should be on a 16A minimum with the 2.5mm cable.
The only 1.5mm cable I would be happy to use for this application is MICC.
Having said that all suggestions mentioned are not incorrect but IMO the circuit design is very poor.
6A protection for such a circuit COME ON.

 

[Andy™]

IMO a radial circuit suppling socket should be on a 16A minimum with the 2.5mm cable.

how you would/wouldnt do it is irrelevant. what matters is does it comply with BS7671

 

[7029 Dave]

how you would/wouldnt do it is irrelevant. what matters is does it comply with BS7671

So electrical craft principles means nothing to you, which we were all taught at college?.
Its not all about BS7671 its about standard working practices.

 

[Andy™]

So electrical craft principles means nothing to you, which we were all taught at college?.
Its not all about BS7671 its about standard working practices.

guess you're the type who would give an unsatisfactory EICR to an installation that's fully compliant with BS7671 but not done to your standards / opinion...

1.5 feeding a socket. is it the way most of us would do it? no. is it compliant? yes. so what's the issue?

 

[7029 Dave]

guess you're the type who would give an unsatisfactory EICR to an installation that's fully compliant with BS7671 but not done to your standards / opinion...

1.5 feeding a socket. is it the way most of us would do it? no. is it compliant? yes. so what's the issue?

It has nothing to do with my standards or option, its how I've been taught out in the field and technical
college. Your answer is very confusing you say you would not do it so you must also have an issue designing such a circuit. Why are you throwing in EICR? With 46 years experience in the industry I can honestly say I'm more than competent in that area.

 

[Andy™]

i wouldnt do it that way, but that doesn't mean its wrong

 

[binky]

IMO a radial circuit suppling socket should be on a 16A minimum with the 2.5mm cable.
The only 1.5mm cable I would be happy to use for this application is MICC.
Having said that all suggestions mentioned are not incorrect but IMO the circuit design is very poor.
6A protection for such a circuit COME ON.

Doesn't matter, how many sockets have been installed in attics tapped into light circuits to power a TV booster?. What matters is that the cable is protected from overload.

I have moved the "debate" here, away from DIY. Please feel free to continue.

 

[SPECIAL LOCATION]

IMO a radial circuit suppling socket should be on a 16A minimum with the 2.5mm cable.
The only 1.5mm cable I would be happy to use for this application is MICC.
Having said that all suggestions mentioned are not incorrect but IMO the circuit design is very poor.
6A protection for such a circuit COME ON.

So electrical craft principles means nothing to you, which we were all taught at college?.
Its not all about BS7671 its about standard working practices.

It has nothing to do with my standards or option, its how I've been taught out in the field and technical
college. Your answer is very confusing you say you would not do it so you must also have an issue designing such a circuit. Why are you throwing in EICR? With 46 years experience in the industry I can honestly say I'm more than competent in that area.

Possibly your craft principles were different to many other industry recognised standards? (also taught going back over many many years?)

e.g. basic design where you have a known load, was to select an overcurrent protective device sufficient to supply the load, and an appropriate cable type and size suitable for the rating of the protective device, allowing for derating correction factors, installation methods and volt-drop... etc..

Then after that comes the business economics element where there is no point over-engineering a solution that is more expensive when a cheaper solution can meet all of the electrical and safety elements of the design.

Hence why back in the days of the old regional electricity boards.. (I am in the midlands and ours was the "MEB")...
When their engineers came and installed economy7 night storage heaters, you often got a 3kW storage heater, off a 13A FCU, (or 20A DP switch), fed by a 1.5mm T&E connected to a 15A 3036 wire fuse in the old Wylex fusebox!
Which is no worse than had it been single 13A socket.... ?

However back to the OPs actual question..
He wants a socket to plug in a "CAMERA" (guessing its a plug-in transformer jobbie)..
It is NOT a socket for general purpose... No kettles/toasters/tumble driers etc..

I am struggling to understand why you would consider it is required to have a 2.5mm 16A supply for a Camera PSU that could probably run off a USB socket from a laptop??

 

[7029 Dave]

Possibly your craft principles were different to many other industry recognised standards? (also taught going back over many many years?)

e.g. basic design where you have a known load, was to select an overcurrent protective device sufficient to supply the load, and an appropriate cable type and size suitable for the rating of the protective device, allowing for derating correction factors, installation methods and volt-drop... etc..

Then after that comes the business economics element where there is no point over-engineering a solution that is more expensive when a cheaper solution can meet all of the electrical and safety elements of the design.

Hence why back in the days of the old regional electricity boards.. (I am in the midlands and ours was the "MEB")...
When their engineers came and installed economy7 night storage heaters, you often got a 3kW storage heater, off a 13A FCU, (or 20A DP switch), fed by a 1.5mm T&E connected to a 15A 3036 wire fuse in the old Wylex fusebox!
Which is no worse than had it been single 13A socket.... ?

However back to the OPs actual question..
He wants a socket to plug in a "CAMERA" (guessing its a plug-in transformer jobbie)..
It is NOT a socket for general purpose... No kettles/toasters/tumble driers etc..

I am struggling to understand why you would consider it is required to have a 2.5mm 16A supply for a Camera PSU that could probably run off a USB socket from a laptop??

e.g. basic design where you have a known load, was to select an overcurrent protective device sufficient to supply the load, and an appropriate cable type and size suitable for the rating of the protective device, allowing for derating correction factors, installation methods and volt-drop... etc..

Agreed

Then after that comes the business economics element where there is no point over-engineering a solution that is more expensive when a cheaper solution can meet all of the electrical and safety elements of the design.

We see this time and time again on Electrical forums, trying to help and advise folk with work arounds because circuits are poorly designed, cables (mostly undersized) being worked to the max ccc not fit for purpose and dont achieve the correct Zs for the circuit.

However back to the OPs actual question..
He wants a socket to plug in a "CAMERA" (guessing its a plug-in transformer jobbie)..
It is NOT a socket for general purpose... No kettles/toasters/tumble driers etc..

I am struggling to understand why you would consider it is required to have a 2.5mm 16A supply for a Camera PSU that could probably run off a USB socket from a laptop??

But one day it could be eg if the house is sold and the new owner wants to plug a heavy load into the socket. The circuit will become useless.
I haven't been a member of this forum very long. I try to give advice as a professional tradesman to the best of my knowledge using my own experience and what ive been taught. I hold C&G 236 A&B core qualification (in the day was a good standard)
I will except my disapproval by some of you and will keep out of the DIY section

 

[UNG]

This debate clearly one that has two sides on the craft principles I was taught the best part of 5 decades ago I would go along with @7029 Dave but there has been in my time in the trade massive changes in the equipment we use and the way electricity is used.
When I first started as an apprentice a weekend foreigner could be a rewire, I was often asked by some of the sparks I worked with to give them a hand and 2 of us could usually get it done, there is no way a spark and an apprentice could do a rewire in 2 days now, the number of sockets required has probably tripled if not more the single pendant has become multiple downlights, back then with the limited amount of sockets available how many did you see with multi gang adaptors and / or extensions hanging off them often not fused and very often overloaded.
In some respects this debate is similar to the aerial amp socket in the loft do you take a spur from the ring possibly damaging the decoration or tag it on the lighting circuit knowing the the load is
The underlying issue here IMO is when the MCB / RCBO keeps tripping because of overload and someone in ignorance changes the MCB / RCBO for a higher current rating without considering the cable size or past circuit design thus putting the existing cable at risk of overload.
The level of testing these days far exceeds what was carried out back in the 70's when circuit design could be and is now considered over engineered while all the testing now allows us to install to a more considered level whilst still being safe, another consideration now is how some of the cable sizing apps give a number of cable size options based on the volt drop losses and periodic cost of those losses when deciding which cable to select so does that count as over engineering
The bottomline line now is how the old rule of thumb decisions have evolved and changed as have the regs we work to and the amount of electrical equipment we use, how it will evolve in the next few decades / changes of regs with the push to make everything electric remains to be seen

 

[ProDave]

Would I install 1.5 for a socket? No

But I once encountered a house with an entire ring final wired in 3c&e 1.5mm I suspect it was an installer error, without stripping the ends it looks very similar in size to 2.5mm and I suspect an "oh s**t " moment when he came to terminate it all.

I resolved that by swapping the MCB for a 16A one. what else can you do when the customer does not want his house ripped apart to replace it?

 

[binky]

Agreed

We see this time and time again on Electrical forums, trying to help and advise folk with work arounds because circuits are poorly designed, cables (mostly undersized) being worked to the max ccc not fit for purpose and dont achieve the correct Zs for the circuit.


But one day it could be eg if the house is sold and the new owner wants to plug a heavy load into the socket. The circuit will become useless.
I haven't been a member of this forum very long. I try to give advice as a professional tradesman to the best of my knowledge using my own experience and what ive been taught. I hold C&G 236 A&B core qualification (in the day was a good standard)
I will except my disapproval by some of you and will keep out of the DIY section

it's not about disapproval, you are entitled to your opinion, but some of us have different opinions

However, the actual requirments for electrical safety are all based on protecting the cable, so a 6A MCB is prefectly adequate for the protection of 1.5mm cable. Once you have your cable suitably protected, then it matters not if you wire a socket, light or anything else to the end of the cable. Consideration obviously has to be given to likely load, and if 6A is insufficent, then rewiring with something more suitable would be the way forward. As this cable is already in situ, and the load is a CCTV camera, ie well below the 1.5kW max the circuit will take, then there is no issue with what is being proposed. The 'whataboutery' of someone changing things is irrelevant, it's like your car MoT, it's only really valid at the time it's issued. You could leave the garage, smack a kerb and damage your susupension, leaving you with a car that would now fail the MoT, but the tester can't and doesn't allow for that. If you wanted to get keen, you could always label the socket as 6A max, or make a note on the board to try and prevent someone with insufficent knowledge from changing the MCB, but like an MoT, it would be correct at time of competing the works, what happens next is not your issue.

 

[7029 Dave]

it's not about disapproval, you are entitled to your opinion, but some of us have different opinions

However, the actual requirments for electrical safety are all based on protecting the cable, so a 6A MCB is prefectly adequate for the protection of 1.5mm cable. Once you have your cable suitably protected, then it matters not if you wire a socket, light or anything else to the end of the cable. Consideration obviously has to be given to likely load, and if 6A is insufficent, then rewiring with something more suitable would be the way forward. As this cable is already in situ, and the load is a CCTV camera, ie well below the 1.5kW max the circuit will take, then there is no issue with what is being proposed. The 'whataboutery' of someone changing things is irrelevant, it's like your car MoT, it's only really valid at the time it's issued. You could leave the garage, smack a kerb and damage your susupension, leaving you with a car that would now fail the MoT, but the tester can't and doesn't allow for that. If you wanted to get keen, you could always label the socket as 6A max, or make a note on the board to try and prevent someone with insufficent knowledge from changing the MCB, but like an MoT, it would be correct at time of competing the works, what happens next is not your issue.

I understand what you are saying.