Outdoor electric circuit

[rustynails]

Hi,

I'd like to install electric to an outside deck I have, supplying three brick lights and a weatherproof socket. It's about 13m to the point where a weather proof junction box is required under the deck, then another 1.5/2m to each fitting. The total wattage of all the fittings is 3240, given that a 13amp outdoor socket is 3120 watts and the lights are E27 lampholder max 40 watts each. I used an SWA calculator and It came back saying that I can use 2.5mm 3 Core SWA? Which means I'll need to install a 13m length of 2.5mm 3 Core SWA, buried 600mm deep, from an outside junction box on the external house wall to a bigger outisde junction box underneath the deck where I can spur off to the 3 lights and the socket, in a radial. Can I use 1.5mm to the lights from the deck junction box? Obviously I need to run 2.5mm to the socket. Does this all sound like good practice?

THanks

 

[rustynails]

* BUMP *

Anyone got anything to say...

 

[rustynails]

According to Table 4D4A p338 in the 17th I could use 1.5mm SWA everywhere because the design current load is 14amps (3240w/230=14.08A) which would make 1.5mm 3 core swa ok as it's max is 18A. Even the 2m drop from the CU could be in standard 1.5mm because according to p334 1.5mm t & e max load is 19.5 clipped direc. I just love talking to myself...

 

[Richard Burns]

You also need to work out your volt drop for the load, which is probably why the calculator said 2.5mm2 SWA.
You can split the volt drop so that you can see if just the lights can be run on a lower csa cable.
For standard light fittings your calculation is based on 100W per fitting.
The lighting should be fused down to say 5A with a SFCU.
The nominal voltage used is 230V not 240V.
The buried cable shoudl also have marker tape above it to prevent damage
You will also need to ensure that you have earthed the SWA armour as an exposed conductive part.
This work is notifiable to building control under part p of the Building regulations.

 

[pencilpusher]

I have a job coming up soon installing outside lighting and power. I have completed all the calcs and am happy 2.5mm SWA is fine BUT when the builders did the customers patio, they installed 2.5mm SWA under the patio and left it coiled up at each end of the run. I will be checking it is 2.5mm cable throughout it's unseen length by measuring the resistance and doing the calcs. However, there are two things I do not know. One is how deep it is buried and the other is if the cable had marking tape above it. As I will be signing the certs and notifying, can I carry on just noting the fact that I cannot check this without ripping up the patio?

Cheers

PP

 

[Guest55]

Dig up patio lol ?
Just make a comment on your EIC that ground works were completed by a third party.

 

[alarm man]

* BUMP *

Anyone got anything to say...

aye,you will answer your own question soon..as per the norm..

 

[pencilpusher]

Dig up patio lol ?
Just make a comment on your EIC that ground works were completed by a third party.

I did not suggest I dug it up! I suggested noting the cert and you have confirmed that. Thanks. PP :8:

 

[rustynails]

You also need to work out your volt drop for the load, which is probably why the calculator said 2.5mm2 SWA.

Using 1.5mm 3 Core SWA PVC

Volt Drop (mV) is 8.8V (mv = 25 (cable voltage drop per amp per metre, table 4D4B) x 14.08 (Cable design current lb) x 25 (Length of run in m)

Using 2.5mm 3 Core SWA PVC

Volt Drop (mV) is 5.28V (mv = 15 (cable voltage drop per amp per metre, table 4D4B) x 14.08 (Cable design current lb) x 25 (Length of run in m)

You can split the volt drop so that you can see if just the lights can be run on a lower csa cable.

Not entirely sure what you mean by splitting the volt drop?

For standard light fittings your calculation is based on 100W per fitting.

I have 3 brick lights, each are E27 lamholder 40w bulb max.

The lighting should be fused down to say 5A with a SFCU.

I think I understand this, but it's outside under a deck. Why would I need a switched fused connection unit. I have an outdoor enclosure box which is where the spurring occurs. I'd need to fuse down inside that ideally because of the glanding. I presume?

 

[HandySparks]

How are you intending to protect this circuit? Fuse/MCB/RCD? Ratings?

 

[HandySparks]

I have a job coming up soon installing outside lighting and power. I have completed all the calcs and am happy 2.5mm SWA is fine BUT when the builders did the customers patio, they installed 2.5mm SWA under the patio and left it coiled up at each end of the run. I will be checking it is 2.5mm cable throughout it's unseen length by measuring the resistance and doing the calcs. However, there are two things I do not know. One is how deep it is buried and the other is if the cable had marking tape above it. As I will be signing the certs and notifying, can I carry on just noting the fact that I cannot check this without ripping up the patio?

I'd say that if it's covered by paving slabs over the whole length then it doesn't matter how deep it is. No one's going to be putting a spade through it.

 

[Richard Burns]

Using 1.5mm 3 Core SWA PVC

Volt Drop (mV) is 8.8V (mv = 25 (cable voltage drop per amp per metre, table 4D4B) x 14.08 (Cable design current lb) x 25 (Length of run in m)

Using 2.5mm 3 Core SWA PVC

Volt Drop (mV) is 5.28V (mv = 15 (cable voltage drop per amp per metre, table 4D4B) x 14.08 (Cable design current lb) x 25 (Length of run in m)

Not entirely sure what you mean by splitting the volt drop?

I have 3 brick lights, each are E27 lamholder 40w bulb max.

I think I understand this, but it's outside under a deck. Why would I need a switched fused connection unit. I have an outdoor enclosure box which is where the spurring occurs. I'd need to fuse down inside that ideally because of the glanding. I presume?

Maximum volt drop for lighting is 6.9V; for sockets 11.5V; the 1.5mm2 does not make it for lighting.
If you calculate the volt drop for each section then the lights may comply using 1.5mm2 for the lighting.
See the diagram below.

Appdx 1 in the OSG suggests using 100W minimum for each light fitting.
Maximum OCPD for lighting with ES lamp holders is 16A (559.6.16) also the fittings may not be rated for taking the current that maybe expected from a socket. Does not need a switch but does need a fuse.

 

[rustynails]

Ok, so your saying my lb = 15 Amps (rounded up)

13amp socket is 2990 watts +
100w(0.5A) for 3 light fittings 300 watts = 3290 watts / 230 = 14.3 Amps

Following the diagram, Volt Drops would be:

17th p339 2.5mm 3 core swa voltage drop per amp per metre = 15
17th p339 1.5mm 3 core swa voltage drop per amp per metre = 25

VdB 2.93 = (15 x 13m x 15A (Total load))/1000
VdC 0.2 = (15 x 1m x 13A (Socket))/1000
VdD 0.02 = (25 x 1.2m x 0.5A (Light))/1000
VdE 0.02 = (25 x 1.5m x 0.5A (Light))/1000
VdF 0.03 = (25 x 2m x 0.5A (Light))/1000

Socket Vd = 3.13V
Light D Vd = 2.85V
Light E Vd = 2.85V
Light F Vd = 2.86V

Lights are way under 6.9V as required and power way under 11.5V so that would be acceptable. Just out of interest I did these calculations using 1.5mm throughout and added on the forgotten 3m drop from the CU in standard 1.5mm two core and earth. Am I right in saying that I could do it in 1.5mm straight from the CU, that can't be right can it. Something wrong with my calculator possibly...?

VdA 1.31 = (29 (p335 17th) x 3 x 15)/1000
so then that would make the following vd when using 1.5mm:

Socket Vd = 4.44V
Light D Vd = 4.16V
Light E Vd = 4.16V
Light F Vd = 4.17V

and using 2.5mm two core and earth for CU drop gives:
VdA in 2.5mm 0.81 = (18 x 3 x 15)/1000

Socket Vd = 3.98V
Light D Vd = 3.66V
Light E Vd = 3.66V
Light F Vd = 3.67V

As for overcurrent protective device I am required to use a maximum 16A as said which Is fine because I have a new board with a spare Type B 16A 30mA RCBO 61009-1.

Only thing is I know that the regs page 426 and table H2.1 p174 OSG say A3 Radial 20A OCPD 2.5mm Minimum live conductor.

Calculations allow acceptable use of 1.5mm 3 core swa throughout the circuit, however like I said my calcs could be wrong and regs state 2.5mm throughout...but picture shows socket radial serving 20m.

If you calculate the volt drop for each section then the lights may comply using 1.5mm2 for the lighting.

It looks that I could.

 

[sedgy34]

sorry to put a spanner in your works but your not a registered electrician and should not be doing these works.

 

[Guest55]

sorry to put a spanner in your works but your not a registered electrician and should not be doing these works.

How have you come to that conclusion ?
And you're incorrect anyway.
Anyone can carry out electrical work in their own home so long as they notify the local council , pay the appropriate fees , and have the work inspected and tested by a competent person.
Simples.

 

[La Poste]

Why do we use 230 Volts as our starting voltage when in reality it is 240 Volts or maybe 235 volts?

It seems these volt drop calculations are making us buy bigger cables than we need to.

 

[EastAnglian]

Why do we use 230 Volts as our starting voltage when in reality it is 240 Volts or maybe 235 volts?

/QUOTE]

From Wikipedia:

"Following voltage harmonization, electricity supplies within the European Union are now nominally 230 V ± 6% at 50 Hz.[SUP][1][/SUP] For a transition period (1995–2008), countries that had previously used 220 V changed to a narrower asymmetric tolerance range of 230 V +6% −10% and those (like the UK) that had previously used 240 V changed to 230 V +10% −6%.[SUP][2][/SUP]No change in voltage is required by either system as both 220 V and 240 V fall within the lower 230 V tolerance bands (230 V ±6%). In practice, this allows countries to continue to supply the same voltage (220 or 240 V), at least until existing supply transformers are replaced. Equipment used in these countries is designed to accept any voltage within the specified range."

 

[La Poste]

So maybe we use 230 Volts as our starting figure just in case the supply companies change the voltage to 230 Volts in the future.

 

[mikehopkins]

Itll work and then when u move a sparky will put it right if it don't kill someone in the meantime,. This is the problem with electrical work, it's works so folks think its fine, a car with no brakes , an aeroplane with no landing gear , need I go on.!

 

[Guitarist]

You sure Part P allows someone else to sign off another's work?

 

[Guitarist]

Itll work and then when u move a sparky will put it right if it don't kill someone in the meantime,. This is the problem with electrical work, it's works so folks think its fine, a car with no brakes , an aeroplane with no landing gear , need I go on.!

I had this discussion the other day regarding adequate earthing. I asked em why they bothered with a seatbelt....

 

[EastAnglian]

You sure Part P allows someone else to sign off another's work?

No, it doesn't!

 

[GLENNSPARK]

as the weatherproof joint box will be under the decking upon completion.....has the O/P considered access for this weatherbox.....and the joints within?...

 

[RISElectrical]

No, it doesn't!

However LABC are allowed to come and see the job and then get someone in to sign of the works?

You don't need to be a member of a scam to do notifiable works

 

[RISElectrical]

1.5mm on a 16A type B MCB would be fine IMO will also need RCD too don't forget.

From your first post, making a few assumptions I got the vd to be 4.6v on the 1.5 cable over 15 meters

 

[GLENNSPARK]

However LABC are allowed to come and see the job and then get someone in to sign of the works?

You don't need to be a member of a scam to do notifiable works

but its whether you can convince a customer to see to that....the extra expense....the hassle...

 

[RISElectrical]

I was referring in the case to the OP as its his own decking so I understood so if he did inform LABC then the cost incurred would probably be < paying an electrician to do the works which is why I thought he would be doing it himself, if that makes sense.

Agree that the most cost effective way to the customer is to be a scam member, if they even know what part p is!

 

[GLENNSPARK]

I was referring in the case to the OP as its his own decking so I understood so if he did inform LABC then the cost incurred would probably be < paying an electrician to do the works which is why I thought he would be doing it himself, if that makes sense.

Agree that the most cost effective way to the customer is to be a scam member, if they even know what part p is!

well its a classic example of where someone may want to install the cable themselves...then see if they can get an electrician to notify it...hense my question about accessability to that IP box....

 

[sedgy34]

How have you come to that conclusion ?
And you're incorrect anyway.
Anyone can carry out electrical work in their own home so long as they notify the local council , pay the appropriate fees , and have the work inspected and tested by a competent person.
Simples.

I come to that conclusion because the law states competent persons!!!
the OP is maxing out a cable he hadn't put in yet and some of you are giving him the answer to his Calcs, Im assuming here he has priced the cable up and is trying to verify 1.5 mm is ok to use rather than spend an extra £3 to get appropriate cable to do the job.
How can the OP be competent when someone has mentioned your calculater says 2.5mm and he's just thrown some Calcs back and referred back to 1.5mm.
Just to clarify law states competent persons!! Not anyone as you said so YOU are incorrect,also if he does do the work is he upgrading any equipotential bonding in his house first that may need doing the OP isn't in my opinion competent to do all this for it to pass labc.

 

[rustynails]

Basically I'm tight as a ducks arse then!

This is just theory. I can read that the regs say use 2.5mm, but calcs are saying that 1.5mm is usable. With copper prices being what they are these days, esp swa prices it's a thought provoking discussion, right?

1.5mm on a 16A type B MCB would be fine IMO will also need RCD too don't forget.

Type B 16A 30mA RCBO 61009-1

From your first post, making a few assumptions I got the vd to be 4.6v on the 1.5 cable over 15 meters

How's that then?

Although, looking at one of my posts I made the length of run too long. Just to re-iterate to everyone whos remotely interested. I'm working out a design as per the diagram posted by Mr Burns:

http://www.electriciansforums.net/a...ircuit-volt-drop-patio-socket-light-split.jpg

Tho this was a helpful diagram created by Mr Burns, cheers for that. It doesnt include the 3m drop from the consumer unit to an outside junction box on the external house wall. That's where the diagram begins. 13m run to 4 smaller runs of less than 2m each see diagram. All wiring in diagram is multicore swa pvc and internal wiring would be standard two core and earth.

 

[Guest55]

I come to that conclusion because the law states competent persons!!!
the OP is maxing out a cable he hadn't put in yet and some of you are giving him the answer to his Calcs, Im assuming here he has priced the cable up and is trying to verify 1.5 mm is ok to use rather than spend an extra £3 to get appropriate cable to do the job.
How can the OP be competent when someone has mentioned your calculater says 2.5mm and he's just thrown some Calcs back and referred back to 1.5mm.
Just to clarify law states competent persons!! Not anyone as you said so YOU are incorrect,also if he does do the work is he upgrading any equipotential bonding in his house first that may need doing the OP isn't in my opinion competent to do all this for it to pass labc.

Ring up your local planning office and pretend to be a diy'er wanting to put up decking lights.
They will confirm what i said in my earlier post.

 

[RISElectrical]

When i said using 1.5 would be ok, i also assumed SWA/XLPE and also that this would be from the DB outwards, not ran in T&E from the DB then changing. If you did run from the DB in 1.5mm SWA/XLPE then this would be fine for carrying the current and for volt drop on a 16A OCPD. To be honest I didn't bother with calcs etc tho as it was a quick "bang it in the computer and computer says yes" exercise. Your doing the job so you need to be 100% sure it checks out first.

As for the needing to be competent, i agree that you do however the argument over needing to be scheme registered is a no brainer and you DO NOT need to be. Nothing anywhere in any legislation says that you need to be to enable you to install anything electrical.

The fact that these "scams" only require a reg qualification to join speaks volumes. Anyone can revise an exam and pass and I am sure with some intense theory practice along with a little coaching it will be equally easy to pass a "scam" assessment considering they want 1 job and that can be in your own home. How do they know you have even done the job they are assessing? Talk the Talk, bang out a few tests that are heavily documented in the OSG and online and pay £500 and boom, your suddenly deemed competent to do the exact same thing that the OP is proposing to do and being told "you cant do it because your not part P". Rubbish.

Part P rant over, its a farce and we all know it is, we just have to live with it.

For example the OP gets a quote from a sparky for labour only, assuming materials are supplied by the OP and the quote is £300. The OP phones LABC, explains the job and position he is in and they charge him £150 for the certifying. That means the OP could do the job at a weekend instead of watching top gear re-runs and saves a tidy £150 in the process. Maybe he isn't competent and in the long run it costs more to put it right, however saying that I have seen DIY'ers that although no formal quals have a lot of experience and are capable of a better install than some of the scam registered sparks that are in circulation.

 

[Guest55]

^^^Agreed , i've seen decent electrical work done by diyers that have never been near a "domestic installers" course.
And i've seen garbage done by electricians with fancy stickers on the side of their van.
Go figure ?

 

[Richard Burns]

1.5mm T&E, if it is run in insulation anywhere, is getting close to the current carrying capacity of the cable if it is protected by a 16A RCBO and could be overloaded if it is surrounded by insulation.
Please remember that the diagram is only intended to describe the voltage drop technique and not to be a design guide for your installation. As I have not seen the installation I cannot provide advice on the way it is installed only information on the cables and currents based on your information.

 

[sedgy34]

Basically I'm tight as a ducks arse then!

This is just theory. I can read that the regs say use 2.5mm, but calcs are saying that 1.5mm is usable. With copper prices being what they are these days, esp swa prices it's a thought provoking discussion, right?


Type B 16A 30mA RCBO 61009-1



How's that then?

Although, looking at one of my posts I made the length of run too long. Just to re-iterate to everyone whos remotely interested. I'm working out a design as per the diagram posted by Mr Burns:

http://www.electriciansforums.net/a...ircuit-volt-drop-patio-socket-light-split.jpg

Tho this was a helpful diagram created by Mr Burns, cheers for that. It doesnt include the 3m drop from the consumer unit to an outside junction box on the external house wall. That's where the diagram begins. 13m run to 4 smaller runs of less than 2m each see diagram. All wiring in diagram is multicore swa pvc and internal wiring would be standard two core and earth.

no intention to offend anyone if your doing the works yourself use the 2.5 swa as stated and fuse down for the lighting the run is neglegable and most sparks dont go into cable calcs for something like this 2.5mm comes to mind automatically.