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T

TPES

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I have been to a job where there is an extension being built. (new lounge)
and the kitchen is being re-wired.

I am not doing the work. Its being done by another electrician.

There is 2 lighting circuits, upstairs & downstairs. Upstairs lighting will not be altered at all

(I have always been told as a rule of thumb by electrical firms not to put more than 9 at most 10 lights per circuit (1mm, 6A) in a domestic property)

Downstairs when all the work has been done and complete there will be...

Kitchen : 8 x downlights, 2 x wall lights, 4 x under cupboard lights.
Lounge : 2 x pendants
Dining room : 1 x pendant
Garage : 1 x pendant
Outside lighting : 5 x bulkheads
Hallway : 1 x pendant

This is all on the downstairs lighting circuit, Also how do you know what wattage bulbs the customer will fit in each light in the future?, you dont.. (aslong as they keep within the limits of the unit)
So i would say this is far too much load on the circuit.

I went to the property when the sparks where doing there 1st fix and voiced my concern. They had told me they had re-wired it all in 1.5mm and were going to uprate the breaker to a 10A.

So i thought fair enough, All should be ok then. Then a few days after i was back at the property and noticed the only lighting cable that had been upgraded was the kitchen and the extension. All the other rooms that were not being touched were all still in 1.0mm and they had just carried on the kitchen and extension in 1.5mm.

Now this seems obvious to me that this is going to cause problems, If they dont upgrade the breaker and keep it on a 6A this will overload the circuit, if they change the breaker to a 10A then they will be pulling far too much current up a 1.0mm.

What do you think to this or is it me that has missed something so very obvious??

Can someone put me in the picture of what this sparks intentions are??
 
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H

hamlettphil

  • Thread Starter Thread Starter
  • #2
i roughly work out that you can have around 1300W on a 6A breaker, what you have described would probably take around 1200W i think, and i would think that the people wouldnt have all the lights on all the time. and dont quote me on this but i think 1mm can take up to around 10ish amps. plaese correct me if im wrong
 
T

TPES

  • Thread Starter Thread Starter
  • #3
How did you work out that the lighting circuit would only use around 1200W ? What if the customer 6 months down the line decides to put 100w lamps into some of the pendants?
I understand its unlikely that all the lights will be on at same time & 100w lamps will be in all fittings but shouldnt you cover your self incase the customer decides to fit 100w lamps or has a party with a house full of people?
Yes i'd like someone else to say if 1.0mm can carry 10A ?

Even better a reminder on the formular for working out what power a conductor can take.
 
1

12345aob

  • Thread Starter Thread Starter
  • #4
you can put 1 mm on a 10 amp breaker, i think 1 mm can go 12amp ish. it sounds like alot off load. cant do any calcs without knowing what lamps will be fitted?
 
I have been to a job where there is an extension being built. (new lounge)
and the kitchen is being re-wired.

I am not doing the work. Its being done by another electrician.

There is 2 lighting circuits, upstairs & downstairs. Upstairs lighting will not be altered at all

(I have always been told as a rule of thumb by electrical firms not to put more than 9 at most 10 lights per circuit (1mm, 6A) in a domestic property)

Downstairs when all the work has been done and complete there will be...

Kitchen : 8 x downlights, 2 x wall lights, 4 x under cupboard lights.
Lounge : 2 x pendants
Dining room : 1 x pendant
Garage : 1 x pendant
Outside lighting : 5 x bulkheads
Hallway : 1 x pendant

This is all on the downstairs lighting circuit, Also how do you know what wattage bulbs the customer will fit in each light in the future?, you dont.. (aslong as they keep within the limits of the unit)
So i would say this is far too much load on the circuit.

I went to the property when the sparks where doing there 1st fix and voiced my concern. They had told me they had re-wired it all in 1.5mm and were going to uprate the breaker to a 10A.

So i thought fair enough, All should be ok then. Then a few days after i was back at the property and noticed the only lighting cable that had been upgraded was the kitchen and the extension. All the other rooms that were not being touched were all still in 1.0mm and they had just carried on the kitchen and extension in 1.5mm.

Now this seems obvious to me that this is going to cause problems, If they dont upgrade the breaker and keep it on a 6A this will overload the circuit, if they change the breaker to a 10A then they will be pulling far too much current up a 1.0mm.

What do you think to this or is it me that has missed something so very obvious??

Can someone put me in the picture of what this sparks intentions are??
Well it all depends upon the rating of the lighting fittings that are being used. As a rough guide I would work out the scenario you have described as follows:

8 x Downlights (mains 50w GU10s?) 8x50 = 400w
2x wall lights (100 w ea?) 2x100=200w
5x pendants 5x100=500w
5x bulkheads (100 w ea?) 5x 100=500w
4 undercupboard lights 100w?
Total assumed load = 1700w
1700/230 = 7.39 A

I have assumed that all the pendants/bulkheads are rated at 100A to err on the side of caution.
The installation reference method will have an effect on the current carrying capacity of the cable. Assuming that the cable used is 70 degree C multicore (T+E) in the worst case, then from table 4D2A BS7671 the current carrying capacity of the cable is reduced to 11Amps.
So I think that a 10 A breaker could be used to protect the cable.
However this basic calculation does not take into account the length of the circuit which will affect voltage drop and therefore may require an increase in cable CSA.

Personally I don't bother with 1mm for lighting. 1.5mm doesnt cost that much more ,is just as easy to terminate and gives you a lot more leeway if additions are required later on. Hope this helps:)
 
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T

TPES

  • Thread Starter Thread Starter
  • #6
Is there no problem mixing the lighting circuit with 1.mm & 1.5mm T&E?

My mistake on this, im glad i didnt say anything to the other sparks, would of made my self look a right plonker!
 
S

sparkyork

hey sid, i thnk your right to be concerned about what they have done as i personally think it sounds crap! for a start as you know there mixing cable sizes that are fed from the same mcb, which is a no no. why didnt they just feed the new lighing off a seperate mcb or something? they will know that there takin the pee really but clearly arnt bothered, unless there that useless that they think there doing a grand job!

either way if they came to my house to do this id of kicked em off the job rapidly....cowboys
 
J

johnnyb

  • Thread Starter Thread Starter
  • #8
Magic Sid
He does NOT know what he is doin my son, get him off the job, before he burns the place down.
Certainly you don,t go mixing 1.00mm and 1.5mm cable, he should be using 1.5 and we to be belt and braces,on the lowvoltage side don,t have more than 6x 12v 50w fittings on any one circuit.
 
T

TPES

  • Thread Starter Thread Starter
  • #9
I agree, I certainly wouldnt be pusshing limits like this if i was doing it. I also would never be mixing the conductors.

Also could you explain why this is..
"on the low voltage side don't have more than 6x 12v 50w fittings on any one circuit."

So when all complete what problems is this work going to cause?
 
J

johnnyb

  • Thread Starter Thread Starter
  • #10
magic sid
Saveloy more a less got the answers, its just our own policy that we only put 6x low-voltage 12v/50 w fittings on each circuit, but mixing 1 and 1.5 is really bad practice on any job, and it will affect your r1 /r2 readings which means in fault condition theres a possibility that breaker may not trip.
 
A

adamh

  • Thread Starter Thread Starter
  • #11
magic sid
Saveloy more a less got the answers, its just our own policy that we only put 6x low-voltage 12v/50 w fittings on each circuit, but mixing 1 and 1.5 is really bad practice on any job, and it will affect your r1 /r2 readings which means in fault condition theres a possibility that breaker may not trip.


???how is the mixing of 1mm and 1.5mm gonna stop a breaker from tripping cant wait for this
 
C

CHRIS-H

  • Thread Starter Thread Starter
  • #12
as far as im aware you are allowed to use 1mm cable on a 10 amp mcb and there will be ample ampage for the lights that are being installed as you dont usually have more than a 60 watt light unless halogen down lights...........
 
T

TPES

  • Thread Starter Thread Starter
  • #13
I think the install is pushing it to the limits, although it may work I would never wire this way.
I would be alot happier pulling in 2 circuits or doing the entire circuit in 1.5mm.
I would never assume that a customer would not exceed putting a 100w bulb in all fittings or be having a party with a house full of people and having nearly all lights on.
I wouldnt want to be the sparky having to explain why all your lights have tripped out and saying "in future dont put all your lights on & try not to fit 100w lamps in your fittings"
 
S

sparkyork

its bad practice to do this. i for one would not be that happy with sticking 1mm on a 10a mcb, yes it may say it can take it but this is an extension and who knows what factors are effecting the 1mm cable prior to the "sparkies" extending it. and what sparky installs a cieling light allowing for a 60watt light bulb? on new builds and previous firms i worked for we had to allow at least 150w per ceiling fitting (diversity)

really dont get why they've also wired the rest in 1.5mm serving no purpose what so ever, unless it makes them think its all rosy, ill argue this thread till im blue in the teath! these guys are cowboys!
 
T

TPES

  • Thread Starter Thread Starter
  • #15
"what sparky installs a cieling light allowing for a 60watt light bulb? on new builds and previous firms i worked for we had to allow at least 150w per ceiling fitting (diversity)"

Agree 100%
 
"what sparky installs a cieling light allowing for a 60watt light bulb? on new builds and previous firms i worked for we had to allow at least 150w per ceiling fitting (diversity)"

Agree 100%
When I did my 2330 we were told to always assume that a normal light fitting (pendant) would be taking a 100 watt bulb so our caculations would have to reflect this. This was to allow for the fact that this is what the end user may fit to the fitting. Not arguing with Sparky york though as his method is even safer. You have to expect that the average house holder is not going to take a blind bit of notice of the rating on the lamp. Invariably they will just stick the brightest bulb they can find, into the fitting!!
 
T

TPES

  • Thread Starter Thread Starter
  • #17
Lets say you have a lounge with 2 x big fancy 5 light chandelier fittings, and the end user fits 60w bulbs in each fitting. 10 x 60w bulbs

Theres 600w on 2 pendants alone in one room.

Then a set of mains downlights in the kitchen.. Its also very likely these 2 rooms will be lit up at the same time.. you could easily be upto or over 1000w just on these 2 rooms never mind the rest of the circuit.

I would always wire and account for these situations.

Best to be safe than sorry.
 

jeremy

-
Mentor
Arms
Can some one please explain to me please as i am having a bit of a senior moment, why you cant have 1mm and 1.5 on the same circuit ? Is it because the 2 numbers don't fit into the box on the Schedule of inspections?

Also having read a bit more, from the recesses of my 1664 addled mind 1mm 6A 1.5 10A 2.5 20A. This I seem to remember takes into account the fact that the eejit householder will try and bugger your plans for providing him with a safe install. Remember divide by 2 if the same eejit covers more than 50mm length of one circuit in insulation.
 
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I also work on the premise that about 12 lights on a circuit is ok as ohms law 1200 divided by 230 = 5.21amps .Other suggestions have said no more than 6x12v 50w fittings on a circuit!! This seems to me to be a restrictive amount to me, i may be wrong & i dont mean to be critical just trying to get an answer.How do you work out the loading to an individual e.l.v 12v 50w lamp if you use ohms law , 50 divided 12 it works out 4.1 which surely cant be 4.1 amp each fitting. Do you also take into account the transformer load??Please could someone tell me the loading of an individual e.l.v 12v 50w lamp & how this is calculated????? It would be very much appreciated if anyone can help with this.
 
S

Stuart King

  • Thread Starter Thread Starter
  • #20
Would someone please come up with the answer
 
T

Tag

  • Thread Starter Thread Starter
  • #21
Evey lighting point should be calculated as a min 100w bulb regardless of whats actually installed ;)
 
T

Tag

  • Thread Starter Thread Starter
  • #23
...what was the question?

From the first post I'm counting 24 lighting points. 24*100w = 2400w / 230 = 10.43A. I'd say 1mm t+e is border line if ref method is 101 but the volt drop is very high. Best use 1.5mm t+e on a 16A breaker in my opinion.
 
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Sintra

Admin
Supporter
...what was the question?

From the first post I'm counting 24 lighting points. 24*100w = 2400w / 230 = 10.43A. I'd say 1mm t+e is border line if ref method is 101 but the volt drop is very high. Best use 1.5mm t+e on a 16A breaker in my opinion.

If you are using ref method 101 as stated you can not use a 16A breaker as your 1.5mm T&E is rated at 13A.

Table 4D5 BS 7671 2008
 
S

Stuart King

  • Thread Starter Thread Starter
  • #26
Its the same question as a year ago but there was no answer
50w at 230v i=p/v i=50/230 i=0.28 amps
50w at 12v i=50/12 i=4.2 amps
Is this correct?
 
T

Tag

  • Thread Starter Thread Starter
  • #27
50w at 12v i=50/12 i=4.16 ;)
 
S

Stuart King

  • Thread Starter Thread Starter
  • #28
Always round up.
Is the 12v sum correct?
 
T

Tag

  • Thread Starter Thread Starter
  • #29
I was told to never round up... I think that WAS how it was done but I was recently told different
 
S

Stuart King

  • Thread Starter Thread Starter
  • #30
Anyway,is the 12v sum correct?
 
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