Feeding cable through insulation

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DIY GUY

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that's not quite how it works to derate the circuit you should make the mcb smaller, or the cable bigger,
what size did you say was the cable you have is ?
the total length of the circuit matters and there is a very long list of things that we need to take into account when designing a circuit ,
I’m linking off my existing downstairs 6a circuit.

Taking 1meter 1mm t&e link from existing switch to new switch to control new exterior lights for maintenance.

From new switch 4meters 1mm 3core&E to photo cell

From photo cell 4meters 1mm t&e to new light

From new light 4meters 1mm t&e to 2nd light

From 2nd light 15meters 1.5 t&e to garage light

From garage light 2meters 1mm t&e to 4th light

From 4th light 2meters 1mm t&e to 5th light

Cable going to Solar cell & new light & 2nd light will be behind wall insulation. Cable runs after that are not in insulation
 

DIY GUY

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1.5mm cable should be used where you encounter said insulation.

Are you sure you have a neutral at the first switch??
Yes I have a neutral. Is there anyway possible that I could get away with 1mm at all.

Making a run in between the insulation for the cable to run up so that it’s not compact in insulation.

Running a piece of 25mm round conduct up the 3 sections of wall that cables are running up.

All cables are now under the floor with new floor laid and buried behind the walls etc. Just nothing is connected yet.
 

DIY GUY

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Yes I have a neutral. Is there anyway possible that I could get away with 1mm at all.

Making a run in between the insulation for the cable to run up so that it’s not compact in insulation.

Running a piece of 25mm round conduct up the 3 sections of wall that cables are running up.

All cables are now under the floor with new floor laid and buried behind the walls etc. Just nothing is connected yet.
@Murdoch what do you reckon?
 

poni

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I’m linking off my existing downstairs 6a circuit.

Taking 1meter 1mm t&e link from existing switch to new switch to control new exterior lights for maintenance.

From new switch 4meters 1mm 3core&E to photo cell

From photo cell 4meters 1mm t&e to new light

From new light 4meters 1mm t&e to 2nd light

From 2nd light 15meters 1.5 t&e to garage light

From garage light 2meters 1mm t&e to 4th light

From 4th light 2meters 1mm t&e to 5th light
i make that 32m of new cable you must add the existing part from the MBC to the switch then add this to give you a total circuit length , you could be over the max length for this cable without the derateing or very close to the max length you may need to use 1.5 T+E
 

DIY GUY

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So am I correct in saying this is not safe at all to do so in 1mm but safe to do so in 1.5mm?

I really didn’t think this would have been that hard to do?

And there is no way that the part in the insulation can be done in 1mm, ie conduct or insulation split apart?
 

DIY GUY

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All can be safely wired in 1.0 mm cable. 1.0 mm cable is OK up 16amps in open air. In insulation down to 8 amps so still OK.
Are you sure about this as I’m slightly paranoid now 😐.

I could have attempted to re cable in 1.5mm but the runs under the floor might have got snagged and fell off underneath.

Should I run the cable up between kitchen and insulation.

Should I run cable up between exterior wall and insulation.

Or should I run it up through 25mm conduct?

Thanks
 

Fleeting

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You will almost certainly exceed the 3% permissible volt drop but this is assuming the full capable load of 6A which is highly unlikely.
This is Table 4D5 from BS7671 showing the rating for the cable in question.20220804_104404.jpg
 

poni

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All can be safely wired in 1.0 mm cable. 1.0 mm cable is OK up 16amps in open air. In insulation down to 8 amps so still OK.
its not in open air ,its more like Method 103, there are still a few unknowns, also we don't know the length of the total circuit to work out the volt drop yet( the max run at 6Amp is about 26m but I could be wrong ), thanks to Fleeting for posting the table,
 

DIY GUY

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So I would be reference method A, in conduct. Would this be safe to do in 1mm t&e or am I going to have to try and change it to 1.5mm t&e possibly screwing it up?

The 5 new exterior lights will be led low watt run from photo cell so 5 of them will be on for quite a few hours throughout the night.
 

poni

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I think you have a bigger problem now that is the volt drop at the last light , as for changing to 1.5 as I said before there are still a few unknowns, someone would need to look at the job to see
 

DIY GUY

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I think you have a bigger problem now that is the volt drop at the last light , as for changing to 1.5 as I said before there are still a few unknowns, someone would need to look at the job to see
Why would there be a voltage drop if the longest piece of cable (15meters) is 1.5 t&e?
 

DIY GUY

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Could someone please clarify if this can or can’t be done in 1mm t&e or do I really need to have it changed to 1.5mm t&e

Again every single light from the downstairs breaker is led and very low wattage.

I’m planning on hopefully solving it by the wknd


Thanks for all your help
 

DIY GUY

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It will be fine with LED lighting the load is very low and this will negate the volt drop.
Thanks for this so my 1mm t&e is all good?

Running the cable in insulation at the 3 points, should I run it plastic conduct or run it up against the inner plaster board wall or run it up against the exterior wall?

@Fleeting thanks for this 👍🏻
 

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