Resistance Of Cable

[steptoe]

anyone have to hand the resistance of 1.00mm copper cable?

for some reason I have 2.14/100m in my head,

I have a table somewhere but for the life of me I cant find it,

 

[Zeespark]

Got a copy of BS7671 Steps? :innocent :slap :coat

Andy Guinness

 

[steptoe]

yes, what page is it on?

I dont have the book to hand but I'll get it up on the phone from the home computer,

and, I am not using my fricking phone to search through it all,  :|

 

[Sidewinder]

18.1 milliOhms per m from the osg, I don't think it is in the BGB

 

[steptoe]

thanks SW,

thats even worse then than I thought for a circuit I tested today,

got 2.6 hms   r1/r2 on a 1mm protected by a B10 60898 running through kingspan 

d'ya think it complies?    :slap

 

[sparkytim]

And what LOAD was on it? 

 

[steptoe]

hardly anything,

8 smoke detectors.!

 

[Sidewinder]

OK, so you could say fixed load then which is I think where sparkytim is going.

If so then you would need to use the adiabatic to ensure that the cable is adequately sized to take the fault current, on all cores, & calculate to ensure that the fault drop was OK at full load at the end of the circuit also, I guess.

 

[steptoe]

well, my thinking was it wont comply with VD or the fact the cable will be derated to 8amps due to the insulation.

also had a lighting circuit, same scenario and it came in at 2.3  hms

 

[Sidewinder]

As a fixed load, would it need overload protection though?

It "could" be considered a fixed load, being 8 hard wired smokes?

No overload could take place, only a fault current of some sort.

However, it is the magnitude & duration of that fault current that cannot be identified as the failure modes of the smokes are unknown.

Just thinking out loud as it were.

 

[steptoe]

I was looking at it as being rubbish design TBH, having the OCPD larger than the CCC of the cable when de-rated, when a 6A  MCB wouldnt be rocket science.

just one of many rubbish parts of the install.

plus the VD, and the sheer length of the cable.!

 

[Sidewinder]

I totally agree Steps, just throwing ideas into the mire!

 

[steptoe]

always good to hear other thoughts on the subject.

also had a 32A protecting a radial to an immersion heater , double socket, and boiler, wired in 2.5mm ,

not even taking into account heating loads over 2kW on their own circuit, or that 2.5 carries 27A,

but what happens if there is a fault on the cable?

NO hot water,,,,,,,

:shakehead

 

[ProDave]

Why waste time fretting about it. Change the B10 for a B6 at least.

 

[Andy™]

always good to hear other thoughts on the subject.

also had a 32A protecting a radial to an immersion heater , double socket, and boiler, wired in 2.5mm ,

not even taking into account heating loads over 2kW on their own circuit, or that 2.5 carries 27A,

but what happens if there is a fault on the cable?

NO hot water,,,,,,,

:shakehead

dont forget water heaters over 15ltr need their own dedicated circuit

 

[steptoe]

dont forget water heaters over 15ltr need their own dedicated circuit

oh, didnt think of that one, I was more on the immersion being a back up for no boiler, and if the MCB went none of them would work, plus >2kW should be on its own too,

never even thought of the >15ltr bit,

is that an actual reg Andy, or guidance though

 

[Andy™]

oh, didnt think of that one, I was more on the immersion being a back up for no boiler, and if the MCB went none of them would work, plus >2kW should be on its own too,

never even thought of the >15ltr bit,

is that an actual reg Andy, or guidance though

its an actual reg, unlike the 2kw thing which is just a recommendation in appendix 15

may be wrong on the volume though, but im sure its 15ltr

 

[Sidewinder]

What can I search the regs for?

 

[steptoe]

its an actual reg, unlike the 2kw thing which is just a recommendation in appendix 15

may be wrong on the volume though, but im sure its 15ltr

cheers Andy,

thanks,

 

[Sidewinder]

I can't find the word litre anywhere in BS7671?

Using the IET electronic regs with proper search facility.