hi guys
is there any where in the regs that will help me with the following as I have a job for a cross the T and dot the i type of bloke

the shed is 40m from the mains intake nothing but a pond,light.and every now and a gain a mower so 16A
2.5mm swa 90 deg has a V/A/mtr of 19
40x16x19 / 1000 = 12.16V

but as the shed is not acualy going to run this continously it seem pointless to upgrade to 4mm for just over.6 of a volt and we are in the realms of changing it because it does'nt comply.

any one got the reg I need

How about note 2 at the side of table 4E2A?

sorry note 2 is for grouping temperatures this is concerning volt drop

OK - you need to recognise that you are under running the cable - ie a 2.5mm2 armoured in the ground can carry mor ethan 16A.

as the cable isn't fully loaded, it won't be as warm in operation, it's resistance won't be as high and consequently the volt drop won't be quite as bad.

as a rough estimate, I get the volt drop to about 10.5 volts

technically, you only need to comply with the lower voltage limit of the equipment - which if CE marked will be much lower than any limit in BS 7671

you are quite right in that the load won't be a constant 16A - so allowing for a bit of thermal cycling, the cable will be even cooler and the volt drop that bit less.

If you are happy that the client isn't suddenly going to demand more capacity then 2.5mm2 XLPE/SWA/LSF will be fine for volt drop

Regards

OMS

-------------------------
Failure is always an option

I may be wrong, but isn't the reference to the the operating temperature capacity of connected equipment rather than grouping? To me it suggests that if you are working to the limit of normal accessories of 70.C, then it makes sense to use the corresponding VD table for the given conductor temp, after all the copper within the cable will have the same voltdrop for the given temperature whether it is covered by pvc or xple insulation?

I think OMS is correct that 2.5 will be fine, but you would make more profit from fitting a larger cable

(ps. if the customer is that on the ball, maybe ask him what size cable he wants installing! )

[]



I may be wrong, but isn't the reference to the the operating temperature capacity of connected equipment rather than grouping? To me it suggests that if you are working to the limit of normal accessories of 70.C, then it makes sense to use the corresponding VD table for the given conductor temp, after all the copper within the cable will have the same voltdrop for the given temperature whether it is covered by pvc or xple insulation?


yes you are right my coment was more that I felt it was not about my question.
the Vdrop table I am using is 90deg as my whole saler as a rule only supplies 90deg swa as do most as far as I have found.but I see your point about copper temperatures

Where do you buy accessories for a temperature of 90°C?, assuming that you do mean °C of course.

Regards

Edited for missed out words! Sign of the times.

Edited: 31 July 2012 at 08:05 PM by Jaymack

As far as I know they don't make PVC/PVC/SWA anymore, the BS has been withdrawn, it's all xple now.

Come on chaps - we are putting 16A max down a 2.5mm2 SWA buried in the ground - do any of you think it's actually going to get above 70C under any forseeable condition.

If you want a quick ready reckoner use table 4D4A for design (ie PVC constrained to 70C) - it'll carry about 29A - and you want 16A down it - it won't get over 50C let alone 70.

Then just buy XLPE and bang it in - job done, no dramas, happy client and cash in the back pocket

Regards

OMS

-------------------------
Failure is always an option

Agreed, that was the intended inference of my first post.

Indeed, but for volt drop you are more interested in the actual conductor temperature and if you only have about 50% of the current flowing through a cable it can't be as hot as the data in BS 7671 suggests - ie 70C or 90c depending on insulation type - so you have margin on the tabulated mV/A/m data - which is effectively resistance

regards

OMS

-------------------------
Failure is always an option

Where do you buy accessories for a temperature of 90°C?, assuming that you do mean °C of course.

I am making no refarence that I talking of any terminals,I am just pointing out that as my suppier only stocks 90deg C swa that is why I was using the 90 degC table

Would some of these: http://www.tlc-direct.co.uk/Products/TLPC15.html do? (with a (relatively short) length of larger CSA cable to make the final connection).
- Andy.