Voltage drop in domestic installation

[charlie76]

Without going in to my calculations and design details (just yet), I have a customer wanting a supply to a summerhouse and workshop which is approx 100m from the source.

My calcs call for a 16mm² feed to overcome voltage drop, well O.T.T for the required Ib but non the less, what it comes out at. Spoke to NAPIT as it is borderline 10mm² feed and they said if the supply voltage is steady and measured at peak, I could use this in my calc rather than the supply nominal voltage.

Is this acceptable as I can't see anything in the regs that permits this. However, I can't see anything that doesn't. 236v at source would allow for a 10mm² feed.

 

[Ian1981]

Just remember your lighting in the summer house still requires a voltage drop of no more than 3% of 230 volts.
The nominal voltage of 230v does often lead to oversized distribution circuits at times but errs on the side of caution.
Quite often round my neck of the woods the voltage when measured is usually around 245 volts which gives me an extra 15 volts to play with but at peak times that voltage may well drop off a bit.
Also if your doing calculations on 16mm remember that if the cables not running at full load you will won't have the full voltage drop on the cable as it won't be running at 70 degrees.

 

[Richard Burns]

Also if your doing calculations on 16mm remember that if the cables not running at full load you will won't have the full voltage drop on the cable as it won't be running at 70 degrees.

If you are borderline on being able to use 10mm² and your calculations do not include corrections for underloaded cables then the above should allow you to use 10mm².
I would not use the actual voltage as this may not be stable over the long term. You are unlikely to have any problems with a low voltage for a domestic situation.