Volt drop

[Traineeboy]

Quick question on volt drop. 

If you run power to an outbuilding ( single phase) when calculating volt drop would you allow the 5% for general or 3% for lighting. The outbuilding would have lighting in it but when I asked the question the chap I worked with he said you allow 5% as it’s not dedicated lighting it’s to a DB when it’s to lighting. 

To me this doesn’t make sense where I would have thought it you are having lighting in the outbuilding you would only be allowed 3% as there is lights in there ? 

Could I get some clarity please. Thanks Chaps.

 

[Murdoch]

You work out the submain using 5% but then you add the lighting circuit at 3% 

 

[Fleeting]

As an unquoted rule of thumb 2% is often used for submains which allows for leeway on the final lighting and power circuit vd. Remember vd is based on the voltage at the source.

 

[Sidney]

The 5%/3% is from the source of supply, as Fleeting has pointed out a good number to aim at for a submain is 2% but this isn't set in stone.

 

[binky]

As an unquoted rule of thumb 2% is often used for submains which allows for leeway on the final lighting and power circuit vd. Remember vd is based on the voltage at the source.

not heard that one before, albeit I have probbaly been doing this for years as I normally work out a cable size for the sub main, then up it one size to allow for 'changes of plan' .