Q & A of the Day - Can I use a larger cable for a final circuit than the consumer unit feed?

Published: 16 April 2010 Category: Q&A

Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, concerning supply to an outbuilding at a farm with power, is answered by BASEC:

Q & A of the Day - Can I use a larger cable for a final circuit than the consumer unit feed?
Question: Is it possible to use a larger CSA cable for a final circuit than the consumer unit feed?

I have been asked to supply an outbuilding at a farm with power. The trouble is, it is 100m away from a sub-board in a garage, which is 15m from the main board. The supply to the sub-board is a 6mm SWA. The outbuilding is to have 2 X 13A sockets, 2 X fluorescent lights and 2 X 2D exterior lights. Using 6mm SWA would exceed the maximum volt drop. Could I up this to 10mm SWA to overcome the volt drop?

Answer: Yes, it is possible to use a larger sized cable for the long run to the outbuilding. The key issue is to minimise voltage drop, which can be achieved using a larger CSA cable. Appropriate protection should be applied to protect the smallest cable in the circuit.

I know of an application similar to yours where the run is about 2km!

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