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Can we use 1.5mm flex for a dedicated washing machine and dishwasher circuits?

We're going to add 2 dedicated radial circuits, one for the dishwasher and one for the washing machine. Can we use a 1.5mm flex cable for this installation?
Additionally, we've got 2 spare 32A RCBO's. Can they be used for the same purpose or should they be replaced by smaller units, e.g. 16A?
What is the risk of using a 32A RCBO?

1 Answer from a MyBuilder Electrician

Best Answer

Very poor design to use 1.5mm flex for a radial circuit. It maybe possible to use it, but you will need to do your adiabetic equation to calculate the voltage drop on the cable based on the length of run at full load. If you don't have a copy of BS7671:2008 to hand you can get one from ebay or buy a new copy (approx. £70 from Amazon). 1.5mm flex is totally unsuitable for a BSEN60898 32amp MCB and 16amp MCB's must be used.

A far better solution would be to wire the circuit properly using 2.5mm cable.

Before you start any work, you will need to apply to your local authority and pay to apply for Part P building regulation consent to carry out the DIY electrical works (approx. £300). The local authority will need to come and inspect and test the work once completed and check that it meets the full requirements of BS7671:2008. depending on the inspector, you may have a job convincing them that 1.5mm flex is adequate!


Answered 1st Jul 2015

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