Connecting a 2.5mm supply to 6mm T&E

4 Aug 2008
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United Kingdom
Thanks to everyones help on this forum i'm in the middle of upgrading my garage supply and overhaul of electrics in the garage.

All the work in the garage and shed etc is complete, and I'm left with the final task of actually upgrading my supply cable from 2.5 to 6mm (already purchased) from the house CU to a junction point in the garage.

The original 2.5mm supply was sufficient for what I currently use it for, and the 6mm plan is to future proof myself.

As an interim measure does anyone see any issue with me hooking up the 2.5m SWA (which is already there) to my new 6mm T&E supply to the garage CU ?

The old 2.5mm SWA is fed from the house consumer unit (via a T&E tail) and protected by a 13amp MCB. Does anyone see an issue with me temporarily hooking up the original 2.5mm SWA feed from the house CU to my 6mm T&E tail to the new garage CU ?

Because the MCB won't let more than 13amps through it, i'm assuming it's not a problem as a temporary measure ? and only a temporary measure.. this is because I simply don't have the time at the moment to lay down my new 6mm SWA.
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In essence, it's fine to connect together two cables of different cross sectional area, as long as the protective device is of a suitable rating to protect the smaller of the two cables. If your old earth loop impedance, volt drop, etc were fine on 2.5mm then you should be fine to upgrade a section of the circuit to 6mm as long as the length of the run is roughly the same. As you say, it's only a temporary fix.

Yes the length of the run is the same, and the original 2.5mm supply was tested as part of a PIR some months ago with no issues.
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The old 2.5mm SWA is fed from the house consumer unit (via a T&E tail) and protected by a 13amp MCB

Are you sure it's 13A- I didn't think there was such a beast :eek:

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