newbie here

[VOLT]

Hey all

New to the forum just saying hello to everyone.
I have a question i need to change a MCB on a consumer unit its quite old i think the make is square D so probs getting on for 15 plus yrs old ? not sure anyway ive managed to source a new 40 amp mcb breaker for the CU which is the same make square D lucky as i think these Square D MCBs are as rare as rocking horse s**t :D.

Now my question is as this installation is pretty old there is no main isolater in the line from the electricity company only the old fuse which i know you cant break and would not want to as its bad practice.

I had a shower fitted and the cable is 10mill the MCB is 30 amp at CU. The rating of the new shower is 8.5 kw so doing the math that is 8500 / 240 which gives me 35.41 amps so this would tell me i need a 40amp MCB.

Now if i just turn off main switch on CU obviously im still gonna have power coming form the meter tails so what is the best way of safely isolating the CU so i can take out the old 30amp MCB and replace it with the new 40amp MCB ?

Any advice would be greatly appreciated thanks

[Ohmslaw]

Hi, and welcome to the forum.

I would say that an 8.5KW shower will sit quite happily on a 32A MCB, for the 30mins at a time or so you will use it as I doubt you will have the temperature set to max. However it's best to upgrade the MCB as the 32A will deteriorate over time, as long as you have the CU main switch open, then the power to the busbar is disconnected and only the top of the main switch will be live, so you will be able to safely change the MCB.

[VOLT]

Thank you very much for your reply much appreciated :)