Am I using the correct size MCB?

[JoeDonnelly1]

Was asked to run a supply for a 2.8kW fan assisted oven (no hob), I done some cable sizing and voltage drop calculations as well as adding 50% overload and found I could do this using 2.5mm twin and earth cable. I also found I could use a 20A MCB as well but a friend said personally he'd use a 32A to be safe but he didn't give any more info as to why. Would it be best for me to use a 32A MCB and why? Or do I just stick with the 20A MCB? I'm also going to install a double pole switch next to the oven for isolation would it be acceptable to use a 20A DP switch?

 

[Guest123]

The 2.8KW will be the maximum current the oven could draw with all parts of it on and working flat out i.e oven, grill (if there is one) etc.

In reality this will never be the case and this is where diversity comes into play.

Even at full load. 2.8KW is only a shade over 12A so a 20A MCB & 2.5mm T&E is more than adequate. In reality a 16A MCB would suffice.

 

[Mark.W]

If you intend on using 2.5mm, then use a 20A or a 16A, do not use a 32A as 2.5mm cable can only safely carry 27A!

 

[ukpablo]

32A to be on the safe side of what?
2800 / 230 = 12.17 Amps.
if you are supplying the oven on its own cct from the board with 2.5mm cable then why not use a 16A MCB.
The mcb protects the cable and should trip before it sets on fire.
2.5mm cable is rated at around 27A run on its own so the 32A breaker is rated too high for the ccts cable.

If you have done ur calcs correctly etc then run in 2.5 and protect with a 16A mcb. Do not protect it with a 32A unless u up the cable size.

 

[Knobhead]

I fitted a similar type of oven in my own house, my brother (another industrial electrician) took the p**s out of me when I ran a 6mm cable. After a year “she who must be obeyed” decided she wanted an electric hob instead of gas. No problem.
She didn’t like the electric hob either, back to the gas!
She is now the Ex.

I’d upsize the cable, just in case!

 

[JoeDonnelly1]

I thought about running a 6mm just incase they changed their mind in the future but this is a brand new extension and the whole wall is kitchen units and the oven is raised about a meter high and slides right into the kitchen unit so its not exactly portable anywhere else, he also has an island in the middle of the new kitchen for where his new 'induction stove' is going to be what ever the hell that is because I've never heard of it

 

[sedgy34]

use a 4/6mm cable and put on a 20a mcb for he appliance, but if its changed in future for a 32a its got the correct cable size

 

[Top Cat]

For the sake of a few pounds i would use a 4mm or 6mm cable. Just so, if sometime in the future the oven gets changed to a double oven.

 

[Top Cat]

use a 4/6mm cable and put on a 20a mcb for he appliance, but if its changed in future for a 32a its got the correct cable size

Blimey sedgy we must have been doing this at the same time. I was a bit late because the phone rang!

 

[JoeDonnelly1]

Just got a bit of annoying news.. Turns out hes infact got 2 ovens.. But only 1 spare way on the board, help??

 

[Top Cat]

Just got a bit of annoying news.. Turns out hes infact got 2 ovens.. But only 1 spare way on the board, help??

That's why we said a 4 or 6mm cable!

 

[JoeDonnelly1]

Flap flap flap! So how is this best done co nsidering im doing this in an hour! In terms of breaker size etc

 

[Plonker 3]

You have been advised accordingly, only you can make the final decision on what size cable and MCB.

 

[sedgy34]

Blimey sedgy we must have been doing this at the same time. I was a bit late because the phone rang!

beat you to it lol GREAT MINDS EHH

 

[sedgy34]

Flap flap flap! So how is this best done co nsidering im doing this in an hour! In terms of breaker size etc

i assume you asking such a question you shouldnt be messing get a sparkie to do it