Potential Overloaded? (Kitchen Oven & Hob)

[Cupa]

Popped round my old dear's yesterday. She quite fancies replacing her ceramic hob with an induction one, so I thought I'd take the oven and existing hob out to see what state the wiring is in (property built 1930s although I expect probably had a refurb at some point in the 70s or 80s, but nothing since).

Anyway, pics attached of what greeted me. The oven & hob are both wired to a single cooker outlet plate, with a cable going back to a 32a breaker on the consumer unit.

Issue I have is that the hob is 2.8kW & oven is 6.6kW (9.4kW). Based on a 32a breaker x 230v = 7.4kW. So that little combo there is 28% over the breaker rating.

However, I think the reason why the CU doesn't kick in is because the old dear hardly ever uses both hob & oven on full whack.

Anyway, my question is, setting aside theory and regs for a sec, in the real world what I found, how much of a potential issue is this?

I'm also itching to change the cooker outlet plate to a nice modern one (I have lying about as a spare).

 

[davesparks]

You need to include diversity in your calculations.

 

[Cupa]

Right, I am a mere novice and know sod all about anything but will have a go. Let me know where I am wrong, haha!

So, we have the following connected loads - a 2.8kW hob + 6.6kW oven = 9.4kW = 9,400, divide by 230v = 40.87.

Unless I am a complete muppet, I read that for a cooker the diversity applicable is 10a + 30% balance?

Based on that you calculate 30 x (40.87 - 10) / 100 = 9.26.

So 10a + 9.26 = 19.26 + allowance for socket outlet of 5 = 24.26?

I probably got that wrong as I have both an oven and a hob together - do I need to do a calc for each instead of joint?

 

[Zerax]

You might find the JW youtube vid helpful...

From about 12min onwards... worked example

 

[davesparks]

Right, I am a mere novice and know sod all about anything but will have a go. Let me know where I am wrong, haha!

So, we have the following connected loads - a 2.8kW hob + 6.6kW oven = 9.4kW = 9,400, divide by 230v = 40.87.

Unless I am a complete muppet, I read that for a cooker the diversity applicable is 10a + 30% balance?

Based on that you calculate 30 x (40.87 - 10) / 100 = 9.26.

So 10a + 9.26 = 19.26 + allowance for socket outlet of 5 = 24.26?

I probably got that wrong as I have both an oven and a hob together - do I need to do a calc for each instead of joint?

Looks right to me, so a 32A circuit is correct for this combination of appliances.
The method of connection to the cooler plate is less than ideal though.

 

[Toneyz]

A Click Scholemore dual cooker outlet would be ideal for what you need.

 

[Cupa]

I have one of these left as a spare (45a cooker outlet plate), and while it can probably accommodate dual inputs, it is not designed as such I don't think.

 

[Taylortwocities]

It’s not designed for dual output. If you think about it you’ll have 3x6mm cables in each terminal. And they aren’t made for that.
This what you need

The existing circuit at 32A is fine for what you plan to connect to it.
While you are at it, PLEASE put some grommets in the holes of that back box!

 

[DT1991]

Although not required does this have a double pole control switch or just come straight from CU.

Helps if cooker or hob ever develop a N-E fault and can be isolated at the switch to avoid any RCD split load tripping issues.

 

[Cupa]

Thanks to all, I'll pop down to TLC and grab one of those. I have some spare grommets, of course, I will whack one on. I was surprised myself when I took the cover off and saw no grommet!

Form what I can tell, the cable goes from the CU to a Schneider cooker switch (double pole), and from there to the cooker outlet plate.

Thanks to all by the way, appreciate you taking the time to reply to me. I am learning new stuff all the time!

 

[telectrix]

Thanks to all, I'll pop down to TLC and grab one of those. I have some spare grommets, of course, I will whack one on. I was surprised myself when I took the cover off and saw no grommet!

Form what I can tell, the cable goes from the CU to a Schneider cooker switch (double pole), and from there to the cooker outlet plate.

Thanks to all by the way, appreciate you taking the time to reply to me. I am learning new stuff all the time!

every day's a schoolday.