Oven and hob on same MCB and diversity.

[HappyHippyDad]

I've just spent an hour getting bogged down with the maths trying to work out diversity for 2 cooking appliances on the same circuit (32A MCB) and same isolation switch,

I thought I would give my workings so others can use it as I wonder if some just assume you can still use the 15kW maximum, which you can't.

In fact the the maximum for 1 cooking appliance seems to be 19.3kW (as long as the switch doesn't incorporate a socket), however, on with 2 appliances....

Diversity is 10A plus 30% of the remaining amps (plus 5A if a socket) but this is for each appliance even if on the same circuit.

Therefore for an oven and electric hob the maximum current we have is:

[10A + ( 0.3 x Q) ] + [10A + (0.3 x Q) ] = 32A

we don't know the maximum size of the cooker and hob (that's what we're trying to find out), so I have just used the letter Q (Q is the current of either the hob or cooker minus the 10A)

Therefore

The above equation is the same as

2 x (10A + 0.3Q) = 32A

20A + 0.6Q = 32A

0.6Q = 12A

Q = 20A

We know that each appliance is allowed to draw a max current of Q +10A, which is 30A. There are 2 of them so 60A.

60A x 230w = 13.8kW (approx)

Therefore maximum combined power for 2 appliances on same circuit with same switch (without a single socket) is 13.8kW.

I think you'll all have had enough now, but the maths works out as a maximum combined power of 10.4kW allowed if the cooker switch incorporates a single socket. (Equation is 25A + 0.6Q = 32A)

If you haven't guessed. I have the day off work! ?

ps.. would you check the maths please @happysteve

 

[stevethesparks]

Generally I would use two circuits. However, as they have two ovens, it may suggest they do a lot of cooking/baking, so if not too far a run I might also consider 3 circuits.

 

[Mike Johnson]

The burners are gas, yes, but for some reason the clock, lights and rotisserie are electric.

I bow to your superior knowledge on all of these things, but can you get gas clocks, light and rotisserie these days, I know about gas lights, but? ?

 

[Midwest]

I realise we have come to the end if this thread, however.... as coincidence happens a slightly different yet similar scenario has arisen.

The customer wants 2 x separate single ovens next to each other with an induction hob above.

The previous answers in this thread suggest treating a separate hob and oven as a single appliance with regards diversity, and I can see that makes sense. We can't just keep adding an appliance on and classing it as one unit though, as single units have thermostatic controls. How would you apply diversity in this case? I'm inclined to use my initial maths here and class it as 2 appliances.

I didn’t agree with that concept myself; I treated individual appliances separately when apply diversity, for the reasons you’ve now been presented with.

 

[Paul508]

This Math looks wrong to me, forgetting the incorrect use of Q,

Incorrect
2 x (10A + 0.3Q) = 32A

20A + 0.6Q = 32A

0.6Q = 12A

Q = 20A

Correct

2 x (10A + 0.3Q) = 32A

20A + 0.6Q = 32A

32A - 20A = 12A

100% of the remaining = 12A

Therefore 60% of the remaining = 7.2A

Value of Q = 7.2A

Circuit then has a 4.8A buffer

Then if you actually take into account load 32A is more than sufficient

 

[123]

This Math looks wrong to me, forgetting the incorrect use of Q,

Incorrect
2 x (10A + 0.3Q) = 32A

20A + 0.6Q = 32A

0.6Q = 12A

Q = 20A

Correct

2 x (10A + 0.3Q) = 32A

20A + 0.6Q = 32A

32A - 20A = 12A

100% of the remaining = 12A

Therefore 60% of the remaining = 7.2A

Value of Q = 7.2A

Circuit then has a 4.8A buffer

Then if you actually take into account load 32A is more than sufficient

This is wrong also though. Q is actually a known value determined by the appliance(s), the 32A is the unknown value which needs to be worked out via calculation.

 

[HappyHippyDad]

Oh dear.

Now Lucien will see it (the ill placed and brazen )

again and get cross with me... again

 

[pirate]

The use of a comma as a separator is not unusual, and as one doesn't usually work in a bilingual situation, it seldom causes confusion. What does confuse me quite often is that the arroba key (@) is in different positions on the keyboard depending on the country you are in at the time, assuming one is using a "local" keyboard of a physical nature...but then, I am easily confused!