Oven Circuit Question?

[rolyberkin]

So luckily I am now onto the design module and by chance a friend asks if it is possible to change her LPG gas hob for an electric one, existing oven circuit is fed by 32amp MCB, 6mm T&E normally clipped with no insulation, 15m run.

Existing double oven is 5.5kw full load and the proposed hob is 7kw full load, my rough and ready calculation is that this is not possible as the current (for both) taking into account diversity is circa 36amp.

I have looked at 'low absorption' 13amp plugged induction hobs which still state they pull 7kw at full load, which to my calculation means 19.12amps considering diversity, what does low absorption actually mean and why do these not blow the fuse at full load, they are clearly designed to be plugged into a ring main? Can someone explain?

 

[Darkwood]

This is an age old topic on here regarding diversity, your diversity is for calculating the avaerage demand on your front end supply, when you come to designing final circuits you need to be careful how you apply said diversity as you are now designing the circuit itself and not averaging the total demand on the property.

Regarding the plugged units - any fixed equipment with a 2kw load or higher should have its own independent circuit, so they may well be designed to plug into a socket but this doesn't mean you can just stick it on the ring final circuit, you still need to wire its own radial.

I'd be interested to know what your tutor says about applying diversity using the guidelines when designing final circuits? I often wonder what advice they are giving out nowadays.

 

[telectrix]

diversity is your key here. your calculation of 36A is way out.

12.5kW = 52A. applying diversity, 10A + ( 30% of 42A ) = 10 + 12.6 = 22.6A. ( using 240V as supply voltage, not the mythical 230 ).

 

[rolyberkin]

diversity is your key here. your calculation of 36A is way out.

12.5kW = 52A. applying diversity, 10A + ( 30% of 42A ) = 10 + 12.6 = 22.6A. ( using 240V as supply voltage, not the mythical 230 ).

Doh, RTFQ, had read it as 30% of maximum load not the remainder after the 10amps, the C&G book uses 230v, so I take it I can use 240v, back to the calculator me thinks!

 

[rolyberkin]

This is an age old topic on here regarding diversity, your diversity is for calculating the avaerage demand on your front end supply, when you come to designing final circuits you need to be careful how you apply said diversity as you are now designing the circuit itself and not averaging the total demand on the property.

Regarding the plugged units - any fixed equipment with a 2kw load or higher should have its own independent circuit, so they may well be designed to plug into a socket but this doesn't mean you can just stick it on the ring final circuit, you still need to wire its own radial.

I'd be interested to know what your tutor says about applying diversity using the guidelines when designing final circuits? I often wonder what advice they are giving out nowadays.

I have a study day next week so will get the definitive and report back, the onsite guide states that a household cooking appliance is the first 10 A of the rated current plus 30% of remainder but the manufacturers state that the low absorption hobs are giving out 7kw of power and yet are fitted with a 13amp plug?

 

[telectrix]

we all make mistakes, as the hedgehog said, climbing off the lavatory brush.

 

[telectrix]

I have a study day next week so will get the definitive and report back, the onsite guide states that a household cooking appliance is the first 10 A of the rated current plus 30% of remainder but the manufacturers state that the low absorption hobs are giving out 7kw of power and yet are fitted with a 13amp plug?

the 7kW is not a true value as rings will be switching in and out through their thermostats.not all will be drawing current simultaneously.if i speltthat rightit means it's time for more beer.

 

[rolyberkin]

the 7kW is not a true value as rings will be switching in and out through their thermostats.not all will be drawing current simultaneously.if i speltthat rightit means it's time for more beer.

Personally if it was my wife I would tell her there was jack all wrong with the hob she had been given and that a bad work(wo)man always blames her tools!