Oven & hob supply

If the total wattage of the hob plus both ovens is under 15kW they can all run off of the existing supply, assuming that it's a 6.00mm cable. (or bigger)

 

11,300 watts divide by 230 volts = 49.13 amps.
Fit a 60 amp mcb. Or if there is no RCD on the system fit an RCBO which is an RCD and an mcb combined. A 50 amp maybe too borderline.
The 6mm cable can take 60 amps maximum.

 

Sadly no where near as simple as that. The OP has to allow for derating factors that may apply depending on how the cable is routed.

 

You are allowed a diversity factor. A simular situation came up a while back but I still think the best, and ONLY way is to run three separate feeds from the cu for each appliance. RCD protection will also be required I expect.

 

Sorry to disagree but when need more information before you can make a decision. What is the distance from fuse board to switch. And how does the cable run is it clipped direct In an insulated wall?? Current rating on 6mm twin and earth is around 45amps depending on how its fitted!!

 

If it were me, I would use the existing cable for the hob and run two separate cable for each over back to the CU using RCBOs on each. Divide and rule.

 

Would you get a qualified spark in to test and certify the work, certify yourself or just not bother and cross your fingers?

 

The regs say you need to. A commercial electrician who does not have Part P has to get one in for work in his own house. Silly of course.

 

I,m a commercial sparks with 2391 inspection and testing and did some work on my house that was covered by building control. The guy was more than happy to except my certificate and test results

 

The following are notifiable:

• Installing a new circuit
• Replacement of a consumer unit.

All other electrical installation tasks are not notifiable. Changing an accessory like a light fitting or switch does not count as an alteration. All other electrical installation is not notifiable. Some tasks that were included in the earlier versions of the Part P such as work in kitchens, and alterations to outdoor installations are not notifiable.

For work that is notifiable and certified:

1. It can be completed and certified by an electrician or registered "competent person" that is a member of a Part P self-certification scheme.
2. Work can be completed by anyone, under supervision of the the local BCO. The building control body issues a certificate.
3. Work can be completed by anyone, and certified by a registered third party electrician.

All domestic DIY electrical work is allowable even CU replacement. All DIY work should be completed to the Wiring Regs. A DIYer just gets a Part P electrician to certify.

He can put in two extra circuits and get a Part P man to certify. He can use the existing cable, if suitable, and not notify.

 

The BCO can certify. If he thinks the man on site is 'competent', he can just accept it. But you cannot self certify.

 

Not so Walter. It depends which part of the country you are in. Wales haven't changed the rules and the original Part P stands.

Kind regards

 

Diversity guidelines for cooker circuits: First 10A + 30% of remaining Amps (+5A if socket incorporated on switch plate).

So rating for circuit is 21.7A from your figures.

 

Sounds like the others haven't heard of diversity Stateit !

 

You are right the diversity factor guide gives 21.7A. As it is a guide I would not take any notice of it in this case. It is to assess the maximum demand for an installation or circuit. It allows all a system's circuits to draw more than say 60A when there is a 60A main fuse. It assumes that the probability of all circuits being fully loaded is near to zero. This applied to a ring circuit. A ring may have ten socket outlets and a 32A mcb. If you plug in ten 2.7kW kettles to each socket and then switch them all on, the mcb will trip as the probability of this event is near zero.

In this case, if the two ovens and all rings on the hob are on for quite a time cooking a big dinner, there will be problems if the diversity factor is applied to this circuit. The mcb is undersized. It will trip. The probability of all rings and two ovens being all on at the same time is high. The diversity factor is NOT applicable in the circuit for this case. It will come into being for the whole system.

So what I wrote stands.

The diverity factor in assessing the limit in a gas installation is to allow the appliances to draw more gas than what the limit of the meters is rated at - 6 cu metres/hr. The meter has a 100% overload, so the odd occurrence of running over 6 cu ft/hr will not harm the meter.

 

The figures Stateit quoted are for "domestic cooking equipment", as stated in BS7671, this is the reason they mention the 13 amp socket. (because cooker outlets often have a 13 amp socket incorporated) The diversity calculations for complete installations are a different matter.

 

Diversity is only applied when there is more than one circuit, the diversity is for the incoming power supply rather than the individual circuit.

The consumer unit will probably have a 100A incomer mains switch with 100A main fuse. But if you add up the individual mcb's you will notice that they will exceed the size of the 100A main incomer. The diversity factor will take it under the 100A as it assumes none of these circuit will be drawing maximum current at the same time. If they were drawing 95% of the mcb rating the main fuse would blow.