overloading the board?

[JoeDonnelly1]

I am supplying 2 new circuits off a 64A DB these will be a 32A oven circuit and a 40A hob/stove circuit. The board already has 2 ring mains off it as well as 2 lighting circuits would adding these in overload the board?

 

[Marvo]

Did you make a diversity calculation?

 

[JoeDonnelly1]

Was really stupid of me to completely overlook this.. ) small question when working out the maximum demand/diversity for an electric hob is it the same as a cooker? E.g first 10A +30% of the remainder?

And also with downlights do we still assume every downlighter is 100W :s or do we work it out say if there are 10 X 30W downlights =300W and would you then apply 66% diversity or just assume it as 300?

 

[telectrix]

hob diversity applies same as cooker, elements are thermostatically controlled, and yes, you allow diversity for lights as well. 66% of full load.

 

[JoeDonnelly1]

Well seems im pretty ****ed already!

The 64A board is a sub mains board if that makes any difference what so ever!

There are 2 ovens which would be 18.64A MD + diversity applied

Kitchen ring 32A no diversity applied

Second ring main 40% of 32= 12.8A

Im already at 63.44A without adding lighting and the hob!


Dohhh

 

[Marvo]

Is this a commercial premises or a domestic one? What's the chance they're going to use 2 ovens plus a hob simultaneously? Sometimes a thick coat of common sense can be as good if not better than a diversity calculation.

 

[JoeDonnelly1]

Its domestic, the submains is feeding an extension though so diversity to the lighting shouldnt be applied surely (considering there is only 3 lampholders in seperate rooms and 10x30W fittings in the kitchen!

Pretty valid point but you could argue that at least 1 oven and possibly the hob could be on when preparing dinner haha

 

[johnboy6083]

I personally only rate the cooker calc. All other circuits, use your experience and knowledge.

 

[Marvo]

Is the extension a separate dwelling or is it just one family living in the whole place?

Why is there a sub DB rather than it all being supplied from the main CU?

Did you just install this subDB or was it existing prior to your arrival? What was your scope of works at this premises?

If the total possible lighting load is <500W then that's only 2A load.

 

[JoeDonnelly1]

The extension will be a living place its mainly a kitchen and a utility room!

Not enough spare ways on the mainCU

Someone else installed the subDB prior to me being asked to carry out works, all rings and lighting circuits were in before I came and from what I understand the projects been on hold for a while and now due to money issues and now that the client has cash again I've been asked to put in a supply for 2 ovens and a seperate induction hob!

 

[Marvo]

I'm not sure about the UK regs as such but if you were just requested to install the supply for the ovens and hob then I would just warn the customer in writing that even with the recommended diversity applied there could be an overload issue that might result in an intermittent tripping of the subDB. If they accept the risks of the annoyance then I don't see any safety reasons why the circuits couldn't be installed as long as the MCB's are correctly rated and RCD's are installed as and where required.

 

[JoeDonnelly1]

No RCD installed!

 

[Marvo]

Like I said, I'm not up on the UK regs....is an RCD required? I thought new circuits might require one but it wouldn't have any relevance to the overloading issue.

Are you qualified and competent to be carrying out this kind of work?

 

[JoeDonnelly1]

Ye an RCD is required for sockets used for general purposes, locations containing a bath/shower, cables buried in walls less that 50mm deep etc, don't know who done this job but I hate them

 

[Guest55]

The extension will be a living place its mainly a kitchen and a utility room!

Not enough spare ways on the mainCU

Someone else installed the subDB prior to me being asked to carry out works, all rings and lighting circuits were in before I came and from what I understand the projects been on hold for a while and now due to money issues and now that the client has cash again I've been asked to put in a supply for 2 ovens and a seperate induction hob!

I'd be telling your customer that their extension C.U. is too small for the extra cooking appliances.
What size / type of cable is it ? Can you go to 80amp without changing the cable ?
With regards to diversity you may get away with it ...but its your signature on the cert if theres problems later on so i wouldnt risk it.
They'll have to pay for an upgrade if they want the cookers.