Domestic Cooker and Hob install - need advice please

[freedomrun]

Domestic Oven and Hob is connected to an existing 45 AMP isolator (including socket outlet) with 6mm T&E back to the CU (about 8 m away) with 30mA RCD & 45A MCB (all existing) new oven rated at 2100W and Hob at 7000W. The 6mm from the isolator goes to a JB on the wall behind the cooker where a 2.5mm T&E supplies the Cooker and a 4mm T&E supplies the HOB. Customer has asked me to check what the Kitchen fitting firm has done, the instructions with the Cooker say that it should be connected to a DP isolator of minimum 20A and a cct protective device of 13A minimum and cable of 1.5mm Minimum. The Hob has no information regarding cable or ratings. If i had installed then i would have put the oven on it's own isolator - but can i tell the customer that the oven is well protected with both the oven and hob connected to the same MCB? I hope this makes sense. Cheers.

 

[Theorysparky]

It is acceptable to have the hob and oven on the same isolator.......

try doing the diversity and the maths for the total cct,,,,,,,,that will tell you if its ok

how much current is the oven likely to pull......do you really need the info for the hob ?????

could search online for it if you need it....

 

[Revved Up Sparky]

With the information given I would explore the idea of: i) derating the MCB to 32A and ii) For the oven consider running a minimum 4mm T&E from the JB to a 13A unswitched FCU from which a 1.5mm HR flex would connect to it.

 

[Doc Hudson]

Domestic Oven and Hob is connected to an existing 45 AMP isolator (including socket outlet) with 6mm T&E back to the CU (about 8 m away) with 30mA RCD & 45A MCB (all existing) new oven rated at 2100W and Hob at 7000W. The 6mm from the isolator goes to a JB on the wall behind the cooker where a 2.5mm T&E supplies the Cooker and a 4mm T&E supplies the HOB. Customer has asked me to check what the Kitchen fitting firm has done, the instructions with the Cooker say that it should be connected to a DP isolator of minimum 20A and a cct protective device of 13A minimum and cable of 1.5mm Minimum. The Hob has no information regarding cable or ratings. If i had installed then i would have put the oven on it's own isolator - but can i tell the customer that the oven is well protected with both the oven and hob connected to the same MCB? I hope this makes sense. Cheers.

What certificates have the kitchen fitting firm left? has the work been notified? is there a compliance certificate issued? Surely if there are any areas of doubt this would first be taken up with the original installer, free of charge. If not resolved it should then be through the complaints procedure of the installers contractor body for self certification. What calculations do you come to following the guidance of BS7671 and the on site guide. Are you been paid for this time and investigations? Aren't these sort of simple diversity cable calculation scenarios covered in the city and guilds courses anymore?

Doc H.

 

[freedomrun]

The Customer is a friend of family - so not charging for my time there. The Kitchen firm informed the customer that as they were swapping old cooker and hob freestanding unit for new (but seperate oven & Hob) and not altering the wiring of the kitchen from the JB to the Isolator, then no need to notify under Part P. They have, however, put the 2.5mm on the Oven and 4mm on the Hob (i'm thinking that the 6mm that was to the JB previously and for the former freestanding cooker/hob unit, would not fit the terminals of the Hob and they required another cable to run the new seperate Oven from the JB. I calculate the total draw of both units with diversity to be 23.7 A (isolator has a socket outlet), the Oven itself drawing 9.13A before diversity taken into account. If i leave the 2.5mm to the oven and 4mm to the Hob, then i derate the 45A mcb to a 30A mcb. The Oven itself will be better protected that way and it has to be on minimum 20A isolator anyway, as the manufacturers instructions take presidence - or have i missed something? Cheers.

 

[Theorysparky]

nope that will be fine....

revved up sparky did suggest an fcu for the cooker which i would do for a new install

but on this occasion it could be said that the oven has a max rating which would never exceed the 2.5 t+e so i would leave it

also on your original post the oven could have been wired in 1.5mm

you cannot fix everything all of the time.....just need to make an informed decision

 

[wozz]

I would suspect the Hob instructions would have required HO5 or HO7 or similar all the ones Ive fitted have asked for it.

 

[freedomrun]

Looks like the Hob instructions have been found by the customer now - seems they state a minimum 20A isolator DP type and cable to consist of 3 lengths of 2.5mm T&E, seems a bit strange - made in Turkey of all places. Just been thinking about the JB situated behind the cooker, does anyone know of a minimum 45A JB with maintenance free terminals to comply with regs. Also, what about PART P notification in a case such as this where Oven and or Hobs are replaced - is this a maintenance issue and no need for a MW Cert.

 

[tom1]

if you want rid of the joint box then click do a decent dule outlet plate. not maintenance free but it does not need to be