installing new hob

[electrician4u]

I have a customer who wants me to put in a Seimens hob. The rating is 10.8kW. he currently has a 32A supply installed from an old Wylex box-the type that takes fuses and Mcb's.this box is fed from a Bill distribution board on a 40A mcb.Can anyone suggest a make to replace the Bill MCB rated 63A?I've worked out the full load current to be 47A. According to the regs, I gather I only have to assume 10A+30% which means 21A. What if it's on full load, though? I don't want to connect to the existing 32A breaker if it's going to be tripping.Any advice please?

 

[ezzzekiel]

Don't matter

 

[telectrix]

what size cable is feeding it?

 

[Marvo]

Your options are more limited by the cable sizes rather than the MCB size.

Edit; Tel beat me to it

 

[electrician4u]

What kind of advice is "don't matter". If that's all you've got to offer, "don't bother".
Did I ask anyone about cable size? forget about that. It's big enough. Can anyone else answer the question I asked?

 

[telectrix]

what's big enough? if it's 6mm clipped direct, then you can up the MCB to 40A. that should solve the issue.

 

[Marvo]

'Don't matter' was because he changed his mind about the post he first made.

Where in the regs did you get '10A+30% which means 21A' and also how did you calculate that 10A plus 30% comes to 21? The cable sizes are very relevant.

Bill MCB's look like they're standard DIN rail fitting so there should be compatable MCB's available locally. Otherwise contact Eaton who have a website.

 

[electrician4u]

my main question was whether there was a 63A MCB that will fit in a Bill distribution box and also to get clarification on the diversity rule in relation to a hob which is rated at 10.8kW cos it seems to me if it's on full and connected to a 32A breaker that's not good practice

 

[telectrix]

the cooker diversity formula has been in use for over 50 years with no problems. i get 22.3A, not 21A. even so, a 32A MCB is fine. the cable size is more important. needs to be 6mm. not sure on a replacement for the bill 63A MCB, though. if it's a standard din rail fit, then most makes will replace it.

 

[electrician4u]

i may have misread the diversity rule. i thought you deducted the 10A from the total then added 30% but even 30% of 47+10 is still only 24A-not a big difference, but still nobody's answered my question about what happens if the hob is on full power?
also, the mcb, although they fit on a DIN rail, are not standard cos they've no cover over the bottom terminal like most modern ones do. i've looked at the Eaton site already. it seems these are obsolete and i'm not paying £20 quid on e-bay for some 2nd hand ****.

 

[Richard Burns]

All cookers rated up to 15Kw can go on a 32A MCB without problem. Because the elements switch on and off as the reach temperature you will not get a point where the MCB will trip. All MCBs must take 150% current for, I think, 1 hour (may be 1.5 hours) before they trip so stick with the 32A MCB. This is in the regs or OSG can't remember which at the moment.
Not sure about the 63A MCB.

 

[electrician4u]

how did you get 22.3A? i've re-calculated and now get 24.1A
The cable installed is 6mm T & E so i already knew it was big enough.

 

[telectrix]

the hob will only be on full power for a few minutes as the thermostats will kick in as the elements heat up. best way is to connect using the 32 MCB, switch on and clamp meter the cable, see what happens. as i said earlier, you can up the MCB to 40A as long as the cable is 6mm min.

 

[Richard Burns]

OSG 8.4 for most domestic cookers up to 15KW.

 

[electrician4u]

Thank you Mr Burns. Sense at last! Hadn't occurred to me that they're actually not on full power at the same time