Isolation switch vs RCBO

tvrulesme · Feb 27, 2022

Planning a kitchen design with a 7.2KW induction hob. The hob will be on its own separate circuit protected by an RCBO.

Best practice seems to be to have an isolation switch for the hob but the ideal switch position would be directly underneath the consumer unit. Given that I would be able to easily isolate the circuit using the RCBO is there any requirement which would still call for a DP isolator for the induction hob?

Distance from the hob to the consumer unit is ~2.1m but I understand that BS 7671 no longer states a maximum distance of 2m so hoping this would be ok? Planning on putting a 10mm2 cable to feed this (slight overkill) so the fewer little terminals to terminate this in the better IMHO.

This will of course be carried out by a qualified electrician. I'm just planning and researching at this stage.

[ElectriciansForums.net] Isolation switch vs RCBO

littlespark · Feb 27, 2022

The idea of a local isolator is that if you’re cooking, and it goes on fire, you can quickly isolate the power to then tackle it safely.

If you get an electrician in, they will probably want to put in an isolator close to the hob, as it’s good practice.

brianmoooore · Feb 27, 2022

As above. The middle of developing fire is not the time to start working out which breaker on the fusebox controls the hob.
Isolator should be adjacent to hob, and its purpose obvious.

tvrulesme · Feb 27, 2022

littlespark said:
The idea of a local isolator is that if you’re cooking, and it goes on fire, you can quickly isolate the power to then tackle it safely.

If you get an electrician in, they will probably want to put in an isolator close to the hob, as it’s good practice.

Thanks for the quick response. So reading this, aside from best practice there are no regs that this would contravene? I'll almost certainly go for your suggestion but just wondering if the regs actually enforce it or not?

Dartlec · Feb 27, 2022

While you're right that BS7671 no longer states a distance, I'd still say that good practise would mean it is easily accessible and identifiable, which IMO wouldn't be covered by an RCBO amongst a bunch of others with small writing - especially for visitors or someone not familiar with the setup.

Table 537.4 in BS7671 does suggest that RCBOs can be used for isolation/emergency switching/functional switching - though not all RCBOs are Double Pole.

If the consumer unit is in the same room as the hob and not in a cupboard or likely to blocked with stuff, then a standard DP switch below it might well be a reasonable option, if it's not possible to have one more adjacent to the hob.

It is something that you will need to discuss with the electrician doing it though, as they may have their own idea of what's good practise or not and they need to be comfortable with what they install, regs or not.

littlespark · Feb 27, 2022

There may be council building control rules that override the regs and demand there be a local isolator.

You have to read bs7671 alongside other documents

Avo Mk8 · Feb 27, 2022

David Savery article on this a while ago (he has updated it to current regs). It's worth a read:

David Savery Electrical Services Ltd. - Does a cooker need an isolator switch...

Does a cooker need a cooker switch?

www.dses.co.uk

tvrulesme · Feb 27, 2022

Avo Mk8 said:
David Savery article on this a while ago (he has updated it to current regs). It's worth a read:

David Savery Electrical Services Ltd. - Does a cooker need an isolator switch...

Does a cooker need a cooker switch?

www.dses.co.uk

Very interesting read and agree with his take. Mine would fall under:

"If you’re remodelling an existing kitchen that lacks one, fit one where practical if possible, ideally within two metres of the appliance and not closer than 300mm."

Decision made, I'll allow for this when I fit the back boxes.