Another oven and induction hob question

[piquet]

Hi,

I have read the recent threads on oven and hob installation and I'd like to run this one by you....

I've ordered a Siemens pyrolitic single oven and induction hob rated as follows:

Hob: 6.8kW total connected load, 30amp maximum draw
Oven: 3.5kW total connected load, 16amp maximum draw

The cooker has its own circuit protected with a 45amp (I think, maybe 40amp - will check tonight!) fuse. It's an old style consumer unit so there are no mcb's, just pull out fuses.

When I removed the old De Dietrich single pyrolitic oven and regular ceramic hob I found that the 6mm cable went to the cooker switch, then there were two sets of 6mm cable coming from the switch - one to the oven and the other to the hob. It all worked perfectly well, the cooker switch controlling both the oven and the hob. In fact, the extractor ran off it as well!

I would like to run the new oven and hob from the same switch again really. I bought a new 45amp switch and a cooker connector unit for under the worktop. Will it be ok to wire from the switch to the cooker connector, then wire both the hob and the oven into this connector? I've no extractor to worry about.

My simple mind adds up the maximum current draw from the new cooker and hob and gets 46amps, which is one more than I think the fuse covers. So if I was running a pyrolitic oven cleaning cycle and boiling 4 pans on the hob I might have a problem...... is it as simple as that ?

I'd be grateful of your advice.

Cheers,

Phil

 

[spark]

Check your fuse size.

 

[piquet]

The fuse size I just checked and I'm afraid to say, it's only 30 amps Well, that's what is says on the front of the fuse, but I guess it could have been rewired with a higher rated fuse wire.

The cooker and hob I just removed were 3.24kW and 6kW respectively, so I make that 40 amps, and that's not accounting for the extractor which was also on the circuit. I never had a problem using the hob, oven and extractor at the same time.

Is it easy to tell what rating fuse wire is ?

Can I simply rewire that fuseway with 45 amp wire and relabel it to make it clear?

Cheers, Phil

 

[alexnic]

You won't get 40amp fuse wire ...30amp is the max, you can get 40amp cartridge fuses but you will need the holder for them. Your cooker + oven will not be drawing the full load you calculated as there will be a diversity factor ie. not all rings and oven likely to be on at once.

What you should do is connect your hob to the existing 30amp cooker circuit and use a 13Amp plugtop (MK type as they are higher rated than most of the other makes) for your oven. Best bet is to spur from the nearest 13amp socket to on behind the oven housing

 

[piquet]

Thanks Alexnic,

Could I get a cartridge fuseholder to fit in my old consumer unit then?

I found a bit in a book last night about the diversity factor which suggested you use 10amp + 30% of the remaining maximum draw as a guidline. If my max is 46amps, that makes it 10amps + 30% of 36amps (10.8amps) = 20.8amps .... which suggests 30amps might be enough as was proved in the past with my old oven, hob and extractor.

What worries me about connecting the 16amp max oven to a 13amp socket is the pyrolitic function, which surely must use close to the max draw. What do you think ?

If I could get a cartridge fuseholder to replace the rewirable 30amp fuse I reckon that would be plenty. Is this possible?

Thanks,

Phil

 

[il78]

Think alexnic maybe getting mixed up........

What you should do is connect your hob to the existing 30amp cooker circuit and use a 13Amp plugtop (MK type as they are higher rated than most of the other makes)

Connect your hob to to the cooker outlet that you said you where installing under the worktop (isolation above worktop) and leave the hob as it is (30Amp fuse)

6.8kW / 230V = 29.5Amps

 

[il78]

Sorry, Miles Away Just Read And Understood.......

alexnic my applogies

 

[alexnic]

No probs il78...had to read it twice myself when I seen your reply..

I have seen them for the WYLEX fuses and for the MEM but as they are all now obsolete, you might find it difficult to obtain one...

If you have the brown WYLEX fuses you can get a plug in MCB to replace the fuse

Wylex Plug-in MCB's
Rated 40 Amps


General Domestic Consumer Unit use

Wylex Plug-in MCB's detect overcurrents due to both overload and fault currents.
The MCB will operate and interrupt the supply to prevent damage to the installation.


Wylex Plug-in Domestic MCBs have a short circuit breaking capacity of 3000A (M3).
The current carrying capacity of the cable should always exceed the current rating of the MCB to prevent damage.
The operating dolly may be locked in either the ON or OFF position without affecting the ability of the trip mechanism to operate.
Direct replacent for Rewireable and HRC Fuse carriers in the Wylex Standard Range

 

[spark]

It's pretty borderline but 6mm T&E should take 47amps if it's installed as per a normal house (ie not in a thermally insulated wall etc) and just buried in the plaster. This current carrying capacity only applies if you don't use a rewirable fuse. You must fit an MCB (as in the picture above).

 

[piquet]

That sounds like a new consumer unit to me. I wasn't bargaining on the expense of that - what am I looking at, all installed? My consumer unit is an old Centaur one with rewirable fuses, 3 @ 30amp, 1 @ 15amp and 2 @ 5amps. I also have a separate box for the shower with a 45amp fuse in it and another modern one for my workshop down the garden with 40amp and 6 amp mcbs. I guess the whole lot could be replaced with a single new unit.

Phil

 

[spark]

A ball-park figure of £300 probably won't be far off. Just think yourself lucky it's not a job for a plumber, you'd be looking at £600 at least

 

[alexnic]

I am 95% sure that the old Centaur rewirable fuses are the same dimensions as the Wylex rewirable fuses and the holder itself is the same as the Wylex one. If the Centaur whole fuse wire cartridge for the 5amp is white (wylex has a white dot), 15amp is blue (wylex has a blue dot) and 30amp red then the plug in MCB above will fit the Centaur CU and at about £7 each, it will do the job .... certainly a cheaper option than your unexpected board change, although that's a job you should probably think about at some point.

 

[piquet]

Alexnic, thanks - that's right, the Centaur has red 30amp, blue 15 amp etc, so that's good news. I think I'll nip down the local electrical wholesalers and see if I can get a plug in MCB - great news !

Cheers,

Phil

 

[piquet]

I got a plug-in MCB just like in the picture you posted Alexnic, and it fits just great in place of the rewireable 30amp fuse, so I'm very happy!


Thanks very much indeed for the help,

Phil