3600 watt oven & 1250 watt microwave - which cabling?

[NHW]

I'm 99% sure that I will need to upgrade the cabling in my kitchen for the new appliances that we have.

The new built-in oven is 3600w max and the microwave is 1250w max, which is 4850w combined. I'm not sure if the cable required is just the maximum required for 1 appliance which would be the 3600w and hence 15amps required. Or would it be both which would be 20 amp cabling?

The sparky that I had to come over and quote literally just said he could run it off a normal 13amp plug which is what I originally thought would be easiest but then I made a post beforehand and was advised that clearly was not the way to go.

I just want the knowledge now so that when I get another sparky over and if he says 15amp would do I would probably have to raise the question why not 20amp (if that is what is required)

Thanks

 

[pete01]

The microwave can be plugged in anywhere, does it not have a plug fitted?

The oven can connect to your cooker circuit if you have one.

If not a 16 or 20 amp circuit would do it, but you could future proof it with a 32 amp 4mm/6mm.cooker circuit

 

[NHW]

Yeah the previous cooker that was there was a gas cooker not electic so I'm not sure if they would've had the adequate cabling required, but I believe that a gas cooker would've used 15amp minimum anyways so that'd be hopeful.

but the kitchen was pretty much the original build which was in the 1970s so I'm guessing itd have been whatever standard it was back then, so to be on the safe side I don't know if I'd just feel better putting in it's own 32amp cooker circuit like you mentioned. I'm just assuming that would require going through floor boards and chasing walls etc

 

[JohnW2]

The microwave can be plugged in anywhere, does it not have a plug fitted? The oven can connect to your cooker circuit if you have one. If not a 16 or 20 amp circuit would do it, but you could future proof it with a 32 amp 4mm/6mm.cooker circuit

His "3600 W" oven will represent well under 13A 'after diversity', so could theoretically also be plugged into 13A socket ,and would not need a 16A or 20A circuit.

Kind Regards, John

 

[NHW]

Oh, what does 'after diversity' mean if you don't mind me asking. Thank you

 

[FrodoOne]

If by :"cooker: you mean a device with an oven and a cook-top, "diversity": means that you are unlikely to have the oven and all hot-plates in operation at the same time.
However. in the future you.may consider the use of an "induction" cook-top, to get back to the benefit of quick heating and control that you had with gas but are now giving up - with "normal' electrical hot-plates.
Hence, it.may be a good idea to provide at least a 4 mm² "feed* to the "cooker", in an attempt to future-proof the installation.
(On average, a standard induction cooktop may use up to 15-20 amps. However, some large high-powered cooktops can use up to 30 amps or more.)

Apart from the "cooker", kitchens need to have the. electrical "capacity" to run microwaves, kettles, toasters etc., all at the same time.
You appear to be using "radial" circuits so you should have multiple socket-outlets - supplied by different "radials:" - in the kitchen, even if one or both "radials" also operate socket- outlets in other rooms.
(Again, diversity !)

 

[JohnW2]

Oh, what does 'after diversity' mean if you don't mind me asking. Thank you

It's a concept that takes into account the fact that with things like cooking appliances, not all of the heating elements (all of which are thermostatically controlled, hence cycling on/off all the time) will be on simultaneously and, even if there is only one element, it will only be on for a fairly small proportion of the time (because of the thermostat) - so the average power/current drawn over a reasonable period of time will virtually always be a lot less that the total of adding up all the heating elements.

The generally-accepted rule for domestic cooking appliances is that one calculates the 'after diversity' (aka 'average') current as 'the first 10A' PLUS 30% of 'the rest' (of the theoretical maximum current, if every element was 'on' simultaneously).

Hence, for example, if the 'maximum' current were, say, 25A (5,750W at 230V), then the after-diversity current would be calculated 10A PLUS 30% of the other 15A, hence 10+4.5 = 14.5A.

Kind Regards, John

 

[pete01]

His "3600 W" oven will represent well under 13A 'after diversity', so could theoretically also be plugged into 13A socket ,and would not need a 16A or 20A circuit.

Kind Regards, John

I understand diversity, but I would never plug in a 3600w item, not in your nelly.

But that's just me.

 

[JohnW2]

I understand diversity, but I would never plug in a 3600w item, not in your nelly. But that's just me.

Fair enough. Some people are more nervous than others about diversity, at least in some contexts.

Like you, I would not 'plug in' a "3,600W item" IF I believed it was likely to draw 3,600W anything like continuously. Indeed, even that is fairly marginal, particularly if (as is usually the case) the "3,600W" quoted relates to 240V, in which case it would only draw about 14.4A at 230V - my only concerns would relate to the plug/socket, not the circuit (even if it were a hypothetical "13A circuit" {maybe via an FCU?}).

However, I wonder how far your nervousness goes - are you concerned about invoking diversity in relation to circuits/cables, as well as plugs/sockets? In other words, are you unhappy with running, say, a "15,000W cooker" (about 60A theoretical 'maximum current') off a 32A 'cooker circuit' wired in 4mm² or 6mm²) cable, even though the 'after diversity' current is only about 25A ?

Some people seem to worry because of 'instantaneous currents' (rather than 'averages over time'). In relation to that it's worth remembering that, with 50Hz AC, on a much smaller time scale, a resistive load of, say, 3,000W at 230V (about 13A) will briefly draw about 18.4A 100 times every second.

Kind Regards, John

 

[pete01]

Fair enough. Some people are more nervous than others about diversity, at least in some contexts.

Like you, I would not 'plug in' a "3,600W item" IF I believed it was likely to draw 3,600W anything like continuously. Indeed, even that is fairly marginal, particularly if (as is usually the case) the "3,600W" quoted relates to 240V, in which case it would only draw about 14.4A at 230V - my only concerns would relate to the plug/socket, not the circuit (even if it were a hypothetical "13A circuit" {maybe via an FCU?}).

However, I wonder how far your nervousness goes - are you concerned about invoking diversity in relation to circuits/cables, as well as plugs/sockets? In other words, are you unhappy with running, say, a "15,000W cooker" (about 60A theoretical 'maximum current') off a 32A 'cooker circuit' wired in 4mm² or 6mm²) cable, even though the 'after diversity' current is only about 25A ?

Some people seem to worry because of 'instantaneous currents' (rather than 'averages over time'). In relation to that it's worth remembering that, with 50Hz AC, on a much smaller time scale, a resistive load of, say, 3,000W at 230V (about 13A) will briefly draw about 18.4A 100 times every second.

Kind Regards, John

I've put 7.5kw hobs and 3.6kw ovens on a 6mm 32 amp mcb many times, obviously no problem.

Theres just something about ovens over 3kw being plugged in, I know it will be fine I just cant do it, I'm a worrier.

 

[EFLImpudence]

To be fair; it depends on the plug - and fuse holder.

Some are fine; some are not.

Can we tell which is which when fitting?

 

[JohnW2]

I've put 7.5kw hobs and 3.6kw ovens on a 6mm 32 amp mcb many times, obviously no problem.

That's only just about a potential issue in anyone's mind, since 7,500W is only fractionally over 32A (and certainly well within the capabilities of 6mm² cable). However, what about a 12kW or 15kW cooker on such a circuit - would that worry you (it's fine 'with diversity)?

Theres just something about ovens over 3kw being plugged in, I know it will be fine I just cant do it, I'm a worrier.

As I said, the potential problem is really with the plugs and sockets (not the MCB or cable), and those problems could (and sometimes do) show their faces with loads appreciably less than 3kW.

Kind Regards, John

 

[JohnW2]

To be fair; it depends on the plug - and fuse holder. Some are fine; some are not.

Quite so

Can we tell which is which when fitting?

Seemingly not. One might hope that things 'rated' at 13A could carry that current (and probably a bit more) continuously for indefinite periods of time without coming to any harm - but, unfortunately, it seems that that is not necessarily the case!

Kind Regards, John

 

[pete01]

However, what about a 12kW or 15kW cooker on such a circuit - would that worry you (it's fine 'with diversity)?

Nope that wouldn't bother me.

It's the oven over 3kw on a plug top that I wouldnt do.

 

[pete01]

One might hope that things 'rated' at 13A could carry that current

Thats never really been the case, 13 amp plug tops are no good for 13 amps for long periods.