220v. 230v, 240v, 250v?

John-SJW · Jun 6, 2021

I saw an oven that was rated at 3,100 watts. Now most would say that cannot be fitted on final ring circuit as rule of thumb. But:
3,100 watts draws amps of:
14.09 amps @ 220v
13.47 amps @ 230v
12.91 amps @ 240v
12.4 amps @ 250v

If the installation is 240v or 250v then it safely inside the 13 amp of a final ring circuit.

The question is, and the regs aficionados can help here, what is the voltage that should be used to assess, as maybe the voltage will vary in an installation over the years.

DPG · Jun 7, 2021

John-SJW said:
That seems very light. Mine is 7,200 watts.

I think that's more of a 'normal' figure, but they do lower power induction hobs that will run from a 13A plug.

John-SJW · Jun 7, 2021

Sparky Pat said:
Had a lady two weeks ago with gas hob and electric oven all controlled with normal cooker point, she wanted to change the hob to electric, no problem, she buys new Bosch induction hob, and I go there with a click dual outlet cooker outlet and some 4.0mm flex to connect it all up.
When we take it out of the box it is rated at 3700 watts and is factory fitted with a lead and 13 amp plug so as we are told to follow manufacturers instructions I then duly fitted a single socket to the cooker outlet circuit and plugged the Hob in.
Did not seem the right thing to do but to date have had no call backs, I do have to go there to do some other work shortly and will check it out and see how it is performing.

Many instruction have a get out clause (for them) of see a competent electrician. In short, he does what he thinks is fit. I would never have connected a hob to 13A plug, irrespective of what the manufacturer sent it with. It is a matter of doing it safely, not covering your rear end - or believing them (some dodgy, and vague, instructions out there from many makers).

nicebutdim · Jun 7, 2021

LastManOnline said:
My "Morphy Richards" kettle is 3kw.It has a lead that is max 3x1.5mm (but probably 1mm. Moulded plugtop so can't check) .Before energy saving appliances came on the scene it was normal to have washing machines, driers etc up to 3.5 kw, all connected with 13amp plugs and usually 1.5 flex. A 1.5mm flex can comfortably handle a continuous current of 13 amp (and above). The key difference between appliances of the same wattage is whether they are designed to be used intermittently (kettle) or in a more sustained way (space heater). A sustained load should really have its own circuit.

Some interesting examples following this post.

My parent's utility room used to be served by a single spur (rubber cable roughly equivalent to 2.5, on 30A circuit), to which someone had fitted a 4 gang unswitched socket that had been lopped off an extension lead. Oddly enough this never caused any issues, although that was likely due to my mother having the good sense to only use one appliance at a time, alongside the freezer.

I still break out in a cold sweat when I think of what passed for wiring in that house.

telectrix · Jun 7, 2021

nicebutdim said:
Some interesting examples following this post.

My parent's utility room used to be served by a single spur (rubber cable roughly equivalent to 2.5, on 30A circuit), to which someone had fitted a 4 gang unswitched socket that had been lopped off an extension lead. Oddly enough this never caused any issues, although that was likely due to my mother having the good sense to only use one appliance at a time, alongside the freezer.

I still break out in a cold sweat when I think of what passed for wiring in that house.

that's nothing.my mam used to have an iron that plugged into the kitchen light via an adapter. that's once she'd learnt not to stand it on the fire iron.

littlespark · Jun 7, 2021

This is starting to sound like a Python sketch again......

telectrix · Jun 7, 2021

littlespark said:
This is starting to sound like a Python sketch again......

it's only a flesh wound.

ipf · Jun 7, 2021

DPG said:
Thanks for correcting my post mods!

wondering what a knuckle screw was ?

ipf · Jun 7, 2021

littlespark said:
This is starting to sound like a Python sketch again......

Flowery Tw*ts in 10 mins on BBC1.
Manuel with his pet 'hamster'.

Julie. · Jun 7, 2021

littlespark said:
This is starting to sound like a Python sketch again......

Oh no it isn't.

Dave OCD · Jun 7, 2021

DPG said:
I think a lot of the problem is some of the cheap plugs that are around these days. Bring back the old MK ones with proper knurled terminal screws with built in washers. Lovely!

As a young apprentice with the local Health Authority I fitted dozens of these, lovely plugs and it brings back memories. Nobody ever questioned why my gran's twin tub had 'Hospital Property' embossed on the lid of the plug,or should that be plug top. ?

westward10 · Jun 7, 2021

MK would brand plugs for people on a raised circular part on the cover I had loads with BBC on them.

John-SJW · Jun 8, 2021

Sparky Pat said:
Had a lady two weeks ago with gas hob and electric oven all controlled with normal cooker point, she wanted to change the hob to electric, no problem, she buys new Bosch induction hob, and I go there with a click dual outlet cooker outlet and some 4.0mm flex to connect it all up.
When we take it out of the box it is rated at 3700 watts and is factory fitted with a lead and 13 amp plug so as we are told to follow manufacturers instructions I then duly fitted a single socket to the cooker outlet circuit and plugged the Hob in.
Did not seem the right thing to do but to date have had no call backs, I do have to go there to do some other work shortly and will check it out and see how it is performing.

This is playing on my mind as the appliance is capable of drawing over 13 amps. If the appliance came with no 13A plug, an electrician would not fit one on this appliance, as it is capable of drawing over 13 amps. Or fit it on a final ring circuit. It is obvious the makers have taken diversity into account, as the load is split between four current drawers, the rings, which will be cutting in and out via thermostats.

This makes me think that the combination oven (microwave and oven in one) example I mentioned at the beginning of this thread at 3,100 watts is suitable for 13A plug and final ring circuit. The instructions do not mention anything about amperage, I posted them, only that a DP isolator needs to be fitted. A 13A sockets have DP isolation. A spur off a ring with 20A DP isolator switch, or a 13A FCU, feeding a 13A socket behind the oven would conform to that.

Yes, I know it is best the oven has its own dedicated supply to be sure, that is not the point. Many would like to fit an oven like this, marginally over the 13 amp cut off point, as it would save ripping a finished kitchen to pieces.

LastManOnline · Jun 8, 2021

Sparky Pat said:
Had a lady two weeks ago with gas hob and electric oven all controlled with normal cooker point, she wanted to change the hob to electric, no problem, she buys new Bosch induction hob, and I go there with a click dual outlet cooker outlet and some 4.0mm flex to connect it all up.
When we take it out of the box it is rated at 3700 watts and is factory fitted with a lead and 13 amp plug so as we are told to follow manufacturers instructions I then duly fitted a single socket to the cooker outlet circuit and plugged the Hob in.
Did not seem the right thing to do but to date have had no call backs, I do have to go there to do some other work shortly and will check it out and see how it is performing.

How many rings did that hob have?

Lucien Nunes · Jun 8, 2021

When we take it out of the box it is rated at 3700 watts and is factory fitted with a lead and 13 amp plug so as we are told to follow manufacturers instructions I then duly fitted a single socket to the cooker outlet circuit and plugged the Hob in.

3700W requires a 16A supply. The hob probably has internal power management setttings to allow the total load to be limited to 16, 13 or 10A which should be set during commissioning. The rating given on the box is 3700W because that is what the hob is physically capable of delivering.

If you scroll down to the 'installation' tab on this link, Bosch have shown the 3700W limit as corresponding to the 13A plug version. I suspect that is a copy-and-paste mistake from the 16A Schuko-plug version and that they do not intend a 13A plug to supply 3700W.