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

[John-SJW]

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.

 

[Vortigern]

One thing occurs is that a 3+Kw oven will probably come with a 2.5mm² lead so that wont be going into a plug. My take is that Appendix 2 suggests 230v for calculation as the nominal voltage. I know of course that 240v + is the real voltage we are dealing with. Put the fact that 3+Kw on a spur very often leads to meltdown of the spur a double pole switch is better. Then you would have to have it on separate circuit. Which is after all (arguably) best practice. Then of course finally diversity would bring the oven load down to about 11.5 amps. So take your pick.

 

[MJPD29]

More like a 20 amp circuit to give some margin.

No, 16 is correct.

 

[John-SJW]

Then of course finally diversity would bring the oven load down to about 11.5 amps. So take your pick.

Good point.

 

[John-SJW]

One thing occurs is that a 3+Kw oven will probably come with a 2.5mm² lead so that wont be going into a plug. My take is that Appendix 2 suggests 230v for calculation as the nominal voltage. I know of course that 240v + is the real voltage we are dealing with. Put the fact that 3+Kw on a spur very often leads to meltdown of the spur a double pole switch is better. Then you would have to have it on separate circuit. Which is after all (arguably) best practice. Then of course finally diversity would bring the oven load down to about 11.5 amps. So take your pick.

I have seen ovens of 3-3.5kW and induction hobs above them, on the same 6mm cable, 40A circuit, treating the two as one large cooker. Diversity can come in, in that case.

Light on electrical connection. 1.5mm lead.

The oven I looked at was a Smeg combination oven of a built-in 1,000w microwave and oven. The microwave and oven can be on at the same time.

 

[LastManOnline]

One thing occurs is that a 3+Kw oven will probably come with a 2.5mm² lead so that wont be going into a plug.

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.

 

[Vortigern]

I take on board the above. I tend to take the belt and braces approach and ensure the installation of a circuit is over-specified. As a built in safety factor. The cost of going up to the next size cable is not usually that much for such an upgrade. Anecdotally, fitting a three phase oven, or kiln (for instance) I had worked out the size of cable and spoke with the manufacturers (who often offer an installation service) and in every case they also go up to the next size cable and recommend to me to do so.

 

[telectrix]

I take on board the above. I tend to take the belt and braces approach and ensure the installation of a circuit is over-specified. As a built in safety factor. The cost of going up to the next size cable is not usually that much for such an upgrade. Anecdotally, fitting a three phase oven, or kiln (for instance) I had worked out the size of cable and spoke with the manufacturers (who often offer an installation service) and in every case they also go up to the next size cable and recommend to me to do so.

which is the logical approach as long as the next size up does not involve a much higher cost, which generally only occurs with the larger size cables in industrual installations, where it could be several 100s.

 

[Sparky Pat]

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.

 

[telectrix]

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.

I'm assuming diversity rules here as not all the hob rings will be drawing current simultaneously, therebyreducing the actual load current.

 

[Sparky Pat]

I'm assuming diversity rules here as not all the hob rings will be drawing current simultaneously, therebyreducing the actual load current.

Got to be, but just does not feel right

 

[DPG]

Got to be, but just does not feel right

I'm sure a reputable manufacturer like Bosch will have done the necessary calcs and have made sure it is safe on the fitted plug.

 

[ipf]

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.

In an old church they had a 3k convector heater in a 'cold' meeting room, plugged into d socket. They would put the heater on for a few hours at a time and the plug and socket became very hot. Think the flex was 1.25mm.
It was wired, very well, 4mm radial, so just replaced with a 20A dp switch.
Point is, it did come with plug and flex....so something wrong in the chain, maybe?
Even considering control 'stat, I would have thought provision would have been made by the manufacturer to have such a heater in constant use.

 

[DPG]

In an old church they had a 3k convector heater in a 'cold' meeting room, plugged into d socket. They would put the heater on for a few hours at a time and the plug and socket became very hot. Think the flex was 1.25mm.
It was wired, very well, 4mm radial, so just replaced with a 20A dp switch.
Point is, it did come with plug and flex....so something wrong in the chain, maybe?
Even considering control 'stat, I would have thought provision would have been made by the manufacturer to have such a heater in constant use.

I suppose that's the problem - when people expect a small heater to heat a large cold area. It's really beyond the expected usage of the device, but obviously it does happen sometimes.

 

[LastManOnline]

Even considering control 'stat, I would have thought provision would have been made by the manufacturer to have such a heater in constant use.

You correct. They are designed for continuous use. I lived in a old (poorly insulated) cottage for 6 years. Went though at least one (sometimes 2) electric heaters every year. They were in constant use. I always periodically check the plugtop for heat. Never had an issue

 

[DPG]

You correct. They are designed for continuous use. I lived in a old (poorly insulated) cottage for 6 years. Went though at least one (sometimes 2) electric heaters every year. They were in constant use. I always periodically check the plugtop for heat. Never had an issue

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!

 

[Julie.]

.....I would have thought provision would have been made by the manufacturer to have such a heater in constant use.

It depends on the instruction manual with the device, they almost all give instructions "suitable for a normal room up to 6m^2" or something similar.

This isn't just buff, it's limiting the use to a place where it can maintain the typical temperature whilst remaining within the duty cycle it's designed for!

If you want a device that may be operated continuously, then you need to buy a suitable device.

 

[ipf]

It depends on the instruction manual with the device, they almost all give instructions "suitable for a normal room up to 6m^2" or something similar.

This isn't just buff, it's limiting the use to a place where it can maintain the typical temperature whilst remaining within the duty cycle it's designed for!

If you want a device that may be operated continuously, then you need to buy a suitable device.

Of course.....but tell that to a cold bunch of old codgers in the room, including 'acting caretakers'.?

 

[ipf]

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 knuckled terminal screws with built in washers. Lovely!

What do you mean, they were a nightmare..................with T+E.

 

[DPG]

Thanks for correcting my post mods!

 

[John-SJW]

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

That seems very light. Mine is 7,200 watts.

 

[DPG]

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]

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]

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]

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]

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