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.

 

[Julie.]

It should be calculated at its rated voltage and power.

At higher voltages it will pass MORE current not less, and lower current at lower voltage.

 

[telectrix]

as above, because it 's power rating is variable, depending on the voltage. higher voltage =higher watts.

 

[John-SJW]

It should be calculated at its rated voltage and power.

At higher voltages it will pass MORE current not less, and lower current at lower voltage.

So what you are saying, if say it is 250v, as mine is, this 3.1kW oven is OK to fit on a final ring circuit as it draws a maximum of 12.4 amps. My concern is that if the supply voltage drops in a few years for whatever reason, the current draw is too large blowing the 13A fuse. So is there a set voltage that is used for these calcs, like say 230v?

 

[telectrix]

all depends on what voltage the manufacturer has used to specify the kW rating.
say he's used 240V, then I= 3100/240 = 12.916 A.
from above you can wirk out the resistance of the cooker. R = V/I = 18.58 ohms.

using the above reisistance at 220V:

I = V/R = 220/18.58 = 11.84A which equates to 2.604kW,

 

[Julie.]

So what you are saying, if say it is 250v, as mine is, this 3.1kW oven is OK to fit on a final ring circuit. My concern is that if the supply voltage drops in a few years for whatever reason, the current draw is too large blowing the 13A fuse. So is there a voltage that should be used for these calcs, like say 230v?

It depends on the figures, say the rated voltage and power is 230V, 3100W

Then the resistance will be around 17ohms (V^2/P) so

220V =220/17 = 13A
230V =230/17 = 13.5A
...
250V =250/17 = 14.7A

There are two answers of course - this would be the sustained current - that current it would take to heat up.

And the average current - which would over a very long time (cooking the turkey for example) where the current switches on and off to maintain the temperature, but you can't use this to cable size.

 

[Julie.]

X post, same principle, different choice of rating!!!

Great minds and all that.


Tbh though just squeezing it to be acceptable does not a good job make.

 

[John-SJW]

Tbh though just squeezing it to be acceptable does not a good job make.

I agree. A border liner. It may be fine then the voltage changes then problems, so best be on the side of caution.

I noticed a number of Continental appliances that are 3.1 kW, so wanted to know if there is a set voltage for these calcs for borderline appliances, irrespective of what voltage is supplied to the premises.

A place I had at one time had the voltage dropped from 240v to 230v over a few years, so relying on what is there now is not a good approach.

 

[DPG]

So what you are saying, if say it is 250v, as mine is, this 3.1kW oven is OK to fit on a final ring circuit as it draws a maximum of 12.4 amps. My concern is that if the supply voltage drops in a few years for whatever reason, the current draw is too large blowing the 13A fuse. So is there a set voltage that is used for these calcs, like say 230v?

But if the supply voltage drops, then the current drops. So there is less chance of the supply fuse blowing.

 

[IAmSparkytus!]

With you mentioning a 13A fuse blowing, are you suggesting putting it on a plug top? I never like running anything close to 13A on a plug top as have seen examples in the past of this causing the plugtop to melt.

If you're suggesting adding a spur into a ring main, isn't there something in Appendix 15 about any heating appliances 2kW and above having to be on a dedicated circuit?

Ps. I'm not a regs expert nor do I do domestic work so could be wrong.

 

[Julie.]

I agree. A border liner. It may be fine then the voltage changes then problems, so best be on the side of caution.

I noticed a number of Continental appliances that are 3.1 kW, so wanted to know if there is a set voltage for these calcs for borderline appliances, irrespective of what voltage is supplied to the premises.

A place I had at one time had the voltage dropped from 240v to 230v over a few years, so relying on what is there now is not a good approach.

Agree, but I think you are still misunderstanding the relationship, if the voltage drops, so does the current, the real issue is if the voltage increases

 

[ipf]

As per tel (#3 and 5), easiest way, as an equation.. Resistance is the constant. Voltage up, more current. Current up more volts......and the opposite downs.

 

[John-SJW]

Agree, but I think you are still misunderstanding the relationship, if the voltage drops, so does the current, the real issue is if the voltage increases

Brain rusty. The resistance mattered.

 

[John-SJW]

With you mentioning a 13A fuse blowing, are you suggesting putting it on a plug top?

I am not suggesting doing anything. I noticed a number of appliances at just over 3kW on the market. One I noticed said 220-230v, 3.1 kW.

 

[Lucien Nunes]

It's important to remember that different loads behave completely differently when the voltage decreases.

Resistive loads e.g. heating elements: Current decreases proportionately with voltage, power decreases as square of voltage. If under thermostatic control, duty cycle increases inversely to square of voltage to maintain constant average power.

Tungsten lamp loads: Current decreases but not linearly and not by much over the usable range of brightness, because positive temperature coefficient of resistance of filament partially compensates.

Linear PSUs (somewhat obsolete): Current remains approximately constant, power decreases, efficiency increases until output falls out of regulation.

Switched-mode PSUs, LED drivers etc: Current increases in inverse proportion to voltage, to maintain approximately constant power input.

Induction motors: Current increases, PF typically increases, the relationship depends on load, motor design etc.

Returning to the subject of the cooking appliance. If the power rating is given at 230V it will take rated current at 230V and more at 240V. If the power rating is given at 240V it will take rated current at 240V and less at 230V. Many heating elements only deliver rated power at their highest rated voltage, making that the worst case for current.

 

[John-SJW]

Agree, but I think you are still misunderstanding the relationship, if the voltage drops, so does the current, the real issue is if the voltage increases

I got that. I wanted to know if there is a set voltage used, as we have variable voltage from premises to premises in the UK.

 

[LastManOnline]

I saw an oven that was rated at 3,100 watts.

Did oven come with a lead and plugtop attached?

 

[John-SJW]

Returning to the subject of the cooking appliance. If the power rating is given at 230V it will take rated current at 230V and more at 240V. If the power rating is given at 240V it will take rated current at 240V and less at 230V. Many heating elements only deliver rated power at their highest rated voltage, making that the worst case for current.

I think I have an answer. It is rated 220-230v. A rating of 220v, find resistance then apply that resistance to a 230v supply to get worse case of those two voltages.

 

[LastManOnline]

I got that. I wanted to know if there is a set voltage used, as we have variable voltage from premises to premises in the UK.

If as you say it was a "continental oven", then 230v is the norm there. It would be connected to a socket via an unfused plugtop to a 16 amp radial circuit

 

[John-SJW]

Did oven come with a lead and plugtop attached?

I do not know.

 

[John-SJW]

If as you say it was a "continental oven", then 230v is the norm there. It would be connected to a socket via an unfused plugtop to a 16 amp radial circuit

More like a 20 amp circuit to give some margin.

 

[littlespark]

I wouldn’t worry about it too much....

As they say “resistance is futile”

?

 

[catdog1121]

Are these Neff ovens by any chance?

Two things:

1. I believe any load above 2kw should not be placed on a ring final circuit unless it is a lightly used circuit, the reason for this is that you overload one leg of the ring, unless you can ensure you are putting the load in the middle.

2. Check the instructions as most of these ovens state they need to be on a 16A circuit, this can often mean you need a separate circuit for the oven and hob. It used to be that you could rely on the oven not being likely to overload but these new ovens have all sorts of features.. You should follow the manufacturers instructions.

 

[LastManOnline]

More like a 20 amp circuit to give some margin.

Not necessary. A 3 kw oven is an entirely different prospect to a 3kw space heater. The oven needs to heat a space of less than a square meter.The space heater, many times more than that and hence works much harder

 

[telectrix]

Not necessary. A 3 kw oven is an entirely different prospect to a 3kw space heater. The oven needs to heat a space of less than a square meter.The space heater, many times more than that and hence works much harder

but... In Space, no-one can hear you scream.

 

[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!