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.