7.6kW Induction Hob - need to select cable and fuse size

[markc123]

If we're going into basics....7.6 x 4.4 = 33.4

What you should use calculations for and what is reality isn't the same. Thats why the regs are non-stat.

end.

 

[Geoffsd]

If we're going into basics....7.6 x 4.4 = 33.4

What's that got to do with anything? 7600 / 240 = 31.7 & 7000 / 230 = 30.4
If you had even done that correctly you would have 7.6 x 4 = 30.4

What you should use calculations for and what is reality isn't the same. Thats why the regs are non-stat.

In what other circumstances do you dismiss the regulations?

Are the regulations only for circumstances when you don't have a silly idea?

end.

If you want but you're still wrong.

 

[yellowvanman]

Don't forget in certain conditions the 6mm can be protected by a 40A MCB anyway. So put in a 32A and if that trips (very very unlikely) then change it top a 40A if the cable current carrying capacity allows.

 

[Geoffsd]

What's wrong with everyone tonight?

The hob doesn't even come to 32A even if you work it out wrongly.

Nearly every cooker, including much larger, is on 6mm and 32A.

 

[shocking_eg]

What's wrong with everyone tonight?

The hob doesn't even come to 32A even if you work it out wrongly.

Nearly every cooker, including much larger, is on 6mm and 32A.

+1 true

 

[Guest55]

[/anger]

lol.
you should follow on with

*shakes fist

 

[markc123]

Look, i said there is pretty much no chance of the cooker tripping and yes it probably never will.

I am aware of the stats that come in and out when the temperature rises ect... thus the cooker never been run at max. But for you to say that there is 100% no chance a 7.6kW cooker not tripping on a 32amp mcb is untrue. All it takes is for the breaker to be soft and it probably would go.

Manufactures instructions aren't always true, have you never come across a 3kW immersion blowing a 13a fuse? because i have

 

[Geoffsd]

But for you to say that there is 100% no chance a 7.6kW cooker not tripping on a 32amp mcb is untrue.

HOW MANY MORE TIMES?

This is nothing to do with diversity.
The hob is LESS than 32A.

As an aside - have you thought about why the hob is 7.6kW?
Could it be so that it can be fed via a 32A mcb?
Or, more likely, two 16A circuits favoured by our continental colleagues.

All it takes is for the breaker to be soft and it probably would go.

Manufactures instructions aren't always true, have you never come across a 3kW immersion blowing a 13a fuse? because i have

Not actually blowing a fuse.
Incorrectly fitted with a plug tends to overheat the plug.

What do you think was the reason for that?
Was it a soft fuse?

Immersion heaters should not be supplied through 13A fuses.
It's not necessary anyway.
Also, they cannot then be fitted with a plug.

 

[Soulsurfer]

What's that got to do with anything? 7600 / 240 = 31.7 & 7000 / 230 = 30.4
If you had even done that correctly you would have 7.6 x 4 = 30.4


In what other circumstances do you dismiss the regulations?

Are the regulations only for circumstances when you don't have a silly idea?


If you want but you're still wrong.

Hi Geoff, I'm just trying to gain an idea of how you can work out what a load such as your information on an induction hob rating can be calculated such as the example you did for someone as a 7.6kW one @ 240V was say 31.66A
and at the 230V was effectively 7.0kW.

Sorry for my stupidity if I have missed basic calcs but I don't get the method to calc the 10V drop to derate down 600 watts. I get that it amounts to approx 4.2% drop on 240V to 229.92V but is there an easy way to work it out ?

Also there is a further posting of yours that refers to another members calc of 7.6 x 4.4 = 33.44A but you refer that the calc is actually 7.6 x 4 = 30.4A therefore fine on 32A RCBO. How do you get the 4 in the x 4 calculation please ?

I have copied the extract in below for reference,
thank you in advance if you can help


Re: 7.6kW Induction Hob - need to select cable and fuse size

All domestic cookers will be ok on a 32A mcb.

In any case 7.6kW @ 240V (which is what the manufacturer will state) is less than 32A.

Equal to 7.0kW @230V = 30.4A.​

Originally Posted by markc123
If we're going into basics....7.6 x 4.4 = 33.4



What's that got to do with anything? 7600 / 240 = 31.7 & 7000 / 230 = 30.4
If you had even done that correctly you would have 7.6 x 4 = 30.4


What you should use calculations for and what is reality isn't the same. Thats why the regs are non-stat.

 

[Richard Burns]

The thread is from 2012 and Geoffsd has not been on the forum for over 5 months!

R = V²/P
240²/7600 = 7.58Ω

So
I = V/R
230/7.58 = 30.34 A

P = VI
230 * 30.34 = 6978 W

or
P=V²/R
230²/7.58 = 6978W

for 4 and 4.4
P=VI
so I =P/V
If P is in kW
Then it would be I= P(kW)*1000/V
So looking at 1000/V
if V is 240V then = 4.166, if V is 230V then = 4.348 roughly 4.4 and 4.0

 

[Soulsurfer]

Ok Richard cheers, just noticed it's just what I've always done as rule of thumb being 1kW = 4.2 A approx. while I'm at it I have a new induction hob at 4.6kW and a separate built in oven to feed at 4kW rated at 16A. I saw, as far as I remember earlier, that apparently induction hobs don't allow for diversity and so far as the built in oven as it's only a single oven I guess diversity won't be applied there as only one heating space ? Kitchen only has 1 x 6mm twin at present from a 32A RCBO. I'm thinking it will be too much and will need a new second 6mm to the oven via an extra cooker switch. Difficult route if able at all from CU.

 

[davesparks]

Is it a very long run or something? Needing 6mm for a 4KW oven sounds a bit much for a domestic installation!

 

[Soulsurfer]

No Dave probably approx 6-8 metres all in to new oven placement when kitchen is fitted, but existing was 6mm into 45A switch then out to wall into an old BICC j.b. with 30A chocky block inside linking feed to old hob and old oven which was approx 4mtrs away in a unit so even then wasn't within 2mtrs of cooker switch ! I'm just trying to work out if I need to run a seperate 6mm to the new oven rather than existing 6mm to cover Induc hob & oven at total of 8.6kW ? As diversity on the oven inclusive of socket outlet incorporated in switch only drops it an amp or less. Running another 6mm would be a nightmare I reckon from CU.

 

[Richard Burns]

With your total load being 37A if all parts are used simultaneously (which is unlikely) you would not have a usage problem (possibly a design problem).
If you apply diversity as recommended in OSG to the whole system then you get 23 A which is fine.
If you assume an induction hob with a power control only has a greater constant consumption of power, then the only diversity available is for the hob's usage and you can consider that in most cases simultaneous use of all elements would be unlikely so perhaps say three on at the same time for a long period (though a long period in cooking might be only 20 mins) this drops the demand to 15A added to the max 17A for the oven (also unlikely in the long term with thermostatic control) gives 32A and would be OK.
Overall it will be fine on one 6mm² supply on a 32A breaker.

 

[davesparks]

No Dave probably approx 6-8 metres all in to new oven placement when kitchen is fitted, but existing was 6mm into 45A switch then out to wall into an old BICC j.b. with 30A chocky block inside linking feed to old hob and old oven which was approx 4mtrs away in a unit so even then wasn't within 2mtrs of cooker switch ! I'm just trying to work out if I need to run a seperate 6mm to the new oven rather than existing 6mm to cover Induc hob & oven at total of 8.6kW ? As diversity on the oven inclusive of socket outlet incorporated in switch only drops it an amp or less. Running another 6mm would be a nightmare I reckon from CU.

My point is why would you run 6mm for a 16A load when you may only need 1.5!