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

[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!

 

[Soulsurfer]

Because the existing useable feed is a 6mm from a 32A RCBO so would be easiest to use the cable and possibly feed hob & Oven, would've thought it would be frowned upon to use anything smaller through a cooker switch which is 45A and therefore large terminals. Suppose could run out a 2.5 T&E from the cooker switch but.

 

[Leesparkykent]

At least with a 6mm it's more future proof.

 

[davesparks]

Because the existing useable feed is a 6mm from a 32A RCBO so would be easiest to use the cable and possibly feed hob & Oven, would've thought it would be frowned upon to use anything smaller through a cooker switch which is 45A and therefore large terminals. Suppose could run out a 2.5 T&E from the cooker switch but.

Wtf? You are talking about running a new circuit from the CU in 6mm and fitting a 45A switch for a 4KW load?
Do you run all 16A radials in 6mm?

 

[davesparks]

At least with a 6mm it's more future proof.

Future proof how?

 

[Leesparkykent]

Future proof how?

Incase a bigger KW induction hob or cooker is installed.......

 

[Soulsurfer]

No of course not 6mm on 16A radials !
I think my point is being lost, right now there is a 6mm fed in, it was jointed in a jb and split to feed old hob & oven, I would like to feed new hob & oven with it and just locate the cooker switch to a position within regs. I had no idea if being induction hob would need full load rated to be calc and no diversity and as oven is seperate and singular there would not be diversity on it due to my understanding it's one element and so can't be diverse. It's themostatically on or off. So I was wondering if I need a new seperate radial run in for oven, and as Lee said I would rather go to 4-6mm if needed to cover any future larger load being fitted e.g. Customer decides they fancy a double oven later to cope with family and for instance 11kW.

 

[Leesparkykent]

No of course not 6mm on 16A radials !
I think my point is being lost, right now there is a 6mm fed in, it was jointed in a jb and split to feed old hob & oven, I would like to feed new hob & oven with it and just locate the cooker switch to a position within regs. I had no idea if being induction hob would need full load rated to be calc and no diversity and as oven is seperate and singular there would not be diversity on it due to my understanding it's one element and so can't be diverse. It's themostatically on or off. So I was wondering if I need a new seperate radial run in for oven, and as Lee said I would rather go to 4-6mm if needed to cover any future larger load being fitted e.g. Customer decides they fancy a double oven later to cope with family and for instance 11kW.

I think Richard has covered it well in #29. Locate the cooker switch in a convenient/correct location and fit a dual connection plate for hob and cooker.

 

[longboat]

Wtf? You are talking about running a new circuit from the CU in 6mm and fitting a 45A switch for a 4KW load?
Do you run all 16A radials in 6mm?[/QUOTE
If it was a new supply for an oven in lets say a kitchen extension to a property, then yes I would run it in 6mm with a 32A breaker on a 45A DP switch and socket. Best start using the push bike to get to work, will save the customer a few quid. FFS.