5.7kw Hob

[ukpita]

Quick question... Electric hob is 5.7kW so could I use 2.5mm heat resistant flex? B+Q has Tower 2.5mm Heat Resistant flex and says that is max rating is 240v, 6000Wats and 25 Amps.... so i think this would be ok?

Just wondering as 4mm is mentioned as the standard however 4mm would be a little difficult to run/connect?? Guess im just looking for a second opinion.

 

[peter_k800]

Would Always use 6mm, much better in the long run and i know how much of a pain it is when anything smaller is installed as a new supply would have to be run if a big oven was to be installed.

2.5 is way to small eventhough its within the limits but for future use if a new cooker was to be installed..

 

[baldsparkies]

Just because Mrs Diversity might not use all hobs at once doesnt mean Mrs Bloggs won't. When all hobs are running (And there are days when they will) The max demand will be met, and the 2.5mm will rob the appliance of much needed voltage. The hobs when all four are running will run hotter on 4mm than 2.5. Tis true sir. All rings running a pint of water boiled on the hob wired in 4mm will reach boiling point faster than the hob wired in 2.5mm. therefore making the hob more efficient.

 

[flukey]

Would Always use 6mm, much better in the long run and i know how much of a pain it is when anything smaller is installed as a new supply would have to be run if a big oven was to be installed.

2.5 is way to small eventhough its within the limits but for future use if a new cooker was to be installed..

read the op again

he is connecting a hob not installing a cooker circuit

had he asked what size cable from cu to isolator then quite rightly it would be min 6mm but he didnt ask that, did he

Just because Mrs Diversity might not use all hobs at once doesnt mean Mrs Bloggs won't. When all hobs are running (And there are days when they will) The max demand will be met, and the 2.5mm will rob the appliance of much needed voltage. The hobs when all four are running will run hotter on 4mm than 2.5. Tis true sir. All rings running a pint of water boiled on the hob wired in 4mm will reach boiling point faster than the hob wired in 2.5mm. therefore making the hob more efficient.

do the cable calcs cable holds full load but will never have to because all 4 rings will never be running at full pelt because of the cutouts which is why we use diversity on cooking appliances

 

[baldsparkies]

do the cable calcs cable holds full load but will never have to because all 4 rings will never be running at full pelt because of the cutouts which is why we use diversity on cooking appliances [/QUOTE]

The theory is sound Flukey I agree.
But in practice its another story.
My experience was based on a top London Restaurant.
The electricians were happy and the calcs were sound.
The chefs being perfectionists were not happy with some of the electric hobs.
They were the same make but some performed better, and those had been wired in a heavier flex.
I remember the situation and the end results when rewiring the remaining hobs.
I learnt something that day, theory and practical don't always go hand in hand.

 

[Forde]

do the cable calcs cable holds full load but will never have to because all 4 rings will never be running at full pelt because of the cutouts which is why we use diversity on cooking appliances

The theory is sound Flukey I agree.
But in practice its another story.
My experience was based on a top London Restaurant.
The electricians were happy and the calcs were sound.
The chefs being perfectionists were not happy with some of the electric hobs.
They were the same make but some performed better, and those had been wired in a heavier flex.
I remember the situation and the end results when rewiring the remaining hobs.
I learnt something that day, theory and practical don't always go hand in hand.[/QUOTE]

Your using an example of a restaurant? assuming the op is of course talking about a domestic two very different things, you play what's in front of you. If and it's a very big if the customer said to me they used this very particular hob very heavily or ran a business from home etc the 4mm is the better option. Per norm nothing wrong with 2.5mm not sure what your trying to disprove.

 

[timo]

2.5 for me.
Had this myself the other week. Diversity is allowed and goes for all elements on and off due to stats. Even with all the rings on full load is not on for long due to the stats. Manual stated 2.5mm so 2.5mm Heat resistant. No way would 6 mm fit with the manus links (i tried all i could before going for the 2.5mm ) They made the unit to run on 2.5 so im sure they know what it will run on. I'd go with what it says in the instructions mate

 

[flukey]

Your using an example of a restaurant? assuming the op is of course talking about a domestic two very different things, you play what's in front of you. If and it's a very big if the customer said to me they used this very particular hob very heavily or ran a business from home etc the 4mm is the better option. Per norm nothing wrong with 2.5mm not sure what your trying to disprove.[/QUOTE]


my thoughts entirely, domestic and commercial are 2 entirely different scenarios thats why no diversity allowable on commercial

you have my opinion, if you doubt it use the 4mm, either way is acceptable, i just choose to do it the right way

night all

I learnt something that day, theory and practical don't always go hand in hand.

when you get the theory right, which you havent the practical works out just fine

 

[ukpita]

Thanks again all, really appreciate all your help...

 

[baldsparkies]

Thanks again all, really appreciate all your help...

Your welcome Ukpita, hope you enjoyed the banter.
As Flukey said time to call it a day. He is right though 2.5mm will suffice.
But not in the commercial world 4mm did a better job, as I found out. Depends on the situation.

Goodnight Flukey, Goodnight Ukpita, Goodnight Grandma, Goodnight Johnboy.

 

[glen.mason]

Is there a diversity factor here with the hob? I think there is mention of this in the Red book. Regardless, for the sake of a few pence more, use 4mm

 

[Amp David]

I''ll get you a shoe horn so you can fit the 4mm into the connection panel on the hob. lol

 

[Davey101]

It always confuses me slightly when people say 'commercial is entirely different from domestic'.

If you have a 5.7KW hob in your house, and have it going full pelt, it will pull exactly the same current as a 5.7KW hob going full pelt in a B+B/restaurant etc.

Does anyone actually KNOW anything about hobs, i.e; how long the hob will be on full chat for, before the stats do their job?
We know we apply diversity to an oven, or cooker, but do we definatley apply it to a stand alone hob?

 

[baldsparkies]

It always confuses me slightly when people say 'commercial is entirely different from domestic'.

If you have a 5.7KW hob in your house, and have it going full pelt, it will pull exactly the same current as a 5.7KW hob going full pelt in a B+B/restaurant etc.

Does anyone actually KNOW anything about hobs, i.e; how long the hob will be on full chat for, before the stats do their job?
We know we apply diversity to an oven, or cooker, but do we definatley apply it to a stand alone hob?

At the risk of opening a can of worms,
Diversity is based on the reliance of the thermal cut outs preventing all rings on the hob being on at the same time. Thats all well and good, but in practice its very different.
If you place (For arguments sake) 4 saucepans on the hob at the same time filled with water. The stats wont be easily satisfied because of heat transfer keeping the hobs energised.
In this instance the hob does run at full capacity, and the difference in volt drop between 2.5mm vs 4mm, will show up in the time it takes for the water to reach boiling point.
This situation is not limited to commercial. Just checkout the average domestic kitchen on Sunday or at christmas time.
On that point look at the way the turkey takes longer to cook, national grid taking a pasting so lower voltages take there toll.
Now I have to duck. Watch out Flukeys about, .4mm, oh yes and a crimper helps get them in a treat

when you get the theory right, which you havent the practical works out just fine (Now who said that ?? answers on a postcard please)

 

[AEC]

Is it me or am I the only one to ask

What is the size of the circuit overcurrent device?
What is the circuit conductor size?

If 32A MCB supplied circuit, wired in 6mm. You still want 2.5 or 4mm?

To reduce a cable size you must reduce the protective device.

 

[flukey]

Is it me or am I the only one to ask

What is the size of the circuit overcurrent device?
What is the circuit conductor size?

If 32A MCB supplied circuit, wired in 6mm. You still want 2.5 or 4mm?

To reduce a cable size you must reduce the protective device.

thats quite right. op never asked us to size his mcb though and hopefully he should know that but still a very relevant point