Question

[carl9254]

Hello all, doing my Part P exam in the morning and feeling confident, so doing a bit of reading up now and ive got the IEE Electricians Guide to Building Reg, and ive come across something which i dont agree with but i may be wrong, the book says, 'A 30 or 32 A circuit is usually appropriate for household or similar cookers of rating upto 15 kW'.

But am i not right in thinking 15000 / 230 = 65 A?????

So 30 or 32 A would be too small???

 

[Graeme Harrold]

hello all, doing my part p exam in the morning and feeling confident, so doing a bit of reading up now and ive got the iee electricians guide to building reg, and ive come across something which i dont agree with but i may be wrong, the book says, 'a 30 or 32 a circuit is usually appropriate for household or similar cookers of rating upto 15 kw'.

But am i not right in thinking 15000 / 230 = 65 a?????

So 30 or 32 a would be too small???

diversity :d

 

[Banjo]

For cookers you must allow for diversity.

Take 10A off 65A = 55A

then find 30% of the remaining current = 16.5A

then add the 10A back on to 16.5A = 26.5A

And if a socket is with the control unit you must add a extra 5A to allow for this.

Hope this helps.

Stu

 

[carl9254]

Thanks, we havent covered that yet, hope its not in the exam i dont understand why im on a 5 day course and the bloody exam is on the 4th morning, crazy.

 

[Graeme Harrold]

For cookers you must allow for diversity.

Take 10A off 65A = 55A

then find 30% of the remaining current = 16.5A

then add the 10A back on to 16.5A = 26.5A

And if a socket is with the control unit you must add a extra 5A to allow for this.

Hope this helps.

Stu

You dont have to apply diversity, nothing stopping you allowing for the full 65A. Think Xmas!!!! All rings on and the oven..... Diversity is there to allow you to design to a compromise given that not everything will be switched on at the same time. Even with a cooker its unlikely that every ring and the oven will be on at the same time given the switching in and out of the elements by thermostats. Just apply common sense and the figures in the OSG are max recomended calcs

 

[carl9254]

So am i right in saying if i put a 32 A protective device in, and on christmas day i turned every hob and the oven full wack on my 14000 kW oven it would be very likely to trip??

 

[happygilmore]

thats one hell of an industrial oven you running!!!

 

[Graeme Harrold]

So am i right in saying if i put a 32 A protective device in, and on christmas day i turned every hob and the oven full wack on my 14000 kW oven it would be very likely to trip??

Its probable, you would likely have an overloaded circuit and again that aint bad in a controlled fashion, but Id hate to be the spark that installed the minimum and get a bad name when it did trip at an emotional time like Xmas.....

Have a look at your curves in the BRB and see when a 32A device trips if the full load of say 65A was applied.......

 

[Banjo]

You dont have to apply diversity, nothing stopping you allowing for the full 65A. Think Xmas!!!! All rings on and the oven..... Diversity is there to allow you to design to a compromise given that not everything will be switched on at the same time. Even with a cooker its unlikely that every ring and the oven will be on at the same time given the switching in and out of the elements by thermostats. Just apply common sense and the figures in the OSG are max recomended calcs

But am i right in saying that the circuit breaker is there to protect the cable. So if there was a fault on the circuit and it may not trip the 63 amp breaker whereas apply diversity it would, and this causing no harm to the cable or the consumer.

 

[Graeme Harrold]

But am i right in saying that the circuit breaker is there to protect the cable. So if there was a fault on the circuit and it may not trip the 63 amp breaker whereas apply diversity it would, and this causing no harm to the cable or the consumer.

Quite right, which is why I mentioned looking at the trip curves and you make an engineering jugement based on the times and current being drawn. 32A breaker will take about 150 seconds to trip at 65A.............

 

[Banjo]

Quite right, which is why I mentioned looking at the trip curves and you make an engineering jugement based on the times and current being drawn. 32A breaker will take about 150 seconds to trip at 65A.............

Not bad for a apprentice hehe.

Stu

 

[carl9254]

Passed my part p this week, easy i can now see what all you experienced electricians are on about, cause i am now nearly as qualified as ou all from a week course ha, its crazy. i now need to get on with the NIC, set my own business up, get my 2391 and get some experiance by following my mates dad around for a bit. Bring it on!!

 

[trebor]

Passed my part p this week, easy i can now see what all you experienced electricians are on about, cause i am now nearly as qualified as ou all from a week course ha, its crazy. i now need to get on with the NIC, set my own business up, get my 2391 and get some experiance by following my mates dad around for a bit. Bring it on!!

Well done for your pass, you hit the nail on the head when you say you need to get experience, I can assure youthat the 2391-10 will not be anywhere near easy, the pass rate nationally went down to 40% in August, keep your head in the books especially GN3, get the hands on experience and you will be ok

 

[Graeme Harrold]

Well done for your pass, you hit the nail on the head when you say you need to get experience, I can assure youthat the 2391-10 will not be anywhere near easy, the pass rate nationally went down to 40% in August, keep your head in the books especially GN3, get the hands on experience and you will be ok

I did my 2391-10 through the Military ressetlement training center in Aldershot..........They have a whopping 94% pass rate..............Must be because of the intensive week course. Teaching Mon - Wed with an past paper to do each night, then Pracrical test on Thursday and then written on Friday. All info in and you dont have time to forget