Cooker

[Young & Keen]

I am installing a cooker in a commercial premises and I am new to installations and trying to use the regs (17th) to do it. I have a 7.9KW oven which is 42m from the dist board. I am trying to calculate Ib whereby I have 16 cables coing out of the board but it is possible to run the cable in a false ceiling away from these. Do I need to use Cg for 16 cables or not?

Also, I am passing through 100mm of insulation in a partition, do I need to use Ci for 100mm? The reason I am asking is the calculations have resulted in me requiring a 50mm cable which of course is impossible.

I also understand that I will need a C40A RCBO as the board is not RCD protected? I hope I am not too far off the mark.

Please help!!

 

[telectrix]

is 7.9KW the total load? if so, then apply diversity to get your Ib . 6mm cable on a 32A MCB will handle the current. but do a VD calc. for that length of run. secondly, is RCD protection required under 522.6.101?

 

[Spoon]

You should use Ci for cables through 100mm of insulation. Check out Table 52.2 (page 129 BGB). Your derating factor is 0.78.

 

[Young & Keen]

is 7.9KW the total load? if so, then apply diversity to get your Ib . 6mm cable on a 32A MCB will handle the current. but do a VD calc. for that length of run. secondly, is RCD protection required under 522.6.101?

Thanks Telectrix, yes that is the total load. Unfortunately it isn't possible to get conduit etc into the wall but I may be able to install it within the parameters of 522.6.101 (v). This is going to sound like a stupid question but could you possibly explain what you mean by diversity? As I said, I'm new to this!!

 

[GLENNSPARK]

so...
how far along does the cables run is this insulation?

if its between 2 points served (such as isolators)..then you only need to go up a CSA for that portion..

 

[Young & Keen]

so...
how far along does the cables run is this insulation?

if its between 2 points served (such as isolators)..then you only need to go up a CSA for that portion..

Glennspark,

It's near the end of the run, about 2 metres from the cooker isolator. Are you saying use a JB and a larger piece of T&E?

 

[Badged01]

Do I need to use Cg for 16 cables or not?

Yes -- if you've grouped them in a big bunch ?!?!

No -- if you can keep the cables a distance of 2 x their diameter apart.

Practically you are probably going to group your cables in bunches so just use the Cg for that particular group

..... and while Im thinking of it Im sure there is something else about if a cable carries less than 40%(?) of the groupings current you can discount it for grouping purposes --- check the notes in the BGB its hidden in the grouping table!

 

[GLENNSPARK]

10mm cable will do it...

 

[Engineer54]

Passing through 100mm/10cm of insulation, i wouldn't dream of derating a suitably sized cable for that sort of distance. Having said that, if you can get a cable to pass through a partition wall then you can surely get a conduit in, to span the partitions wall boards!!

 

[Spoon]

.. and while Im thinking of it Im sure there is something else about if a cable carries less than 40%(?) of the groupings current you can discount it for grouping purposes --- check the notes in the BGB its hidden in the grouping table!

30% mate. Just found it. Table 4C1 note 9. (page 327)

 

[telectrix]

Passing through 100mm/10cm of insulation, i wouldn't dream of derating a suitably sized cable for that sort of distance. Having said that, if you can get a cable to pass through a partition wall then you can surely get a conduit in, to span the partitions wall boards!!

just what i was thinking. for the sake of 4", rip a handful of the crap out and bang in a short length of tube.

 

[Guitarist]

Thanks Telectrix, yes that is the total load. Unfortunately it isn't possible to get conduit etc into the wall but I may be able to install it within the parameters of 522.6.101 (v). This is going to sound like a stupid question but could you possibly explain what you mean by diversity? As I said, I'm new to this!!

I know that you're young and keen, but are you suitably trained to carry out this kind of work?

 

[SPARTYKUS]

The question asked above really is a ... Well... Leading question 'young and keen'.

 

[telectrix]

cooker diversity. calculate the total rated current from the kW. say that comes to 40A. so applying diversity, you allow for 10A + 30% of the remainder ( in this case 30% of 30A ), so 10A + 10A = 20A ( add 5A id the cooker point incorporates a socket outlet. ). this diversity is to allow for the fact that not all elements will be on at the same time as they are thermostatically controlled and switching on and off during cooking.

 

[Young & Keen]

cooker diversity. calculate the total rated current from the kW. say that comes to 40A. so applying diversity, you allow for 10A + 30% of the remainder ( in this case 30% of 30A ), so 10A + 10A = 20A ( add 5A id the cooker point incorporates a socket outlet. ). this diversity is to allow for the fact that not all elements will be on at the same time as they are thermostatically controlled and switching on and off during cooking.

Thanks a lot mate. Can diversity be applied to all installations? If so, is it the same formula?