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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!!
 
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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?
 
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You should use Ci for cables through 100mm of insulation. Check out Table 52.2 (page 129 BGB). Your derating factor is 0.78.
 
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telectrix said:
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?
Click to expand...

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!!
 
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Young & Keen said:
Do I need to use Cg for 16 cables or not?
Click to expand...

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!
 
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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!!
 
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Badged01 said:
.. 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!
Click to expand...

30% mate. Just found it. Table 4C1 note 9. (page 327)
 
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Engineer54 said:
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!!
Click to expand...

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.
 
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Young & Keen said:
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!!
Click to expand...

I know that you're young and keen, but are you suitably trained to carry out this kind of work?
 
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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.
 
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telectrix said:
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.
Click to expand...

Thanks a lot mate. Can diversity be applied to all installations? If so, is it the same formula?
 
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Guitarist said:
I know that you're young and keen, but are you suitably trained to carry out this kind of work?
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Well, you may be able to help me with that. I trained originally as an Electrical Maintenance Engineer and did my 4-year apprenticeship at college. Since then I have worked alongside Installation sparks and even worked overseas in construction. As far as the practical work goes, I am fully competent. I have just completed my 17th Edition and I due to start my 2394/2395 in January. Do you know what else I need to do to be fully qualified without doing 2-4 years at college in installation?
 
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Young & Keen said:
Thanks a lot mate. Can diversity be applied to all installations? If so, is it the same formula?
Click to expand...

Do you have a copy of the On-Site Guide? There is a section on diversity in there. Appendix A.
If you don't then PM me your email address and I will email the section to you. The book is worth getting, its a good little book.
 
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Young & Keen said:
Well, you may be able to help me with that. I trained originally as an Electrical Maintenance Engineer and did my 4-year apprenticeship at college. Since then I have worked alongside Installation sparks and even worked overseas in construction. As far as the practical work goes, I am fully competent. I have just completed my 17th Edition and I due to start my 2394/2395 in January. Do you know what else I need to do to be fully qualified without doing 2-4 years at college in installation?
Click to expand...

I too trained as an electrical maintenance engineer with 4 years at College and all that jazz. What surprises me is that in all that time, you've never heard of diversity. I think you are smiling right now ;)
 
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here. y'are:


[ElectriciansForums.net] Cooker
 
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basically it's just using common sense, estimating the actual current drawn when not all loads will be switched on simultaneously. for example, if you add up all the MCB ratings in a CU, you may get a total of 250A, but in actual fact, the load on the supply will be only be around 60A.
 
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hi mate
your lucky then because i qualified a couple of years ago and in the final year there were loads of diversity calculations e had to do and quite a few diversity questions popped up in my exams.
 
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