Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus
Ok.. well.. judging by the way every other aspects of electrical install has been carried out at this place i would hate to guess... duct is perhaps 12 inches across.. ceramic.. in the building.. but when it comes out of the building and down the wall.. it disappears into the road with tarmac covering any sign of ducting... Anyway.. im going to submit a report advising what the regs say.. and advising what a cable manufacturer would say.. and tell them that whatever happens.. they are at capacity.. THEN wait and see if they tell me tto investigate how to pull a new feed in..
Best go check to make sure conductors are copper first lol...although im sure they are..
Thanks for your time.. very much appreciated.
P.S. you are right.. would be worth a few... if i can get it away..
As i recall been taught that the unique nature of a ring main and its normal operating conditions give an exemption from grouping factor to itself where as supply cables with no spurs which are designed to handle up to full ccc of both cables have to include grouping factor... if you flick through the regs regarding Parallel cables you often see that ring mains are exempt from the regulation or are noted that the specific reg shouldn't be applied to ring mains ....
523.8 .... discussing achieving load sharing later states this does not preclude the use of ring mains with or without spurs....
This is repeated with many regulations regarding parallel cables and gives the overall impression that the nature of our flawed ring-main system is in itself a seperate area requiring its own regulation hence appendix 15 or reg 433.1.5 which all through there implementation give the ring main its exemption for the need to apply a grouping factor...
As i recall been taught that the unique nature of a ring main and its normal operating conditions give an exemption from grouping factor to itself where as supply cables with no spurs which are designed to handle up to full ccc of both cables have to include grouping factor... if you flick through the regs regarding Parallel cables you often see that ring mains are exempt from the regulation or are noted that the specific reg shouldn't be applied to ring mains ....
523.8 .... discussing achieving load sharing later states this does not preclude the use of ring mains with or without spurs....
This is repeated with many regulations regarding parallel cables and gives the overall impression that the nature of our flawed ring-main system is in itself a seperate area requiring its own regulation hence appendix 15 or reg 433.1.5 which all through there implementation give the ring main its exemption for the need to apply a grouping factor...
There is nothing flawed in the nature of a ring circuit, so let's not go there!! lol!! If there was going to be any detrimental effect on ring circuit, you can be dammed sure a factor would be placed against it!! Grouping factors have always been about grouping of circuits rather than conductors/cables, otherwise you can start adding Trefoil-ed conductors into the equation too!!...
Never, and i do mean never, have i applied a grouping factor to a Paralleled single circuit. And many of those parallel circuits were feeders from TX's to main switchboards consisting of multiple conductors per phase, in fact i'm looking at a project drawing consisting of a similar situation now, consisting of 9 X 95mm insulated & sheathed singles per phase!! run on tray in trefoil (or should i say quad-foil lol!!) Can you imagine what any grouping factor for this single circuit would do to the size of those conductors!! Jesus, they would end up as 185mm's ... Other de-rating factors to apply Yes, grouping de-rating of conductors of a single circuit, ...No!!
Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus
I have to disagree with you there Eng54. Single Circuit or Multiple Circuits, its all the same. Its all about dispersal of heat from the cables. If the cables are spaced correctly then you do not need to apply the grouping factors. As darkwood said "Ive been digging wider trenches for years and spacing the cables subject to calculation relative to diameter for yrs to avoid derating for grouping"
I have to disagree with you there Eng54. Single Circuit or Multiple Circuits, its all the same. Its all about dispersal of heat from the cables. If the cables are spaced correctly then you do not need to apply the grouping factors. As darkwood said "Ive been digging wider trenches for years and spacing the cables subject to calculation relative to diameter for yrs to avoid derating for grouping"
On a trench with a single parallel circuit?? I don't think so!! On any trench with multiple cables, parallel circuit or otherwise, you would space out your cables, purely for natual movement of the ground.
Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus
All a parallel circuit is, is replacing a single large CSA sized cable with smaller CSA cables, that can give many advantages and equally shares the current flowing. It remains at all times a SINGLE circuit, it cannot influence any other circuit!! (unless run with other cable/circuits of course)
All a parallel circuit is, is replacing a single large CSA sized cable with smaller CSA cables, that can give many advantages and equally shares the current flowing. It remains at all times a SINGLE circuit, it cannot influence any other circuit!! (unless run with other cable/circuits of course)
Come on Eng54, you have to be taking the ---- now....
Ok, just look in the regs at correction factors for cables... they are all about heat dissipation of the cables.. Ambient temp, thermal insulation, buried in the ground.....
Look at the tables for the current capacity of cable eg. Table 4E4A the more surface area of the cable is in contact with the air the higher the current is.. Also heat dissipation...
Therefore two cables touching will not dissipate the same heat as two cables apart. Therefore you have to de-rate the cable. Again, single circuit or multi-circuits its all the same. The physics of it cant distinguish between 2 cables supplying 100A each for one circuit and 2 cables supplying 100A for 2 circuits. They are both producing the same heat....
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