95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fuses

[markc17]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

just found this on the IET forum.. a guy that used to be a cheif electrical engineer for BACO posted it...
''This BACO company had a cable manufacturing company in Swansea producing their "Solidal" cable.''


Qustion to post - ''I guess that was the old Aluminium Wire and Cable Co (AWCO) Jaymack ?''

Reply ''Correct, I took a couple of BACO maintenance electricians there for 2 day's hands on training.''

Hmmm.. anyone enlighten me on this soidal cable? if that is what it is?

- - - Updated - - -

Aluminium wire and cable co, good chance this is a Soidal Aluminium cable?

Very kind.. have you worked with it before?

 

[Gage]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Found this: 5000 Amp Fuse + Tools Melt With High Current - YouTube Yikes!!! I bet their mum isn't going to be pleased with the carpet.

(Disclaimer: contains a very rude word)

That's it! I love his vids haha

 

[Stroppy]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

They will keep me amused tomorrow when I'm snowed off work.

 

[Darkwood]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Alot of confusion in this thread regarding grouping and same source/supply parallel cables...

Im on the understanding myself the grouping factor is to be applied to parallel runs same circuit too, the reason is the derating factor is designed to allow for the reduced surface area of which the thermal energy can dissapate away from the copper, with this in mind the fact it the same circuit has no bearing as surface area will still be reduced and cable sized will be selected with relation to ccc of each cable added together. When running parallel cables in trenches or cable-tray its common to seperate them apart so grouping isnt applicable....

The problem and why i believe most are misled is the reg's titles grouping factor for cables of different circuits but if you refer to appendix 10 and read the first paragraph of no'2 (overload protection....) then at the end of this paragraph it does clearly state 'with the appropriate grouping and other factors applied'.

In essence of the reason grouping factor is applied in the first place then both cables of a parallel supply are still subject to dissapating their thermal energy much the same as cables of different circuits i cant see the any reason why having parallel 'same circuit' cables would be exempt from the grouping factor.

Ive been digging wider trenches for years and spacing the cables subject to calculation relative to diameter for yrs to avoid derating for grouping :uhoh2:

 

[Gavin A]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Elecsa table actually confirms the rating of 169 Amps as it is a 4 core cable. The switch for the building is fed via main busbars.. 200 amp fuses... then a 30 m run underground up into an intake cupboard to main isolator for building. I can probably see a metre of the cable at each end if i am lucky so am honestly asking how i find out manufacturers information on the cable.. if i cant see anything pointing to manufacturer.. surely then tables must be used.... i would understand if the drop was negligeable.. but 169 amps.. to 200 amps is not...

that elecsa table is based on the following

Table 4D1A – Single core 70[SUP]0[/SUP]c thermoplastic insulated cables (e.g. PVC Singles), non-armoured with or without sheath. All values assume an ambient temperature of 30[SUP]0[/SUP]c and a conductor operating temperature of 70[SUP]0[/SUP]c.

Ambient ground temperature peaks at more like 15 deg C in summer, maybe a little more under a building if the basement is heated and not insulated from the ground, but it'll never get anthing like 30 deg.

 

[shanky887614]

200 amp fuses

best to follow manufacturers data rather than book.

for example 2.5 twin can carry around 27 amps ish

but 1.5 tri rated can carry 21 amps but they would question it if you put it on a 16a breaker

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Alot of confusion in this thread regarding grouping and same source/supply parallel cables...

Im on the understanding myself the grouping factor is to be applied to parallel runs same circuit too, the reason is the derating factor is designed to allow for the reduced surface area of which the thermal energy can dissapate away from the copper, with this in mind the fact it the same circuit has no bearing as surface area will still be reduced and cable sized will be selected with relation to ccc of each cable added together. When running parallel cables in trenches or cable-tray its common to seperate them apart so grouping isnt applicable....

The problem and why i believe most are misled is the reg's titles grouping factor for cables of different circuits but if you refer to appendix 10 and read the first paragraph of no'2 (overload protection....) then at the end of this paragraph it does clearly state 'with the appropriate grouping and other factors applied'.

In essence of the reason grouping factor is applied in the first place then both cables of a parallel supply are still subject to dissapating their thermal energy much the same as cables of different circuits i cant see the any reason why having parallel 'same circuit' cables would be exempt from the grouping factor.

Ive been digging wider trenches for years and spacing the cables subject to calculation relative to diameter for yrs to avoid derating for grouping :uhoh2:

No confusion here!! lol!!

So you too would apply a grouping factor to a ring circuit if both legs were run in a conduit or other containment. That'll be a first for me!!! lol!!

 

[Gavin A]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

So you too would apply a grouping factor to a ring circuit if both legs were run in a conduit or other containment. That'll be a first for me!!! lol!!

Can you explain why not?

Is the derating factor not down to the additional heat stemming from the additional cable, and the lower surface area available for heat to be lost through?

And why would this not apply just because both cables are part of the same circuit?

if anything I'd think it should apply even more, as both cables will always be under full load at the same time, whereas in cables on different circuits will be under different loading levels to each other.

The only logical reason I could see for this not being the case would be if this was automatically taken into account already in the figures for those cables.

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Jesus, ...I give up!!

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

It does enter the building in a duct...Im trying to explain the installation without EVERY detail.. but that duct goes out under the floor... a meter down the side of a buildingoutside into a duct in the road.. then around multiple bends with no access panels of any type..There are no draws in.. from my experience.. pulling any sort of heavy duty armoured around corners is tough.. i dont have any groundworks drawings or a CAT scanner to hand...lol... so i think my observations are a fair assessment.. but still..

Let's get things absolutely clear on the length of this cable, it's approximately 30m Yes?? What size is the duct this cable is running through and what's it made of ?? (Metal, PVC, Ceramic)

It's extremely unlikely that any of the bends in this duct are going to be tight bends, otherwise they would never have been able to pull the cable into the duct in the first place. All professionally installed ducting will have slow/long bends, for this very reason. So there shouldn't be any need to dig up a road or whatever to replace this cable. The only time you would need to dig up this road would be, if clowns installed this duct and fitted the duct over the cable during installation, a bit at a time! ...lol!! But then why bother installing a duct system, you might just as well direct bury the cable for what good or use the duct would be!! lol!!

Depending on the amount of bends in this shortish duct, you may well need to hire a pulling machine (and maybe cable rollers) to remove old cable and replace with new!!

The copper should be worth a few bob from the old cable, at the scrapie's!! lol!!

 

[markc17]

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..

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

How about taking a few pictures of this 95mm cable installation when your back down there. It'll give a much clearer veiw of what were talking about!!

By the way, are there any other cables within this duct with the 95mm cable??

 

[Darkwood]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

No confusion here!! lol!!

So you too would apply a grouping factor to a ring circuit if both legs were run in a conduit or other containment. That'll be a first for me!!! lol!!

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...

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

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!!

 

[Spoon]

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"

 

[Engineer54]

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"

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.

 

[Rockingit]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

...in fact i'm looking at a project drawing consisting of a similar situation now...

Get back to work then!

 

[Engineer54]

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)

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Get back to work then!

I'm thinking more of going to bed, rather than trundling off back to site!! lol!!

 

[Spoon]

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)

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....

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

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....

I don't take the ****!!

Oh i forgot, none of this applies to a ring circuit does it!! It somehow doesn't need to have the same heat dissipation requirements of a similar circuit!!

Whatever you guy's want to do when running parallel circuits is up to you lot!! You'll be, all but defeating to whole point of a parallel circuit!!
I know that i'll wont be adding a grouping factor to any parallel single circuits i'll be seeing on this project!! And i'll be happily sleeping like a baby to the end of my days, in that knowledge!! lol!!!

 

[Rockingit]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

I think what people may be overlooking here E54 (and I'm in full agreement with you), is that when you do the maths you'll find that N + N has a greater surface area than (2N) [if you see what I mean]. This is why two parallel conductors together can still dissipate more heat.

 

[Spoon]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Ok mate, it looks like you are not going to change your mind. I have tried to tell you the physics behind grouping factors. I just hope that the people who search this site looking for info on parallel circuits just dont look at your post count and then mine and say "Eng54 has to be right" and they look at the whole picture.
Anyhow Im going home in 5 mins, so the kids can bully me. Ill see in the morning if anyone agrees with me. Have a good one mate.

 

[Rockingit]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

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....

a
Sorry mate, I'm with E54 on this. They're not producing the same heat! Two parallel conductors of identical nature carrying I current at U voltage along R resistance will both be identical, whereas two different circuits will be operating at different lengths and voltage drops, hence they will never create the same amount of heat - hence one can induce heat in the other, whereas our parallel conductors are incapable of transferring heat energy one to the other as the figure is the same for both of them to start with.

If I put a jug of boiling water next to another jug of boiling water I don't create 200 degrees in between them, I've still got 100 degrees. But if I place one jug at 50 and one at 90 side by side then we get (in a perfect sealed system) 70 degs resulting between them.

 

[Darkwood]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

I think what people may be overlooking here E54 (and I'm in full agreement with you), is that when you do the maths you'll find that N + N has a greater surface area than (2N) [if you see what I mean]. This is why two parallel conductors together can still dissipate more heat.

Im always open to debate and just as you posted this i was thinking the same ... the surface area of 2 cables is larger than that of 1 conductor of twice the size thus could omit the grouping factor this would be in agreement of E54's posts but up until this point was made it was hard to understand the reasoning but yep E54 can sit down with his cuppa and slightly smug smile il possibly re-think this area of the regs and may explain why it dosn't actually mention grouping factor directly in association of a multi cable parallel supply ..... but hey all ive wasted is a few half charlies spacing the swa's before overfill so if im gonna be wrong id rather it not effect the integrity of my previous work lol....

Browsing the tinterweb though i get conflicting results so assume some countries base ccc calculations different to ours and thus do apply this grouping factor for parallel cables of 1 circuit as their initial ccc of cables may be higher but subject to more derating.

 

[Chr!s]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Im always open to debate and just as you posted this i was thinking the same ... the surface area of 2 cables is larger than that of 1 conductor of twice the size thus could omit the grouping factor this would be in agreement of E54's posts but up until this point was made it was hard to understand the reasoning but yep E54 can sit down with his cuppa and slightly smug smile il possibly re-think this area of the regs and may explain why it dosn't actually mention grouping factor directly in association of a multi cable parallel supply ..... but hey all ive wasted is a few half charlies spacing the swa's before overfill so if im gonna be wrong id rather it not effect the integrity of my previous work lol....

Browsing the tinterweb though i get conflicting results so assume some countries base ccc calculations different to ours and thus do apply this grouping factor for parallel cables of 1 circuit as their initial ccc of cables may be higher but subject to more derating.

Work it out, 1 cable 300mm and 2 150mm, work out the mW/m, the larger cable will emit more heat.

When enclosed or grouped, the radiated heat loss is dramatically reduced, this is why we derate.

Practical tests were used with upto 37 grouped cables, if all were parallel, how would you expect the cables in the middle to perform?

There is also the theoretical models, all of which the table within BS 7671 is based upon.

I sure the NEC use the same method too, they just calculate In differently.

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Im always open to debate and just as you posted this i was thinking the same ... the surface area of 2 cables is larger than that of 1 conductor of twice the size thus could omit the grouping factor this would be in agreement of E54's posts but up until this point was made it was hard to understand the reasoning but yep E54 can sit down with his cuppa and slightly smug smile il possibly re-think this area of the regs and may explain why it dosn't actually mention grouping factor directly in association of a multi cable parallel supply ..... but hey all ive wasted is a few half charlies spacing the swa's before overfill so if im gonna be wrong id rather it not effect the integrity of my previous work lol....

Browsing the tinterweb though i get conflicting results so assume some countries base ccc calculations different to ours and thus do apply this grouping factor for parallel cables of 1 circuit as their initial ccc of cables may be higher but subject to more derating.

I'm not being in anyway smug here, It's what and how i was taught, and what i've been applying for too many years to be told any differently now!! I've also never once seen a calculation placed in front of me, by any contractors Engineer, for approving parallel cable sizes, that have included a grouping factor. I work with quite a few different national standards, and too my knowledge, none of them apply or require a grouping factor for paralleled single circuits either!!

You haven't wasted anything, if your talking about spacing cables in a trench, I do the same. But my reasoning is for any future ground movement. I never run cables in trenches straight either, they are always laid with slight snaking along it's length for the same reason and to allow for any seasonal expansion/contraction that may occur etc....

 

[Rockingit]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Work it out, 1 cable 300mm and 2 150mm, work out the mW/m, the larger cable will emit more heat.

When enclosed or grouped, the radiated heat loss is dramatically reduced, this is why we derate.

Practical tests were used with upto 37 grouped cables, if all were parallel, how would you expect the cables in the middle to perform?

There is also the theoretical models, all of which the table within BS 7671 is based upon.

I sure the NEC use the same method too, they just calculate In differently.

The larger won't emit MORE heat, it will emit the same amount of heat energy dissipated over a smaller surface area than the two parallel conductors which have a greater surface area - this is basic radiator principle. If N amount of electrical energy passing down R resistance of copper will produce J amount of heat, J becomes a fixed form. So all we are left with is simply J/circumference, of which 2 x ccc's are roughly 1/3 larger than a single one double the size. Do the maths if you don't believe me!

 

[Darkwood]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

I'm not being in anyway smug here, It's what and how i was taught, and what i've been applying for too many years to be told any differently now!! I've also never once seen a calculation placed in front of me, by any contractors Engineer, for approving parallel cable sizes, that have included a grouping factor. I work with quite a few different national standards, and too my knowledge, none of them apply or require a grouping factor for paralleled single circuits either!!

You haven't wasted anything, if your talking about spacing cables in a trench, I do the same. But my reasoning is for any future ground movement. I never run cables in trenches straight either, they are always laid with slight snaking along it's length for the same reason and to allow for any seasonal expansion/contraction that may occur etc....

The smug was just humour and im not worthy ....:mickey:

 

[Knobhead]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Like E54 I've run countless parallel feeds, never applied a de-rating to them. As has been said it would make the whole exercise pointless.

 

[High Tower]

I'm with e54, why would you derate a parallel cable, it seems pointless, they are both of the same origins and circuit destination so why would you not treat them as 1 cable.?? Or am I missing something?

 

[Spoon]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

OK guys, it looks like I'm the only one here that applies a grouping factor to cables that are run in parallel (that are touching, Table ), when they feed a single source. So please can someone explain why they don't. As I posted in #40

(example 1:same source supply) We have 2 cables (touching, in ducting) each drawing 100A (the source requires 200A) The cables are of the same size and are both 30 meters long. You are saying you would not de-rate these cables as they are supplying a single sourse

(example 2: 2 separate sources) We have 2 cables (touching, in ducting) each drawing 100A (each source requires 100A) The cables are of the same size and are both 30 meters long. You are saying you would de-rate these cables.

You de-rate the cables due to heat disipation. Example 1 cables are producing the same heat as example 2 cables. In layman's terms, so a thicko like me can understand, why de-rate example 2 but not example 1? What is the logic in that... They are the same..

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

I think Rockingit has given you a more than good enough explanation!!

Again i stress, that were talking here about a single parallel circuit, not a situation where there are two or several parallel single circuits grouped/run in a containment. In this case you ''Would'' apply a grouping factor for the multiple ''circuits'', as you would normally, for running multiple ''circuits'' in a given containment.... But notice that i stated circuits and not conductors/cables!! lol!!

On another note, ''All'' these de-rating tables (correction factors) are based on the worst case scenario, which can be quite misleading to say the least, for those that lack experience. Blindly using these tables verbatim, can and will lead to grossly over sized cables if they aren't anywhere near worst case in the first place... The times i've seen a cable on paper, that has gone through a number of correction factors, without any thought being applied, ending up too large to be physically possible to connect!! lol!!

 

[Chr!s]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

The larger won't emit MORE heat, it will emit the same amount of heat energy dissipated over a smaller surface area than the two parallel conductors which have a greater surface area - this is basic radiator principle. If N amount of electrical energy passing down R resistance of copper will produce J amount of heat, J becomes a fixed form. So all we are left with is simply J/circumference, of which 2 x ccc's are roughly 1/3 larger than a single one double the size. Do the maths if you don't believe me!

I have done the Maths lol, if think you need to!!


Example Table 4E1A

Ib = 700 amp, 2 Phase, Cables touching Ref Method C

2 x 150mm CSA

1 x 300 mm CSA

Your argument is missing a few key point's

2 x 150 = ccc = 952 amps
1 x 300 = ccc = 743 amps

Power dissiapted = I2R

 

[Chr!s]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

OK guys, it looks like I'm the only one here that applies a grouping factor to cables that are run in parallel (that are touching, Table ), when they feed a single source. So please can someone explain why they don't. As I posted in #40

(example 1:same source supply) We have 2 cables (touching, in ducting) each drawing 100A (the source requires 200A) The cables are of the same size and are both 30 meters long. You are saying you would not de-rate these cables as they are supplying a single sourse

(example 2: 2 separate sources) We have 2 cables (touching, in ducting) each drawing 100A (each source requires 100A) The cables are of the same size and are both 30 meters long. You are saying you would de-rate these cables.

You de-rate the cables due to heat disipation. Example 1 cables are producing the same heat as example 2 cables. In layman's terms, so a thicko like me can understand, why de-rate example 2 but not example 1? What is the logic in that... They are the same..

No your not on your own, i derate to!!

 

[Spoon]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Eng54. I understand that we are talking about a single parallel circuit. If you are also refering to Rockingit post #75 then he deviates from my examples of the cables being of the same length and carrying the same current. It does not answer my question in post 83.

Chris. Regarding your post #85: My argument is about applying groupling factors to parallel cables that are touching. Not what your maths are about.. Thanks for your post #86

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

I have done the Maths lol, if think you need to!!


Example Table 4E1A

Ib = 700 amp, 2 Phase, Cables touching Ref Method C

2 x 150mm CSA

1 x 300 mm CSA

Your argument is missing a few key point's

2 x 150 = ccc = 952 amps
1 x 300 = ccc = 743 amps

Power dissiapted = I2R

Exactly my point about using worst case correction factors!! Your actually reducing any heat, by using two smaller CSA cables that ''CAN'' carry considerably more current, but actually isn't!! Who in their right mind would install a circuit that is going to be on it's limits?? lol!!

Do you apply a grouping correction factor to a circuit run in trefoil too?? Adds up to exactly the same thing after all!!

 

[Spoon]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Deviating from me learning here
In my examples (post 83) all the cables are carrying the same current, are of the same length, same type of armoured cable.... therefore producing the same heat.
Please explain why you only apply de-rating factors for example 2.

If you use the argument ' ''All'' these de-rating tables (correction factors) are based on the worst case scenario' and 'Who in their right mind would install a circuit that is going to be on it's limits' then you wouldn't apply the correction factors for example 1 and 2. (This is not meant to come across insulting in any way or form)

 

[Chr!s]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Exactly my point about using worst case correction factors!! Your actually reducing any heat, by using two smaller CSA cables that ''CAN'' carry considerably more current, but actually isn't!! Who in their right mind would install a circuit that is going to be on it's limits?? lol!!

Do you apply a grouping correction factor to a circuit run in trefoil too?? Adds up to exactly the same thing after all!!

Yes in open air the conductor operating temp will be lower in the parallel, but when we enclose and group the cables this greatly effects the parallels cable to effectively radiate that heat, thus causing the opersti.g temp to dramatically rise, so we have to derate.

 

[Silly Sausage]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

I have done the Maths lol, if think you need to!!


Example Table 4E1A

Ib = 700 amp, 2 Phase, Cables touching Ref Method C

2 x 150mm CSA

1 x 300 mm CSA

Your argument is missing a few key point's

2 x 150 = ccc = 952 amps
1 x 300 = ccc = 743 amps

Power dissiapted = I2R

Great discussion!

Even if you applied worst case group factor from Table 4C1 of 80%, the 2 cables above would be 762A.

Exactly my point about using worst case correction factors!! Your actually reducing any heat, by using two smaller CSA cables that ''CAN'' carry considerably more current, but actually isn't!! Who in their right mind would install a circuit that is going to be on it's limits?? lol!!

Do you apply a grouping correction factor to a circuit run in trefoil too?? Adds up to exactly the same thing after all!!

So, your effectively derating the cable yourself.

Re the Trefoil, single cores, Note 5 of 4C1, if a group consists of n single core cables it may be considered as n/2 circuits of 2 loaded conductors or n/3 circuits of 3 loaded conductors. ie 1 circuit.




I think I'm starting to get it?!?!?!?

 

[Spoon]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Re the Trefoil, single cores, Note 5 of 4C1, if a group consists of n single core cables it may be considered as n/2 circuits of 2 loaded conductors or n/3 circuits of 3 loaded conductors. ie 1 circuit.QUOTE]

This post and my question is about 4 core cable. Note 5 of Table 4C1 doesnt apply. Also note on Table 4C1 the title: Rating factors for one circuit or one multicore cable or a group of circuits, or a group of multicore cables, to be used with current-carrying capacities of Tables 4D1A to 4J4A

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Great discussion!

Even if you applied worst case group factor from Table 4C1 of 80%, the 2 cables above would be 762A.




So, your effectively derating the cable yourself.

Re the Trefoil, single cores, Note 5 of 4C1, if a group consists of n single core cables it may be considered as n/2 circuits of 2 loaded conductors or n/3 circuits of 3 loaded conductors. ie 1 circuit.




I think I'm starting to get it?!?!?!?

Would you call sizing a circuit cable correctly, as ''de-rating''?? ...If so, ...Yes!! lol!!
It's not ''all'' about CCC, the circuit is also required to be sized to provide suitable limitations on volt drop etc. A parallel single circuit can and does have many advantages over the use of a single cable. Start treating it as a multiple circuit installation by applying unnecessary correction factors, and those advantages disappear over the hill!! ...lol!!

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Yes in open air the conductor operating temp will be lower in the parallel, but when we enclose and group the cables this greatly effects the parallels cable to effectively radiate that heat, thus causing the opersti.g temp to dramatically rise, so we have to derate.

Your quite at liberty to de-rate a parallel circuit, fortunately those that know better will not!! Your making it sound as if a parallel single circuit radiates heat like no tomorrow, when in fact sized correctly will do nothing of the kind!! The individual cables will be carrying far less current and thus less heat dissipation, than a far larger single cable, that even in itself won't be dissipating heat to anywhere near worrying levels. Your seeing/creating overblown problems, where none really exist!!

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Re the Trefoil, single cores, Note 5 of 4C1, if a group consists of n single core cables it may be considered as n/2 circuits of 2 loaded conductors or n/3 circuits of 3 loaded conductors. ie 1 circuit.QUOTE]

This post and my question is about 4 core cable. Note 5 of Table 4C1 doesnt apply. Also note on Table 4C1 the title: Rating factors for one circuit or one multicore cable or a group of circuits, or a group of multicore cables, to be used with current-carrying capacities of Tables 4D1A to 4J4A

I think you'll find, they are in all cases above, referring to circuits, rather than same circuit conductors!!
Or..... we go back yet again, to circuits run in Trefoil and even the humble ring circuit!!

 

[Chr!s]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Your quite at liberty to de-rate a parallel circuit, fortunately those that know better will not!! Your making it sound as if a parallel single circuit radiates heat like no tomorrow, when in fact sized correctly will do nothing of the kind!! The individual cables will be carrying far less current and thus less heat dissipation, than a far larger single cable, that even in itself won't be dissipating heat to anywhere near worrying levels. Your seeing/creating overblown problems, where none really exist!!

We are talking about bunching cables together, 2,3,4 circuits and enclosed at that, now it's not all just Thermal, there is a thing called the proximity effect too, all this effects the conductor temp, it's well documented, these are IEC standards.

 

[Chr!s]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Your quite at liberty to de-rate a parallel circuit, fortunately those that know better will not!! Your making it sound as if a parallel single circuit radiates heat like no tomorrow, when in fact sized correctly will do nothing of the kind!! The individual cables will be carrying far less current and thus less heat dissipation, than a far larger single cable, that even in itself won't be dissipating heat to anywhere near worrying levels. Your seeing/creating overblown problems, where none really exist!!

That's my point, parallel cables bunched and enclosed don't dissipate their heat well at all, add inductive issues like the proximity effect and the cable gets hotter with less current and can't dissipate that heat as quickly causing the conductor temp to increase.

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

We are talking about bunching cables together, 2,3,4 circuits and enclosed at that, now it's not all just Thermal, there is a thing called the proximity effect too, all this effects the conductor temp, it's well documented, these are IEC standards.

No we are not, ...we are talking about a paralleled single circuit, If we were talking about multiple parallel single circuits in an enclosure or whatever, then yes i would agree, the grouping correction factors would certainly apply!!

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

That's my point, parallel cables bunched and enclosed don't dissipate their heat well at all, add inductive issues like the proximity effect and the cable gets hotter with less current and can't dissipate that heat as quickly causing the conductor temp to increase.

What's your point?? What sort of heat increases are you actually talking about here, temperature increases that will affect current ratings, that's just nonsense!! Your far more likely to find a larger single cable getting a bit warm, than it's equivalent paralleled circuit, run in exactly the same conditions. Your still seeing a problem that doesn't exist!!

So you would add a grouping correction factor to a trefoil run circuit would you?? Exactly the same conditions apply, it's a single circuit made up with 3 or 4 single conductors bunched together!!

 

[Gavin A]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

Your far more likely to find a larger single cable getting a bit warm, than it's equivalent paralleled circuit, run in exactly the same conditions. Your still seeing a problem that doesn't exist!! !

but given the same level of current flowing through the following circuits, which would be warmer?

2 x 25mm cable in parallel, on a tray in free air but touching, carrying a combined 270 amps

2 x 25mm cable in parallel, on a tray in free air and spaced by one cable diameter, carrying a combined 270 amps


Seems to me that the first set of touching cables would always be warmer (all other things being equal), so I can't understand why it shouldn't be derated slightly relative to the spaced out cables.

 

[Engineer54]

Re: 95 mm 4 core cable, 30 m run, in ducting under buildings backed up by 200 amp fus

I wouldn't run a 2 X 25mm parallel circuit to carry 270A current!!

But in a correctly sized/installed paralleled circuit, it wouldn't and shouldn't make much of a difference, be the conductors touching or not touching, to need a grouping de-rating correction factor to be applied!! Again, ...please tell me what sort of tempreture rises/differences are you all assuming/ expecting for these touching cables, to want to derate them for gods sake??