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

[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??