Parallel conductors 3.4.3

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DougP
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Parallel conductors 3.4.3

Post by DougP »

Can conductors within a multi core cable smaller than 4mm², be used in parallel? Such as a 2.5mm² 4c+e used with two sets of parallel conductors.

3.4.3 says "Current-carrying capacities for circuits comprising parallel multi-core cables or groups of single-core cables...."
To me, that means paralleling one multi core cable with another multi core cable.

I believe that the clause shouldn't have any relevance for conductors within a cable.

I'm sure I've seen this done within large multi cores, where some cores are paralleled to reduce voltage drop on long runs.
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Re: Parallel conductors 3.4.3

Post by gregmcc »

DougP wrote:
Fri Apr 17, 2020 10:15 am
Can conductors within a multi core cable smaller than 4mm², be used in parallel? Such as a 2.5mm² 4c+e used with two sets of parallel conductors.

3.4.3 says "Current-carrying capacities for circuits comprising parallel multi-core cables or groups of single-core cables...."
To me, that means paralleling one multi core cable with another multi core cable.

I believe that the clause shouldn't have any relevance for conductors within a cable.

I'm sure I've seen this done within large multi cores, where some cores are paralleled to reduce voltage drop on long runs.
Looking at "(a) cables shall be not less than 4mm2....."

the way I read it 2.5mm2 would not be allowed to be paralleled up
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Re: Parallel conductors 3.4.3

Post by DougP »

gregmcc wrote:
Fri Apr 17, 2020 10:39 am

Looking at "(a) cables shall be not less than 4mm2....."

the way I read it 2.5mm2 would not be allowed to be paralleled up
Except that the requirements of the clause should only apply, when the whole clause is applicable to the situation.
So if the conductors being paralleled aren't included in the clause, then none of the requirements of the clause apply?
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Re: Parallel conductors 3.4.3

Post by AlecK »

The conductors of a single multicore cable would be a group of single-core cables; so the way I read it parallelling 2.5s within a single multicore is forbidden, same as for multiple multicores.
Reading it any other way is basically ignoring the underlying theory.

That said, I believe this clause would be better if it referred to "conductors" instead of "cables"
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Re: Parallel conductors 3.4.3

Post by DougP »

Except that it does say "cables". Multiple times. And conductors, zero times.

And as you keep telling us, read the words that are written, and/or the words that aren't used are just as important.
(going off memory, not direct quotes) ;)

1.4.17
1.4.19
1.4.31
?
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Re: Parallel conductors 3.4.3

Post by AlecK »

Note that in 1.417 (2007+A1+A2), definition of "cable" includes "a single cable core";
and 1.4.19 "cable core" is any "conductor" with its insulation.
So any individual cable core within a multicore cable is itself a cable.
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Re: Parallel conductors 3.4.3

Post by DougP »

Ok, I guess we could discuss the words for quite some time. To me, it doesn't seem to be the intention of the clause though.

So back in reality, what's the problem with paralleling two pairs smaller than 4mm² in a 4 core conductor?
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Re: Parallel conductors 3.4.3

Post by DougP »

In other words, what outcomes are they looking to achieve?
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Re: Parallel conductors 3.4.3

Post by AlecK »

I am not certain of the reason(s) for the restriction.
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Re: Parallel conductors 3.4.3

Post by pluto »

The outcomes for 4 mm2 min conductor parallel limitation comes from the IEC 60364.

The outcome required is the distribution of the total current evenly between all cable cores in parallel so they must have the same impedance for this to occur. This means the conductor material, cross-sectional area and the length must also be the same.

The IEC does not consider that this does happen reliably in conductors under 4 mm2 so do not permit paralleling of under 4 mm2
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Re: Parallel conductors 3.4.3

Post by DougP »

pluto wrote:
Sat Apr 18, 2020 12:12 pm
The outcomes for 4 mm2 min conductor parallel limitation comes from the IEC 60364.

The outcome required is the distribution of the total current evenly between all cable cores in parallel so they must have the same impedance for this to occur. This means the conductor material, cross-sectional area and the length must also be the same.

The IEC does not consider that this does happen reliably in conductors under 4 mm2 so do not permit paralleling of under 4 mm2
That's interesting thanks Pluto!
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Re: Parallel conductors 3.4.3

Post by JamieP »

Interesting

I can understand how those requirements may not be met in separate cables but isn't that more due to the cable runs could end up at different lengths/routes etc?

If they were in the same cable sheath like Doug suggested would that almost guarantee those conditions be met?
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