paralleling conductors

M cebee

555.1.3
annex 55a

paralleling of conductors?

can someone tell me if this means paralleling 2.5 T+E 's at a 20amp socket mcb for example or

does it mean paralleling conductors to increase the overall csa
(2.5+2.5 =5sq for example)

thanks

Stoner

M cebee wrote: »

555.1.3
annex 55a

paralleling of conductors?

can someone tell me if this means paralleling 2.5 T+E 's at a 20amp socket mcb for example or

does it mean paralleling conductors to increase the overall csa
(2.5+2.5 =5sq for example)

thanks

they way I read that is as your second example i.e. increasing the CSA of conductors, something you see on large SWA cables a lot where the current carry capacity of the copper has become saturated.

It makes a point that a ring final ring circuit is not considered to be a parallel circuit, so its ok to have a ring circuit, but for example not ok to have a dedicated 13amp supply fed by two number 2.5.sq.mm PVC/PVC T+E cables as this is a final circuit i.e a circuit supplying a single point, or a radial circuit supplying two or more points.


That's my understanding of it anyway.

mazthespark

+ 1 to what stoner said. and afaik your are not permitted to parallel conductors below 10mm2

M cebee

so the rule relates to putting conductors in parallel to increase overall csa ya?

it doesn't relate to paralleling 2.5 radials for example on a 20amp mcb

Stoner

yes as you said, that's how i read it.

edit, it does not relate to two radials on one MCB, that's a different issue IMO

M cebee

so if you were paralleling a second swa to add capacity it would have to be the same size to maximize capacity

the new capacity will be twice the capacity of the smaller parallel conductor obviously if they're different

Bruthal

M cebee wrote: »

555.1.3
annex 55a

paralleling of conductors?

can someone tell me if this means paralleling 2.5 T+E 's at a 20amp socket mcb for example or

does it mean paralleling conductors to increase the overall csa
(2.5+2.5 =5sq for example)

thanks

Yes parallel would be your second example, your first example is 2 seperate circuits connected to a single MCB, second example is 2 conductors connected between the MCB board and the same single outlet.

As stated its used a lot for larger swa cables, as example if a 4 x 240 square cable is required, 2 cables 4 x 120 could be used connected in parallel, and would have a higher capacity than the 4 by 240 even though the CSA (cross sectional area) is the same in the 2 smaller cables as the one bigger one, although the MCCB would be the same as if a 4 x 240 cable was used.

Bruthal

M cebee wrote: »

so if you were paralleling a second swa to add capacity it would have to be the same size to maximize capacity

the new capacity will be twice the capacity of the smaller parallel conductor obviously if they're different

I would of thought the capacity would be more than twice that of the smaller cable would`t it? Although definitely could not see any scenario where 2 different size cables would ever be used. That would seem a right cowboy job.

M cebee

if you had a 25sq and paralleled a 6sq with it the load would 'split' nearly evenly so the new capacity would be twice the capacity of the 6sq
i figure

pointless obviously

Bruthal

M cebee wrote: »

if you had a 25sq and paralleled a 6sq with it the load would 'split' nearly evenly so the new capacity would be twice the capacity of the 6sq
i figure

pointless obviously

Well that cant be correct at all, if you have a 50 square cable, then decide to connect a 6 square between the same points, you reckon the capacity is now reduced to 12 square, i would`t think so. The load certainly would`t split 50/50. The 50 square cable would have 9 times lower impedence than a 6 square, so the current would split in a ratio of about 9/1. Not a hope it split 50/50.
At the end of the day a cable with for example 50 strands of copper has 50 strands in parallel, adding in a seperate cable although smaller is just adding more strands into the circuit.

A 120 square cable parallel`d with a 50 square would give 170 square equivelent

If you had a 1 meter long link of 50 square cable carrying 100 amps, and connected an ammeter to each end so its in parallel with the link, and if current split 50/50 between cable and ammeter then you would see 50 amps on ammeter, but in reality you would see little or nothing on the ammeter, because the vast majority of the load will flow through the 50 square cable. If you removed the 50 square link
then 100 amps would show on the ammeter, once its capabable of carrying that. Replace the 50 square link and the ammeter goes back to near nothing.

M cebee

you're right i wasn't thinking(2 yrs.full-time electronics student and all !!)

the current will split according to voltage drop/r

i'm sure different size conductors wouldn't be allowed for paralling.

Bruthal

M cebee wrote: »

you're right i wasn't thinking(2 yrs.full-time electronics student and all !!)

the current in each conductor will be the voltage drop/r

ideally they should be same size as these calculations would be fiddly

Yes in reality only 2 cables of equal size would ever be used in parallel, ie if 95 and 50 were used its pointless, 2 no. 70 square cables would be used. I think 2 smaller cables can carry a higher load as well than a single big one even if the CSA`s are the same as in 1 no. 240 v 2 no. 120.