Which reg number....

[not clever]

So everyone got taught to do it but didn't get taught the reason. I too was taught to do it that way but was told the reason also.

Once upon a time single phase boards didn't have busbars. You had to install a wire link from the incomes to one side of each fuse, they would daisy chain the fuses together with an ever decreasing size of conductor to match the loads.

And you would have found fused neutral in the same fuse box......yes I mean fuse box as they were wooden boxes with dove tail joints and fuse carriers were screwed to thin batten inside the box.
Have one in the garage that I stripped out last year, still in use with lead sheathed twin on all circuits.

 

[Tiny Spark]

So everyone got taught to do it but didn't get taught the reason. I too was taught to do it that way but was told the reason also.

Once upon a time single phase boards didn't have busbars. You had to install a wire link from the incomes to one side of each fuse, they would daisy chain the fuses together with an ever decreasing size of conductor to match the loads.

I have seen boards wired in this fashion but never with decreasing conductors.
Surely they should all be the same as unless they were daisy chained from the load side of the fuse (which would be daft) then they should all be capable of taking the same loading?

I can understand that in the event of a fault the fault current would be flowing through one circuit but if they are all linked then you would get some leakage surely?

Just seems a odd way of doing it although I can appreciate the logic.

 

[telectrix]

if clearly marked as to what the cables are, i'd code it as a C3.

 

[Sparky83]

Not sure why you think this is a fault, as long as all 3 phases can be isolated at once. Are the conductors correctly sized etc?
Could have been single phase originally and they added 2 extra phases later.

I guess i was thinking about it from the point of view that i wouldn't install it like that as it just seems plain wrong. But i guess your right, it could well have been single phase and converted.

Regulation 521.8

Note that it saysEach circuit shall be arranged such that the conductors are not distributed over different multi core cables
then note it says parrallel cables exempt
then note what it says in the last bit of that sentence

Then you can decide what it is actually telling us

For me,its very poor practice,but if they are parallel cables there is no more risk than if they were all singles in trunking

So am i right in thinking that as long as the cables are run together from point to point that it is ok?

 

[Andy78]

As SJM says, are all phases isolated from one TP device at the supply end of this feed ?

To me a parallel supply would be two equally sized TP+N cables, not the arrangement you have there. I'm really not sure it classes as a parallel supply, but I am open to being corrected on this.

 

[davethsparky]

It's not a parallel supply, it is a single circuit split down two cables.

I'm pretty sure this ain't allowed, definitely going to have some eddy current issues I should have thought.

 

[Paultrim123321]

With regard to the OP, I have never coded an installation where MCBs are not in a particular order of breaking capacity. I would be more concerned if multiple single phase circuits share close proximity for example multiple socket circuits on separate phases in one room, even tho as long labelling is visible at the socket outlets it is acceptable.
A lot of the older installs I have come across it would be nigh on impossible to feasibly reorganise the order of circuits due to conductor length etc

 

[Guitarist]

Metal DB with cables going through 2 different holes? As dave says, eddie current issues if that's the case.

 

[sjm]

Metal DB with cables going through 2 different holes? As dave says, eddie current issues if that's the case.

Unless there is a suitable slot cut between the two holes.

 

[Guitarist]

Unless there is a suitable slot cut between the two holes.

Of course.

 

[ackbarthestar]

Unless there is a suitable slot cut between the two holes.

Interesting....
Each of the two sets of conductors, L1,L2 and L3, N, surrounded by ferrous SWA ?

 

[sjm]

Interesting....
Each of the two sets of conductors, L1,L2 and L3, N, surrounded by ferrous SWA ?

You make a good point, I may not have thought this through completely.