Which reg number....

[Sparky83]

Hi,

The company i work for require that we put down the reg that is contravened when we find a fault on a EICR.

Having looked through the book there are a few that i cant find, I'm sure they are there but its a big book!

Any help would be great, just the part of the BGB would be helpful.

MCB's out of sequence? ie Main switch - 40A,32A,6A,6A,40A,6A,32A

DB is supplied from 2 different Armored cables - 3Phase DB - 2 phases in one cable and 1 phase and neutral in another ?

Thanks!

 

[davethsparky]

Hi,


MCB's out of sequence? ie Main switch - 40A,32A,6A,6A,40A,6A,32A

!

What do you mean by out of sequence? I can't see much wrong with the order you have listed, could possibly have put a 6 between the first 40 and 32.
The only thing you could say really is manufacturers instruction I guess, most manufacturers say you should alternate high load and low load MCBs to reduce the heating effects of having heavily loaded MCBs in contact with each other.

 

[Sparky83]

I was always under the impression (and possibly wrongly) that from the main switch you would then connect the highest current using circuits down to the lowest. (I'm talking a single phase board in this example.)

So what i had above should be.... 40A, 40A, 32A, 32A, 6A, 6A, 6A

I could be wrong though...

 

[davethsparky]

Have you ever had a reason for putting them in size order? I mean a technical reason.

There was a good reason for it once upon a time but that is in the dim and distant past.

 

[polo1]

Have you ever had a reason for putting them in size order? I mean a technical reason.

There was a good reason for it once upon a time but that is in the dim and distant past.

Interesting! When installing new or replacing existing CUs, I always run my breakers/rcbos from highest to lowest, starting with the highest next to the main switch/rcd. Now I have just got to remember why! On EICR's I do not code breakers which do not follow my preferred order of installation.

 

[ackbarthestar]

We were always taught to place the highest down to the lowest in order from the main isolator.

There is no regulation in BS7671 that states that you should do it this way only that it is likely to reduce the strain on the busbar.

It is probably safer to alternate the breaker size, as Davethesparky says, to reduce the combined heating effect on the high loading breakers.

So no coding......

 

[Sparky83]

Thanks guys,

It was something i'd always been taught but didn't really get told a definitive reason why, and again not regulation was given. I'll forget about it from now on then.

Any thoughts on the cable?

 

[Kingy2512]

You would only code it if the all conductors didn't follow the same sequence.
look at (433.1 533.2.1) think the reg numbers are right or look at page 72 gn3

 

[ackbarthestar]

Thanks guys,

It was something i'd always been taught but didn't really get told a definitive reason why, and again not regulation was given. I'll forget about it from now on then.

Any thoughts on the cable?

Copper conductors covered with PVC insulation would be a good start ......

 

[Tiny Spark]

I to was taught to order the breakers from highest to lowest.
Although thinking about it I was never given a reason why.
I just assumed it was a unwritten standard like many other things.

 

[Sparky83]

Copper conductors covered with PVC insulation would be a good start ......

I ment from the fault i mentioned above in my OP,

DB is supplied from 2 different Armored cables - 3Phase DB - 2 phases in one cable and 1 phase and neutral in another ?

 

[chrish_1977]

Same here, always taught highest to lowest from the main switch, I think it looks better anyway

 

[davethsparky]

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.

 

[sjm]

I ment from the fault i mentioned above in my OP,

DB is supplied from 2 different Armored cables - 3Phase DB - 2 phases in one cable and 1 phase and neutral in another ?

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.

 

[Des 56]

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

 

[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.