Bus Bar Regs?

[IATservices]

Does anybody know the regulations regarding cable sizes and lengths that can be fed from a bus bar.

Eg. I have just been testing an installation which has a 400amp switched fuse supplying a bus bar, then fed from this bus bar is another 63amp switch fuse and 10mm cable running 4 meters (length) between the two.

Could someone please tell me the regulations and hopefully regulation number for me to be able to assess this situation.

Thanks

 

[spark 68]

Hi,

The regs you are looking for are not specific to the bus bar in this case.

The cable capacity has to match the protective device, 63A in this case, as long as the protective device is suitable for connection to the bus bar (Icn) and this is between the bus bar and the cable.

You have not said what type the cable is, whether it is 70 or 90 degree, double insulated etc. and how it is mounted.

The regs are in the big red book, specifically the tables in Appendix 4 etc.(current capacity in A, and voltage drop mv/A/M) and the voltage drop requirements section 525.

I hope this helps

Ps. 10mm^ does seem on the small side for the length of the run

Also if the cable is supplying the 63A switched fuse, ie. the cable is connected directly to the bus bar, then this should be double insulated, I don't know the reg for this off the top of my head.

 

[IATservices]

The cable is standard 70 degree 10mm PVC singles and below is how it is wired

400amp Switch Fuse>240mm cable> BUS BAR > 10mm cable running 4meters >63amp Switch Fuse

I don't know if this highlighted 10mm cable complies with the regs (although i guess not), the 10mm 70degree cable is on the incoming side of the switch fuse not the outgoing?

Thanks

 

[spark 68]

Hi again,

When I worked for panel builders in the past, any cables connected to the bus bar had to be double insulated,ie. have insulation and a sheath, this was Higher temp than pvc, and carried a greater current.
The only reg in the BRB I can see is 526.4

 

[IATservices]

Yeah that's the only reg I can see as well, but there must be something, somewhere, because there are many standard rated cables being lugged and bolted onto this copper bus bar and NONE of them can take 400amps!

Thanks

 

[spark 68]

Hi,
They don't have to take 400 amp (the bars do) they only have to take whatever the downstream protective device demands, as this is to protect the cable.

Ps. as regards reg 526.4,and appendix G6 (guidance note 1) this refers to the manufacturer recommendations, and every panel wiring firm I have worked for (multi-nationals) said as above, double insulated only, to be connected directly to the bus bars

 

[Sintra]

Why would they need to take 400A if they are only supplying a 63A switchfuse?

edit: too slow

 

[IATservices]

OK, i don't suppose you know any regulation number regarding to this, because how else would that make electrical sense, the 63amp fuse cant protect backwards. I phoned my authorized body the other day and they couldn't give me the answer.

I have seen 6mm T+E cables fed out the bottom of mains switches on DB boards. This is probably electricians mistaking this rule?

Thanks For help.

 

[IQ Electrical]

Hi,
They don't have to take 400 amp (the bars do) they only have to take whatever the downstream protective device demands, as this is to protect the cable.

Precisely, overcurrent protection can be upstream or downstream.

There is no 'double insulation' requirement unless the cables are running exposed.

 

[IATservices]

Yeah i understand the 63amp BS88 fuse can only demand 63amps, but what happens in the case of the cable supplying the 63amp switch fuse shorts out?

Thanks

 

[spark 68]

Hi IQ,

I was editing my previous post as you were typing.

There is no 'double insulation' requirement unless the cables are running exposed.

Cheers

Ps. as regards reg 526.4,and appendix G6 (guidance note 1) this refers to the manufacturer recommendations, and every panel wiring firm I have worked for (multi-nationals) said as above, double insulated only, to be connected directly to the bus bars

Spark 68

 

[spark 68]

but what happens in the case of the cable supplying the 63amp switch fuse shorts out?

But why would this be the case ?, shouldn't these cables be in good order, and be adequately protected ? reg 522.8.1

 

[IATservices]

yeah that would normally be the case but these cables are in a grain mill and mice have a nasty habit of finding their way into the trunking and chewing the insulation off the cables. I have found a few fried mice. :-0

 

[spark 68]

But the answer to that is the reg 522.10 protection against fauna (AL) or dead mice :cheesy:, no seriously the cable would burn out, in the worst case, or trip a device upstream possibly

 

[IATservices]

Thanks all.

IATservices