Bus Bar Regs?

[MarkieSparkie]

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

If you understand how a '63A BS88 fuse can only demand 63A', perhaps you be kind enough to enlighten myself and the masses on here, because I fail to see how what is effectively a fusible conductor of negligible impedance limits the current to just 63A. Contrary to your 'understanding' I know that a BS88-6 fuse, for example, has a short circuit capacity of 80,000A@415V.

 

[spark 68]

Hi Markie,

I know that a BS88-6 fuse, for example, has a short circuit capacity of 80,000A@415V

Isn't this the maximum prospective fault current for this device ? or is this the Icn, the absolute maximum fault current this device can clear ?

The 63 A part is the In or nominal trip rating, and this is time dependent, in this case APP 3(fig 3.3B) BRB, would pull 400 A for 1 sec and 280 A for 5 secs before clearing the fault.

 

[malcolmsanford]

Spark 68 have a read of 433 and 434 of the Regulations and see if it helps as well

 

[spark 68]

Ah! Thanks Malcom, The cable, which is a reduction (in relation to the bars) should have been 3 M or less, or the protective device (63A) should have been within 3 M of the bars, I had a look at the original post

Also we don't know if the circuit only provides overload protection only, or short circuit protection only

 

[Chr!s]

There are standards (BS 159) for busbars, busbars may operate above the 70 C so cables and terminations need to be considered.

433.2 allows us to position the protective device along the conductor providing that certain requirements are met. I we use (i) of 433.2.2 then we need to povide fault current protection to the 10mm cable.

So we need to consider the I2T in relation to K2S2.

Chris

 

[spark 68]

Hi Chris,

There are standards (BS 159) for busbars, busbars may operate above the 70 C so cables and terminations need to be considered

This is probably one of the reasons why the panel builders I worked for insisted on DI cables, as these were rated IIRC @ 90 degrees or higher, and had a higher CCC than both PVC and LSF for an equivalent csa (we were issued with CCC cards).

Ps. I wasn't a designer, just a cable monkey :stooge_moe:

 

[Chr!s]

There a few standards with give guidance on busbar temps, IEC 439,BS EN 60439-1, BS 159, there is guidance within these documents on how to terminate cables which have a limiting temp of 70 C, though most would go for a cable which is suitably rated.

Chris

 

[oxocube]

The applicable regs are 433.2.22 and 434.2.1.

The cables must be less than 3 mts long. And must have enhanced fire and personnel protection eg steel containment and in a normally unoccupied area.

 

[netblindpaul]

Also please don't mix up insulated & sheathed wires like "meter tails" with double insulated.