Irish and British Standards

These figures relate to a nail penetration test, and subtleties of what is assumed in  the test method.

Of course (like the cores for that matter) the jacket cannot withstand 200A or even 160A continuously, but equally it could take  a good deal more for a very short duration, potentially a few kA for less than a millisecond without burning back from the ‘nail’.

Rather these figures relate to the fast tripping of the slowest MCB, and highest likely external PSSC, to give the highest  let-through energy.

In reality a breaker does not alter the magnitude of the fault current,  rather it alters how long it flows for, hopefully by shutting it off PDQ ?.

The let through energy of an MCB depends on the external PSSC, as unlike a fuse, although it speeds up with higher fault current to a degree, beyond a certain point, the moving contacts will not go any faster.

In any case if you are wiring up in the UK and the earthing is TNC-s or TNS, use the BS figures, and all will be well. In practice this 160A limits you to a B32 or a C16 breaker.

Obviously on TT it is the RCD tripping time that would matter, and the fault current will not really come into it, as Zs will limit the current.

mike.

These figures relate to a nail penetration test, and subtleties of what is assumed in  the test method.

Of course (like the cores for that matter) the jacket cannot withstand 200A or even 160A continuously, but equally it could take  a good deal more for a very short duration, potentially a few kA for less than a millisecond without burning back from the ‘nail’.

Rather these figures relate to the fast tripping of the slowest MCB, and highest likely external PSSC, to give the highest  let-through energy.

In reality a breaker does not alter the magnitude of the fault current,  rather it alters how long it flows for, hopefully by shutting it off PDQ ?.

The let through energy of an MCB depends on the external PSSC, as unlike a fuse, although it speeds up with higher fault current to a degree, beyond a certain point, the moving contacts will not go any faster.

In any case if you are wiring up in the UK and the earthing is TNC-s or TNS, use the BS figures, and all will be well. In practice this 160A limits you to a B32 or a C16 breaker.

Obviously on TT it is the RCD tripping time that would matter, and the fault current will not really come into it, as Zs will limit the current.

mike.