BS88 Fuses

Well, yes it is. But it gets worse, not better ... the 160 A fuse will pass an infinite amount of energy at 160 A ... it would never blow, so t = ∞, therefore I²t = ∞.

So, I'm not taking the micky by stating the above... I'm trying to illustrate that let-through energy takes on a different meaning with long-duration faults, over short-duration faults, or indeed when there is no fault at all. Similarly, the adiabatic criterion k²S²≥I²t is valid only for short-duration faults, and for longer duration faults, other methods (non-adiabatic) would be needed to take into account that the cable loses heat to the outside world (air or other material around the cable) as well as gaining it from the energy transferred by the passage of electrical current.

So, to illustrate what's going on, a cable rated for 160 A can get rid of the heat generated within it by passing 160 A quickly enough through its outer insulation or sheath, so it never gets above a certain conductor operating temperature (usually 70 deg C, occasionally higher if the cable is terminated in products that can cope with a higher temperature).

Can I help further, by asking why you are thinking about at a 70,000 second fault?

Well, yes it is. But it gets worse, not better ... the 160 A fuse will pass an infinite amount of energy at 160 A ... it would never blow, so t = ∞, therefore I²t = ∞.

So, I'm not taking the micky by stating the above... I'm trying to illustrate that let-through energy takes on a different meaning with long-duration faults, over short-duration faults, or indeed when there is no fault at all. Similarly, the adiabatic criterion k²S²≥I²t is valid only for short-duration faults, and for longer duration faults, other methods (non-adiabatic) would be needed to take into account that the cable loses heat to the outside world (air or other material around the cable) as well as gaining it from the energy transferred by the passage of electrical current.

So, to illustrate what's going on, a cable rated for 160 A can get rid of the heat generated within it by passing 160 A quickly enough through its outer insulation or sheath, so it never gets above a certain conductor operating temperature (usually 70 deg C, occasionally higher if the cable is terminated in products that can cope with a higher temperature).

Can I help further, by asking why you are thinking about at a 70,000 second fault?

Thank you for your reply.

Didnt know adiabatic equation was valid only for short duration faults - presumably in the range of seconds only ?

Not thinking about a 70,000 second fault, just trying to understand sizing of cables and protection etc.