Nick Parker:
Say, if the fault is at the beginning of the cable, it is thus deemed as damage has already been done, and hence replacing the cable is the only option. If this is so, why to verify the thermal stress at the beginning of the cable?
Consider not just faults right at the start of the cable, but one at the first accessory - perhaps only a short distance along the cable (socket or light next to the DB for instance) - the fault current will be less than immediately after the MCB, but not by much - and normally there wouldn't be any need to replace the cable. You could calculate individually for every such situation, but it's a lot simpler just to take the absolute worst case (at the MCB) and do it once, which also guards against future alterations.
Similarly damage to a cable might be repaired or a short replacement spliced in to replace just the damaged section - rather than the entire cable replaced - especially where a cable is buried over a considerable distance or embedded in building materials which might make replacement all the way back to the DB difficult or expensive.
- Andy.
Nick Parker:
Say, if the fault is at the beginning of the cable, it is thus deemed as damage has already been done, and hence replacing the cable is the only option. If this is so, why to verify the thermal stress at the beginning of the cable?
Consider not just faults right at the start of the cable, but one at the first accessory - perhaps only a short distance along the cable (socket or light next to the DB for instance) - the fault current will be less than immediately after the MCB, but not by much - and normally there wouldn't be any need to replace the cable. You could calculate individually for every such situation, but it's a lot simpler just to take the absolute worst case (at the MCB) and do it once, which also guards against future alterations.
Similarly damage to a cable might be repaired or a short replacement spliced in to replace just the damaged section - rather than the entire cable replaced - especially where a cable is buried over a considerable distance or embedded in building materials which might make replacement all the way back to the DB difficult or expensive.
- Andy.
We're about to take you to the IET registration website. Don't worry though, you'll be sent straight back to the community after completing the registration.
Continue to the IET registration site