Post No.28 above is important, because it debunks one of the most common incorrect arguments used against the 2.5sq.mm. 32A ring. It is often said that if one leg becomes disconnected or the circuit is badly arranged leaving all or most of the 32A load on one leg of 2.5, that cable presents a fire risk through overload. It does not.
As stated in the above post, the most likely result is a minor reduction in cable service life, and the worst reasonably likely result is a more significant reduction in cable service life. A length of 2.5 carrying any level of current that a 32A MCB will give it, will not burst into flames nor set anything else on fire. It will be hot to the touch and a bit floppy and that is all. It will withstand perhaps 80A before anything dramatic happens, and even then that is not generally fire.
To re-state that in practical terms, a defective ring of 2.5T+E with spurs off spurs, inappropriate load distribution and one leg open circuit, will support four 12A heaters plugged into a row of adjacent sockets anywhere until the 32A OCPD trips, without anything catching fire and probably without any further damage of any sort.
Fire does not start with marginally-overloaded conductors, which rise to an elevated but not extreme temperature and then reach equilibrium, never to get hotter. Much more likely to start a fire is the uncontrolled temperature that can be reached by arcing connections, since these can just go on getting hotter and hotter as their resistance rises. Where a connection fails high-resistance, the parallel paths available in the RFC can replace a potential arcing scenario with a marginal conductor overload one, in which case it probably reduces the risk of fire. It does then reduce the likelihood of fault detection, but the very fact that we do find burnt terminals still in service shows that detection is not by any means guaranteed in use.
As stated in the above post, the most likely result is a minor reduction in cable service life, and the worst reasonably likely result is a more significant reduction in cable service life. A length of 2.5 carrying any level of current that a 32A MCB will give it, will not burst into flames nor set anything else on fire. It will be hot to the touch and a bit floppy and that is all. It will withstand perhaps 80A before anything dramatic happens, and even then that is not generally fire.
To re-state that in practical terms, a defective ring of 2.5T+E with spurs off spurs, inappropriate load distribution and one leg open circuit, will support four 12A heaters plugged into a row of adjacent sockets anywhere until the 32A OCPD trips, without anything catching fire and probably without any further damage of any sort.
Fire does not start with marginally-overloaded conductors, which rise to an elevated but not extreme temperature and then reach equilibrium, never to get hotter. Much more likely to start a fire is the uncontrolled temperature that can be reached by arcing connections, since these can just go on getting hotter and hotter as their resistance rises. Where a connection fails high-resistance, the parallel paths available in the RFC can replace a potential arcing scenario with a marginal conductor overload one, in which case it probably reduces the risk of fire. It does then reduce the likelihood of fault detection, but the very fact that we do find burnt terminals still in service shows that detection is not by any means guaranteed in use.
