I'm just planning various electrical jobs around the house and I'm contemplating installing a replacement shower cable to my downstairs bathroom while I have all the floors etc up.
My current shower is only 8.5kW but if I'm replacing the cable I'd like to be able to accommodate 9.5kW or 10.5kW when I come to replace the shower.
I can get a cable from the consumer unit to the shower with around 17.5m of cable, but let's say 20m to allow a bit of leeway. Some of the route will be through the garage loft space which is uninsulated, part under a bedroom floor upstairs, and the last 2-3m will be through the loft space in a single storey extension. This loft space is insulated however the cable could easily be run on top of the insulation or even clipped to a brick wall around two sides of the loft space.
While I'm at it I'm planning to install a 10mm cable as the cost difference over 6mm is minimal and it makes sense to be over-rated rather than borderline, however from an academic point of view I'd like to confirm my understanding and thought process.
1) Am I right in assuming the cable could be sized using reference method C so long as I'm not running any length of it under insulation? Is it acceptable for the last few metres to be simply placed loosely over insulation or would it have to be clipped to the wall to satisfy this method? Assuming reference method C that would give me a current carrying capacity of 47A for 6mm?
2) 10.5kW at 230V is 45.6A so while close to the limit, would be within the above limit of 47A and so considered acceptable?
3) Voltage drop for this setup would be 7.3mV x 45.6A x 20m = 6.66V = 2.9% so within the limit of 5% allowable voltage drop?
4) Assuming all the above is acceptable from a mathematical perspective, I'm guessing in reality I couldn't install a 10.5kW shower on a 6mm cable anyway. I'm assuming it would be unacceptable to run a 45.6A load on a 45A MCB even though the MCB wouldn't trip at that current (?) and increasing the MCB to 50A would mean the cable was insufficiently protected?
My current shower is only 8.5kW but if I'm replacing the cable I'd like to be able to accommodate 9.5kW or 10.5kW when I come to replace the shower.
I can get a cable from the consumer unit to the shower with around 17.5m of cable, but let's say 20m to allow a bit of leeway. Some of the route will be through the garage loft space which is uninsulated, part under a bedroom floor upstairs, and the last 2-3m will be through the loft space in a single storey extension. This loft space is insulated however the cable could easily be run on top of the insulation or even clipped to a brick wall around two sides of the loft space.
While I'm at it I'm planning to install a 10mm cable as the cost difference over 6mm is minimal and it makes sense to be over-rated rather than borderline, however from an academic point of view I'd like to confirm my understanding and thought process.
1) Am I right in assuming the cable could be sized using reference method C so long as I'm not running any length of it under insulation? Is it acceptable for the last few metres to be simply placed loosely over insulation or would it have to be clipped to the wall to satisfy this method? Assuming reference method C that would give me a current carrying capacity of 47A for 6mm?
2) 10.5kW at 230V is 45.6A so while close to the limit, would be within the above limit of 47A and so considered acceptable?
3) Voltage drop for this setup would be 7.3mV x 45.6A x 20m = 6.66V = 2.9% so within the limit of 5% allowable voltage drop?
4) Assuming all the above is acceptable from a mathematical perspective, I'm guessing in reality I couldn't install a 10.5kW shower on a 6mm cable anyway. I'm assuming it would be unacceptable to run a 45.6A load on a 45A MCB even though the MCB wouldn't trip at that current (?) and increasing the MCB to 50A would mean the cable was insufficiently protected?
). However ....
