Coding question - 8.5kw shower, B32

[loz2754]

I think these responses back up my thoughts that it should be a C2.

 

[pc1966]

Here I would query the "long duration" of a small overload. MCB curves allow for trip times from about an hour all the way down to the 10ms or so magnetic trip time.

To me a long duration is then something lasting longer than an hour that won't trip the MCB but is above the ratings. For any sane use of a shower I doubt it would be on for more then 30 minutes once or twice a day, so unless you already see signs of thermal stress, I would say C3 as poor design but not ever likely to be running for more than the max design trip-time of a MCB.

We allow diversity on cookers for rating the cable and MCB on a similar basis, it is in that region of overload only for several minute but below the MCB's thermal time-curve until the thermostats start cycling and the cooker demand drops down.

Had it been something like an immersion heater that could well be on for hours at a time then I would think it merits C2.

 

[loz2754]

Here I would query the "long duration" of a small overload. MCB curves allow for trip times from about an hour all the way down to the 10ms or so magnetic trip time.

To me a long duration is then something lasting longer than an hour that won't trip the MCB but is above the ratings. For any sane use of a shower I doubt it would be on for more then 30 minutes once or twice a day, so unless you already see signs of thermal stress, I would say C3 as poor design but not ever likely to be running for more than the max design trip-time of a MCB.

We allow diversity on cookers for rating the cable and MCB on a similar basis, it is in that region of overload only for several minute but below the MCB's thermal time-curve until the thermostats start cycling and the cooker demand drops down.

Had it been something like an immersion heater that could well be on for hours at a time then I would think it merits C2.

I guess that's reasonable thanks for your input.

 

[brianmoooore]

In the real world, I still think that if a clamp meter was put on the supply to this shower, you'd find that the actual current is considerably less than the simple theoretical one.

 

[Pretty Mouth]

In the real world, I still think that if a clamp meter was put on the supply to this shower, you'd find that the actual current is considerably less than the simple theoretical one.

I'll try to remember to do this when I return for remedials, it'll be interesting to see what the actual current drawn is.

Well, I'm settled on a C3 now, which will delight the tight fisted old landlord no end, as he won't have to shell out for a new CU.