Shower circuit design.

gkenyon: 
The issue being, that OCPDs heat up. We simply don't have enough information to determine whether it's dangerous … if the mcb's either side of the shower breaker are often well loaded up to a good percentage of their capacity whilst the shower is running the shower breaker ABOVE it's capacity, we really don't know what will happen (except we do, because we've all seen overheating occuring at the CU for various reasons)!

I have had a look at some Hagar data, but this current revision of the forum makes it difficult to paste them in.

32 A MCB: Loss per pole @ rated current = 3.9 W. From which R = 3.81 milliohms.

40 A MCB: Loss per pole @ rated current = 4.3 W. From which R = 2.69 milliohms.

Now run the 32 A MCB at 40 A: Loss per pole @ rated current = 6.1 W. That is 40-odd per cent greater than the loss for a 40 A MCB at 40 A load. (In general this holds approximately true across the range of MCBs.)

It may not seem much, but we do not know whether this is safe. However, as Alcomax points out, if there are no signs of thermal damage (have a close look all round out of the board), it may be appropriate to leave it alone and grade C3. Of course, if there are any signs of thermal damage, it is a C2 from me.

gkenyon: 
The issue being, that OCPDs heat up. We simply don't have enough information to determine whether it's dangerous … if the mcb's either side of the shower breaker are often well loaded up to a good percentage of their capacity whilst the shower is running the shower breaker ABOVE it's capacity, we really don't know what will happen (except we do, because we've all seen overheating occuring at the CU for various reasons)!

I have had a look at some Hagar data, but this current revision of the forum makes it difficult to paste them in.

32 A MCB: Loss per pole @ rated current = 3.9 W. From which R = 3.81 milliohms.

40 A MCB: Loss per pole @ rated current = 4.3 W. From which R = 2.69 milliohms.

Now run the 32 A MCB at 40 A: Loss per pole @ rated current = 6.1 W. That is 40-odd per cent greater than the loss for a 40 A MCB at 40 A load. (In general this holds approximately true across the range of MCBs.)

It may not seem much, but we do not know whether this is safe. However, as Alcomax points out, if there are no signs of thermal damage (have a close look all round out of the board), it may be appropriate to leave it alone and grade C3. Of course, if there are any signs of thermal damage, it is a C2 from me.