Why would an electrician install a 10 mm twin and earth circuit protected by a B32 MCB for a 8.5 kW shower?
Why would an electrician install a 10 mm twin and earth circuit protected by a B32 MCB for a 8.5 kW shower?
davezawadi (David Stone):
the thermal section is pretty accurate, because it also needs to be very repeatable.
For the 32 amp MCB the thermal section tripping current is between 41 amps and 24.3 amps depending on the temperature, the stated 32 amps is what it is calibrated to at 30 degrees centigrade.
As well as the ambient temperature within the consumer unit enclosure you also need to consider the grouping factor. Inside enclosure the heating effect of MCBs installed in close proximity (in groups) needs to be taken into consideration. Certain amount of watt loss from each device will contribute to raise the ambient temperature of the breaker above the ambient temperature of the enclosure.
In reality a B40 MCB may have a trip current of around 38 amps just sufficient for a 8.5 kW shower depending on the location of the consumer and the temperature of it as well as what level of loading is on the adjoining MCBs , however on the other hand my consumer unit is mounted on a single brick exterior wall in an unheated garage and the MCBs may be barely adequate for circuit overload protection in the middle of the winter when the temperature of the devices in the consumer unit may be 5 degrees or less.
https://www.hagerelectro.com.au/files/download/0/32587_1/0/TECHINFO_MCBS.PDF
davezawadi (David Stone):
the thermal section is pretty accurate, because it also needs to be very repeatable.
For the 32 amp MCB the thermal section tripping current is between 41 amps and 24.3 amps depending on the temperature, the stated 32 amps is what it is calibrated to at 30 degrees centigrade.
As well as the ambient temperature within the consumer unit enclosure you also need to consider the grouping factor. Inside enclosure the heating effect of MCBs installed in close proximity (in groups) needs to be taken into consideration. Certain amount of watt loss from each device will contribute to raise the ambient temperature of the breaker above the ambient temperature of the enclosure.
In reality a B40 MCB may have a trip current of around 38 amps just sufficient for a 8.5 kW shower depending on the location of the consumer and the temperature of it as well as what level of loading is on the adjoining MCBs , however on the other hand my consumer unit is mounted on a single brick exterior wall in an unheated garage and the MCBs may be barely adequate for circuit overload protection in the middle of the winter when the temperature of the devices in the consumer unit may be 5 degrees or less.
https://www.hagerelectro.com.au/files/download/0/32587_1/0/TECHINFO_MCBS.PDF