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Fuses for showers.

Sparkingchip
From a electric shower installation manual:


Circuit Protection Table

Circuit Protection Device


Unit Rating (@ 240V)

8.5kW

MCB 40A

Cartridge Fuse 45A


9.5kW

MCB 40/45A

Cartridge Fuse 45A


Why a 45 amp cartridge fuse for a 8.5kW shower or for that matter even the 9.5 kW shower?


I presume it must be time related as the 8.5 kW shower will only load a 40 amp fuse to around 90% of its capacity.


How long can cartridge fuses be run at 90% capacity for?


 Andy B.
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    I do not think he does mean that. Simple electric showers that are a resistive heating element will draw current in proportion to the supply voltage, so on  a low volts day, your shower will be cooler for a given flow rate.


    Only a shower with an electronic thermostat, that actually modulates the current drawn to try and  maintain a constant temperature will use less current on average when the supply  voltage is higher.

    My experience  of showers that change temperature in time with the washing machine fill cycle is that they are  constant resistance loads, and outlet temperature is set by adjusting the flow rate, as that affects the time that any given body of water is in contact with the heater.
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  • 0


    I do not think he does mean that. Simple electric showers that are a resistive heating element will draw current in proportion to the supply voltage, so on  a low volts day, your shower will be cooler for a given flow rate.


    Only a shower with an electronic thermostat, that actually modulates the current drawn to try and  maintain a constant temperature will use less current on average when the supply  voltage is higher.

    My experience  of showers that change temperature in time with the washing machine fill cycle is that they are  constant resistance loads, and outlet temperature is set by adjusting the flow rate, as that affects the time that any given body of water is in contact with the heater.
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