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Fuses for showers.

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.

0 mapj1 over 5 years ago

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 geoffsd over 5 years ago

Shower rating label.
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0 Chris Pearson over 5 years ago

mapj1:

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.

Or in simple plumbing terms, if Mrs P runs a bath, the "voltage" of the hot water supply falls, but the "resistance" being constant, the flow falls and I get a cold shower. That's without any electrics. ??
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0 Sparkingchip over 5 years ago

Manufacturer's instructions.

Andy B.
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Fuses for showers.

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