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60A main Fuse, should I upgrade?

Former Community Member
Former Community Member

Supplier main Fuse is 60A and current consumer unit has 80A RCD (61008) as isolator with a notice saying 'Max load not to exceed 80A". Property is one storey with 5 rooms. Currently have 8 circuits, 2 lights with B10s, 2 ring finals with B32s, Cooker with B40, Shower with B40, Water Heater with B16 & Garage feed to a sub board with C40. Want to add a new 10.5kw shower so will need 50A protective device but not sure if should be approaching the DNO for an upgrade of the main fuse as running both showers together alone will draw a decent load

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    A 60A fuse will carry 80A for hours without failure, but you knew that didn't you? See fig 3A3 in the BBB.

    You need to be a bit careful with the BS 7671 graphs - as they only show the slowest allowable disconnection times (useful for doing calculations for ADS, less so for discrimination). As all device standards allow quite a wide range of operating characteristics, if you want to be sure it won't open it's the fastest operating times you need to be looking for.

    Suitable graphs are quite rare, but most cartridge fuses have a non-operating (or non-fusing) current (in conventional time) of around 1.25x In (compared with an operating current of 1.45x or 1.5x) - so it would be quite allowable for a 60A fuse to blow within an hour at 75A, or even shorter time at higher currents - although any individual fuse might last longer.

       - Andy.

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  • 0

    A 60A fuse will carry 80A for hours without failure, but you knew that didn't you? See fig 3A3 in the BBB.

    You need to be a bit careful with the BS 7671 graphs - as they only show the slowest allowable disconnection times (useful for doing calculations for ADS, less so for discrimination). As all device standards allow quite a wide range of operating characteristics, if you want to be sure it won't open it's the fastest operating times you need to be looking for.

    Suitable graphs are quite rare, but most cartridge fuses have a non-operating (or non-fusing) current (in conventional time) of around 1.25x In (compared with an operating current of 1.45x or 1.5x) - so it would be quite allowable for a 60A fuse to blow within an hour at 75A, or even shorter time at higher currents - although any individual fuse might last longer.

       - Andy.

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