13A Switch fuse spur

Hello, Does anyone know if there are regulations stating that the 13A switch fuse spur can run Continuously at is rated current for long hours? I find this intriguing because, when a spur operates at its maximum rating, it tends to overheat, but i can't find any regulation that explicitly states this isn't allowed. The only regulation i can find in the 7671 concern installation cable size, etc. I know that electricians need to take cable size into account during installation but most of them just follow the standard, without considering the 80% rule from current capacity. the issue i have is that, although it's good practice, i can't find a regulation explicity stating this. So, i'm not sure what to rely on when it comes to the regulations. Does anyone have any insights?? 

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  • The answer is not simple. I have had a look at the 2018 version of BS 1363-4.

    Ambient temperature -5ºC to +40ºC with an average not to exceed 25ºC.

    The type testing to ensure compliance uses a 20 A supply with a 14 A load on the output and a further 6 A on the input (presumably simulating a ring, or a load further along a radial). The ambient temperature is to be 20ºC ± 5ºC. A maximum temperature rise of 52ºC is permitted after a minimum of 4 hours, but there is a caveat that an FCU is designed for a maximum cable temperature of 70ºC.

    Type testing is, however, not normal use. BS 1363 states that FCUs "... shall not attain excessive temperatures in normal use." Some manufacturers exceed the minimum standards, so if you want to run a long 13 A load, I think that unless the ambient temperature is no higher than 18ºC, it would be wise to monitor the temperature, at least initially.

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  • The answer is not simple. I have had a look at the 2018 version of BS 1363-4.

    Ambient temperature -5ºC to +40ºC with an average not to exceed 25ºC.

    The type testing to ensure compliance uses a 20 A supply with a 14 A load on the output and a further 6 A on the input (presumably simulating a ring, or a load further along a radial). The ambient temperature is to be 20ºC ± 5ºC. A maximum temperature rise of 52ºC is permitted after a minimum of 4 hours, but there is a caveat that an FCU is designed for a maximum cable temperature of 70ºC.

    Type testing is, however, not normal use. BS 1363 states that FCUs "... shall not attain excessive temperatures in normal use." Some manufacturers exceed the minimum standards, so if you want to run a long 13 A load, I think that unless the ambient temperature is no higher than 18ºC, it would be wise to monitor the temperature, at least initially.

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