Auxiliary supply within LV switchboards

Auxiliary supplies within LV switchboards, to serve a power monitoring meter, for example, are commonly taken from the main busbars via DIN or Red Spot fuses. However, the installation between the main busbars and these fuses is in no way rated for the prospective fault current. Is this practice recognised/formalised in regulations or codes of practice, somewhere? Ta!

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  • I'd suggest this is one for BS EN 61439 rather than BS 7671;  but this is not my specialty.

    At least it's fuses which likely have a reasonable fault withstand... occasionally suppliers propose MCBs on high Ipfc boards, which doesn't go down too well with me. Granted the impedance of the wiring will significantly reduce the prospective fault but I rarely see any calculations to justify that assumption.

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  • I'd suggest this is one for BS EN 61439 rather than BS 7671;  but this is not my specialty.

    At least it's fuses which likely have a reasonable fault withstand... occasionally suppliers propose MCBs on high Ipfc boards, which doesn't go down too well with me. Granted the impedance of the wiring will significantly reduce the prospective fault but I rarely see any calculations to justify that assumption.

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