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Regulation 534.4.4.6

MG
Greetings to the forum.

Can someone clarify this for me. Regulation 534.4.4.6 says:
"In general, the short-circuit current rating ISCCR of an SPD, as stated by the manufacturer, shall not be lower than the maximum prospective short-circuit current at the connection points of the SPD assembly"

Then Note 1 below the regulation says:
"The SPD alone, or as an assembly in conjunction with its disconnector and/or overcurrent protective device (OCPD), is required to withstand the short-circuit current rating ISCCR as stated by the manufacturer. This value is defined and tested according to BS EN 61643-11, in conjunction with the disconnector and/or OCPD as stated by the manufacturer"


I understand that ISCCR (in kA) is a short circuit withstand capability value given by the manufacturer on the condition the maximum upstream protective device rating is not exceeded.


If the upstream SPD protective breaker/fuse has a breaking capacity higher than the system fault level, can an SPD with a ISCCR lower than the system fault level be used? I am confused because Note 1 says either the SPD alone or SPD+Disconnector as an assembly has to withstand the system fault level.


Reason for all this scenario is because I have come across an SPD with short circuit withstand capability of 25kA protected upstream by a breaker with Icu of 50kA is specified on a system with 37kA fault level.


Thanks,

M.


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  • 0
    Also, we must not forget that a B.S. 88-3 H.R.C. fuse will interrupt a short circuit current long before its maximum value is reached. The cut off effect greatly reduces both thermal and magnetic stresses on the equipment being protected. The fuse clears a short circuit fault well within the first quarter of a cycle.


    Z.
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  • 0
    Also, we must not forget that a B.S. 88-3 H.R.C. fuse will interrupt a short circuit current long before its maximum value is reached. The cut off effect greatly reduces both thermal and magnetic stresses on the equipment being protected. The fuse clears a short circuit fault well within the first quarter of a cycle.


    Z.
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