Once - with the DNO`s (unwritten) consent. Same as main fuse replacement - one client is loaded very close ( i.e. over) their 100A/phase supply - the DNO don`t know what the supply cable is; cos its that old - so they won`t upgrade the main fuses. From their side, only option is cable replacement ( underground, to middle of commercial premises = expense & disruption). Client is leasing the building - so doesn`t want to pay £X,000 for someone else`s benefit. So DNO give me "spare" fuses, rather than have records of frequent calls to replace blown fuses - which will incur charges to the client. The only caveat I have is that I must not leave the fuses on site.......