John, Regarding your comment:
"Aren't you trying to conform to IEC 60950? If so, the code that I posted is what is required. I am surprised that clause 1.7.6 is so vague, when the corresponding clause in IEC 60065 is very explicit that the code specified in IEC 60127 shall be used" There are plenty of fuse standards other than IEC 60127 and unfortunately there is little or no commonality in marking requirements between them. Also, the upper limit of 6.3A for IEC 60127 fuses is far too limiting for certain types of IT equipment (some telecomms equipment use DC rated fuses in the hundreds of amps range, for example). To make matters worse, it is possible to get fuses that are both 5x20mm and 6.3x32mm that are approved to UL 198G rather than IEC 60127 and these fuses are 'normal blow' or 'slow-blow' rather than 'F' or 'T' (or even 'M') and the calibration points are different such that replacing a T3A IEC rated fuse with a 3A Slow-blow UL rated fuse could lead to unexpected safety problems. [It is also possible to get dual-approved fuses.] Another characteristic that is seemingly significantly different is the prospective fault current. As an example, the Littlefuse 239 series of 5x20mm slow-blow fuse is approved only to UL/CSA/METI requirements and a 3.15A rated fuse is stated as having an 'interrupting rating' of 10 kA @ 125Vac and 100 A @ 250Vac. The 218 series of 5x20mm T fuses is designed to meet IEC 60127 and has both European and North American approvals, the corresponding 'interrupting rating' for a 3.15A rated fuse is 31.5A @ 250Vac. Having spoken to fuse manufacturers in the past, I am told that these seemingly very different interrupting ratings between two fuses that are visually very similar (both glass, no sand filling etc.) has to do with the different test criteria contained within the UL vs. IEC standards. I can see only problems in a product standard requiring a marking that is different to that of the fuse standard. If an equipment manufacturer selects a fuse that is, for example, designed to a UL standard and the fuse is marked (for instance) "3A slow-blow" then having a marking on the product that says "T3A/250V" is no help whatsoever to the consumer or service person. Of course, if the product standard were to say that all replaceable fuses must be of the IEC 60127 type then that would be consistent, but very limiting. Therefore, IEC 60950-1 is not vague in the sense that it lacks precision where such is required. It is, however, flexible enough to cope with the fact that not all fuses are the same. Of course, come the advent of the hazard based standard that will replace and supersede both IEC 60950-1 and IEC 60065 we will all be able to fit square pegs into round holes and vice-versa ;-) Best regards, Richard Hughes Safety Answers Ltd.
