If you are purchasing fuses online, we recommend only using a reputable supplier such as RS Components or Farnell. Both of these companies are able to provide data sheets and compliance documentation for the products they sell. Identifying counterfeit electrical equipment is becoming an important part of the inspection process and is something that we cover in our courses. Counterfeit BS1362 Fuse Testing I was able to rustle up a short length of 2.5mm cable off the end of a reel, and the use of another car battery from an alarm engineer.

The length of the fuse measures 24.91mm. A BS1362 fuse should have a length of 25.4mm with a tolerance of +0.8/-0.4mm. I'd never have dared to do anything like that - 2.5mm is for 16 amps innit ?” well maybe under some condition, not sure what alarm chaps get taught about installation methods and de-rating..Where I'm getting turned around. The current (I2) causing effective operation of the protective device does not exceed 1.45 times the lowest of the current carrying capacities (Iz) of the conductors of the circuit. Well a 13 A fuse will carry 13A all day, and may not blow in any sensible time even at 20-25A, depending on manufacturing tolerances and environmental temperatures. A few months ago I found myself with mapj1 junior in the car at a remote place with a defective battery. The jump leads were in Mrs mapj1s car at the time. Then it began to rain. That sort of day.

The rated current or current setting of the protective device (In) is not less than the design current of the circuit andThe rated current may be any value not exceeding 13A. For use in plugs, the preferred rated currents are 3 A and 13 A." In reality only AWE or CERN will install a cable in vacuum like that, and of course any real cable will heat quite a lot more slowly. Unfortunately this proves how difficult it is to tell the difference between counterfeit and genuine BS1362 fuses. The ASTA, BSI or Nemko approved symbols do not prove authenticity. At the beginning, 100% of the heat generated in the live conductors is available to heat the cable. At 21 deg C, only 98% of the heat is available because the loss is 1/50 of the amount at the steady state. At 22 deg C, only 96% is available and so on. So looking at 1 deg C increments, it takes in fact 45 min to get to 69 deg C and you never quite get to 70 deg C. Please forgive me for having forgotten the calculus which I learned 45 years ago. NOTE 2: Protection in accordance with this regulation may not provide protection in all cases, for example, where sustained

The fuses have the ASTA approval symbol and appear to be branded 'CF' and marked AF63. (A BS1362 fuse must have the manufacturer's name or identifying mark.) They also have a number printed on them: SS157.So there we are, a 2.5 sqmm cable loaded at 20 A will take over 45 minutes to get up to 70 deg C from 20 deg C enclosed in conduit in an insulated wall. Any smaller loading or less lagging and it will never get there because the heat generated in the conductors will always be less than the available heat loss.

I appreciate that there will be manufacturers tolerances both for the device and the cable (which could go both ways) and that there is undoubtedly going to be some headroom in the cable. I've seen a plumber leave a 9.0kW electric boiler on a bit of 1.5 flex before and yeah (prior to me fixing it) it was pretty hot after a few hours but it hadn't melted! Is the answer just that we're only talking about an extra amp in the example and whilst it may get a bit hotter than would be ideal this isn't the end of the world or are we into the realms of trying to work out how much heat is being dissipated during the fault by the flex as it is going to be happening over quite a prolonged timeframe? It may not be immediately apparent, but a 13A rated fuse is not designed to actually blow at 13A. In fact, a 13A fuse will allow a current of 20A to pass indefinitely without blowing. If we look at the graph in Fig 1, it shows the operating characteristics for both 3A and 13A BS 1362 fuses. The grey shaded area is the point where the fuse is designed to operate. So for example, a 13A fuse will blow within 0.01 - 0.3 seconds for a fault current of 100A; shown in red on the graph. For a current of 20A, shown in blue on the graph, a 13A fuse will not blow! Why does a 13A rated fuse not blow at 13A? Part 2: Overcurrent: A current exceeding the rated value. For conductors the rated value is the current carrying capacity. iii) the current (I2) causing effective operation of the protective device does not exceed 1.45 times the lowest of The length of the fuse is too short. A plug top fuse should have a length of between 25.0 - 26.2 mm. The diameter of the of the end cap measures 6.05mm and does not meet BS 1362 either. It should be 6.25 - 6.5 mmThe 3A and 5A fuses also have larger than normal dimples on the caps. A requirement of BS1362 is that "The end surfaces shall be substantially flat". There is no evidence of a trapped fuse wire, although the large dimples indicate that these could also be fake. I find it quite common to see 13A 1362 fuses inline on 32A cooker circuits protecting 1.5mm2 flexes to ovens. Is this deemed acceptable even though the oven isn't strictly speaking a fixed load (fan motor etc.)? Now I did not quite use Chris's figure of 3 mins at 20 A, but if I had it would have scaled to 3mins/100 at 200A, or about 2 seconds for a 40 degree rise. I had a more optimistic figure, allowing a bit for the PVC, and as I did not have the regs with me, so used a pidooma figure from memory. The shiny metal end caps are also a good indicator that the fuse is not genuine. The end cap on the genuine Cooper Bussmann fuse is not as shiny. This fake fuse also has a larger than normal dimple in the end of the cap.