Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It only takes a minute to sign up.
Sign up to join this community
I just learned that lots of fuse in 3-pin plug of an electrical equipment are actually are blindly fitted and rarely correspond to the correct amperage rating of the electrical equipment, for example most of these fuses are rated 13A when your electrical equipment only pull 3A at most.
I'm getting these fuses replaced with ones of the correct ampere rating. What do I need to know besides ampere rating on those fuses must be equal or slightly higher than what my electrical equipments use?
The standard fuses supplied with these plugs are normally rated at the circuit capacity of the supply outlet and associated wiring. They blow when the current exceeds that of the circuit and the current rating of the plug itself and the connected wiring.
Your idea to replace these with a current reading closer to the load rating is a good idea if the plug and cord is directly attached to the appliance or fixture load. If the plug and cord is part of an "extension cord" or "outlet strip" it may be more appropriate to set the amperage reading of the fuse closer to the rating of the plug / cord / outlet strip.
For a direct attached load only a general guideline can be given for the fuse rating. Certainly the current load listed on the name plate of the device is a very good starting place. But if the load is a motor or other inductive type load the startup current surge can be much higher than the listed running current level. This needs to be taken into account for fuse selection.
A final comment is that it would always be a good idea to leave some margin between fuse rating and running current. Fuses used at their rated level or more can age and eventually fail before expected.
What do I need to know besides ampere rating on those fuses must be equal or slightly higher than what my electrical equipments use?
Nothing much. Use a BS1363 fuse.
The job of the fuse in the plug is to prevent the wire between plug and appliance from overheating (and setting your home ablaze). The size of wire (cross-sectional area of conductors) should normally suit the appliance - if the wire is a fixed cord. In which case the only thing you need to take into account is the appliance rating (if lower).
If the cord is removable at both ends, EU standards usually ensure that the type of connector used at the appliance end (e.g. IEC 60320 C7 = 2.5A) is such that any pre-made cord that fits will be made with wire that has adequate current capacity for the appliance.
In theory there exist 1, 2, 3, 5, 7, 10 and 13 Amp fuses, however only the 3 and 13 Amp sizes are mostly used. So 0.75mm to 1mm cable would usually be protected by a 3 amp fuse and 1.25 and 1.5mm cable would be protected by a 13 amp fuse.
