Home20A Fuse for 13A Plug
Following on from our previous article on counterfeit plug fuses, we were recently made aware of 20A plug top fuses being sold on Ebay. These fuses do not comply with BS 1362 and represent another example of the counterfeit and unsafe electrical accessories increasingly encountered during inspection and PAT testing.
“The rated current may be any value not exceeding 13A. For use in plugs, the preferred rated currents are 3 A and 13 A."
BS 1362 also specifies the information that should be on the fuse and also the colour.
Each fuse link shall be clearly and indelibly marked with the following:
1) the manufacturer’s name or identifying mark,
2) the number of this British Standard, i.e. BS 1362,
3) the rated current in amperes.
The fuse link barrel shall be marked in red for 3 A and brown for 13 A; for all other ratings the marking shall be black.
The 20A fuses we purchased are marked with ‘BS 1362’ and have the manufacturer's name 'Xingguang’. They are also marked red, which should be used only for 3A fuses. They do not have any approval marks, such as ASTA, Nemko, or a BSI Kitemark.
The manufacturing standard of these fuses is particularly poor. The fuse wire is simply trapped between the end cap and body. A genuine BS1362 fuse has the internal wire connected to an eyelet inside the centre of the cap.
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 mm.
Surprisingly the fuse does contain the sand filling required, most counterfeit fuses do not have any filling. The sand is required to control the breaking operation of the fuse. Without this filling material, the air within the fuse expands as the fuse wire melts and arcs, causing the fuse to explode, as demonstrated in our previous article on fake fuses.
The fuse wire is a flat tape rather than round wire. In comparison with a 13A fuse wire, it’s considerably larger. Although we haven’t measured the actual fusing current, the significantly greater cross-section and thermal mass of the tape element suggest that it would operate only at a current substantially exceeding the stated 20 A, providing very limited protection. Our article on plug fuse operation characteristics explains how fuse size and construction affect operating time and protection.
Identifying substandard electrical equipment is an essential part of the inspection process and is something that we cover on our PAT testing courses. British wiring regulations permit ring circuits protected by a 30A fuse or 32A circuit breaker, which makes the plug fuse critical for protecting the appliance flex.
A standard 13A plug (BS 1363) is designed to fit cables up to a maximum of 1.5mm2. The maximum current capacity of a 1.5mm2 cable is approximately 15A and must be protected by a fuse rated no higher than 13A. Using an overrated fuse removes this protection and creates a serious fire risk. See our guide on selecting the correct fuse rating for further guidance.
This type of non-compliant fuse should be treated as unsafe and replaced immediately. If newly purchased equipment contains a 20A fuse, this is a strong indication that the equipment or plug itself may be counterfeit or substandard. The appliance should be inspected carefully before replacing the fuse. Further examples of dangerous and counterfeit accessories can be found in our counterfeit electrical equipment guide.
Frequently Asked Questions
Are 20A plug fuses legal in the UK?
No. BS 1362, the British Standard for plug fuses, permits fuse ratings up to a maximum of 13A for use in BS 1363 plugs. Any fuse rated above 13A is non-compliant and should not be used in a standard 13A plug.
Why are plug fuses limited to 13A?
The plug fuse is designed to protect the flexible cable connected to the appliance. Most appliance cables fitted to BS 1363 plugs have a maximum current capacity of around 13–15A. Using a larger fuse may allow excessive current to flow without disconnecting the supply, causing the cable to overheat and potentially start a fire.
What happens if an overrated fuse is fitted?
An overrated fuse may fail to operate during an overload or fault condition. This removes the protection provided by the fuse and can result in overheating of the cable, damage to the appliance, or fire.
How can you identify a counterfeit or non-compliant fuse?
Genuine BS 1362 fuses should be marked with the manufacturer’s name, the BS 1362 standard number, the current rating, and an approval mark such as ASTA, BSI, or Nemko. Counterfeit or non-compliant fuses often have incorrect markings, no approval mark, poor construction, or unusual ratings such as 20A.
How do you select the correct fuse rating for an appliance?
The fuse rating must be chosen to protect the flexible cable connected to the appliance. Most appliances require either a 3A or 13A fuse, depending on their power rating and cable size. Using an overrated fuse may allow dangerous overheating to occur without disconnecting the supply. See our guide on selecting the correct fuse rating for detailed guidance.
What should you do if a 20A fuse is found during PAT testing?
The fuse should be replaced immediately with a correctly rated and approved fuse. The presence of a 20A fuse should also raise concerns about the quality and safety of the equipment itself, and further inspection may be required before returning it to service.