Rewirable Plug With ISOD (Non-Compliant With BS 1363)

From time to time we come across plug designs that look convincing but don’t comply with the BS 1363 requirements for 13 A plugs. The example in Fig.1 is a rewirable plug fitted with an insulated shutter opening device (ISOD). Under BS 1363-1, plugs fitted with an ISOD must be non-rewirable, so this design should be treated as non-compliant and failed on formal visual inspection during PAT testing.

What is an ISOD and why is it restricted?

An Insulated Shutter Opening Device (ISOD) is a plastic replacement for the earth pin found on some non-rewirable plugs. Its purpose is to open the shutters in a UK socket outlet without providing an electrical earth connection. ISODs are found on some Class II (double insulated) appliances, where no protective earth is required.

Under BS 1363-1, a plug fitted with an ISOD must be of a non-rewirable (moulded) type. The reason is safety: a rewirable plug could be removed and reused on another appliance. If that appliance were Class I equipment requiring a protective earth connection, the ISOD would not provide an earth path. The equipment would appear to be correctly plugged in, but would not be earthed.

For this reason, ISODs are restricted to moulded plugs supplied permanently attached to suitable Class II equipment. A rewirable plug incorporating an ISOD does not comply with BS 1363-1.

Why this is a warning sign

Finding a rewirable plug with an ISOD is often not an isolated design error. It can be a sign that the manufacturer has ignored other safety requirements such as fuse compliance, insulation distances, terminal design, cord anchorage, or the quality of the flexible cable conductors. For this reason, the plug should be viewed as a warning indicator of potential wider non-compliance of the appliance itself.

What to do during PAT testing

• Fail the item on visual inspection and record the reason (e.g. “Rewirable plug fitted with ISOD. Non-compliant with BS 1363”).
• Remove from service pending further investigation. In many cases the safest option is to replace the complete appliance with a compliant product from a reputable supplier.
• Do not assume that replacing the plug makes the appliance safe. This type of plug is often found on low-cost or counterfeit equipment that may have additional compliance issues.
• Check other similar items purchased from the same source, particularly low-cost marketplace listings.

See also our guide to visual inspection and our page of real examples: counterfeit and dangerous electrical equipment.

Below are two other examples of non-compliant and unsafe plug designs we’ve found during PAT inspection. These are the sort of issues that can often be spotted quickly during a careful visual inspection.

Frequently asked questions