N Pin of a UK Type G Plug

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N rectangular brass pin for a UK Plug with melted insulation

Problem

The N rectangular pin of a UK type G plug (BS1363) was left stuck in the wall socket after detaching the plug.

Troubleshooting

The base and and the insulation for the N pin of a UK plug melted due to overloading. The socket looked intact without carbonization.

Solution taken

The stuck pin was extracted from the wall socket after disconnecting the circuit at the MCB.

The impact of not solving the problem

  1. The wall socket cannot be used.
  2. An exposed pin in a socket, even if it is the neutral (N), presents a potential electric shock hazard.

Unit-specific parameters

  1. Cable: 3C 1.25 mm²
  2. Cable length: 5 m
  3. Cable conductor: copper, stranded
  4. Plug material: nylon
  5. Plug current rating: 13 A
  6. Appliance power rating: 2200 W
  7. Current = I = P/V = 2200W/220V = 10 A

Notes

  1. Either the N or L pin may overheat and melt during an overload, depending on the contact resistance at the pin. In this case, the N wire detached along with the plug, leaving the N pin in the socket, which indicates a loose connection. Loose connections increase resistance, leading to localized heating.
  2. The overload occurred because the 3C 1.25 mm² cable was marginal for 10 A, and the 5 m length added excessive resistance. Cable resistance increases with length.
  3. A 3C 1.5 mm² cable at 5 m is sufficient for 10 A. However, for improved safety and longer cable lifespan, a 3C 2.5 mm² cable is recommended, provided the additional weight is acceptable.
  4. If a low-cost plug is labeled “unbreakable,” it is likely made of nylon. If it is not labeled as such, it is likely made of polycarbonate.
  5. Since the load current is 10 A, a 15 A UK round pin type M plug (BS546) is not necessary.
  6. For greater safety, use a plug made of urea formaldehyde or phenol formaldehyde.
  7. A light-colored plug made of urea formaldehyde is often referred to as a “Bakelite” plug. However, Bakelite is actually phenol formaldehyde and is typically dark-colored.
  8. Replace the socket if there is carbonization, as carbon is conductive.
  9. Stranded conductor size can also be expressed in stranding format: number of strands / strand diameter. The slash (/) does not indicate division. To determine the cross-sectional area, use the circular area formula (A = πr²). For example: 40/0.193 = 40 × π × (0.193/2)² = 1.17 mm², 70/0.193 = 2.05 mm², 110/0.193 = 3.22 mm².
  10. IEC 60228 classifies conductors by nominal cross-sectional area in mm². Stranding format is still compliant with IEC 60228 because the cross-sectional size in mm² is obtainable, albeit after calculation.

Tools used

  1. A pair of plastic pliers to flip the MCB switch.
  2. An NCV tester to ensure the socket has no electricity.
  3. A test pen to further check that the L has no electricity.
  4. A pliers type screw extractor to extract the stuck pin from the wall socket. If the jaw opening can be adjusted, adjust for comfortable hand grip.

This is problem-first learning. The knowledge was learnt because there was a problem to solve.

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