Twisted Flex Joints

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Twisted Flex Joints have been used to extend mains leads for a long time on electrical goods. They were even sometimes used as part of fixed house wiring in the early 20th century.

What's the problem?

Fire

'In 1999 an estimated 466 deaths were recorded in dwelling fires and compares with 519 in 1998 and 562 in 1997.' And these joins are one of the causes.

To be reliable, any electrical connection has to be gas-tight. This means that ambient oxygen must not get between the metal surfaces. If it does, the surfaces gradually oxidise, and after a while the joint resistance gets higher and higher. In other words the join starts to heat up. This causes accelerated oxidation, increasing joint resistance. This causes increased heating and the cycle goes round until it either burns away and goes open circuit or it catches fire. Shorting can also happen, causing touchable surfaces to become live, and severe overheating elsewhere.

The way to make a conection gas-tight is pressure. Wrapping it in tape, however tightly, gives nowhere near enough pressure. These joins are a fire risk.


Shock Risk

Taped twisted flex lacks any effective cordgrip, and such joints are easily pulled apart. Insulating tape offers some resistance to this, but not any great amount. Tripping on the lead is likely to pull the joint apart, fully or partly.

When a twisted joint is pulled apart, the conductors touch each other randomly. This is likely to result in sparks, fuse blowing, or L touching the appliance E wire, making the appliance case live.

Also bare live flex ends aren't a good thing to have lying around. And if when you trip the whiskers on the broken end stick in your sock, as they do tend to, electrocution is not a particularly peaceful way to die.

Fires kill many more people than shock, so shock is the lesser risk.

More

Taped joints also lack tensile strength, abrasion resistance, general robustness, spillproofness (they can make a small spill live), good insulation, petproofness & small childproofness.


Better Options

  • Replace the flex with a longer one
  • Use an extension lead
  • Use a purpose made flex connector, which conists of screw connections in a hard plastic case with a cordgrip on each side. These are less than £1 and its good to keep a spare one in the drawer. (pic) (pic) (pic)
  • Use a mini plug & socket to extend the lead, as is usually done with electric lawnmowers. (pic)

See Also

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