My house has a Coughtrey outside light that fits on the corner of thehouse such that the opel glass 'dome' (it points down) casts lightalong both walls.It is fed by a cable that goes through the cavity and while thebayonet connector has a blue and brown wire (house built 1976)the internal light switch, connected into the downstairslighting circuit has a pair of 1mm/sq red/black T&E cableswith the neutrals joined by a choc block. The cables wereobviously done while the house was built but after 1st/2ndfix but before the ceilings and downstairs partition wallswere done. The cable to from the light switch run inside thecavity and the feed out to the light is 1mmT&E. Thereforethere must be a joint somewhere inside the cavity somehow.I have the kitchen ceiling down so I can see where the 2red/black cables pass through holes in the inner leaf intothe cavity at the corner where the outside light.This annoys me and because the light fitting has a 20mm?metal plug close to the Y arms of the unit and underneathI was hoping to screw a 20mm gland into this socket andrun some new cable in that way.I got a pack of 20mm glands from toolstation and took the20mm plug from the light unit with me and they lookedto be an identical thread but annoyingly they wontengage with the thread in the socket on the light.How does todays 20mm electrical connectors (thinkingof metal conduit) differ from what was used in the mid 1970's ?.

Having done a quick google search, my first hit came up with these lights and a question about the thread. It appears to be 1/2" BSP as the person asking there tried a plumbing fitting in it.

When is an electrical 20mm fitting not a 20mm thread ?

Dec 01, 2021 Last reply: 4 years ago 23 Replies

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Andrew 4 years ago

Which would explain why a 20mm metric spiggot does not screw into the threaded socket on the coughtrie arm (the latter approx 19 mm).

I'll probably end up shaving off the threads on the plastic gland and hammering it into the socket, with some silicone to hold it. all I want is something to avoid metal to electric cable contact. Why are some simple tasks so difficult ?.

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Andrew 4 years ago

Just had a reply from Coughtrie in Glasgow. It is a 3/4 inch female thread, so a suitable (brass/stainless steel) adapter is needed to use a 20mm cable gland.

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Tricky Dicky 4 years ago

Andrew I have pointed you twice to exactly the type of adaptor you need.

Here it is again:

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Richard

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Andrew 4 years ago

Ugly, and I want a brass one, but will end up sticking the plastic gland in my neighbours lathe and reducing its diameter by about a mm then it can be 'persuaded' to fit the socket.

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