Insulator Collecting UK — Teleramics

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The Pot-Head

pothead insulator cross section

Key distinguishing points

  • Internally threaded
  • Single or Double wire groove
  • Screw lid fitted on top.
  • Predominately white / cream in colour
  • black composite also made
  • Used all over the country by the railways and GPO

3 Potheads..

pothead insulator pothead insulator pothead insulator

Left to Right : Taylor Tunnicliffe, (LMS) ; Black composite with BR moulded inside top and a Bullers No.16 GPO double groove, 1970

 pothead insulator top view pothead insulator top view  pothead insulator top view

Left - Taylor Tunnicliffe. Center - Black No.16 with BR(W) impressed mark. Right - Bullers No.16 in ceramic.

inside a pothead insulator

Some terminators were fitted with a fuse link to allow easy sectorisation of a line and provide protection across sections without the need for a cable to be dropped down the pole into a fuse box.

No example exists within the collection, although I am sure a example is not far away.

Update August 2006

Gene Kingsley has kindly sent me this image showing the inside of a Pothead with what appears to be a fuse holder

And 3 lids -

insulator lid insulator lid insulator lid

Left - 'E'. Center - British Rail (Western Region). Right - General Post Office

See the acronym page for a breakdown of these manufacturer codes as used by the GPO

Other marked composite caps within the collection include:

Standard Height, Side Castellated design
Medium Height, Side Castellated design
Standard Height, Ridged and flat
Standard Height, Domed

A Large TTC terminator ?

A large Taylor Tunnicliffe example has come to light, stamped 'Patent No. 295?-01 Reg No. 563022-520335. This unit is incomplete but certain dimensions can be ascertained. The Diameter is 79mm and made with a 5/8" thread. A large cap is also needed as the thread diameter has increased by 5mm to 65mm. If the height were to increased by the same ratio, we could expect it to be approximately 116mm high.

pothead insulator top view pothead insulator top view

Standard TTC top view and larger TTC top view with patent number on rim.

A Taylor Tunnicliff Trio

This image capture the relative size of 3 variants of the pothead made by Taylor Tunnicliff. The right hand example is what I would call the 'Standard' size, the left hand is a tad larger and the middle, broken Pothead is larger again, the very example I have just mentioned in the previous segment.

Pothead insulator
Taylor Tunnicliff Cross Section
Pothead insulator

This cross section of a TTC standard size Pothead clearly illustrates the wire access holes, lack of inner shed and wire joining space.

The Pothead has actually broken slightly off centre across the wire access holes, the weakest point.

It is easier to imagine the method of wire fixing with this piece. The incoming wire is tied off around the single wire groove and is dropped down under the outer shed and up through one of the access holes. Here it terminates by joining the outlet wire which has been fed from the appliance being connected up through the other access hole. The join is then covered in a waterproofing mixture, (tar I believe) and the lid screwed on the top.

A fraction of the spindle thread can be seen dead centre along with the screw cap threads top left and top right

Very Large Bullers No.16

pothead insulator

This Bullers variation of the double grooved pothead is considerably larger in diameter than a conventional No.16 and probably has its own designated number. A faint bullers logo is visible on the front along with P.8411, most likely a pattern number.

pothead insulator top view pothead insulator top view

As can be seen from these two top views, this insulator is a good bit larger, diametrically, than the standard No.16

Hole spacing, internal depth, thread pitch and pin size seems to remain unchanged, it's just larger!

pothead insulator

This large pothead, recovered from The Newcastle to Carlisle line is clearly stamped LNER on the front and has the Bullers logo dated 1939 on the rear.

It's looks identical to the P8411 except the threaded section is slightly smaller in diameter and as a consequence the black composite lid that came with it will not fit the P8411, very odd!

There are other minor variations, the P8411 has sharper curves in particular steeper more angular returns on the sheds, suggesting to me the P8411 is older than the LNER 1939


Hmmm, I have 5 large Terminators, P8411 (undated), LNER 1935, LNER 1937, LNER 1939, LNER 194? MADE IN ENGLAND and 2 lids. One lid fits the LNER 1935, 1939 and LNER 194? MADE IN ENGLAND examples but not the LNER 1937 and P8411 (undated). The other lid must be a tad larger as it fits all. Closer examination of the thread reveals there to be 2 sizes. The LNER 1937 and P8411 (undated) measure 68.5mm maximum diameter whereas the LNER 1935, 1939 and LNER 194? MADE IN ENGLAND measure 67.5mm maximum diameter.

Latest find

insulator fragment

This appears to be a fragment of a normal pothead insulator except it is not. The most obvious difference is the large wire groove across the top and a thin rounded ridge below the threads.

Normally the lid would seat down upon a flat ridge and form crude seal but in this instance the thin ridge appears to be a wire groove ridge and maybe the lid was more of an overall cover.

Pothead lid

This superb pothead screw lid was recovered by Tris Horton early in 2005. It's obviously of LMS origin and is unusual in having the date impressed as well, 1925. A clear Taylor Tunnicliff logo proclaims its supplier.