North Clyde Line Overhead Line Upgrade

QueensCurve · 16 Jul 2026

GRALISTAIR said:
Insulators are polymeric and not ceramic like they used to be.

No doubt cheaper than the old ones and possibly just as durable but definitely less aesthetic.

RailUK Forums

59CosG95 · 17 Jul 2026

QueensCurve said:
No doubt cheaper than the old ones and possibly just as durable but definitely less aesthetic.

Perhaps, but definitely safer. To paraphrase what the late, great John Candy once said about bobsledders' bones in the event of a crash: "Always remember, your porcelain insulators will not break if they get dropped or struck by a projectile. No, no, no. They shatter."
There's a reason why you need gloves and eye protection when handling them!

That said, they are still used in specific safety cases - I think certain tunnels still use them for their superior thermal resistance in the event of a fire. Australia's had to go back to using glass insulators as the local avian (both Cacatuidaean and Psittacoidean) populace fancied polymeric insulators for a spot of lunch!

== Doublepost prevention - post automatically merged: 17 Jul 2026 ==

And to update further, here's some new equipment at Scotstounhill:
https://www.linkedin.com/posts/scot...p&rcm=ACoAAC29QcQB4BRtM6sjQemXdhgEbl9XuYQAEhI

⚡ Great to see some shiny new overhead line equipment supporting the wires at Scotstounhill in Glasgow. These wires power electric trains and carry 25kV.

It's part of our £20m project to upgrade overhead wires on the North Clyde route, boosting reliability and helping to keep our electric trains moving.

https://lnkd.in/eGj-2BwA
Network Rail | Transport Scotland | ScotRail
Activate to view larger image,

Note how the stovepipes supporting the new F+F Single Insulator Cantilevers (SICs) have been hoiked up; when it was only supporting the registration, it was much lower down below the boom. Now of course it doesn't need to be.

GRALISTAIR · 17 Jul 2026

59CosG95 said:
Perhaps, but definitely safer. To paraphrase what the late, great John Candy once said about bobsledders' bones in the event of a crash: "Always remember, your porcelain insulators will not break if they get dropped or struck by a projectile. No, no, no. They shatter.

Correct. Polymeric materials have better impact and shatter resistance than ceramics.

59CosG95 said:
--- certain tunnels still use them for their superior thermal resistance in the event of a fire.

Correct again. Ceramics have far superior heat and fire resistance to polymerics.

McRhu · 17 Jul 2026

Glass insulators replaced porcelain insulators at the infamous sea wall spot near Largs where waves often crash over the line. (I'm not sure of they in turn have been replaced by something else.) What was the advantage of glass in that scenario?

RichardAsh1981 · 19 Jul 2026

McRhu said:
Glass insulators replaced porcelain insulators at the infamous sea wall spot near Largs where waves often crash over the line. (I'm not sure of they in turn have been replaced by something else.) What was the advantage of glass in that scenario?

When porcelain insulators get wet enough, especially with conductive (salty) water, they "track" - an arc which follows the surface of the insulator. If this happens enough, it burns the surface, leaving a conductive carbonised path which makes further tracking easier, eventually leading to a permanent flashover, or mechanical failure of the insulator.

Glass is somewhat better at resisting tracking, but more importantly it doesn't burn in the same way, so regular tracking doesn't damage the insulator surface. This makes toughened glass much longer lasting than porcelain in polluted (either man-made or salt spray) locations, where they were preferred. On the down side, glass insulators shatter more readily, and into a mass of small pieces of glass.

Polymeric insulators work differently, they should force the water into droplets which run off, and so never track. If they do track, then it burns through them very quickly indeed, which can be an issue if there isn't enough rain to wash industrial pollution off (under bridges or canopies).

McRhu · 19 Jul 2026

RichardAsh1981 said:
When porcelain insulators get wet enough, especially with conductive (salty) water, they "track" - an arc which follows the surface of the insulator. If this happens enough, it burns the surface, leaving a conductive carbonised path which makes further tracking easier, eventually leading to a permanent flashover, or mechanical failure of the insulator.

Glass is somewhat better at resisting tracking, but more importantly it doesn't burn in the same way, so regular tracking doesn't damage the insulator surface. This makes toughened glass much longer lasting than porcelain in polluted (either man-made or salt spray) locations, where they were preferred. On the down side, glass insulators shatter more readily, and into a mass of small pieces of glass.

Polymeric insulators work differently, they should force the water into droplets which run off, and so never track. If they do track, then it burns through them very quickly indeed, which can be an issue if there isn't enough rain to wash industrial pollution off (under bridges or canopies).

Thanks very much for that; very informative. I had wondered about the glass insulators and liked the look and wondered why they weren't more widely used. I think the epitome of OLE aesthetic would be MKIIIa with armoured Triplex glass insulators to resist shattering, and titanium tubes for strength and to prevent corrosion.

OLEngineer · 19 Jul 2026

RichardAsh1981 said:
When porcelain insulators get wet enough, especially with conductive (salty) water, they "track" - an arc which follows the surface of the insulator. If this happens enough, it burns the surface, leaving a conductive carbonised path which makes further tracking easier, eventually leading to a permanent flashover, or mechanical failure of the insulator.

Glass is somewhat better at resisting tracking, but more importantly it doesn't burn in the same way, so regular tracking doesn't damage the insulator surface. This makes toughened glass much longer lasting than porcelain in polluted (either man-made or salt spray) locations, where they were preferred. On the down side, glass insulators shatter more readily, and into a mass of small pieces of glass.

Polymeric insulators work differently, they should force the water into droplets which run off, and so never track. If they do track, then it burns through them very quickly indeed, which can be an issue if there isn't enough rain to wash industrial pollution off (under bridges or canopies).

Just to confirm, is that what polluted area means with respect to OLE? I was creating Ellipse OLE assets on behalf of NR for the Poplars Electrification project and I remember a data dropdown asking if the area was polluted. It was asking to check if the insulators were at risk of tracking! Is this the only concern with polluted areas?

D6130 · 19 Jul 2026

McRhu said:
Glass insulators replaced porcelain insulators at the infamous sea wall spot near Largs where waves often crash over the line. (I'm not sure of they in turn have been replaced by something else.) What was the advantage of glass in that scenario?

Stevenston-Saltcoats.

McRhu · 20 Jul 2026

D6130 said:
Stevenston-Saltcoats.

That's right. The other hot-spot was a place called Craigendoran; not entirely unfamiliar to us both. I only ever recall porcelain insulators in use there and never glass, but I suppose the heavier MK1 insulators' longer creepage path saw off Poseidon's best efforts more easily than the lighter MKIII's.

RichardAsh1981 · 20 Jul 2026

OLEngineer said:
Just to confirm, is that what polluted area means with respect to OLE? I was creating Ellipse OLE assets on behalf of NR for the Poplars Electrification project and I remember a data dropdown asking if the area was polluted. It was asking to check if the insulators were at risk of tracking! Is this the only concern with polluted areas?

No idea for rail specifically, but in DNO networks it is the main one. High levels of pollution from combustion (soot and acid gases) will also increase corrosion of metallic parts - shortening the life of galvanising, paint and steelwork. But I don't believe this is usually a consideration at design time. It is an input to CNAME asset management models for OFGEM.

OLEngineer · 20 Jul 2026

RichardAsh1981 said:
No idea for rail specifically, but in DNO networks it is the main one. High levels of pollution from combustion (soot and acid gases) will also increase corrosion of metallic parts - shortening the life of galvanising, paint and steelwork. But I don't believe this is usually a consideration at design time. It is an input to CNAME asset management models for OFGEM.

Thanks Richard for the clarification, still helpful!

North Clyde Line Overhead Line Upgrade

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