Covered, covered and covered

Covered conductor is not a line cover — and a line cover is not insulation

A 300 sq.mm bare conductor is 22 mm across the strands, takes a GOC 2 cover, and stays at full phase voltage under it.

The covers themselves, by conductor size

Neither one is safe to touch

A retrofit line cover is insulation enhancement against momentary contact. It does not make an energised conductor safe to touch. Factory-covered conductor does not either. Both are worked as live conductors, under the same isolation, proving and earthing you would apply to bare metal, and nothing described below changes one step of that procedure. The manufacturer publishes this range as Insulation Enhancement Products; no part in it carries a rating for contact by a person, because no such rating was ever sought for it.

Three different purchases answer to the word "covered"

The search term hides the decision. When an asset engineer types covered conductor they may be pricing any of three things, and the three differ in what comes down, what goes up, and who is on the pole.

Factory-covered conductor arrives as wire. The covering is extruded over the conductor at the wire mill and the conductor is bought covered, so putting it on an existing feeder means restringing that feeder. It carries its own product standard — EN 50397-1 covers covered conductors for overhead lines above 1 kV and not exceeding 36 kV — and its own family of accessories, which is why covered conductor accessories is a different enquiry from anything on this page.

A retrofit cover arrives as material by the metre. The wrap-around polyolefin cover (Insulcover) is supplied on 30 metre rolls in five sizes, from GOC 1 at 10 mm across up to GOC 4 at 38 mm and 800 sq.mm. The silicone cover (GSOC) is supplied on 15 metre rolls in four voltage classes — GSOC-M to 12 kV, GSOC-H and GSOC-H3 to 36 kV, GSOC-EH to 765 kV. Nothing is restrung. The conductor stays where it is and the cover goes over it, so the unit being bought is metres of exposure, not a span.

Fully insulated cable is a third thing entirely. Aerial bundled cable is a cable: insulated cores hung as a bundle, rated and tested to a cable standard, terminated with cable accessories, and needing its own pole hardware. It is the only one of the three whose covering does the whole insulating job, and it is still installed and maintained dead.

The same three, set against the questions that decide between them

Read the middle column first. It is the only one that can be done to a line that is already up.

Question	Factory-covered conductor	Retrofit line cover	Insulated cable (ABC)
What is delivered	Conductor with the covering already on it, on a drum	Cover material on rolls — 30 m/roll polyolefin, 15 m/roll silicone	A complete insulated cable on a drum
What happens to the existing line	It comes down and is restrung	It stays up; the cover is fitted over the conductor in place	It comes down, and pole hardware usually changes with it
How much of the route is treated	Every metre of what was ordered	Only the metres carrying the risk — one jumper, one crossarm, one tree-side length	The whole route
Sized on	The design, at the point the line is built or rebuilt	Conductor diameter: 10, 15, 22, 28 and 38 mm across the GOC chart	The design, at the point the line is built or rebuilt
Voltage stated	By the covered-conductor specification the utility buys against	GSOC-M 12 kV, GSOC-H/H3 36 kV, GSOC-EH 765 kV; the polyolefin cover is published at 66 kV on one manufacturer page and 400 kV on another	By the cable's own rating
Effect on conductor rating	Set by the covered product's own rating table	The silicone cover is published as not requiring further derating of the conductor	Set by the cable's own rating table
What it is designed to stop	Bridging along the whole strung route	Momentary bridging by branches, birds and wind-blown debris at the metres fitted	Contact with the conductor at any point on the route
Safe to touch while energised	No	No	No

What the published test regime is actually testing

The retrofit cover is designed against a bridge: a branch laid across two phases in a storm, a bird whose wingspan exceeds the phase-to-earth gap, a jumper swinging near a crossarm. Momentary events, at the few metres where the geometry is tight. The numbers on the datasheet describe exactly that duty and nothing wider — no tracking, erosion or flame failure up to 3.25 kV for 20 min (ASTM D2303); dielectric strength 20 kV/mm min. (ASTM D149); continuous temperature limit −45 to +105 °C (IEC 216); no colour change after 5000 hours of ultraviolet exposure (ASTM G154); tensile strength 9 N/mm² min. and ultimate elongation 250% min. (ASTM D638) on the wrap-around polyolefin.

Every one of those is a material property measured on a specimen. None is a fault-current test. None is a contact test with a person at the other end of it. A cover that passes all of them will still be at line potential on its inner face for its whole service life, and the outer face is not guaranteed to be at anything in particular once it is wet, salted or dusted.

Derating is the question the retrofit answers best, and it is the one the T&D engineer asks second. The silicone cover is published as not requiring further derating of the conductor it is fitted over — the wall is thin, at 2.0 mm on GSOC-M, 2.7 mm on GSOC-H, 3.0 mm on GSOC-H3 and 5.0 mm on GSOC-EH, and it is applied to selected metres rather than to the whole thermal length. On a feeder with no headroom left, that published line is the sentence to lift into the specification and have confirmed in writing before an order is raised.

Why the retrofit is usually what gets bought

Not because it insulates better. It does not. It wins on what does not have to happen.

No conductor replacement and no added line hardware. The conductor, poles, insulators and fittings all stay in service, so the work is an access job rather than a rebuild.
The treated length is chosen, not inherited. A recurring fault at one crossarm consumes a few metres off a roll; restringing consumes the span either side of it as well.
Two fitting methods, and they decide the crew. The polyolefin cover is installed with the Split Insulation Tube Tool, which stays at one stationary location for the fit. The silicone cover self-locks and field-installs with no special tool. Compare that before comparing the materials — polyolefin or silicone turns on it.
Stock sizes, not made-to-measure. Five polyolefin sizes cover 99 to 800 sq.mm; the silicone chart runs 15 mm to 38 mm across four voltage classes. Match the conductor on the size chart before naming a part code.
One caveat worth pricing in. The manufacturer's two pages for the polyolefin cover state different voltage ceilings — 66 kV on the Insulation Enhancement Products page, 400 kV on the Polyolefin Overhead Line Cover page. Ask for the figure that applies to your class in writing rather than taking the higher one.

What a retrofit line cover does not do

A line cover is not an insulated conductor. It does not carry a touch rating. It does not clear or survive a sustained fault — the published electrical figures stop at 3.25 kV for 20 min on a specimen (ASTM D2303). It does not protect a single metre beyond where the crew fitted it, so it is not a substitute for vegetation management across the rest of the span. And it is not a reason to reduce a working clearance, shorten an approach distance or leave a line energised for work that would otherwise be done dead. A covered line is worked as a live line.

The questions this page exists to answer

If the line is covered, is it safe to touch?

No. One of the searches that reaches this page is a full sentence rather than a phrase: "some overhead power lines have a protective covering that protects them from exposure to the elements. however, the covering does not protect workers from electrocution. if you touch a power line, covered or bare, death is probable." That is accurate as written. It is repeated here verbatim because it deserves confirming, not softening, and it applies equally to factory-covered wire and to a cover fitted last week.

Is a retrofit cover the same product as covered conductor?

No, and they are not bought by the same person or from the same budget. Covered conductor is bought by whoever specifies the line and installed by restringing it. A retrofit cover is bought by whoever owns the outage record and installed over a conductor already in the air. Only the second one can be applied to a fault that has already happened three times at the same pole.

What is a tubular covered conductor?

In this range it is the Overhead Line Tube: a medium-voltage line cover in non-tracking polyolefin supplied as a tube rather than as a wrap-around section, for the same duty of keeping trees and wildlife off a distribution conductor. Its published values differ from the wrap-around and are worth checking against the right sheet — tensile strength 10 N/mm² min. and ultimate elongation 350% min. (ASTM D638), hardness 30 ± 5 Shore D (ASTM D2240), dielectric strength 20 kV/mm min. (ASTM D149), volume resistivity 1 × 10¹⁴ ohm.cm min. (ASTM D257).

What is the purpose of additional covering over the insulation of an already-insulated conductor?

It is not adding a voltage class, because the cable already has one and the added layer is not qualified with it. The extra covering is doing mechanical, ultraviolet, chemical or wildlife duty at a place where the cable or its termination is exposed — and at a termination the part that does that job is a boot or a shroud sized on the interface, not a line cover sized on a conductor diameter.

How many metres should be ordered?

Measure the exposure, not the span: the length of jumper near a crossarm, the length of conductor within reach of a limb, the length passing an animal route into a substation. Then round to the roll — 30 metres on the polyolefin cover, 15 metres on the silicone. Ordering by span length is how covers end up fitted where nothing was ever going to touch them.

Does fitting covers let the crew work closer to the conductor?

No. Nothing described here is qualified as protection for a worker, and treating a fitted cover as one inverts what it is for. It exists so that a branch, a bird or a rodent cannot bridge a gap that a person should not be in either.

Once the retrofit is the decision

Four steps, in the order a line crew hits them.

Send the conductor and the metres, not the span

Conductor size in sq.mm and in mm across the strands, the phase voltage, the metres genuinely at risk, and whether the feeder can be taken out for the work. Those four decide the code, the material and the fitting method in one reply.

What to put in the enquiry Check the size chart first