Safety before handling medium and high-voltage cable

The rule that covers everything else

Treat every cable as energised until a qualified person has proved otherwise at the point where work will happen, and has grounded it. That single rule covers almost every accident in this trade, because the failures that hurt people are almost never the ones the drawings predicted. A cable that was switched out last month can still be connected to something at the far end.

The buying desk works from this rule rather than around it. We do not ask a seller to test, cut, strip, unbolt or move cable that has not been released by its owner, and we do not treat a seller's assurance that it is dead as evidence. What we ask for is identification — tags, photographs, a manifest — and for the release to come from whoever controls the circuit.

If you are not the qualified person for that circuit, the safe contribution is to stop and report. That is not a failure of nerve; it is the correct answer, and any buyer who pressures you past it is not a buyer worth dealing with.

Isolation is not de-energisation

Opening a breaker removes the normal source. It does not remove every source. Cable can be back-fed through transformers, through a ring that is fed from the other end, through transfer switches and tie breakers, through customer-owned generation, through a battery or UPS system, or through a temporary jumper somebody forgot. Street lighting and signal circuits are notorious for being fed from a point that is not the one on the drawing.

Proper isolation is a sequence, not a switch. The circuit is identified and switched out under the owner's switching procedure, locked and tagged so that nobody can restore it while people are working, proved dead with an instrument that has been checked against a known live source before and after use, and then grounded at the point of work. Each of those steps exists because the previous one has failed for somebody. Proving dead with a tester that is itself faulty is how people die on circuits that were genuinely isolated.

For a seller, the practical consequence is that the release has to come with a name and a scope. A note saying the cable is dead is worth much less than a switching record or a release document that says which circuit, which date, and who released it. If your contact cannot produce that, the cable is not ready to be moved, whatever its condition.

Stored charge and induced voltage

Cable is a capacitor. A long length of insulated cable holds charge after it has been disconnected, and the longer and higher the voltage class, the more it holds. The charge is not large in energy but it is more than enough to injure somebody who puts a hand on a conductor that was disconnected an hour ago. Discharging and grounding are therefore part of making the cable dead, not an optional extra afterwards.

Induced voltage is the second trap, and it is the one that catches experienced people. A de-energised conductor running parallel to an energised one picks up a voltage from it, capacitively and magnetically, and a long run in a shared trench or on a shared pole line can carry a shock even though it is isolated at both ends. This is why crews ground at the point of work rather than only at the ends, and why a cable that has been proved dead can still bite when the grounding is removed.

Both problems have the same field answer: test before touch, and keep the grounding on until the work is finished. A seller who has been told the cable is dead has been told half of what matters. The other half is that it has been discharged, grounded, and that the grounding will stay in place while it is moved.

Approach distances and the people allowed inside them

Standards set minimum approach distances that grow with voltage, and they apply to any part of your body, any tool and any object you are holding. The distances are not the same for every situation — they differ between live-line work by qualified people and ordinary work near energised equipment — and they are not something to memorise from a website. What matters here is the shape of the rule: as voltage rises, the distance grows, and at transmission levels the safe distance is larger than a person's reach by a wide margin.

The practical version for anyone moving cable is to keep well outside the distance the owner's safety rules specify, to work only with people qualified for the voltage class involved, and to stop when the plan changes. Substation yards add their own hazards — live bus, live transformer leads, grading and cable trays, and vehicles moving under clearance. A forklift mast or a crane boom near overhead conductors is a hazard that has killed people who never touched anything electrical.

Personal protective equipment does not substitute for any of this. Voltage-rated gloves with leather protectors, arc-rated clothing, a face shield, insulating mats and insulated tools are the last line, chosen for the task and inspected before use, not a licence to work closer. Where the rules require a qualified person and a second person present, that is a requirement about the job, not about your confidence.

Oil, lead and what is inside older cable

The outside of a cable is not the only hazard. Paper-insulated lead-covered cable, still common in the older parts of New York's underground network, is impregnated with oil or a resin-oil compound and sheathed in lead. High-pressure fluid-filled cable goes further: it runs inside a steel pipe with oil under pressure, and the oil is a stored-energy and environmental problem as well as a fire one. Neither construction should be opened, drained or cut by anybody who is not set up for it.

Lead is a cumulative poison and a sheath is a lot of lead. Handling it with bare hands, abrading it, heating it or taking offcuts home are all avoidable exposures, and the correct approach is gloves, washing, and proper disposal rather than a workshop bin. Oil from older cable may contain polychlorinated biphenyls, which is why fluid from cable of uncertain age is tested rather than assumed clean, and why draining is a regulated activity rather than a convenience.

There is a commercial point buried in this. Cable that has been cut open and drained to make it lighter, or stripped in the yard to expose the copper, has lost value and created a waste problem at the same time. Keep it intact, keep it labelled, and let the buyer's process deal with it.

What the desk asks for instead

Everything the desk needs can be gathered without touching the conductor. Photographs of the reel, the tag, the jacket print and the cut end. A note of the voltage class and the construction. A stores record, a switching record or a release letter. A description of where the cable has been and how it has been stored since.

That is enough to start a valuation and often enough to finish one. Where it is not, the next step is a site visit by somebody qualified and insured to be there, with the owner's permission and the owner's crew present. Removal itself is done by the owner's qualified personnel, under the owner's safety rules, with the cable de-energised and released before anyone touches it. A buying desk that offers to skip that step is offering you a liability, not a service.

• Never move, cut or test cable that has not been released by the owner.
• Ask for the switching or release record, and for the name behind it.
• Keep the grounding on until the cable is where it is going.
• Report damage, leaks and unknown cable rather than improvising around them.
• Nothing in this guide replaces your employer's safety program or the standards that apply to your site.