The first question most buyers ask about a portable earthing set — "what voltage is it?" — is the one the product standard does not answer. Under IEC 61230 the withstand capability is rated as current, time and peak factor, and voltage enters only through the insulating component and the geometry.
A portable earthing set is bought to do one thing: hold the worksite at earth potential, and survive the current that flows if the circuit is energised while the crew is still on it. Most enquiries we receive open with a different question — *what voltage is the set?* — and that is the one question the product standard does not answer.
The standard gives no rated voltage
IEC 61230:2008 is the second edition of the standard for portable equipment for earthing or earthing and short-circuiting. It was prepared by IEC technical committee TC 78 (Live working) and published in July 2008; it cancels and replaces the first edition of 1993.
Its scope is wider than most buyers assume. It applies to portable equipment, with or without matching connection points, for temporary earthing or earthing and short-circuiting of electrically isolated or de-energised installations and networks — overhead or underground, low or high voltage, a.c. and d.c. The equipment itself comprises the earthing or short-circuiting device and an insulating component.
Now the paragraph that decides how the product is bought:
The performance of equipment, devices and components covered by this standard is based on electro-dynamic and electro-thermal effects acting during short-circuit. The withstand capability of the devices and equipment is expressed by their rated values of current, time and peak factor. No rated voltage is given, but the geometrical dimensions of the equipment are also linked to the voltage of the installation.
Read that last sentence again, because it is the whole problem in one line. There is no "35 kV earthing set" in the sense most buyers picture. The set is rated by how much current it can carry, for how long, and with what peak — and the system voltage does not appear in the rating at all.
What the rating actually consists of
Three numbers define a portable earthing set, and each of them comes from the installation rather than from a catalogue:
- Rated current. How much current the set can carry without being damaged — in practice, the prospective short-circuit current at the worksite. A set located close to a large transformer sees a very different figure from one at the far end of a feeder.
- Rated time. How long it has to carry that current: the clearing time of the upstream protection. This is what makes the difference between a set that survives and one that anneals or fuses.
- Peak factor. The asymmetry of the first cycles. The electro-dynamic force on conductors and clamps is driven by the peak, not by the r.m.s. value, which is why the peak factor is a rated value in its own right.
The thermal duty (current × time) and the mechanical duty (peak) are separate verification questions. A set that satisfies one and not the other is a set that fails at the moment it is needed.
Where voltage does enter the specification
Voltage is not absent from the standard — it is simply not the rating. It enters in two places:
- 1The insulating component. The equipment includes an insulating element, and its electrical requirements come from a separate standard rather than from the current rating. This is the part that lets the set be applied to, and removed from, the conductor safely.
- 2Geometry. As the scope states, the geometrical dimensions of the equipment are linked to the voltage of the installation. The insulation distance on a clamp or bar for a 110 kV station is not the same as for a 10 kV board, even when the fault duty is comparable.
So "what voltage?" remains a legitimate question — for the insulating element and the physical arrangement. It is simply not the answer to "how strong is this set?".
What Edition 2 changed, and why it matters to a buyer
The 2008 edition is a technical revision with several changes that affect procurement:
- The scope was extended to cover d.c. installations, not only a.c.
- The use of aluminium was extended to all conductive parts of the device. The standard applies to equipment using copper cables, copper bars or aluminium bars as the earthing and short-circuiting medium — those are the only permitted media.
- It became possible to apply the standard to separate components of the equipment rather than only to a complete assembly.
- Requirements and tests were revised, and two annexes were added: an informative annex giving guidelines for determining the equivalent r.m.s. value of a short-circuit current, and a normative annex on the classification of defects.
Two consequences for a buyer. First, a d.c. installation is now inside the standard's scope, so a supplier claiming the standard covers only a.c. systems is out of date. Second, because components can be verified separately, it is legitimate to buy and document a set as a device plus its insulating element rather than demanding a single type test of the assembly — provided the documentation says which is which.
The cable in a set is not an anonymous item either: portable earthing and short-circuiting cables are covered by their own standard, IEC 61138, separate from the device standard. Conformity assessment for live-working equipment sits with IEC 61318, and the general requirements for how live-working devices are to be used are in IEC 61477.
The specification line that can actually be checked
| Field on the enquiry | Where the value comes from | Why it cannot be defaulted |
|---|---|---|
| Prospective short-circuit current at the worksite | The fault level at that point of the network | Varies between substations on the same network |
| Clearing time of the upstream protection | The protection scheme serving that circuit | Determines the thermal duty with the current |
| Peak factor / asymmetry | System and point of the fault | Drives the electro-dynamic force on clamps and conductors |
| Installation voltage | The installation | Sets the insulating component and the geometry, not the current rating |
| Conductor medium | Fixed by the standard: copper cable, copper bar or aluminium bar | A set outside these media is outside the standard |
| Conductor cross-section and clamp geometry | The conductor and earthing arrangement in place at the site | The most common cause of a set that does not fit |
| Complete device or separate components | How you intend to document it | Changes what the type test covers |
Every row except the conductor medium is a site fact. That is why a useful quotation request reads like a network description, not like a catalogue number.
The routine failure is the fitting, not the cable
In our experience the set that causes trouble is rarely the one with the wrong conductor. It is the one whose clamps do not fit what is actually at the substation: a conductor geometry the jaw cannot close on, a bar too wide or too narrow, an earthing point that has been modified since the set was bought.
None of these are visible on an inspection sheet. They become visible at the moment the set is applied, which is the worst possible time to discover them. This is why we ask for the clamp arrangement in use rather than only the system voltage, and why a non-standard clamp or a specific conductor length is a drawing question for a manufacturer rather than a sourcing problem for a trader.
The same logic applies to the other conductor-side items in a worksite package — grounding conductors, cable lugs and the earth rods a set is finally connected to.
Frequently asked questions
Is a 110 kV earthing set rated at 110 kV?
No — 110 kV describes the installation, not the equipment's rating. Under IEC 61230 the withstand capability is expressed as rated current, time and peak factor, and no rated voltage is given. The 110 kV figure sets the insulating component and the geometry of the set. See the IEC 61230 110 kV portable grounding kit for how one such set is specified.
Can one set be used across a whole network?
Only if the fault current and clearing time are the same at every location, which is rarely true. A set selected for a station close to generation is over-specified at the end of a feeder, and a set selected at the feeder may be under-specified at the station. Sets are quoted per worksite duty.
Does the standard cover d.c. installations?
Yes. The extension to d.c. installations is one of the specific changes introduced by the 2008 second edition.
What documentation should come with a portable earthing set?
The equipment is rated by current, time and peak factor, so that is what the documentation has to state. Ask for the rated values the set is verified against, which standard the cable was made to, and — where the set is supplied as a device plus insulating element — which components the verification covers. In our case the test documentation for the set is supplied with the order.
Specifying a set for a specific worksite
Send us the prospective fault current, the clearing time of the protection, the conductor and earthing arrangement at the point of work, and the installation voltage. We will confirm the conductor cross-section, the clamps and the insulating component against that duty, and return the rated values for the set quoted.
Browse the full range of portable earthing and grounding equipment, including the 110 kV / 220 kV three-phase portable grounding device and the 27.5 kV railway catenary grounding set. If your work is on live-line tooling rather than earthing, the companion guide is how insulating matting is selected by class and thickness.
Need this confirmed against your own installation?
Send us the network voltage, the standard you are specifying against and the ambient conditions. Our engineers will confirm the class, thickness and test report, and reply with lead time.
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