Cable Sizing and Current Rating to IEC 60287

Steady state current rating is the calculation that usually sets the conductor size, and it is the one most sensitive to the things a catalogue table cannot know: how deep the cable is, what the ground is made of, what else is in the trench, and how hard the circuit actually runs. We solve it to IEC 60287 for the installation as designed, and report the size that passes with the margin stated rather than implied.

When You Need It

  • · A connection design needs a conductor size justified to the DNO or the client
  • · A manufacturer or contractor has sized a cable and you want it independently verified before it is ordered
  • · An existing circuit has to carry more than it was designed for and you need to know whether it can
  • · Several routes or installation methods are in play and you need the sizes compared on the same basis

Standards Applied

IEC 60287IEC 60228ERA 69-30BS 7671

The report states the clause and the edition it works to, so the calculation can be reproduced by whoever reviews it.

What You Get

Rated current for each circuit in the installation conditions as designed, with every derating factor listed and sourced
The minimum acceptable conductor size, and where asked, the sizes for a set of scenarios side by side
Volt drop and, where it governs, the length at which it starts to
Independent verification of somebody’s sizing, run as our own model rather than a check of their arithmetic, across every installation case that matters
Cable losses: conductor I²R plus screen and dielectric losses, where efficiency or cooling matters
A stated set of inputs: burial depth, soil thermal resistivity, ambient ground temperature, grouping, duct arrangement and load factor, so the calculation can be reproduced

The analytical IEC 60287 route is the proven one and it is what we issue. Where a route has crossings, external heat sources or an unusual backfill, that is flagged and handled explicitly rather than absorbed into a factor.

Try It Yourself First

Cable volt drop calculator

Volt drop against route length, with the limits plotted.

Frequently Asked Questions

Will you take a single calculation, or is there a minimum package?

A single calculation is fine. There is no minimum package, and one circuit checked properly is a normal piece of work for us.

What do you need from us to start?

The cable datasheet or a proposed construction, the circuit rating or load profile, the route length, and the installation arrangement. If the soil thermal resistivity has not been measured, say so and we will state the assumption we use.

Can you verify a cable somebody else has sized?

Yes, and it is a large part of what we do. We build our own model rather than checking theirs, and we run every installation case that matters: one and two circuits, flat and trefoil, ducted and direct buried, and the mutual heating from a later phase. That way the answer is independent rather than a repeat of their assumptions. Where the proposed size fails, we say what does pass.

How is this different from a manufacturer’s rating table?

A table gives a rating for reference conditions. Your trench is not the reference condition. The derating for depth, grouping, ducts, backfill and ambient is where the size is actually decided.

The Rest of the Cable Chain

Review, calculation, drawings, testing and fault location, from one place. See the whole picture.

Cable Design Review

Cyclic and Emergency Ratings

Short Circuit and Screen Sizing

Induced Voltage and Bonding

Thermo-mechanical and Fault Forces

EMF Assessment

Cable Pulling Calculations

Route Design and Drawings

Testing and Fault Location

Request a Cable Sizing Study

A free calculator answers one question at standard conditions. A study takes the actual route, burial depth, soil resistivity, grouping and load profile, and gives you a signed report you can issue to the DNO or the client. We take single calculations as readily as full cable system designs.

Or call 07951 651 013 or email enquiries@stardeltapower.co.uk