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
The report states the clause and the edition it works to, so the calculation can be reproduced by whoever reviews it.
What You Get
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
Frequently Asked Questions
How many circuits can the grouping calculation handle?
There is no limit in the method. Grouping is solved by image-source superposition to IEC 60287-2-1 clause 4.2.3, and it carries as many circuits as the corridor has. A recent ten-circuit case of three single-core cables in individual ducts converged in six iterations and took the rating from 873.2 A isolated to 636.4 A grouped, a factor of 0.729, with a 15 K spread from the centre of the group to the edge.
When does a case actually need finite element analysis?
Not because of circuit count, which is the usual assumption. The closed-form method assumes uniform soil across the whole envelope, and on a wide corridor with mixed backfill, a water table or a thermal backfill only under part of the route, that assumption fails before the arithmetic does. Soil uniformity is what decides it, not how many circuits are in the trench.
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.