A Design Package, Not a Spreadsheet
A cable rating on its own does not build anything. Somebody still has to decide the route, the trench formation, where the joint bays fall, how the screens are bonded and whether the pull is achievable. A cable system design is all of that, issued together, so the calculation and the drawing agree with each other.
The calculations here are automated on software we wrote and maintain rather than bought in, which is what makes an expedited turnaround possible when a programme demands it. The design judgement is not automated, and that is the part you are buying.
One calculation is a job. There is no minimum package.
What Is In The Package
Ten deliverables, with the standard named against each. Any of them can be bought on its own.
| # | Deliverable | Standard |
|---|---|---|
| 01 | Cable route layout | Drawn to the survey |
| 02 | Trench cross-sections | Per formation and depth |
| 03 | Joint bay layout | Sized to the pulling sections |
| 04 | Termination and bonding | CIGRE TB 347, ENA ER C55 |
| 05 | Cable schematic | Circuit and earthing arrangement |
| 06 | Rating calculations | IEC 60287 |
| 07 | Cyclic and emergency ratings | IEC 60853 |
| 08 | Short circuit and screen sizing | IEC 60949 |
| 09 | Pulling calculations | CIGRE TB 889 |
| 10 | Bill of materials and design risk assessment | CDM 2015 |
Duct route design to DNO and Openreach specification sits alongside these: cover depths, duct type and bore, marker tape, chamber and joint box details, road crossings and building entries.
What We Need To Start
Rarely does anyone have all of it on day one, and a design does not have to wait for the lot. Tell us what exists and we will say what is genuinely blocking and what can be carried as a stated assumption.
The route
An OS map of the corridor and the utility search records. The route survey if one has been done, ideally as a KMZ. Where the route crosses somebody else’s land, the easement plan.
The electrical duty
Maximum circuit load, and its shape if it cycles. The fault level and clearance time at the point of connection, which more often than not is what sets the minimum conductor size. Whether N-1 applies.
The ground
Soil thermal resistivity if it has been measured, or a note to proceed on the IEC 60287 default. Verified trial hole records, and HDD profiles wherever the route passes under something.
Whatever is already fixed
A cable already chosen, a trench standard or DNO detail you are aligning to, datasheets for existing cables sharing the route, and drawings for the termination structures and any bridges or culverts on the way.
If the fault level and the clearance time are not known yet, say so and we will state the assumption in the report rather than hold the design up. The short circuit withstand check usually sets the minimum conductor size, so it is worth pinning down early.
Scale
Highest connection voltage designed
Longest single cable route
Pulling sections on that route, cut down from 23
From a single circuit inside a substation up to a multi-kilometre 132 kV route with HDD sections and joint bays. Drafting is brought in as the package needs it, so the drawing standard stays consistent without carrying a drawing office.
Common Questions
What is a cable system design?
The whole design package for a cable circuit, not just the sizing calculation. It covers the route layout, the trench and duct formations, the joint bays, the terminations and bonding, the thermal rating, the pulling and force calculations, the bill of materials and the design risk assessment. The output is a set of drawings and calculations an installer can build from and an owner’s engineer can approve.
Can I buy one calculation rather than the package?
Yes. A single calculation is a job and there is no minimum package. Plenty of work here is one rating check or one bonding assessment. The package exists because the calculations are only half of a design, not because the halves cannot be bought separately.
What scale of route do you work on?
From a single circuit inside a substation up to a multi-kilometre 132 kV route with multiple HDD sections and joint bays. The method does not change with length; what changes is the number of pulling sections and the amount of survey data the design has to reconcile.
Do you produce the drawings yourself?
The engineering, the calculations and the design decisions are ours. Drafting is brought in as the package needs it, which keeps the drawing standard consistent without carrying a drawing office. You deal with the engineer either way.
What sizes the cable, the current or the fault?
Often the fault, and it catches people out. A conductor that carries the load comfortably can still fail the short circuit withstand check, so the minimum size is set by the fault level and the clearance time rather than by the rating. That is why the fault level at the point of connection is on the list of things needed to start.
Do you design the ducts as well as the cable?
Yes, including duct routes to DNO and Openreach specification: cover depths, duct type and bore, marker tape, chamber and joint box details, road crossings and building entries. Duct bore is worth getting right early, because a duct sized close to the cable diameter risks jamming the pull even though it looks adequate on paper.
Tell Us About The Route
Voltage, load, route length and installation method is enough to come back with a scope and a fee. If you only want one calculation, say which one.