SANS 10198-2 Cable Selection Checker

What SANS 10198-2 is and who publishes it

SANS 10198-2 is a South African National Standard issued by the South African Bureau of Standards, the SABS. Its full title is "The selection, handling and installation of electric power cables of rating not exceeding 33 kV, Part 2: Selection of cable type and methods of installation." The series began as SABS 0198 in the 1980s, was reissued as SANS 10198 in 2004, and Part 2 was updated again in the 2021 edition 2.1 that the SABS webstore sells today.

In plain terms, the document is a checklist with rules attached. Before a cable goes in the ground, on a tray or in a duct, the standard asks the designer to show that the chosen cable can carry the load, survive a fault, fit the route, and stay out of the way of other services. The scope covers cables up to 33 kV, which reaches from a house supply up to medium voltage distribution feeding a factory or a suburb.

It is also the document South African tenders cite. Government procurement documents, such as those published on the eTenders portal, routinely list SANS 10198-2 among the referenced standards for cable work, which is why searches for it spike whenever a project specification lands on a contractor's desk.

The fourteen parts and where Part 2 sits

SANS 10198 is a series, and each part owns one slice of the cable life cycle. The first five parts handle design decisions; the rest handle the hands-on work of hauling, jointing and testing. Knowing which part owns which question saves hours, because the answer to "what size" lives somewhere different from the answer to "how deep".

Part 2 is the hinge between the two halves: it takes the criteria (current, voltage drop, fault level, environment) and turns them into a cable type and an installation method that the later parts then execute. When a specification says "install per SANS 10198-2", it means the selection reasoning must be on record, not just the final cable.

The selection criteria Part 2 asks you to check

The standard frames cable selection as a set of criteria that every candidate cable must satisfy. The core checks, in the order a designer usually works through them, are:

Sustained current rating. The cable must carry the design load continuously without overheating its insulation. The ratings themselves live in Part 4, but Part 2 is where the decision to apply them belongs, together with the derating factors for ambient temperature, grouping and installation method.

Voltage drop. The route length converts a perfectly sized cable into an undersized one. A cable can pass every thermal check and still deliver 8% less voltage at the far end, which no motor tolerates. The worked examples below show the arithmetic, and the checker on this page runs it for you.

Short circuit capacity. During a fault the conductor absorbs a burst of heat. The cable's cross section must withstand the prospective fault current for the time it takes protection to clear it. This is the criterion most often skipped on small jobs, and the one that turns a nuisance fault into a destroyed cable.

Mechanical protection and environment. Buried cable needs depth, bedding and marking; tray cable needs support spacing; anything near traffic or excavation needs armor or conduit. Part 2 also requires attention to thermal surroundings and to interference with telecommunication cables, which must be separated from power routes to keep noise out of phone and data lines.

Voltage drop, worked step by step

Voltage drop comes from the resistance (and a little reactance) of the conductors between the source and the load. For copper at a typical operating temperature near 70 degrees C, the resistance is about 0.0206 ohm for a conductor of one square millimeter cross section and one meter length, so the per conductor value is 0.0206 / A ohm per meter. The values here are illustrative for checking; the tables inside the standard and manufacturer data govern real installations.

Single phase example: a 20 A load sits 25 m from the board, on 2.5 square millimeter copper, at a 230 V supply and a power factor of 1. The loop resistance is 0.0206 x 2 / 2.5 = 0.01648 ohm per meter. The drop is 20 x 25 x 0.01648 = 8.24 V, and 8.24 / 230 = 3.58%, inside a 5% limit with little room to spare.

Three phase example: a 63 A route runs 60 m at 400 V, power factor 0.85, on 35 square millimeter copper. The current and length multiply to 63 x 60 = 3,780, and the full chain is 3,780 x 1.732 x 0.0206 / 35 x 0.85 = 3.28 V. As a share of the supply, 3.28 / 400 = 0.82%, comfortably inside any limit.

The tables show the trade in both directions: doubling the copper roughly halves the drop, but the sustained current rating and short circuit checks from the previous section decide whether the smaller size is even allowed to run at the load in the first place.

Sustained current rating and derating

Current rating is a thermal statement: the current a cable can carry forever without pushing its insulation past its design temperature. The base tables live in Part 4 of the series, and Part 2's job is to make sure the designer applies the right corrections. Three factors dominate in practice.

Ambient temperature. Ratings are tabulated for a reference air or soil temperature. A route through a hot roof space or across sun-baked ground carries less current than the table value, so a correction factor scales it down.

Grouping. Cables bundled together heat each other. A dozen circuits on one tray each carry less than a lone cable could, and the grouping factor falls as the count rises. Spacing them out recovers some rating, which is why Part 2 discusses installation method alongside the electrical numbers.

Ground conditions. For buried cable, soil thermal resistivity decides how easily heat escapes. Dry sand traps heat; wet clay carries it away. Part 5 supplies the measurement methods, and Part 2 turns the result into a derating choice.

Applied together, these factors can halve a cable's table rating on a crowded, hot route. That is the quiet reason a cable that "looks big enough" fails its inspection: the selection record never showed the derating arithmetic.

Installation methods the standard covers

Part 2 closes with the methods available for laying power cables, and the choice is never purely electrical. Direct burial is the cheapest route for long runs but exposes the cable to excavation damage, so depth, protective tiles and warning tape matter as much as the conductor size. Ducts cost more up front but let a failed cable be pulled and replaced without re-digging the whole trench.

Cable trays and ladders suit buildings and plants, where routes change often and many circuits share the same corridor; the grouping derating from the previous section applies in full here. Aerial routes, including the bundled conductor systems covered in Part 14, trade ground risks for weather and clearance rules.

Two cross-cutting rules appear in nearly every method. First, keep power and telecommunication cables separated, so fault currents and load currents do not induce noise into communication circuits. Second, the earthing of the installation is not improvised per route: Part 3 of the series owns the general provisions, and the installation method must connect to that earthing design rather than replace it.

Where to get SANS 10198-2, and about free downloads

The standard is a copyright document sold through the SABS webstore, in print and as a licensed PDF. Edition 2.1, dated 2021, is the current one, and it replaced the 2004 edition 2, which itself replaced SABS 0198-2 from 1988. Citations should carry the year, because the selection criteria and referenced documents have shifted between editions.

The searches that lead people here are full of phrases like "SANS 10198-2 PDF" and "free download". The honest position is short: copies posted on file sharing and homework sites are not licensed, and a design done against a scanned third edition has no standing in a dispute. For a one-off project the purchase price is small against the cable cost it governs; libraries and some industry associations hold reference copies; and tender documents bought from a client sometimes include the extract you need.

If you only need the shape of the rules to plan a budget or sanity check a quote, the sections on this page give the framework and the checker gives the voltage drop arithmetic. For anything that gets signed, built and energized, work from the purchased edition and the current local wiring regulations.

How the checker on this page maps to the standard

The widget below runs the voltage drop criterion from Part 2's checklist. It takes the load current, route length, supply voltage, number of phases, power factor and a candidate copper size, then reports the drop in volts and as a share of the supply, alongside a pass or fail line against your limit. It also lists every copper size at or above your choice so you can see the nearest size that clears the limit.

Three boundaries matter. The resistance figures assume copper at a warm operating temperature, around 70 degrees C, so they are deliberately on the safe side of a cold cable. The checker does not evaluate sustained current rating, short circuit capacity, derating or mechanical protection, which need Part 4 data and site conditions. And aluminum conductors need their own resistivity, about 1.6 times copper's, so do not reuse the copper result for an aluminum route.

Treat the output as a selection sanity check, the kind a designer does before opening the standard itself. If the drop fails, step up a size and re-run; if it passes with a wide margin, the sustained current table may still force a bigger cable, which is exactly why Part 2 insists on checking every criterion rather than one.