IEC 61537 cable tray explained: Safe Working Load, deflection, and how it maps to NEMA and SNI.

TL;DR

IEC 61537:2023 is the international standard for cable tray and cable ladder systems. It does not use a letter-class system like NEMA. Instead, it classifies a system by its Safe Working Load (SWL) — the uniformly distributed load it can carry, expressed in Newtons, at a stated support distance, while staying within a deflection limit.

NEMA VE 1 says: “this is a Class 8C tray.” — a letter code.
IEC 61537 says: “this system has an SWL of X Newtons at a support distance of Y metres.” — a force, a span, and a deflection criterion.

Both frameworks rest on the same physics: a uniformly distributed load (UDL) applied across a span between two supports, with deflection capped. Metosu’s Sucofindo reports are structured to satisfy both IEC 61537:2023 and NEMA VE 1-2017. The concrete tested anchors are the NEMA figures: cable ladder 1,340 kg/span (Class 8C), cable tray 420 kg/span (Class 8B), both at a 2,400 mm span, both held within an L/250 = 9.6 mm deflection limit.

	NEMA VE 1-2017	IEC 61537:2023
Classifies by	Letter class (8A / 8B / 8C…)	Safe Working Load (SWL) in Newtons
Span statement	First digit (8 = 8 ft / 2,400 mm)	Stated support distance, in metres
Load unit	kg or lbf per metre, mapped to a class	Newtons (UDL across the span)
Test method	UDL across rated span	UDL across stated support distance
Deflection	L/100 serviceability limit	Deflection criterion at SWL

What “Safe Working Load in Newtons” actually means

NEMA’s letter classes are convenient shorthand — but the shorthand hides the underlying quantity. IEC 61537 strips the shorthand away and states the quantity directly.

A Safe Working Load is the uniformly distributed load a tray or ladder can carry across a defined support distance without exceeding the standard’s deflection criterion. It is expressed as a force, in Newtons, because that is the SI unit of load. The classification is therefore a triplet, not a single code:

The SWL — the load itself, in Newtons (N) or, on longer systems, Newtons per metre of run.
The support distance — the span between supports the SWL is valid at. An SWL only means something attached to a span. Double the span and the same section carries far less.
The deflection criterion — the serviceability ceiling the system must stay under while carrying the SWL.

Read an IEC classification and you get all three at once. A statement like “SWL of X N at a 2.0 m support distance” tells you exactly what the section carries and on what geometry — no class table lookup required.

Reading the unit: kgf and Newtons

Engineers in Indonesia and Singapore routinely work in kilograms-force (kgf); IEC works in Newtons. The conversion is the gravitational constant:

1 kgf = 9.81 N (load in kg × 9.81 = force in Newtons)

So a test load measured on a rig in kilograms converts straight to the Newton figure IEC speaks in. Expressed this way, Metosu’s NEMA-tested loads become:

Tested load (NEMA rig)	Same load in Newtons (kgf × 9.81)
Cable tray — 420 kg/span	≈ 4,120 N
Cable ladder — 1,340 kg/span	≈ 13,145 N

These Newton values are simply the NEMA test loads expressed in Newtons — the unit IEC uses. They are not a published IEC SWL classification or class code for Metosu product. They show that the same measured capacity reads consistently across both unit systems. The formal IEC SWL classification for any specific section is established on the IEC test method; Metosu’s reports are structured to carry both the NEMA result and the IEC framing.

The test method: UDL across a span, deflection capped

The reason NEMA and IEC produce compatible results is that they test the same way. Both apply a uniformly distributed load — load spread evenly along the run, simulating cables resting in the tray — across a defined span between two supports, and both cap deflection so the system stays serviceable, not just unbroken.

The differences are in units and presentation, not in the physics:

NEMA VE 1-2017 reports the result as a letter class at a span encoded in the class number, with an L/100 working-load deflection limit (24 mm at a 2,400 mm span).
IEC 61537:2023 reports the result as an SWL in Newtons at a stated support distance, with a deflection criterion applied at that load.

Because the load case is identical — UDL, defined span, deflection ceiling — a section that performs to a NEMA class will perform predictably under the IEC method, and vice versa. The engineering principle is the same; the certificate wording differs. For the full breakdown of why a class is a floor and a tested figure is the real number, see NEMA class vs tested capacity.

How to read an IEC classification

When a consultant hands you an IEC 61537 figure, parse it in this order:

Find the SWL value and its unit. It will be in Newtons (or N/m for a per-metre rating). This is the load.
Find the support distance it is stated at. No span, no meaning. Confirm it matches your support layout.
Find the deflection criterion. Check whether it is L/100, L/200, L/250 or another ratio — the tighter the ratio, the stiffer the system at that load.
Compare against your actual load case. Sum your cable weight per metre, multiply by your span, convert to Newtons (× 9.81), and confirm it sits under the SWL at your span.

If the IEC figure is quoted at a different support distance than your design uses, do not interpolate by guesswork — ask the manufacturer for the SWL at your span, or the underlying load/deflection table.

Cross-walking IEC, NEMA, and SNI

On an Indonesian or Singapore project you will see all three frameworks, sometimes on the same drawing set. Here is how they relate:

Framework	What it is	How it classifies	Where you’ll see it
IEC 61537:2023	International standard for cable tray/ladder systems	SWL in Newtons at a stated support distance, with a deflection criterion	International design bases; specs from UK/EU-trained consultants
NEMA VE 1-2017	North American metal cable tray standard	Letter class (8A/8B/8C…) at a span, L/100 deflection	US-authored and hyperscale DC template specs
SNI IEC 61537:2016	Indonesia’s national adoption of IEC 61537	Same SWL-in-Newtons method as IEC; SNI mark mandatory for government projects	Indonesian government and TKDN-driven procurement

Two points that resolve most confusion:

SNI for cable tray is IEC 61537. Indonesia adopts the IEC standard as its national standard — the current Indonesian edition is SNI IEC 61537:2016. A section evaluated to IEC 61537 satisfies the core technical requirements of SNI IEC 61537; the remaining step is the certification mark, not a re-test of the physics.
NEMA and IEC are complementary, not contradictory. They report the same UDL behaviour in different units. A section with a credible NEMA class result and a credible IEC SWL result describes one physical capacity two ways.

For the NEMA-vs-SNI side of this in full — corrosion test references, bonding test current, and the SNI mark requirement — see NEMA VE 1 vs SNI for Singapore consultancies.

How Metosu’s testing satisfies both frameworks

Metosu’s cable ladder and cable tray were tested by Sucofindo against the NEMA VE 1-2017 method, at a 2,400 mm support span, on 14 July 2025. The reports are structured so the same test data supports both the NEMA letter class and the IEC SWL framing.

Cable ladder (SLW / SLU) — NEMA Class 8C

Parameter	Value
Test span	2,400 mm
Load held	1,340 kg/span (≈ 13,145 N, kgf × 9.81)
NEMA Class 8C minimum	534.4 kg → 2.5× the requirement
Deflection limit	L/250 = 9.6 mm at 2,400 mm
Sucofindo report	E26929/FNBPAS

Cable tray (TRC / TRU) — NEMA Class 8B

Parameter	Value
Test span	2,400 mm
Steel thickness	2.02 mm
Load held	420 kg/span (≈ 4,120 N, kgf × 9.81)
NEMA Class 8B minimum	403 kg
Deflection limit	L/250 = 9.6 mm at 2,400 mm
Sucofindo report	E26933/FNBPAS

Two details matter for the IEC reading:

The deflection ceiling is stricter than NEMA requires. NEMA VE 1’s working-load limit is L/100 (24 mm at this span). Metosu’s results are verified against L/250 = 9.6 mm — a deflection ceiling 2.5× tighter than NEMA itself mandates. Against any IEC deflection criterion in the same range, that margin carries over.
The Newton figures above are the tested loads in IEC’s unit — not an assigned IEC class. Metosu does not publish a fabricated IEC class code or SWL value; the reports carry the measured capacity, expressed in whichever unit the reviewing framework speaks.

Both finishes are specified separately from load: hot-dip galvanised to ISO 1461, with an optional Jotun powder topcoat at 60–80 µm to ISO 12944 corrosivity categories C3–C5M. See Metosu’s manufacturing capabilities for the full finishing and testing scope.

Practical guidance: which framework, when

If the spec references…	Do this
IEC 61537 (SWL in Newtons)	Confirm the support distance and deflection criterion, convert your load case to Newtons (kg × 9.81), and check it under the SWL at your span. Request Metosu’s report structured to the IEC framing.
NEMA VE 1 (Class 8A/8B/8C)	Match the class to your per-metre load and span. Metosu ladder = Class 8C, tray = Class 8B at 2,400 mm. See NEMA load classes explained.
SNI IEC 61537:2016	Treat it as IEC 61537 plus the mandatory SNI mark. The physics is the IEC method; the deliverable adds the certification mark for government/TKDN procurement.
Two or three of the above on one drawing	Don’t argue equivalence in the submittal — supply the report structured to each framework. One tested capacity, presented in each framework’s language.

When a consultant quotes an IEC SWL and you only hold a NEMA class (or the reverse), the bridge is the shared UDL test method: both describe the same uniformly distributed load behaviour at a defined span. Convert units, confirm the span matches, and the comparison is direct.

Contact engineering

For project-specific load calculations, the SWL-at-your-span figure, or Sucofindo report copies structured to IEC 61537 or NEMA VE 1, email [email protected]. We review cable-management specifications as a pre-sales service — send a cable schedule and support layout and we will confirm the SWL, class, product line, and finish within one business day.