In the Netherlands, the 230 V to 110 V transformer question is settled by two documents: NEN 1010 for the installation and the IEC 61558 series for the product. Get those right and the rest is arithmetic. Get them wrong and you end up with a correctly sized transformer that fails inspection because the protective device cannot see a fault on the 110 V side. This guide covers what a 230V to 110V transformer needs to satisfy on a Dutch site.
It is written for electrical designers, machine builders and buyers in the Netherlands. For the Dutch-language version, see Spanningsomvormer 230V 110V.
NEN 1010 is the Dutch safety standard for low-voltage installations and the national implementation of IEC 60364. Where the UK works from BS 7671 and the US from the NEC, the Netherlands works from NEN 1010 — with local amendments that are stricter than the base standard in a few places, notably around earth leakage protection.
The clauses that matter for a step-down transformer installation:
| Area | What NEN 1010 expects | Effect on the transformer installation |
|---|---|---|
| Earth leakage protection | Socket circuits for general use protected by an RCD with a maximum trip current of 30 mA | Primary feed protected as any other circuit; the secondary needs its own scheme |
| Earthing | Continuous protective conductor, defined earth electrode resistance | Enclosure and terminal box bonded to the earth rail without exception |
| Overcurrent protection | Device matched to conductor and load | Primary protection rated at full-load current × 1.25 |
| Isolation and switching | Each circuit isolatable from every active conductor, with defined exceptions for TN-C and TN-S | Affects the upstream switch-disconnector, not the transformer itself |
| Circuit grouping | Limits on the number of final circuits per 30 mA RCD | Relevant when the transformer adds a new group to an existing meterkast |
The grouping limit is easy to miss. A single 30 mA RCD covering many final circuits accumulates capacitive leakage from switch-mode power supplies, and adding a transformer-fed group can push it over the trip threshold. Modern practice in the Netherlands favours an aardlekautomaat per circuit rather than one shared aardlekschakelaar, precisely to avoid nuisance tripping.
| Dispositivo | Función | When it is the right choice |
|---|---|---|
| Aardlekschakelaar (RCD) | Earth leakage only | Retrofit into an existing meterkast with separate MCBs; subject to the four-circuit grouping limit |
| Aardlekautomaat (RCBO) | Earth leakage plus overcurrent in one module | New circuits; keeps a fault on the transformer feed from taking down the whole installation |
For a new 110 V supply, specify an aardlekautomaat. It combines the overcurrent protection the transformer needs with the 30 mA leakage protection NEN 1010 requires, in one module width, and it isolates the consequences of a fault to a single group.
This is the single most important thing to get right, and the most commonly missed item in Dutch installations.
A step-down transformer with separate windings creates an electrically isolated secondary circuit. A residual current device monitors the balance between line and neutral current in the conductors passing through it. A fault on the secondary side does not return through those primary conductors — it returns through the earthing system to the earth electrode. The RCD sees no imbalance and does not operate.
The consequence: a 30 mA aardlekschakelaar on the 230 V feed of an isolated transformer provides no earth fault protection for the 110 V circuit. Options to resolve it:
The counter-intuitive result deserves repeating: for a purely isolated secondary in permanent use, a single insulation fault goes completely unnoticed. It stays invisible until a second fault appears, at which point the protective device may not operate in time. The verification method is documented in how to ground a transformer secondary. Wiring in the verdeelkast must be carried out by a vakbekwaam persoon working to NEN 1010.
| Configuración | Secondary treatment | Fault disconnection | Fit |
|---|---|---|---|
| Auto-transformer | No discrete secondary earth | Via primary RCBO | Non-critical loads where separation is not needed |
| Earthed isolated secondary | Neutral bonded to earth at a single point | Via secondary RCD | Permanent 110 V distribution |
| Isolated and monitored | Floating, with insulation monitoring | Alarm on first fault | Laboratory, test bench, diagnostic work |
Dutch low-voltage installations are predominantly TT, so the earth electrode and the protective conductor system carry the return path for fault current. That reinforces the same conclusion: without a secondary reference, there is no return path for a 110 V fault and therefore no automatic disconnection.
| Aplicación | Dutch designation | What it covers |
|---|---|---|
| General requirements and tests | NEN-EN-IEC 61558-1 | Base safety standard for the series |
| Scheidingstransformatoren (isolating) | NEN-EN-IEC 61558-2-4 | Separate windings, general applications |
| Veiligheidstransformatoren (safety isolating) | NEN-EN-IEC 61558-2-6 | Additional limits on output voltage and current |
| Spaartransformatoren (auto) | NEN-EN-IEC 61558-2-13 | Step-up and step-down auto configurations |
| Medical isolating transformers | NEN-EN-IEC 61558-2-15 | Medical examination and treatment rooms |
| CE marking | LVD 2014/35/EU and EMC 2014/30/EU | EU declaration of conformity |
Dutch buyers frequently ask about KEMA. Strictly, KEMA is a certification body rather than a standard, and KEMA marking is not a legal requirement for a transformer placed on the EU market — a valid CE declaration is. That said, an independent test report from a recognised body is a useful risk-reduction signal on imported product, particularly for medical-adjacent applications where NEN-EN-IEC 61558-2-15 may apply.
| Construcción | Separation | Typical Dutch application |
|---|---|---|
| Spaartransformator | Ninguno | Verwarming, verlichting, simple motor loads |
| Scheidingstransformator | Full galvanic | Machine control, measurements, noise filtering |
| Veiligheidstransformator | Full, limited output | Portable tools, damp or confined locations |
| Ringkerntransformator | Model dependent | Audio, laboratory, low stray field |
For continuous duty in a machine or verdeelkast, the DT/ST range covers 100 VA to 10 kVA with a consistent terminal scheme: transformer DT/ST series 100VA–10KVA. Keeping one series across the power range is what makes spare parts and terminal labelling predictable in a machinebouw programme.
Transformer ratings are in VA, not watts. Dutch machine builders deal frequently with servo drives, switched-mode supplies and refrigeration compressors, all of which have poor power factor or high inrush.
| Aplicación | Rated power | Recommended transformer |
|---|---|---|
| Machine control cabinet | 600 VA | 900 VA |
| Workshop 110 V tool circuit | 1,500 W | 3,000 VA |
| Refrigeration compressor | 800 W | 2,000–2,500 VA |
| Drive-fed machine input | 2,000 VA | 3,000–4,000 VA |
En DT-3000VA step-up step-down transformer handles most workshop and small-machine cases, and a ST-2000VA step-up and step-down transformer is a good fit for control-cabinet and compressor duty.
The export range is set out at Johsun step-up and step-down transformer supplier. For custom windings, alternative terminals, enclosure forms or OEM branding, see ODM / OEM.
| Error | Consequence | Fix |
|---|---|---|
| Assuming the primary aardlek covers the 110 V side | Secondary earth faults never cleared | Reference the secondary or use an auto-transformer where separation is not required |
| Secondary left floating in permanent use | First fault undetected | Bond the secondary at one point, or install insulation monitoring |
| One shared 30 mA RCD across too many groups | Nuisance tripping once the transformer group is added | Use an aardlekautomaat per circuit |
| Reading appliance watts as VA | Undersized transformer, thermal trips | Use the VA figure with real margin |
| No protective conductor continuity check | Protection ineffective despite correct design | Verify enclosure-to-earth-rail continuity before energising |
On Dutch projects, compliance comes from two decisions made in the right order: choose the construction that matches the separation requirement, then define how the secondary is earthed, before sizing in VA with margin for inrush. NEN 1010 governs the wiring; IEC 61558 governs the product; the documentation proves both.
Send the supply voltage, frequency, load profile and earthing arrangement and we will come back with the matching type: Contacto.
The 230 V primary feed needs protection as any other circuit under NEN 1010 — 30 mA maximum for socket circuits for general use. The 110 V secondary needs its own arrangement, because a residual current device on the primary cannot detect a fault on an isolated secondary.
An aardlekschakelaar provides earth leakage protection only. An aardlekautomaat combines earth leakage and overcurrent protection in one module. For a new transformer-fed circuit, an aardlekautomaat is the practical choice.
Yes, where the application does not require galvanic separation. Because primary and secondary share a winding, the primary protective device also covers the secondary circuit, which simplifies compliance considerably. Where separation is required — medical, laboratory, certain machine safety functions — a scheidingstransformator is mandatory.
No. KEMA is a certification body, not a legal requirement. What is required is a valid CE declaration of conformity under the Low Voltage and EMC Directives. An independent test report is nevertheless a useful signal of product quality on imported equipment.
IEC 61558 in its Dutch implementation, NEN-EN-IEC 61558 — 2-4 for scheidingstransformatoren, 2-6 for veiligheidstransformatoren, 2-13 for spaartransformatoren, and 2-15 where medical isolating transformers apply.
Size at 70–80 % of rated VA for continuous duty. Add 20 % on resistive loads, a factor of 2 on motor loads and 30–50 % on switched-mode supply loads to cover inrush current.
