230V to 110V Transformer for the Netherlands: NEN 1010 Guide

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.

The Dutch starting point: NEN 1010

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:

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.

Aardlekschakelaar or aardlekautomaat — which matters here?

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.

The key technical point: a primary RCD cannot see the secondary

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:

1. Reference the secondary to earth at one point — then the fault current can return through the protective conductor system and an RCD on the secondary will operate.
2. Use an auto-transformer instead — with a shared winding, primary and secondary share a conductor, so the primary RCD covers the secondary circuit. This is only legitimate where the application does not require separation.
3. Leave the secondary isolated and monitor it — an insulation monitoring device gives an alarm on the first fault. Appropriate for test benches and laboratories, not for ordinary production circuits.

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.

Earthing the secondary in a Dutch TT stelsel

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.

NEN-EN-IEC 61558 and KEMA certification

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.

Construction choice

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.

Sizing in VA for Dutch machinebouw and installatietechniek

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.

• Resistive load (verwarming, verlichting): +20 %
• Motor load: +100 % (factor 2) — higher for compressor hard starts
• Switched-mode supplies and drive inputs: +30 to +50 %
• Continuous duty: keep at 70–80 % of rated VA
• Multiple simultaneous loads: sum the ratings, do not use the largest load as the reference

Bu 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.

Inkoop checklist for Dutch buyers

1. NEN-EN-IEC 61558 part reference for the construction supplied.
2. Type-specific EU declaration of conformity naming the ordered model.
3. ErP data — no-load loss and efficiency figures for small transformers.
4. Test record — turns ratio, insulation resistance, no-load current.
5. Aansluitschema showing the protective conductor connection, so the installer can confirm NEN 1010 compliance.
6. Series consistency across the power range, to keep terminal labelling and spares stable.

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.

Mistakes that recur on Dutch sites

Next step

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: Bize ulaşın.

SSS

Does a 230V to 110V transformer need earth leakage protection?

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.

What is the difference between an aardlekschakelaar and an aardlekautomaat?

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.

Can an auto-transformer be used for a 230 V to 110 V conversion in the Netherlands?

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.

Is KEMA certification required?

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.

Which standard applies to the transformer itself?

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.

How much margin should a transformer have?

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.