If you are sourcing a 230V to 110V transformer for a German site, the technical selection is the easy part. The hard part is documentation: German procurement teams and machine integrators expect the standard reference on the datasheet, the declaration of conformity for the exact type ordered, and a test record that survives an audit. This guide covers what that means in practice.
It is written for buyers, electrical designers and maintenance engineers who need a 230 V to 110 V transformer to sit inside a German installation — for imported US machinery, a test bench, workshop tools or a permanent 110 V circuit. For the German-language version of this guide, see Spannungswandler 230V 110V.
The device is a step-down transformer: a passive magnetic component that reduces 230 V AC to 110 V AC (commonly tapped at 115 V or 120 V). Two windings share a magnetic core, and the turns ratio sets the voltage ratio. There is no active regulation.
Three consequences matter in German projects:
Germany runs a nominal 230 V / 50 Hz supply. DIN EN 50160 defines the voltage characteristics of the public network with a ±10 % tolerance band, so a transformer specified at exactly 230 V primary must tolerate roughly 207–253 V at the input. That is well within the design envelope of a correctly rated transformer, but it is a reason not to run a unit at 100 % of its VA rating continuously.
| Paramètres | German practice | Consequence for the transformer |
|---|---|---|
| Nominal voltage | 230 V / 50 Hz | Primary rated 230 V; allow ±10 % |
| Socket system | Type F (Schuko, CEE 7/3) | Primary plug to match; 16 A per circuit typical |
| Plug current limit | 16 A standard socket circuit | A 3.6 kVA load is the practical socket limit |
| Installation code | DIN VDE 0100 series | Governs final wiring, protection and earthing |
| Machine electrical equipment | DIN EN 60204-1 | Applies to the machine the transformer feeds |
German buyers usually ask for “the 61558 reference”. The IEC 61558 series is the transformer safety standard, and its German implementation carries both a DIN EN IEC number and a VDE 0570 number. Which part applies depends on the transformer construction.
| Application | German designation | What it covers |
|---|---|---|
| General requirements and tests | DIN EN IEC 61558-1 (VDE 0570-1) | Base standard for all parts |
| Separating transformers | DIN EN IEC 61558-2-1 | General-purpose separation |
| Isolating transformers | DIN EN IEC 61558-2-4 (VDE 0570-2-4) | Galvanic separation for general applications |
| Safety isolating transformers | DIN EN IEC 61558-2-6 (VDE 0570-2-6) | Additional limits on output voltage and current |
| Auto-transformers | DIN EN IEC 61558-2-13 | Step-down/step-up auto configurations |
When a supplier claims “VDE approved”, ask which part number and for which type. A DIN EN IEC 61558-2-13 test report for an auto-transformer does not transfer to the isolation unit you actually ordered.
Practical note: for a 230 V to 110 V auto-transformer (Spartransformator), the 2-13 route is correct and cost-effective. As soon as the load needs galvanic separation — medical, laboratory, marine or any circuit where fault current must not reach the primary — you are in 2-4 or 2-6 territory and the product changes construction.
| Exigence | Legislation | What a German buyer will check |
|---|---|---|
| Low Voltage Directive | 2014/35/EU | EU declaration of conformity naming the type |
| EMC Directive | 2014/30/EU | Emissions and immunity evidence for the finished unit |
| Ecodesign (small transformers) | ErP Regulation (EU) 2019/1782 | Efficiency and no-load loss data, product information sheet |
| RoHS | 2011/65/EU | Material compliance statement |
| Type test record | Supplier quality system | Turns ratio, insulation resistance, no-load current per unit or per batch |
The ErP angle is where buyers most often get caught out. The EU ecodesign regulation for external power supplies and small transformers requires published no-load power consumption and efficiency figures. If a supplier cannot produce that data, the unit is likely a generic export product that was never documented for the European market.
Wiring follows a consistent pattern: supply to the primary terminals (H1, H2), load to the secondary terminals (X1, X2), and both the enclosure and the terminal box bonded to the site earth bar. The protective conductor goes to the enclosure, never to a secondary terminal.
The subtle part is the secondary. Whether it is earthed at all depends on the system:
This is the single most misunderstood point in the whole topic: a 30 mA RCD on the primary feed cannot protect an isolated secondary circuit. If secondary protection is required, it has to be designed on the secondary side. The step-by-step method is documented in how to ground a transformer secondary. Final wiring must be carried out by a qualified electrician working to DIN VDE 0100.
| La construction | Galvanic separation | Efficacité | Best fit in German projects |
|---|---|---|---|
| Auto-transformer | No — common winding | Very high | Heating, lighting, non-critical motor loads |
| Isolating transformer | Yes — separate windings | Haut | Machine control, test equipment, noise filtering |
| Safety isolating transformer | Yes, with limited output | Haut | Hand tools, wet or confined locations |
| Torique | Model dependent | Very high | Audio, medical, low stray field requirements |
For continuous duty in a machine or control cabinet, the DT/ST range covers 100 VA to 10 kVA in a consistent series: transformer DT/ST series 100VA–10KVA. Keeping the same series across the power range is what makes terminal labelling, accessories and spare-part holding predictable across a German machine programme.
Transformers are rated in VA, not watts. On resistive loads the two are close; on motors, pumps and switched-mode supplies the power factor is below 1 and the transformer has to be larger. Add inrush current on top:
| Chargement | Rated power | Recommended transformer |
|---|---|---|
| US test-bench control cabinet | 600 VA | 900 VA |
| Workshop power tools on one 110 V circuit | 1,500 W total | 3,000 VA |
| US machine control + sensors | 1,000 VA | 1,500 VA |
| Mixed workshop load with motor start | 2,000 W | 4,000–5,000 VA |
A 3 kVA unit such as the DT-3000VA step-up step-down transformer is the usual entry point for workshop and small-machine duty, and a 2 kVA unit such as the ST-2000VA step-up and step-down transformer covers control-cabinet loads with margin.
The export catalogue is here: Johsun step-up and step-down transformer supplier. For custom windings, non-standard terminals, enclosure forms or OEM branding, the route is ODM / OEM — useful when one transformer needs to cover several primary and secondary voltages to reduce SKU count.
| Erreur | Consequence | Avoid by |
|---|---|---|
| Reading the appliance wattage as VA | Overheating, thermal cut-out | Use the VA figure and add margin |
| Auto-transformer on a load that needs separation | No galvanic isolation, no noise filtering | Specify 61558-2-4 or 2-6 construction |
| Assuming a primary RCD covers the secondary | Secondary earth faults are never cleared | Define the protection concept before wiring |
| No ErP or test documentation | Fails supplier audit | Request data per type at quotation stage |
| Running continuously at 100 % VA | Reduced service life, high case temperature | Size at 70–80 % of rated VA for continuous duty |
German-market selection comes down to three things: the correct DIN EN IEC 61558 part for the construction, a VA rating that matches the real load profile including inrush, and a protection and earthing concept that holds up in a TN or TT installation. Documentation for the exact type is what separates a compliant supply from a future audit finding.
Send us the primary voltage, frequency, load profile and mounting situation and we will come back with the matching type: nous contacter.
The IEC 61558 series, published in Germany as DIN EN IEC 61558 with the parallel VDE 0570 designation. Part 2-4 covers isolating transformers, part 2-6 safety isolating transformers and part 2-13 auto-transformers. DIN VDE 0100 governs installation.
Yes, for non-critical loads such as heating, lighting and simple motor loads. It is not acceptable where galvanic separation is required, which includes medical equipment, laboratory instrumentation and any circuit where a fault current must be prevented from reaching the primary side.
Often not — many US machines accept 200–240 V directly through a selector or a terminal change. Check the nameplate before ordering a transformer, because a dual-voltage machine may only need the correct plug and a wiring change.
No. With isolated windings, the secondary fault current returns through the earthing system rather than through the primary current transformer, so the RCD sees no imbalance. Secondary protection must be provided on the secondary side.
The DIN EN IEC 61558 part number, the EU declaration of conformity for the ordered type, ErP no-load loss and efficiency data, a test record with turns ratio and insulation resistance, and German-language datasheet and terminal diagram.
Size at roughly 70–80 % of rated VA for continuous duty, add 20 % on resistive loads and a factor of 2 on motor loads to cover inrush current.
