Isolation transformers

Our isolation transformers, single-phase and three-phase

An isolation transformer electrically separates the installation it supplies from the mains that feeds it. We manufacture them in single-phase, from 63 VA to 20 kVA, and in three-phase, from 1 to 100 kVA, with a price shown online for every power rating.

Single-phase isolation transformers, 63 VA to 20 kVA

• 230 V / 230 V isolation transformer: for a boiler, audio equipment, a repair bench or a machine, with a 1:1 ratio. It suits UK mains, whose nominal voltage is 230 V, often still called 240 V.
• 400 V / 230 V transformer: connected between two phases of a 400 V supply, it provides an isolated 230 V output with no need for a neutral.
• 220 V / 110 V transformer: an isolated 115 V supply for equipment designed for 110 to 120 V.
• 110 V / 230 V transformer: isolated 220 V on a 110 V network, 230 V on a 120 V network.
• 230 V / 400 V transformer: an isolated single-phase 400 V supply from 230 V.

Three-phase isolation transformers, 1 to 100 kVA

• 3-phase isolation transformer, 400 V / 400 V + N: isolates an installation and creates a neutral, with 230 V between each phase and neutral.
• Other voltages, up to 1,000 V between phases, are available on request.
• Our other three-phase transformers with separate windings (400 V / 230 V, 230 V / 400 V, 230 V / 230 V, 208 V) are isolation transformers too: see our three-phase transformers.

What is an isolation transformer?

In an isolation transformer, the primary and secondary are two separate windings with no electrical connection between them: energy is transferred through the magnetic core, not through a conductor. This is called galvanic isolation. The EN 61558-2-4 standard uses the term isolating transformer: isolation transformer and isolating transformer are two names for the same device.

It can keep the same voltage, like the 230 V / 230 V model, or change it: a 400 V / 230 V or 230 V / 115 V transformer also isolates its secondary from the mains. On all our isolation transformers, an earthed electrostatic shield is fitted as standard between primary and secondary: it limits the transfer of interference from one side to the other.

What is an isolating transformer used for?

It protects against faults carried over from the mains and lets you choose the earthing arrangement on the secondary side, TN-S or IT for example:

• Electrical separation: with the secondary left unearthed, a first earth fault does not cause a dangerous current to flow.
• Earth-referenced neutral: one secondary terminal connected to earth becomes a neutral, with no voltage between neutral and earth. This is the solution for boiler control boards that monitor the flame relative to neutral and earth.
• Audio and hi-fi: breaking earth loops and cutting noise carried by the mains.
• Machinery and control systems: when their leakage currents trip the RCD.
• Creating a neutral in three-phase: the 400 V / 400 V + N model in vector group Dyn11 recreates a 3 × 400 V + N network on an installation without a neutral.

An EN 61558-2-4 isolation transformer is not suitable for medical locations: these require transformers complying with EN 61558-2-15, with reinforced insulation and limited leakage currents.

How to choose the right model

Single-phase or three-phase

For an appliance, a boiler, an audio rack or a single-phase machine: a single-phase isolation transformer, usually 230 V / 230 V. For a three-phase cabinet or machine, or to create a neutral: a three-phase isolation transformer in vector group Dyn11, with the neutral brought out on the secondary.

Power rating

In single-phase, add up the power of the equipment to be supplied, multiply by 1.25 and choose the next rating up: a 150 W boiler needs 188 VA, so a 200 VA model; a circuit protected at 16 A represents 3,680 VA at 230 V, so a 4 kVA model. In three-phase, multiply the current per phase by the line-to-line voltage and by √3, divide by 1,000 and choose the next standard rating up.

IP rating

IP00 open frame, for cabinet mounting; IP23 with a ventilated cover, for a dry room; IP54, protected against dust and splashing water. See our page on IP and IK protection ratings.

Protection

On the primary side, an aM fuse or a type D circuit breaker, both of which withstand the inrush current at switch-on; on the secondary side, protection rated for the output current. The recommended ratings are given on each product page.

Standards: EN 61558-2-4, and 2-6 for extra-low voltage

Our isolation transformers come under EN 61558-2-4, which covers isolating transformers; our three-phase models come under EN IEC 61558-1 and EN IEC 61558-2-4. For a safety extra-low voltage (SELV, 50 V maximum), Part 2-6 applies, the part covering safety isolating transformers: see our safety transformers. Thermal protection can be added on request.

Wound and tested in our workshop in Gailhan

ABL Transfo has been manufacturing transformers since 1993 in Gailhan, in the Gard (southern France). Every isolation transformer is wound, wired and 100 % tested there before it leaves. Standard single-phase models are dispatched from France within 24 to 48 hours and carry a 2-year warranty; three-phase models, built to order, leave the workshop within 3 working days from 1 to 50 kVA and within 6 working days from 63 to 100 kVA, and carry a 5-year warranty. With a trade account, prices are shown excluding VAT, with an immediate 5 % discount.

Another voltage, or more than 100 kVA?

For a voltage that is not available as a standard model, configure a custom single-phase transformer or a custom three-phase transformer, with its price shown online. Above 100 kVA, up to 1,000 kVA, we manufacture on request: request a quote and we will reply within 48 hours.