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230V isolation transformer buying guide

Updated: October 2026

You want galvanic separation at mains voltage for one appliance, and the amazon.co.uk results mix chassis parts, Schuko boxes and units that are really 110 V site transformers. A 230V isolation transformer is the right class only when the secondary stays at mains voltage and the windings are separate. This page is the order to use before you compare brand names: the standard part, the continuous VA, the voltage on the plate, then the plug. The product rows and shelf prices sit on the [isolation transformer comparison](/hub/electrical-equipment/isolation-transformer). Prices are the saved amazon.co.uk figures. We did not lab-test a winding. A qualifying purchase can earn us a commission at no extra cost to you.

You want galvanic separation at mains voltage for one appliance, and the amazon.co.uk results mix chassis parts, Schuko boxes and units that are really 110 V site transformers.

Our top picks

Watts Control Watts Control 1.5 kVA cased isolator

Best overall

Watts Control Watts Control 1.5 kVA cased isolator
7.0/10about £149.99
View offer
SACVXOKD SACVXOKD BK150VA 150 VA chassis

Best value

SACVXOKD SACVXOKD BK150VA 150 VA chassis
4.6/10about £41.99
View offer
FUNTLY FUNTLY DB-20VA 20 VA chassis

Rank 3

FUNTLY FUNTLY DB-20VA 20 VA chassis
2.8/10about £22
View offer
On this page
  1. 1.Which standard part you are buying
  2. 2.Continuous VA, the intermittent figure and the trip
  3. 3.Voltage and the UK plug
  4. 4.What the three listings actually state
  5. 5.When to stop and call an electrician

Which standard part you are buying

Start with the part of the standard, not the word isolation on the box. A general isolating transformer with a secondary above 50 V AC sits in BS EN IEC 61558-2-4. Part 2-6 is the SELV family, so a 230 V secondary does not belong there. Part 2-15 is fixed medical IT, not a portable workshop box. Part 2-23, with the secondary centre-tap earthed, is the reduced-low-voltage transformer used on UK construction sites. A line that only says “BS EN 61558” has not told you which of those jobs the maker tested for.

Continuous VA, the intermittent figure and the trip

Read the continuous rating first. Intermittent kVA is a second figure, and it only means something when the page also tells you the duty. Carroll & Meynell define intermittent as 25% duty on their CM750/230 trade page. That definition belongs to that trade range. Do not paste 25% onto B0GV3XRSCG, because that amazon.co.uk listing states 1.5 kVA continuous and 3 kVA intermittent and never states a duty cycle. That duty figure stays on the trade page. It is not a legal minimum in the Electrical Equipment (Safety) Regulations 2016.
Watts Control Watts Control 1.5 kVA cased isolator

Testsieger

Watts Control Watts Control 1.5 kVA cased isolator
7.0/10about £149.99
View offer

Voltage and the UK plug

UK public supply in Health and Safety Executive guidance is 230 V. A plate that says 220 V to 220 V is a different statement. The two chassis listings are 220/220. You do not relabel them as 230/230 because the mains in the house is nominally 230 V. You also do not expect 110 V out of any of these three pages. None of them describes a centre-tapped secondary. The plug is the next reject. B0GV3XRSCG states a 16 A Schuko input plug and two 16 A Schuko sockets. A Schuko plug does not enter a shuttered BS 1363 socket, and 16 A is the wrong current for a 13 A UK outlet. Forcing the pins damages the socket.

What the three listings actually state

If the job is a building site rather than 230 V separation, leave this set and read the isolation transformer vs site transformer page before you add anything to the basket.

When to stop and call an electrician

This buying order stops at a portable unit for one appliance. Fixed wiring, a medical IT system under part 2-15, and an EV separating supply under BS 7671 regulation 722.413.1.2 are design work. A construction site wants cordless tools or a 110 V centre-tapped supply so that voltage to earth does not exceed 55 V. That is the Health and Safety Executive’s construction guidance, not a 230/230 isolator.

Common questions

Is BS EN 61558-2-4 the right part for 230 V out?
Yes, for a general isolating transformer whose secondary is above 50 V AC, which is where a 230 V output sits. BSI’s scope for BS EN IEC 61558-2-4:2025 is that general application, up to 25 kVA single-phase in the ordinary range. Part 2-6 is SELV. Part 2-15 is fixed medical IT. Part 2-23 is the site transformer with the centre tap earthed. A bare “BS EN 61558” line, as on B0GV3XRSCG, does not name any of those parts.
What is the difference between continuous and intermittent kVA if the duty cycle is missing?
Continuous is the figure you use for a load that stays on. Intermittent is a higher figure that only makes sense with a stated on/off duty. Carroll & Meynell use 25% for intermittent on a trade page for the CM750/230. B0GV3XRSCG prints 1.5 kVA continuous and 3 kVA intermittent and does not print a duty, so you do not borrow 25% from the other maker. A 3 kW kettle, about 13 A at 230 V, is above the 1.5 kVA continuous rating and above the 10 A trip.
Can a 16 A Schuko plug go into a UK 13 A socket?
No. The pin pattern is different, and a BS 1363 socket is shuttered for its own plug. Regulation 35 requires a BS 1363 plug, or a non-UK plug with a conversion plug and a BS 1362 fuse, for equipment intended for domestic use on a UK socket. B0GV3XRSCG states 16 A Schuko connectors. Forcing the plug damages the socket and still leaves you without the fuse arrangement the regulation describes.
Is 20 VA or 150 VA enough for a kettle or a drill?
No. B0CKBSHQR9 is 20 VA and B0DKBZT4LV is 150 VA at 0.68 A. A kettle is a kilowatt-class load, and a 3 kW kettle is about 13 A at 230 V. A mains drill is usually hundreds of watts, which is already past both chassis ratings, and you still read the drill’s own plate. Those two listings are small components, not tool supplies. The cased unit’s continuous rating is 1.5 kVA, which still does not cover that 3 kW kettle.
Does “UK manufactured” mean the plug is BS 1363?
No. B0GV3XRSCG names Watts Control Transformers LTD as the manufacturer and leaves country of origin blank. The connectors on the same page are a 16 A Schuko plug and two Schuko sockets. A company name, or a seller’s “UK manufactured” line elsewhere, does not change the plug that is printed. You buy the connector the listing states.

Related pages

Best isolation transformer

How to use an isolation transformer

Isolation transformer

Isolation transformer for electronics repair limits

Isolation transformer vs site transformer explained

Sources

Public UK sources from the research digest. Shelf prices are the amazon.co.uk figures in the display file. We did not treat trade-catalogue prices as amazon.co.uk prices.

  1. HSE: electricity on construction sites (retrieved 22 October 2026)
  2. HSE: electrical equipment (retrieved 22 October 2026)
  3. Electrical Equipment (Safety) Regulations 2016, regulation 35 (retrieved 22 October 2026)
  4. GOV.UK: Electrical Equipment (Safety) Regulations 2016 (retrieved 22 October 2026)
  5. BSI: BS EN IEC 61558-2-4:2025 (retrieved 22 October 2026)
  6. IET Wiring Matters: separation and isolation (retrieved 22 October 2026)
  7. Carroll & Meynell: 230 V to 230 V isolation transformer duty (retrieved 22 October 2026)
  8. ABL: isolation transformer sizing (retrieved 22 October 2026)