Variac Electrical Labs Lab Equipment Manufacturer, Supplier and Exporter in India

Three variable transformers are listed here, VEL-0001 to VEL-0003: one single-phase and two three-phase, offered in portable, table, floor-mounting, panel-mounting, enclosed and open forms. The names concatenate those options rather than describing one product, so tell the supplier the configuration you want and quote the code. Before any of that, one point matters more than every specification on the page: a variable transformer of this type does not isolate the output from the supply. It is not a substitute for an isolation transformer, and the section below explains why that matters in a student laboratory.

What is in the range

A variable transformer is not an isolation transformer

A variable transformer of this kind is an autotransformer: it has one winding, and the output is taken from a brush running along that winding. Because the winding is shared, the output is electrically connected to the incoming supply. Turning the dial to a low voltage reduces the voltage between the output terminals; it does not make either output terminal safe with respect to earth, and the neutral or one line of the supply remains connected through to the output. Two consequences follow, and both are routinely got wrong:

• Setting a variable transformer to a low voltage does not make the circuit downstream safe to touch. Treat the output as live at mains potential with respect to earth whatever the dial reads.
• It does not solve the oscilloscope earth problem. If the reason you want a variable supply is to probe a mains-referenced circuit safely, what you need is a genuine isolation transformer, or a differential probe, in addition to the variable transformer. Feeding a circuit from a variable transformer and then clipping an earthed probe ground into it is exactly as dangerous as doing so without one.

If your laboratory needs both a variable voltage and isolation, ask the supplier whether an isolating variable transformer, that is a variable autotransformer followed by a separate isolation transformer, can be supplied as one unit, and what its rating is. Ask the question explicitly, because catalogues frequently use the words interchangeably.

The specification to ask for

• Current rating, and whether it holds across the whole range. This is the specification most often misread. Ask for the continuous output current and whether that figure applies at every dial setting, and ask for the rating in kilovolt-amperes as well, since a transformer rated for a current at full output may not deliver it at a low setting without overheating the winding.
• Input voltage and output range. Ask whether the output runs from zero to the input voltage or beyond it, since many of these transformers are wound to give an output above the input at the top of the dial, which is useful for over-voltage testing and a hazard if nobody expects it.
• For the three-phase units, whether the three sections are ganged on one shaft and tracked together, how closely they track, and whether the output is a three-wire or four-wire arrangement with a neutral.
• Protection. Ask what protection is built in: an input fuse or breaker sized for the transformer, an output fuse, and a voltmeter and ammeter on the panel, which for a teaching bench are worth having so students see the loading.
• Enclosure and terminals. For a student laboratory specify an enclosed unit with shrouded terminals, an earthed case and a cable gland, not an open frame. Ask for the ingress protection rating and whether the dial has a scale that can actually be read from a standing position.
• Duty and cooling. Ask whether the rating is continuous or intermittent, whether cooling is natural or forced, and what the permitted ambient temperature is, which matters in an unconditioned laboratory.
• Brush life. The carbon brush is the wearing part. Ask the expected life, the replacement price and whether a technician can change it, and ask what happens to the output if the brush sticks.

What these are used for in a teaching laboratory

A variable transformer earns its place in several standard practicals: bringing a machine or transformer up slowly so starting current can be observed; running the open-circuit test on a transformer at reduced voltage; varying the supply to a lamp or heater load to plot a characteristic; checking how a power supply or an appliance behaves at the low and high ends of its input range; and feeding a rectifier or converter experiment at a chosen voltage. For every one of those, size the unit on the current the load actually draws, including its inrush, rather than on the load's steady rating, and ask the supplier to confirm the choice against the load you describe.

Also worth confirming

The quantity per bench; the weight, since these are heavy for their size and a floor-mounting unit is not moved casually; the supply voltage, frequency and plug type for your country, and the terminal arrangement; whether a test certificate is supplied; spares, in particular brushes and fuses; and the warranty. Note that the three product names in this listing are strings of mounting options rather than product names, so state the phase, rating, mounting and whether you want it enclosed on your enquiry. Any rating quoted is confirmed in writing on the quotation; ask for the test conditions and the temperature rise behind it.

Related ranges on this site

Machines, transformers and the tests these supplies are used for are under Electrical Engineering Trainers and Electrical Training Equipment, with motors under Electric Motors. Converter and drive experiments, where the oscilloscope earth problem is set out at length, are under Power Electronics Trainers. Measurement is under Testing and Measuring Lab Trainers and Power and Instrumentation Lab. Parent range: Training Kits.

Request a quote

Describe the load, including its inrush, and state the phase, mounting and enclosure you need. For example a single-phase enclosed table-mounting unit (VEL-0001) at the current rating your load requires, six benches, with the continuous rating, the output range and the protection fitted confirmed in writing, and state separately whether you also need isolation. Contact Ray Export for prices, ratings and lead times.

Frequently asked questions

Is a variable transformer the same as an isolation transformer?

No. The units on this page are autotransformers: they have one winding, and the output is taken from a brush running along it. Because the winding is shared, the output is electrically connected to the incoming supply. Turning the dial down reduces the voltage between the output terminals, but it does not make either terminal safe with respect to earth, and the neutral or one line of the supply remains connected through. Treat the output as live at mains potential, whatever the dial reads.

Can I use a variable transformer to probe a mains circuit with an oscilloscope?

Not on its own. The page is direct: feeding a circuit from a variable transformer and then clipping an earthed probe ground into it is exactly as dangerous as doing so without one. To probe a mains-referenced circuit safely you need a genuine isolation transformer or a differential probe in addition. If you need both a variable voltage and isolation, ask whether an isolating variable transformer, a variable autotransformer followed by a separate isolation transformer, can be supplied as one unit, and at what rating.

What current rating should I specify?

The continuous output current, and whether that figure applies at every dial setting; the page calls this the specification most often misread. Ask for the rating in kilovolt-amperes as well, since a transformer rated for a current at full output may not deliver it at a low setting without overheating the winding. Size the unit on the current your load actually draws, including its inrush, rather than its steady rating, describe the load in your enquiry, and have the choice confirmed in writing on the quotation.

Does the output go above the input voltage?

It may, so ask. Many variable transformers are wound to give an output above the input at the top of the dial, which the page notes is useful for over-voltage testing and a hazard if nobody expects it. Ask whether the output of the unit you are buying runs from zero to the input voltage or beyond it. For the three-phase units, ask whether the three sections are ganged on one shaft and track together, how closely, and whether the output is three-wire or four-wire with a neutral.

Which form is best for a student laboratory?

An enclosed unit with shrouded terminals, an earthed case and a cable gland, not an open frame. VEL-0001 and VEL-0003 are offered in portable, table, floor-mounting, enclosed and open forms; VEL-0002 is listed for flush and back-of-panel mounting, open. Ask for the ingress protection rating and whether the dial scale can be read from a standing position. For protection, ask for an input fuse or breaker sized for the transformer, an output fuse, and a voltmeter and ammeter so students see the loading.

What wears out on a variable transformer, and what should we keep in spares?

The carbon brush is the wearing part. Ask its expected life, whether a technician can change it, and what happens to the output if the brush sticks. Keep brushes and fuses as spares. Ask also whether the rating is continuous or intermittent, whether cooling is natural or forced, and the permitted ambient temperature, which matters in an unconditioned laboratory. These units are heavy for their size, so ask the weight too; a floor-mounting unit is not moved casually.

Key takeaways

• Three units: VEL-0001 single-phase; VEL-0002 and VEL-0003 three-phase, in a choice of mounting forms.
• Not isolated: the output stays connected to the supply; treat it as live at mains potential whatever the dial reads.
• Isolation is a separate purchase: probing mains circuits needs an isolation transformer or a differential probe as well.
• Rate for the whole dial: ask the continuous current at every setting and the kVA, and size for inrush.
• Check the top of the dial: some units give an output above the input voltage.
• Enclosed for students: shrouded terminals, an earthed case, fuses and panel meters, not an open frame.

About this page

Ray Export is a manufacturer and exporter of laboratory, scientific and educational equipment based at Plot No. 449, HSIIDC Industrial Area, Saha, Ambala, Haryana 133104, India. Enquiries: [email protected], +91-9817319615.

Written by Palak Mall, Senior Content Writer. Technically reviewed by Arvind Kumar, Lab Equipment Specialist, 12+ years in laboratory and testing instrumentation. Last updated: 17 October 2026.

Specifications for VEL-0001 to VEL-0003, including phase, continuous current and kVA rating, output range, mounting, enclosure, protection, duty and brush arrangements, are confirmed in writing on the quotation. For a test certificate or other certificates, contact us for the latest copies of the relevant certificates. No price is quoted on this page. Listing notes: the three product names are strings of mounting options rather than descriptions of one product, and no current or kVA rating is stated for any code, so state the phase, rating, mounting and enclosure on every enquiry.