JMB Safe Portable Lighting Transformer 220V/380V to 12V/24V/36V

On a mine face, inside a ship hull, or in a tunnel with water running down the walls, mains voltage and portable hand lamps are a dangerous combination. The JMB safe portable lighting transformer exists to remove that risk: it takes 220V or 380V mains and steps it down to a safety extra-low voltage of 12V, 24V or 36V, so the lamp a worker is holding cannot deliver a lethal shock even if the cable is damaged and the fitting is standing in water. The secondary winding is galvanically isolated from the mains, which means the output has no reference to earth at all. We build the JMB range in Yueqing with cold-rolled oriented silicon steel cores and oxygen-free copper windings, in enclosures built for rough handling, and we supply them with the explosion-proof and waterproof lamp heads that site work actually requires.

Key Specifications

What You Get

• JMB safety isolation transformer wound to your specified input and output voltages
• Galvanically isolated secondary – the output is floating and safe to touch
• Oxygen-free copper windings on a cold-rolled oriented silicon steel core
• Portable steel enclosure with carry handle, built for site conditions
• Thermal cut-out and earthed screen between primary and secondary
• Terminals clearly marked, wiring diagram fixed to the case
• 12-month replacement-first warranty

Why Choose This Model

The safety case for a JMB lighting transformer is simple and worth spelling out. A shock becomes lethal because current flows through the body to earth. On a 220V supply in a wet tunnel, a damaged lamp cable can easily deliver that current. On the isolated 12V, 24V or 36V secondary of a JMB transformer, there is no path to earth at all, because the secondary winding has no electrical connection to the mains or to ground. A worker can touch a live conductor and feel nothing. That is why safety rules in mining, tunnelling, shipbuilding and confined-space work call for safety extra-low voltage on portable lamps, and why inspectors look for the transformer before they look at anything else. Beyond safety, the practical case matters too: the JMB is built to be carried, dropped and used in the rain. The core is cold-rolled oriented silicon steel for low loss and low heat, the windings are T1 grade oxygen-free copper so they run cool and resist oxidation, and the case is steel with a handle rather than a plastic box that cracks the first time it is knocked off a scaffold. We build these for contractors working in African mines, Southeast Asian construction sites and Middle Eastern oilfield maintenance, where the equipment has to survive conditions that would finish a consumer-grade unit in a week.

How to Size It

Size the transformer on the total wattage of the lamps it will run at the same time, then add roughly 20 percent headroom so the unit is not sitting at its limit all shift. A single 100W portable lamp on a 36V circuit needs a transformer rated at about 120VA or larger; four of them need 500VA. Cable length matters more than people expect: at 12V the current is high and voltage drop over a long run is significant, so if the lamp is more than about 20 metres from the transformer, either move the transformer closer or specify 24V or 36V instead of 12V to halve or third the current. Tell us the lamp wattage, the number of lamps and the cable run, and we will specify the right rating and output voltage for the job.

How It Works

The protection a JMB provides comes from galvanic isolation, not from the voltage reduction alone, and the difference matters. A transformer transfers energy through a magnetic field: the primary winding and the secondary winding are physically separate coils with no electrical connection between them. So the 12V, 24V or 36V secondary circuit has no reference to the mains and no reference to earth. Touch one conductor and no current flows, because there is nowhere for it to flow to. Touch both conductors and you still only have 12V, 24V or 36V across you. This is why safety extra-low voltage circuits are specified for portable hand lamps in conductive locations, and why the rules require the transformer to be a genuine safety isolating transformer rather than an autotransformer or a switched-mode supply. An autotransformer shares a winding between input and output, so the output is still referenced to mains and provides no protection at all. We build the JMB with a true double-wound isolating construction, plus an earthed screen between the windings so that a primary-to-secondary insulation fault shows up as an earth fault rather than putting mains on the lamp lead.

Typical Applications

• Underground mining and tunnel boring
• Confined-space work in tanks, boilers and pressure vessels
• Shipbuilding, ship repair and hull inspection
• Oil and gas maintenance in hazardous areas
• Construction sites and temporary site lighting
• Maintenance work in wet or conductive locations
• Any application where portable hand lamps run near earthed metal

Testing Before Shipment

Each JMB is tested before it leaves the bench. We verify the turns ratio, measure the output voltage on load to confirm regulation, and check the insulation resistance both between windings and from each winding to the core and frame – the latter being the test that matters most for a safety transformer, since it is what guarantees the secondary is genuinely floating. We confirm the earthed screen is continuous and correctly bonded, check that the thermal cut-out operates, and run the unit at rated load until the temperature stabilises. Each order ships with a test report covering these results. If your project requires third-party certification, dielectric testing to a specific standard, or particular documentation for a mine safety inspector or a site approval, tell us when you enquire so we can confirm exactly what we can supply before you commit.

Ordering, Samples and Shipping

The JMB range is made to order with a 10 pcs minimum and a 15-25 day lead time, and we need four things to quote: the input voltage (220V or 380V), the output voltage (12V, 24V or 36V), the capacity in VA, and the quantity. If you need a particular enclosure – waterproof, explosion-proof, or a specific ingress rating – tell us at the same time, because it changes both the build and the lead time. We can also supply the matching portable lamp fittings if you want the transformer and the lamps as one line item. Samples are available and are paid by T/T before production, with the sample cost credited against a subsequent production order. Standard shipping is FOB Ningbo or Shanghai, and sample quantities can go by air courier.

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