Volt Ratio Box Manufacturer,Supplier and Exporter in India
Product Code : EL-SI-8124
Jlab Export is a leading Volt Ratio Box Manufacturer,and suppliers in India
Volt Ratio Box (code EL-SI-8124) is a tapped resistive divider for extending the range of a Crompton potentiometer, so that voltages well above the potentiometer’s own range can be measured and voltmeters calibrated in electrical measurement labs. Its tapping points give multiples of 1.5 V, up to 750 V on the main model or 300 V on Volt Ratio Box 1. It is made by Jain Laboratory Instruments Pvt Ltd (JLab) at its works in Ambala, India.
Specifications
| Parameter | Detail |
|---|---|
| Purpose | Extends the range of the Crompton potentiometer |
| Tapping points | A number of tapping points giving multiples of 1.5 V |
| Ranges, 750 V model | 1.5, 15, 30, 150, 300 and 750 V |
| Resistance, 750 V model | 37,500 ohms |
| Ranges, Volt Ratio Box 1 (300 V model) | 1.5, 15, 30, 150 and 300 V |
| Resistance, Volt Ratio Box 1 (300 V model) | 15,000 ohms |
| Accuracy | +0.02% (as listed, both models) |
| Quality check | Each volt ratio box is visually inspected before dispatch |
| Pack quantity | Each (sold individually) |
| Minimum order quantity | 10 units |
| Dispatch time | Usually 7–10 working days |
| Product code | EL-SI-8124 |
| Manufacturer | Jain Laboratory Instruments Pvt Ltd (JLab) — OEM |
| Country of origin | India (made in Ambala, Haryana) |
Which Volt Ratio Box Model?
| Model | Ranges | Total resistance | Multiplying factors | Current at top range |
|---|---|---|---|---|
| Volt Ratio Box, 750 V (EL-SI-8124) | 1.5, 15, 30, 150, 300, 750 V | 37,500 ohms | 10, 20, 100, 200, 500 (and 1 on the 1.5 V range) | 20 mA (750 V / 37,500 ohms) |
| Volt Ratio Box 1, 300 V (EL-SI-8124) | 1.5, 15, 30, 150, 300 V | 15,000 ohms | 10, 20, 100, 200 (and 1 on the 1.5 V range) | 20 mA (300 V / 15,000 ohms) |
Choose the 750 V model if you calibrate or measure above 300 V; Volt Ratio Box 1 covers the same lower ranges up to 300 V with a smaller total resistance. Both are listed with the same accuracy and draw the same current at their top range.
What Is a Volt Ratio Box Used For?
A potentiometer can balance only voltages smaller than the potential difference across its own measuring circuit, which is set by its working battery — a 2 V battery in the case of the Crompton potentiometer. The volt ratio box is a precision divider placed in front of it: the voltage to be measured is connected to the terminal for the chosen range, the potentiometer measures the small voltage across the low section of the divider, and that reading is multiplied by the ratio of the range in use. Because every range is a multiple of 1.5 V, the multiplying factors are simple numbers.
In degree, diploma and polytechnic labs it is used to calibrate DC voltmeters at several points across their scales and to measure higher DC voltages with potentiometer accuracy. The divider takes a small current from the source — 20 mA at the top range of either model — which is negligible for a supply but should be allowed for with a high-resistance source. Voltages of hundreds of volts are dangerous: connect leads and change ranges with the supply switched off, use insulated leads, and keep the box on a dry bench.
What to Specify When Ordering
- Model — the 750 V box (37,500 ohms) or Volt Ratio Box 1 for up to 300 V (15,000 ohms).
- Accuracy wording — if a tender needs the tolerance stated as plus-or-minus, ask for it to be confirmed in the quotation.
- Quantity — the minimum order is 10 units.
- Companion items — Crompton potentiometer, standard cell, galvanometer and standard resistance, quoted together if required.
Frequently Asked Questions
What does a volt ratio box do?
It extends the range of a Crompton potentiometer. Its tapping points give multiples of 1.5 V, so a high voltage is divided down to a level the potentiometer can balance.
Which ranges are available?
The main model has ranges of 1.5, 15, 30, 150, 300 and 750 V with 37,500 ohms resistance. Volt Ratio Box 1 has ranges of 1.5, 15, 30, 150 and 300 V with 15,000 ohms.
What accuracy is listed?
The listing gives +0.02% for both models. If your tender needs the tolerance written as plus-or-minus, ask JLab to confirm it in the quotation.
How is the potentiometer reading converted to the actual voltage?
Multiply the reading by the ratio of the range in use: 10 on the 15 V range, 20 on the 30 V range, 100 on the 150 V range, 200 on the 300 V range and 500 on the 750 V range.
How much current does it draw from the source?
At the top range, 750 V across 37,500 ohms or 300 V across 15,000 ohms, the current is 20 mA in both models.
Who manufactures the volt ratio box?
JLab (Jain Laboratory Instruments Pvt Ltd) makes it at its works in Ambala, Haryana, India, alongside the Crompton potentiometer it is designed for.
OEM Manufacturer
JLab is the trading name of Jain Laboratory Instruments Pvt Ltd, a manufacturer of electrical measurement and physics lab instruments in India, incorporated in 2017 and based on Hargolal Road, Ambala, Haryana. The volt ratio box is built at JLab’s own works rather than sourced from a trader, so colleges, polytechnics, dealers and importers order direct from the maker; every box is visually inspected before dispatch, and repeat orders are handled by the same team. Its registrations include CIN U29309HR2017PTC069123 and MSME Udyam registration UDYAM-HR-01-0003849 (manufacturing enterprise). JLab exports worldwide and ships to buyers in every region — for example Brazil in South America, Afghanistan in South Asia, Samoa in Oceania, Estonia in Northern Europe and Ukraine in Eastern Europe. Tender buyers can refer to the JLab lab tenders page.
Instruments for Voltage Calibration
- Crompton Potentiometer — the potentiometer whose range this box extends.
- Standard Cell — a stable voltage reference for standardising the potentiometer.
- Standard Resistance — aged manganin coils in oil-filled metal vessels, for current measurement by potentiometer.
- Moving Coil Galvanometer — a centre-zero galvanometer for the balance point.
- Voltmeter Laboratory Type — multi-range laboratory voltmeters of the kind checked with a potentiometer.
- Calibration of Voltmeter & Ammeter — a calibration unit with digital panel meters and a built-in standard cell.
More instruments are in the Scientific Instrument range and the Indian Instruments section.
Request a Quote
JLab quotes directly as the manufacturer. Use the Add To Cart enquiry button, or send the model (750 V or 300 V), the quantity (minimum 10 units), any potentiometer or standard cell to go with it and your delivery location through the contact page.
Last updated: 8 October 2026
