Digital Ammeter (Amp Meter): How to Choose and Connect It with a CT

A digital ammeter (amp meter) shows the current flowing in a circuit on an LED display. Panel ammeters measure up to 5 A directly; above that they read through a current transformer (CT) with a 5 A secondary, and you program the CT ratio into the meter. Selec panel ammeters cost ₹526 on Voltkart.

By Team Voltkart · Reviewed by Amit, Voltkart · Last updated 28 September 2026 · Prices checked 28 September 2026

This guide covers what a digital ammeter is, how it differs from a clamp meter, which setup to use on a 3-phase feeder, how to size the CT, how to wire and program the meter, and what it costs. For the wider picture of voltmeters, VAF and multifunction meters, see our digital panel meter guide.

What is a digital ammeter?

A digital panel ammeter is a meter fixed in a control-panel door that continuously shows the current in one line of a circuit. Operators use it to see whether a motor, heater or feeder is running at normal load, running light, or overloaded.

Digital vs analogue ammeter

An analogue ammeter has a printed scale that must match the CT (a 100/5 scale for a 100/5 CT). Change the CT and you must change the meter. A digital ammeter reads the CT secondary and multiplies it by the ratio you program, so one model covers everything from small feeders to large incomers. On the Selec MA series, the CT primary can be set anywhere from 5 A to 4000 A, and the meter also shows a clear "Or" (over-range) warning if the input exceeds 6.2 A.

Panel ammeter vs clamp meter

People searching for an "amp meter" often mean one of two different tools. A panel ammeter is permanently installed and gives a constant reading for operators. A clamp meter is a portable test instrument an electrician clamps around a cable to take a spot reading. If you want to monitor a feeder every day without opening the panel, you need a panel ammeter.

Types of digital ammeter

Single-phase, CT-operated panel ammeters

The workhorse is a single-phase (1Ø-2W) ammeter with a 5 A CT input. Selec makes the same meter in three front sizes: Selec MA12 (48x96 mm), Selec MA202 (72x72 mm) and Selec MA302 (96x96 mm), each ₹526. According to the Selec datasheet, the MA302 measures true RMS current with a 4-digit LED (14.2 mm digits), ±0.5% of full-scale accuracy, a 50 mA to 5 A AC input, and a 240 V or 110 V AC ±20% auxiliary supply.

Three-phase current

For a 3-phase feeder you have three choices, compared in the table below: three single-phase ammeters, one ammeter with a selector switch, or a single meter that shows all three phase currents, such as a VAF meter (volts, amps and frequency together) or a multifunction meter.

DC ammeters

DC current (battery banks, solar strings, DC drives) is measured with a DC ammeter and a shunt rather than a CT. Voltkart does not currently list DC panel ammeters; send your requirement on WhatsApp and we will help source one.

How to choose a digital ammeter: 5 checks

1. Maximum load current. This sets the CT primary. Take it from the motor nameplate or the feeder's breaker rating.
2. CT secondary. The Selec MA series takes a 5 A secondary (fixed), so buy 5 A-secondary CTs.
3. Panel cut-out. 96x96, 72x72 or 48x96 mm. The MA302 needs 46 mm of depth behind the door.
4. Auxiliary supply. 240 V AC or 110 V AC ±20% on the MA series.
5. Do you need more than current? If you also want voltage and frequency, a VAF meter is cheaper than separate meters. If you want kW and kWh, choose a multifunction meter.

CT basics for ammeters

What the CT ratio means

A CT ratio of 100/5 means that 100 A flowing in the primary (the cable or busbar through the CT) produces 5 A in the secondary wired to the meter. The meter's input range is 50 mA to 5 A, and it multiplies the reading by the ratio you set.

Worked example: sizing the CT for a motor

Say you want to monitor a 7.5 kW, 415 V, 3-phase motor.

1. Read the full-load current (FLC) from the motor nameplate. Always use the nameplate value, because it varies with motor make, efficiency and power factor.
2. Choose the next standard CT primary above the FLC, with some headroom so normal running sits in the upper half of the scale. For a motor of this size that typically means a CT such as 20/5 or 25/5, depending on the nameplate FLC.
3. Enter the same primary value (for example 20 or 25) in the ammeter's CT primary setting.

The Selec MA302 datasheet lists these CT primary settings: 5, 10, 20, 30, 40, 50, 60, 75, 80, 100, 150, 200, 250, 300, 400, 500, 600, 800, 1000, 1200, 1500, 1600, 2000, 2500, 3000 and 4000 A. Pick the value that matches your CT exactly. For setting motor overloads from the same FLC, see motor full-load current and overload setting.

Setting the CT primary in the meter

The CT primary is selected in the meter's setting menu using the front keys. The exact key sequence is given in the Selec operating manual, which is linked from the product page. After setting it, check the reading against a clamp meter on the same cable.

Safety: never open a live CT secondary

Never open-circuit the secondary of a CT while current flows in the primary. An open CT secondary can develop a dangerously high voltage. Wire the CT through a shorting link or CT test terminal block, and short it before disconnecting or replacing the meter.

How to connect a digital ammeter

Direct connection (up to 5 A)

For loads up to the meter's 5 A input, the meter's current terminals are connected in series with the load, and the CT primary is set to 5. This is uncommon on power panels but useful on small control circuits.

CT connection (the normal method)

1. Pass the phase conductor through the CT (or fit it on the busbar), with the P1 side facing the supply.
2. Run the CT secondary (S1, S2) through a shorting link or test terminal to the meter's current input terminals. Use 0.5–2.5 mm² cable, as the MA302 datasheet specifies.
3. Earth the CT secondary at one point only.
4. Connect the auxiliary supply (L and N) to the meter's supply terminals, through a small fuse or MCB.
5. Remove the shorting link, power up, and set the CT primary.

Terminal numbers differ between models, so always follow the terminal diagram printed on the meter and in its datasheet.

Three-phase with a selector switch

With three CTs and one ammeter, an ammeter selector switch routes one CT at a time to the meter while shorting the CTs that are not selected. That shorting function is why an ammeter selector switch must be used, not an ordinary rotary switch. Voltkart does not currently list CTs or selector switches. Send your CT ratio and quantity on WhatsApp to 8800754881 and we will quote.

Digital ammeter price in India (Voltkart, incl. GST)

Prices checked 28 September 2026; the product page always shows the live price. Voltkart is an authorised distributor of Selec and Cautoni Swastik, with a GST invoice on every order and delivery in 2–3 days to Delhi NCR, UP and Haryana (5–6 days elsewhere). The minimum online order is ₹1,001, so pair an ammeter with the matching voltmeter, the Selec MV305 (₹550; ₹1,076 together), or choose a 3-phase VAF meter. See all digital ammeters and panel meters or Selec products.

Troubleshooting

• Reads zero. The CT shorting link is still closed, the CT is on a different phase or cable from the one you expect, or the CT secondary is not connected.
• Reads too high or too low by a fixed factor. The CT primary set in the meter does not match the CT fitted.
• Shows "Or". The input is above 6.2 A. The CT is too small for the load, or the wrong CT is connected.
• Display blank. Check the auxiliary supply voltage at the meter's supply terminals.

Frequently asked questions

What is the price of a digital ammeter in India?

Selec MA12 (48x96), MA202 (72x72) and MA302 (96x96) digital panel ammeters are ₹526 each on Voltkart, including GST. Three-phase VAF meters that also show current start at ₹1,181.

Can a digital ammeter be connected without a CT?

Only up to its direct input, which is 5 A on the Selec MA series. For any higher current, connect it through a CT with a 5 A secondary and program the CT primary (5–4000 A) in the meter.

How do I choose the CT ratio for an ammeter?

Pick a CT whose primary rating is just above the maximum load current (for example 100/5 for a load of about 80 A), then enter the same primary value in the meter's settings.

How do I measure 3-phase current with one ammeter?

Use three CTs and an ammeter selector switch to read one phase at a time, or fit a VAF or multifunction meter that shows all three phase currents together.

Is it safe to open a CT secondary?

No. An open CT secondary under load can develop a dangerous high voltage. Always short the secondary (with a shorting link or test terminal) before removing the meter.

Related guides and products

• Digital panel meter guide: all meter types, sizes and prices
• VAF meter (volts, amps and frequency together)
• Digital ammeters and panel meters
• Overload relay sizing for motors

Need help choosing a CT ratio or meter? WhatsApp 8800754881 (Mon–Sat, 12:30–7 pm). Online orders at voltkart.in are open 24×7.