Ammeters Selection Guide

An ammeter is a measuring instrument that shows the current flowing through a circuit in amperes; this guide covers panel-mount models, the AC-DC distinction and current transformer selection.

What is an ammeter? An ammeter is a measuring instrument that shows the electric current flowing through a circuit in amperes, and it is connected in series with the circuit being measured. A panel-mount ammeter fixes this readout to the enclosure door; the current can be monitored continuously without opening the door. For large currents, the device measures through a current transformer; there are separate models for AC and DC.

This guide explains what to look at when choosing products in the Ammeters category.

Types of ammeters

• Analog ammeters: Tense's pointer-type models with a 90° scale connect directly to the line. In 72 × 72 and 96 × 96 mm housings, they are listed by their full-scale values such as 5 A, 30 A, 60 A and 100 A.
• Digital ammeters: Offered in three input types. Models with an X/5 A input connect to the secondary of the current transformer on the line. On Tense models ending in D such as DJ-A48D and DJ-A72D, and on DIN box DA models, the current transformer is included in the box contents according to the product data. DC models read the current through a measuring shunt.

Digital models are available with 36 × 72, 48 × 48, 72 × 72 and 96 × 96 mm panel housings or with DIN rail mounting. The product data of the Tense DJ-A72S and DJ-A96S models lists a high-low current protection function, adjustable set values, a start-up delay time and a contact output.

What to look at when choosing an ammeter

1. Current type. A current transformer works with alternating current; a DC circuit requires a DC ammeter and a shunt.
2. Input type. In a directly connected model, the entire line current passes through the device. In measurement with a current transformer, a conductor is passed through a current transformer and the ammeter is connected to the secondary of the transformer. In current transformers the secondary rated current is standardized as 1 A or 5 A; the transformer-connected models in this category are listed in the product data with an X/5 A input.
3. Transformer ratio and scale. The primary value or the analog scale full-scale value is chosen as a value close to, and above, the highest continuous operating current of the line. With a value chosen too large, low loads cannot be distinguished legibly. If you do not know the current of the line, you can find a preliminary value with the calculating current and fuse from active power tool.
4. Housing and mounting. The 48 × 48, 72 × 72 and 96 × 96 mm values are the front frame dimensions; the cut-out to be made in the enclosure door is smaller than this and is made according to the dimension in the product manual. DIN rail models are mounted inside the enclosure.
5. Supply. The supply voltage of digital models is stated in the product name with values such as 110/230 V AC or 24-250 V AC/DC; match it to the control voltage in the enclosure.
6. Number of phases. To monitor all three phases together, either one ammeter is fitted to each phase or a model that measures three phases is chosen.

Connection with a current transformer and a shunt

In measurement with a current transformer, the ammeter is the load that completes the secondary circuit of the transformer. Leaving the secondary circuit open while current flows in the primary creates a dangerous voltage; for this reason, connection and removal work is carried out according to the manufacturer's instructions. The rated power (VA) of the transformer must cover the total burden of the ammeter and the connecting conductors; a long, thin conductor increases this burden.

In DC measurement, the current passes through a measuring shunt connected in series with the line; the ammeter displays the millivolt-level voltage across the shunt terminals as current. In the product data of the DC models in this category, the shunt input is stated as 60 mV; the millivolt value and rated current of the shunt must match the setting on the ammeter.

Choosing between an ammeter, a multimeter and an analyzer

• If current and voltage are to be seen on a single device, panel-mount multimeters are suitable.
• If power, energy and power factor are also to be monitored, see the power network analyzers category.
• If only a 22 mm hole can be drilled in the enclosure door, ammeter pilot lights can be used.
• Handheld clamp meters for temporary measurements without opening the circuit when troubleshooting are in a separate category.

Brands in this category

• Tense: analog direct ammeters with A72 and A96 codes; digital panel ammeters with DJ-A codes, DC models and DIN box models with DA codes.
• Entes: EPM series digital ammeters; housings such as 48 × 48, 72 × 72 and 96 × 96 mm, with 110/230 V AC or 24-250 V AC/DC supply.
• Schneider Electric: ammeters with LED displays that measure single-phase and three-phase.

Order notes

• Sales are by the piece. Some of the products are listed as made-to-order; for these models the lead time is confirmed before ordering.
• For models with an X/5 A input, the current transformer is ordered separately; models where the transformer is included in the box contents are indicated in the product data.
• The manufacturer code in product names (for example DJ-A96, EPM-4D-72) can be used when searching.

Comparison and selection table

Frequently asked questions

What does an X/5 A ammeter mean?

X/5 A indicates that the ammeter measures the line current not directly but through the 5 A secondary current of the current transformer. X is the primary rated current of the transformer: with a 200/5 A transformer, when 200 A flows in the line, 5 A reaches the ammeter input. In digital models the transformer ratio is entered into the device and the display shows the actual line current. In current transformers the secondary rated current is standardized as 1 A or 5 A.

How do I choose the current transformer ratio for an ammeter?

The primary rated current is chosen as a value close to, and above, the highest continuous operating current of the line. With a transformer chosen too large, the secondary current becomes small at low loads and the reading gets coarse; a transformer chosen too small is overloaded. The secondary value must be the same as the ammeter input; the transformer-connected models in this category have a 5 A input. The busbar or cable size must also fit the transformer window.

How is DC current measured with a panel ammeter?

Because a current transformer works with alternating current, it is not used in a DC circuit. DC current is measured with a measuring shunt connected in series with the line: the current flows through the shunt, a millivolt-level voltage proportional to the current develops across the shunt terminals, and the DC ammeter displays this voltage as current. The product data of the DC models in this category states a 60 mV shunt; the rated current of the shunt is matched to the setting on the ammeter.

Should I choose an analog ammeter or a digital ammeter?

A pointer-type analog ammeter shows at a glance, through pointer movement, the current rising and falling, and it does not need an auxiliary supply. A digital ammeter gives the value as a number, the current transformer ratio can be set, and some models have a high-low current protection function; on the other hand, it needs a supply voltage. The analog models in this category are directly connected; digital models are listed for measurement with a current transformer.

What is the difference between a panel-mount ammeter and a clamp meter?

A panel-mount ammeter is permanently connected to the circuit and shows the current continuously. A clamp meter is a handheld measuring instrument; its jaws are closed around the conductor to take an instantaneous measurement without opening the circuit, and it is used in troubleshooting and commissioning work. If continuous monitoring in the enclosure is wanted, a panel-mount ammeter is suitable; if temporary measurements at different points are wanted, a clamp meter is suitable.