Ammeter and voltmeter

An ammeter and voltmeter refers to an analogue measuring device with a needle and graduated dial, intended for permanent indication of current or voltage on the front face of an electrical panel. These instruments work in conjunction with current transformers (CTs) or voltage transformers (VTs) depending on the network monitored. The common accuracy class is 1.5 or 2.5 depending on the reference, complying with the IEC 60051 standard.

Operating principle and measurement types of ammeters and voltmeters

Current measurement with a panel ammeter

The analogue ammeter indicates the RMS value of the current flowing in a circuit. On low-voltage installations, we systematically recommend pairing it with a current transformer (CT) when the current exceeds the value directly admissible by the instrument's movement. Our standard practice favours a 5 A secondary CT rating, standardised for most industrial panel ammeters.

Voltage measurement with a panel voltmeter

The analogue voltmeter displays the voltage between phases or between phase and neutral. On medium-voltage networks, we frequently see a voltage transformer (VT) used in the field to bring the measurable value down to the instrument's standardised ratings. Feedback from installers confirms that the rating choice must anticipate network variations without saturating the dial.

Technical characteristics and standards for analogue measuring instruments

Accuracy classes and normative compliance

The accuracy class defines the maximum permissible error as a percentage of the full-scale value. A class 1.5 guarantees a maximum error of 1.5% of full scale, while a class 2.5 allows 2.5%. We observe that design offices reserve class 1.5 for critical measurement points and class 2.5 for basic visual supervision. Compliance with IEC 60051 ensures consistency of tests and performance between manufacturers.

Construction materials and mounting modes

The housing of panel ammeters and voltmeters comes in plastic or metal versions depending on the installation environment. Our installation feedback shows that metal housings are preferred in industrial panels for mechanical strength, while plastic versions suit tertiary distribution panels. Front-face mounting is by flush fitting with the supplied fixing and connection accessories.

Applications and value of needle-based measuring devices in electrical panels

Permanent visual supervision with no auxiliary power

The decisive advantage of the analogue instrument lies in its immediate, permanent reading with no need for external power or a digital screen. We find that this energy independence is decisive in unconditioned technical rooms or as a backup to digital systems. The needle allows an instant sense of the order of magnitude and variation trends, useful for quick diagnosis.

Preferred installation contexts for analogue meters

Typical applications include direct reading on the front face of distribution panels, motor control panels and metering boards. Our installation experience confirms that these devices remain relevant as a local backup indicator, complementing digital remote-monitoring systems. The robustness of the moving-coil or moving-iron movement provides high longevity in electromagnetically disturbed environments.

Frequently asked questions

Which accuracy class should be chosen between 1.5 and 2.5 for a panel ammeter?

Class 1.5 suits measurements requiring better fidelity, such as consumption monitoring or machine protection. Class 2.5 is sufficient for basic visual supervision where order of magnitude matters more than absolute accuracy.

Can an analogue ammeter work without a current transformer?

Only very low direct ratings, typically under 5 A, allow direct connection. For usual industrial currents, pairing with a CT is mandatory to adapt the current and isolate the instrument from the network.

Does the IEC 60051 standard apply to digital voltmeters and ammeters?

IEC 60051 specifically covers direct-acting analogue indicating electrical instruments. Digital instruments fall under other standards, notably IEC 61010 for safety requirements.

Which type of housing should be preferred for an installation in an industrial environment?

We recommend the metal housing for its resistance to impacts, vibration and chemical agents present in workshops. The plastic housing remains suited to tertiary or protected environments where mechanical stress is lower.

Do analogue voltmeters need a voltage transformer at low voltage?

At direct low voltage, voltmeters generally connect without a VT on 400 V or 500 V ratings. The voltage transformer becomes necessary as soon as the voltage exceeds the maximum value of the available rating, or at medium voltage for insulation reasons.