What Is a Voltmeter-Ammeter Pilot Light? Wiring and Selection Criteria
A voltmeter-ammeter pilot light is a panel door indicator in a 22 mm pilot light housing that shows voltage and, via a current transformer, current on an LED display.
A voltmeter-ammeter pilot light is a panel door indicator in a 22 mm pilot light housing that shows both the voltage (V) and the current flowing through a conductor (A) on an LED display. In compact panels with no room for a separate voltmeter and ammeter, it shows the voltage and load current of a supply or motor line through a single hole without opening the door.
How is it connected?
The indicator has two separate measuring inputs:
- Voltage input: Connected in parallel across the two points to be measured (e.g. phase-neutral).
- Current input: The measured current does not flow through the indicator. The phase conductor is passed through a small ring-shaped current transformer, and the transformer leads are connected to the indicator's current input.
Because a current transformer only works with alternating current, these indicators are not used in direct current (DC) circuits. The terminal layout can vary between models; wire it according to the diagram on the product, with the power off.
Pilot light type measuring indicators
| Type | What it shows | In the catalogue |
|---|---|---|
| Voltmeter pilot light | Voltage only | 15 products: Gwest, Isıso, KSN |
| Ammeter pilot light | Current only | 15 products: Gwest, Isıso, KSN |
| Voltmeter-ammeter pilot light | Voltage and current | 5 products: KSN |
Selection criteria
- Voltage range: The models in the catalogue measure 50–500 V; both 230 V phase-neutral and 400 V phase-phase voltages fall within this range. They are not connected directly to higher voltages such as 690 V.
- Current range: Measurement is 0–100 A. The line's continuous operating current must stay within this range; larger currents need a panel ammeter working with an X/5 A current transformer.
- Current transformer: Check on the product page whether the transformer comes with the product; the transformer hole must suit the cross-section of the conductor passing through it.
- Colour: The display colour does not change the measurement. IEC 60204-1 reserves red for emergency or dangerous conditions, yellow for abnormal conditions and green for normal conditions on machine indicators; on a permanently lit measuring indicator, red can give the operator a false impression of a warning.
Common mistakes
- Passing both phase and neutral through the transformer: The currents of the two conductors cancel out and the display shows a value close to zero. Pass only the phase conductor to be measured through the transformer.
- Connecting the voltage leads to the transformer input: The indicator can be damaged; keep the leads separate according to the product diagram.
- Treating the indicator as a protective device: The indicator only measures; it does not open the circuit on overcurrent or when the voltage goes out of limits, and it does not replace an overcurrent or voltage protection relay.
Voltmeter-ammeter pilot lights in the catalogue
The Voltmeter-Ammeter Pilot Lights category has 5 active products, all from the KSN KSN-22-VAD series: Ø22 mm, LED display, 50–500 V and 0–100 A. Five colours are offered and the last letter of the code shows the colour (Turkish initials):
| SKU | Model | Colour |
|---|---|---|
| `KSN5075` | KSN-22-VAD-K | Red |
| `KSN5076` | KSN-22-VAD-Y | Green |
| `KSN5077` | KSN-22-VAD-S | Yellow |
| `KSN5078` | KSN-22-VAD-M | Blue |
| `KSN5079` | KSN-22-VAD-B | White |
Frequently asked questions
How is a voltmeter-ammeter pilot light connected?
The voltage leads are connected in parallel across the two points to be measured. The phase conductor is passed through the hole of the current transformer and the transformer leads are connected to the indicator's current input. Wire it with the power off, following the product diagram.
How many indicators does a three-phase line need?
One indicator shows the voltage between the two points it is connected to and the current of the single conductor passing through its transformer. Monitoring all three phases separately needs three indicators; with a single indicator, undervoltage and current imbalance on the other phases stay invisible.
What is used for currents above 100 A?
These indicators measure 0–100 A. For larger currents an X/5 A current transformer is fitted on the line and a panel ammeter set to the transformer ratio is used.
Can a voltmeter-ammeter pilot light be used in a DC circuit?
No. Because current is measured through a current transformer, it only works in alternating current (AC) circuits.