What Is an Arc Fault Detection Device? Types and Selection Criteria
An arc fault detection device recognises an electric arc from the current waveform or its light and trips the circuit; it comes as the building AFDD or the switchgear arc protection relay.
An arc fault detection device is a protective device that recognises an electric arc and causes the circuit to be opened. Two different product families go by this name: the AFDD, which recognises an arc from the current waveform in final circuits of buildings, and the arc protection relay, which detects the light of an arc in switchgear with optical sensors and trips the circuit breaker within milliseconds. The products in the Welibaba catalog belong to the second group.
Types
| Feature | AFDD | Switchgear arc protection relay |
|---|---|---|
| Where used | Socket and lighting final circuits in homes, hotels, dormitories and similar buildings | MV and LV air-insulated switchgear |
| Detects | Arcs from loose connections or crushed or worn cables | The light of an arc inside the panel, optionally together with overcurrent |
| Tripping | With its own contact or an integrated circuit breaker | Sends a command to the circuit breaker's trip coil |
AFDDs are made under IEC 62606 for household and similar use, up to 440 V AC and 63 A. Since miniature circuit breakers and residual current devices do not detect series arcs, the AFDD complements them. There are currently no AFDDs in the catalog.
How does a switchgear arc protection system work?
The Siemens Reyrolle 7XG35 ReyArc relay works with the light signal from P1X point or line optical sensors. Tripping can be set up on light alone or only when light and overcurrent are seen together (Siemens' "2-out-of-2" logic). Siemens states that tripping takes less than 2 ms on light alone and less than 7 ms with light and current check. The relay continuously supervises the sensors and fibre connections and includes circuit breaker failure protection (50BF).
Selection criteria
- Sensor type: A point sensor monitors one compartment, for example the breaker or cable compartment. A line sensor runs along the busbar and monitors a wide area on one channel.
- Trip logic: Tripping on light alone is the fastest route. A current check prevents trips from light not caused by an arc but requires current transformer inputs on the relay; the 7XG3552's product name lists 4 current inputs.
- Sensor cable: The P1X37 point sensor comes with a 5 m cable. The P1X107 line sensor is sold without a cable; the P1X152 (3 m) connection cable is chosen separately.
- Trip path: The relay's high-speed outputs must be wired to the trip coil of the breaker feeding the compartment where an arc can occur.
Common mistakes
- Confusing an AFDD with an arc protection relay: One protects building final circuits, the other switchgear; they are not interchangeable.
- Forgetting the line sensor cable: The P1X107 is sold without a supply cable; a suitable cable must be chosen separately (P1X152, 3 m, in the catalog).
- Ignoring breaker opening time: Although the relay issues its command within milliseconds, the arc lasts until the breaker contacts open.
- Using arc protection instead of overcurrent protection: The arc relay targets arc faults only; line and transformer protection is provided separately.
Products in the Welibaba catalog
The Arc Fault Detection Devices category has 6 active Siemens products:
- 2 arc protection relays: Reyrolle 7XG3551 and 7XG3552 (7XG35 ReyArc)
- 2 optical sensors: P1X37 point type, P1X107 line type
- 1 line sensor cable: P1X152, 3 m
- 1 low-power voltage sensor: 6MD2320-0AA07-1AA0, 20 kV; Siemens lists it in the SICAM FCM family and it is not part of the arc protection system
Secondary overcurrent relays are in the Overcurrent Secondary Protection Relays category, and the breakers that receive the trip command are in Medium Voltage Circuit Breakers.
Frequently asked questions
What is the difference between an AFDD and a residual current device?
A residual current device detects current leaking to earth, and a miniature circuit breaker detects overcurrent. A series arc at a loose terminal does not raise the current, so neither sees it; the AFDD recognises the arc signature in the current waveform.
How fast does a switchgear arc protection relay trip?
The Siemens 7XG35 trips in less than 2 ms on light alone and in less than 7 ms with light and current check. The breaker's opening time is added before the arc is extinguished.
Should I choose a point sensor or a line sensor?
Choose a point sensor in each compartment if you want to tell which compartment the arc is in, and a line sensor if you want to monitor long busbar sections on one channel.
How can I find out the price of these products?
Products in this category are supplied on a lead-time basis. For price and delivery time, use the product advisor, WhatsApp or e-mail option on the product page.