Relay technical terms explained
What do contact set, micro disconnection or the utilization categories AC1 to DC13 mean? The most important relay technical terms at a glance.
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Contact Types at a Glance
- Single Contact: Contact with only one contact point
- Double/Twin Contact: two parallel contact points – increases reliability for small contact loads such as measured values or PLC inputs
- Bridge Contact: two contact points arranged in series – advantageous when switching off DC loads
Micro, Full and All-Pole Disconnection
- Micro Interruption: simple circuit interruption by contact opening, without special requirements for dielectric strength or contact gap
- Micro Disconnection: adequate contact opening with requirements for dielectric strength – fulfilled by all our relays
- Full Disconnection: contact opening with insulation equivalent to basic insulation, including requirements for dielectric strength and dimensions
- All-Pole Disconnection: full disconnection of all mains conductors by a single switching operation
Utilization Categories according to EN 60947-4-1 / EN 60947-5-1
| Category | Current Type | Application |
|---|---|---|
| AC1 | AC 1~/3~ | Resistive or slightly inductive load |
| AC3 | AC 1~/3~ | Starting cage motors, direction reversal only after a pause |
| AC4 | AC 3~ | Starting, jogging, counter-current braking, reversing (not possible with relays) |
| DC1 | DC | Resistive or slightly inductive load |
| AC14 | AC 1~ | Control of small electromagnetic loads (< 72 VA) |
| AC15 | AC 1~ | Control of larger electromagnetic loads (> 72 VA) |
| DC13 | DC | Control of auxiliary contactors, solenoid valves, electromagnets |
AC4 (reversing) is not possible with standard relays – reversing creates a phase short circuit across the arc.
Practical Example: Reversing Capacitor Motors
With capacitor motors in a 230 V AC network, the inrush current is around 120 % of the rated current. The situation becomes critical during direct reversal of the direction of rotation: the capacitor is recharged across the arc that forms when the contact opens, which can result in peak currents of several hundred amperes – inevitably leading to welding of the contacts. The direction of rotation may therefore only be reversed via two relays with a current-free pause of approx. 300 ms between switching operations (e.g. by means of time-delayed control). Pure mutual interlocking of the relay coils does not generate any time delay and is not sufficient for this purpose.
Still Have Questions about a Technical Term or Your Application?
Contact us – we will be happy to classify your application in the appropriate category and recommend the right relay.
Frequently asked questions
Mikro-disconnection only meets requirements for the dielectric strength of the contact opening. Full disconnection additionally provides insulation equivalent to basic insulation between the disconnected parts – with higher requirements for dimensions and dielectric strength.
Without a currentless pause (ca. 300 ms), the capacitor is recharged via the arc generated during switching – the peak currents that occur can reach several hundred amperes and weld the contacts.