KNX time switch devices

Three main device categories handle time-based control in KNX projects. Each has different capabilities for time accuracy, astronomical function, and channel count. Choosing the right device depends on whether you need GPS/NTP-accurate time, astronomical switching, or just a simple weekly schedule.

Daily program structure

Each time switch channel supports up to 24 switching events per day. An event defines a time (absolute HH:MM or relative to sunrise/sunset) and an action (ON, OFF, value, scene). The week program assigns different day-programs to weekdays, Saturday, and Sunday.

Event 1:  sunset − 15 min  → ON   (100%)  ← welcome lighting, still daylight
Event 2:  23:00            → DIM  (20%)   ← reduced night mode
Event 3:  00:00            → DIM  (10%)   ← security minimum
Event 4:  sunrise + 10 min → OFF          ← off after daylight established

Weekend program (Saturday):
Event 1:  sunset − 15 min  → ON   (100%)
Event 2:  00:00            → DIM  (20%)
Event 3:  02:00            → DIM  (10%)   ← later for weekend
Event 4:  sunrise + 10 min → OFF

Sunday program: same as Saturday

Using sunset/sunrise-relative events means the exterior lights automatically adjust through the year — coming on later in summer, earlier in winter — without any reprogramming. In Stockholm (lat 59°N), sunset varies from 15:53 in December to 22:00 in June; the time switch handles this automatically.

Astronomical clock function

The astro function calculates precise sunrise and sunset times from the configured GPS coordinates and the current date. It outputs a binary group address signal that goes TRUE at sunrise and another that goes TRUE at sunset — other automations subscribe to these group addresses to trigger their actions.

NTP time synchronisation

All KNX time switch devices rely on an accurate real-time clock. Without external synchronisation, the internal crystal oscillator drifts — typically 2–5 minutes per year for MDT devices, up to 15 minutes per year for cheaper modules. NTP synchronisation from the internet keeps the KNX bus clock accurate to within 1 second.

Parameter page: Time synchronisation

  NTP server:          pool.ntp.org     ← public pool (requires internet)
                   or  192.168.1.1      ← local router NTP (offline capable)
  Sync interval:       1 hour           ← re-sync frequency
  Time zone:           Europe/Riga      ← IANA timezone (includes DST rules)
  DST handling:        Automatic (EU)   ← see DST section below
  Bus time broadcast:  Yes              ← sends KNX time telegram to all devices
  Broadcast interval:  1 hour           ← GLK and actuators sync from broadcast
  Broadcast GA:        0/0/1            ← KNX time group address (DPT 10.001)
  Broadcast GA (date): 0/0/2            ← KNX date group address (DPT 11.001)

Daylight saving time (DST)

In the EU, clocks go forward 1 hour on the last Sunday in March (02:00 → 03:00) and back 1 hour on the last Sunday in October (03:00 → 02:00). A KNX time switch that does not handle DST will trigger exterior lighting 1 hour early through the summer months.

MDT SCN-TU.01 and MDT IP Router both apply DST transitions automatically when configured. The transition happens at the correct clock time: at 02:00 on the last Sunday in March, the internal clock jumps to 03:00 — all time switch events from that point use the new time without any re-programming.

Manual override and inhibit

When a user manually overrides a time-controlled output (e.g. switches exterior lights ON during the day), the time switch resumes normal control at the next scheduled event. This is the default behaviour — no configuration needed.

For a persistent override (cleaning mode, maintenance, event lighting), use the inhibit input built into MDT time switches. Sending binary 1 to the inhibit group address pauses all time switch outputs until the inhibit is released.

MDT SCN-TU.01 — Inhibit configuration (ETS6)

  Inhibit GA:        5/0/1   (DPT 1.001)
  Inhibit action:    pause all channel outputs
  Resume action:     automatic on inhibit = 0
  Resume behaviour:  apply current schedule immediately

User workflow — event mode (garden party):
  1. Press "Event mode" button on wall panel
     → KNX binary input sends 1 to GA 5/0/1
     → time switch suspends exterior lighting schedule

  2. Exterior lights stay ON or OFF as manually set
     (time switch does not override during event)

  3. Press "Event mode OFF" or next morning:
     → KNX sends 0 to GA 5/0/1
     → time switch resumes: applies current time-of-day schedule
     → if current time is within "ON" window → lights ON
     → if current time is outside "ON" window → lights OFF

Week programme example: office lighting

A complete office lighting week programme demonstrates weekday/weekend differentiation, after-hours dim mode, and full-off for unoccupied periods.

Channel: Office main lighting (GA 1/0/5 — DPT 5.001 brightness %)

Monday–Friday:
  07:30 → 100%    (full occupancy start)
  12:00 → 80%     (lunch hour dim — energy saving)
  13:00 → 100%    (afternoon full occupancy)
  17:30 → 50%     (after-hours reduced — cleaning, late workers)
  20:00 → 0%      (off — no access after 20:00)

Saturday:
  09:00 → 100%    (reduced weekend hours)
  17:00 → 0%

Sunday:
  (no events — always OFF)
  Default state: 0% (off)

Public holidays:
  Override GA 5/0/5 = 1 → activate Sunday program for that day
  → time switch applies weekend schedule
  → managed via HA automation on public holiday calendar

Annual programme and special days

MDT SCN-TU.01 supports an annual calendar for exception days — specific dates that override the week programme. This covers public holidays, company-specific closure days, and seasonal schedule changes (e.g. summer reduced hours in August).