Nothing close enough? Start from a blank ladder logic → Describe it in one paragraph.
How to use a ladder logic template.
- 01Choose your starter and control mode
Specify DOL, star-delta, or VFD, and whether you need Hand-Off-Auto (HOA) or just Hand-Auto. ChatDiagram routes the start command through the appropriate selector logic.
- 02Define interlock inputs
List protecting devices — low-level float (LSL), high-pressure switch (PSH), motor overload (OL), and dry-run protection timer — with their NC or NO wiring.
- 03Set fault and reset behaviour
Describe when the pump should latch off on fault versus automatically retry, and where the reset push-button is. ChatDiagram adds a latched fault coil with a reset rung.
- 04Add lead-lag logic (duplex systems)
For two-pump systems, specify the alternation trigger — elapsed run-time, manual selector, or duty-standby on fault — and ChatDiagram generates the alternation bit logic.
- 05Export for panel build
Download the finalised diagram as PNG or PDF to attach to your panel schedule and hand to the electrician.
Questions about ladder logic templates
How does Hand-Off-Auto (HOA) logic work in ladder programming?
An HOA selector switch is wired to two input bits (HAND and AUTO). The HAND rung examines the HAND bit and directly energises the pump output coil, bypassing all auto interlocks. The AUTO rung examines the AUTO bit and the process demand signal (e.g., level switch or SCADA command) in series before energising the coil. The OFF position simply means neither HAND nor AUTO is active.
What is dry-run protection in pump ladder logic?
Dry-run protection prevents a pump from running without liquid — which would overheat the mechanical seal. A low-level float switch (LSL) or a flow switch is wired as a normally-closed series contact on the pump output rung. Alternatively, a TON timer detects current draw below threshold (via an overload relay auxiliary contact) and trips the pump if flow is not confirmed within the preset.
How do I alternate two pumps in a duplex system?
A common method uses an elapsed-time counter (CTU) or a run-hour integrator. When the duty pump has run for the preset interval, an internal alternation bit flips, reassigning the duty and standby roles. The lead pump stops and the lag pump starts. Many designs also swap roles automatically when the duty pump trips on fault.
How should motor overload faults be handled in the ladder program?
Wire the overload relay auxiliary contact as NC to an input bit. In the program, that NC contact sits in series on the motor output rung. When the overload trips, the NC contact opens, de-energising the motor coil. A latched FAULT coil records the event for the operator HMI, and a RESET pushbutton clears the latch after the overload is manually reset.