Input voltage has dropped below about 18 V DC on a supply that should be 24 V. The IO-Link ports and the port-powered Modbus devices lose power, so connected sensors and switches stop working while this fault is active.
On the controller the description reads: Input power faulted: IO-Link, flow switches and port-powered Modbus devices are affected. See the manual (info button) for what to check. This page is that manual entry.
The 18 V trip point is deliberate: many smart sensors stop working below 18 V, so the controller raises this fault before peripherals start misbehaving. An alarm here is an early warning about the supply, not a report that something has already failed.
| At a glance | |
|---|---|
| Code | 600 |
| Shown as | Power Fault |
| Severity | Severe |
| Category | 6xx — Hardware |
| Clears | Automatically, when input power recovers |
| LED | Power light, red fast blink |
| Trips below | About 18 V DC (nominal input 24 V) |
When the input power fault triggers, the InteliHive:
| Affected | Why | What you see |
|---|---|---|
| Every IO-Link port and the sensors on it | Both the sensor supply (L+) and C/Q are lost | The sensors drop out |
| Flow switches and other contacts on the IO-Link ports | Their inputs lose power | They read as no flow, or as a blocking contact, so interlocked modes stop |
| Port-powered Modbus devices | The bus supply is switched off | They drop out |
| Externally powered Modbus devices — a NextStep pump | Not powered by the controller | Keep running |
| Wireless devices | Their own mains supply | Keep running |
When acceptable voltage returns, all of that reverses automatically: Modbus port power is re-enabled and the alarm clears itself. You do not need to acknowledge or reset anything to recover.
Clear the power fault first. It brings a burst of knock-on alarms — Device Disconnected (100) for each sensor, and Policy Blocked (200) from flow switches and interlocks. They are consequences, not separate faults, and the controller does not hide them. Fix the power, and most of them clear on their own.
Most common first:
| Cause | What to look for |
|---|---|
| Undersized power supply | The supply cannot deliver enough current once peripherals draw load. Voltage sags under load but reads fine unloaded. |
| Loose or corroded connection | Barrel jack not seated, terminal screw loose, oxidised contact. Often intermittent — comes and goes with vibration. |
| Voltage drop in a long cable run | 24 V at the supply but under 18 V at the controller. Thin conductors over distance. |
| Overloaded peripherals | Too many devices, or one drawing far more than expected — a shorted sensor cable, a stalled actuator. |
| Failing supply | Output has drifted low or collapses under load. Common as supplies age. |
| Wrong supply | A supply of the wrong voltage, or an AC adapter substituted for DC. |
Before you start: Safety — isolate power before touching terminals, and treat the relay contacts on output devices as live even when the controller is off.
1. Check the LEDs. Blinking red confirms the fault is currently active. Solid green on the Power light means it has already cleared and you are looking at history.
2. Measure the supply voltage at the controller’s own input terminals — not at the supply, and not at the far end of the cable. Measure with everything connected and running, because the fault typically appears only under load.
| Reading at the input | Verdict |
|---|---|
| ~24 V | Healthy. |
| 18–22 V | Marginal. Not yet faulting, but there is no headroom — investigate now. |
| Below ~18 V | Faulting. Connected sensors may be unreliable at this level. |
A reading that looks fine while you watch it can still be the problem: if the fault comes and goes, the dips are happening under load transients you may not catch. Measure while a pump or valve actuates.
3. If the voltage is low at the controller but correct at the supply, the loss is in the cable or connections:
4. If the voltage is low everywhere, the supply is the problem:
5. If the supply is adequate and voltage still collapses under load, look for something drawing too much:
6. Confirm recovery. The Power light returns to solid green and the alarm clears on its own. If it clears and returns repeatedly, treat it as an intermittent connection or a marginal supply — it is not spurious.