Symptom: the motor runs from the keypad, but the buttons stay silent
A typical picture after installation: the Veichi VFD starts from the keypad, the parameters are entered, but the external Start/Stop buttons produce no response at all. In nine cases out of ten the common button wire is on the wrong terminal — on GND instead of COM. They look the same ("zero"), but their purpose is different.
COM and GND are not the same thing
The Veichi control board has two separate common points:
COM— the common point for the digital inputs (X1–X6) and outputs. It is through COM that the internal +24V source, which powers the digital inputs, closes its loop.GND— the common point for analog signals: the +10V potentiometer and inputs AI1/AI2. Electrically, GND is bonded to the device chassis.
The AC310 manual (section 3.5.2) shows this directly: the +10V output and the analog output AO "form a loop with GND", while +24V "forms a loop with COM". In other words, the button logic must close to COM, and GND should be left to the analog side.
Why GND in particular corrupts the button signal
At its output the VFD forms voltage by pulse-width modulation — a source of high-frequency noise that also "drains" onto the chassis. Because GND is bonded to the chassis, a button wired to GND receives this noise on top of the useful signal. The result — the input either fails to trigger or switches on falsely on its own. COM, by contrast, is isolated for digital logic, so the button signal stays clean.
Hence a rule worth memorizing once and for all: wire all digital inputs X1–X6 to COM, and leave GND exclusively for analog signals (potentiometer, sensor).
The same principle applies beyond the buttons. A remote keypad over an RJ45 cable, external relays, NPN proximity sensors — anything that is a "digital" signal references COM. And everything "analog" (frequency reference from a potentiometer, a 4-20 mA pressure sensor) — references GND. As soon as you lay out the terminals by this split, most "magical" faults disappear.
AC10, AC310 and AC01 series nuances
Here the series behave differently, and this is a source of confusion:
| Series | COM and GND |
|---|---|
| AC310 | COM and GND are always separate. Buttons — to COM, analog — to GND. |
| AC10 0.4–5.5 kW | COM and GND "two in one", externally combined as GND (manual note 5). |
| AC10 7.5–22 kW | COM and GND are separate — as on the AC310. |
| AC01 | The digital and analog "ground" are merged into a single COM terminal; there is no separate GND. |
The practical conclusion: on the AC310 and the larger AC10 do not confuse the terminals; on the smaller AC10 and on the AC01 the common point is physically one, but the rule "the buttons are controlled through COM logic" does not go away.
Why did the manufacturer combine COM and GND on the smaller frames at all? Because at low power the leakage currents are smaller and board space is tight — an acceptable compromise. But as soon as the power rises (7.5 kW and above) the noise becomes noticeable and the terminals are separated. So anyone used to the smaller AC10 with "one ground" must adjust the habit on a larger frame or on the AC310: now COM and GND are two different points, and they must not be confused.
Tip: a quick check of the input logic
If you are unsure whether a button is wired correctly, there is a simple test on a de-energized bench: temporarily link the needed input Xn to COM with a jumper and apply power. In NPN logic (the factory setting) the input should "activate" immediately — this is visible in the terminal-state indication (monitoring group C00). If the input responds to the Xn–COM closure, then the logic is NPN and the buttons must be wired that way. If it does not respond — the drive is most likely in PNP mode, or the command source is not on the terminals.
How to check and fix it in 5 minutes
- De-energize the drive.
- Find the common wire from the buttons and check which terminal it goes to.
- If it is GND — move it to COM.
- Make sure the command source is set to the terminals:
F01.01 = 1. - Check the input assignment: X1 — forward run (
F05.00 = 1), X2 — reverse (F05.01 = 2). - Apply power and check the input response via the terminal-state indication.
If control runs through a remote keypad or a long line, see also the guide on Veichi remote control. And for the full migration map from a European drive — see the cornerstone article on NPN/PNP and COM vs GND.
A case from the field
A classic case: a pump station was assembled, the drive starts from the keypad, the motor check is OK. They connect an external Start/Stop station — zero response. The first thing they say is: "the VFD is defective". In reality the installer wired the station's common wire to the nearest "ground" terminal — and that turned out to be GND. They moved it to COM, set F01.01 = 1 — and the station worked on the first press. No replacement, no repair: just the correct common point.
Hence a simple habit for work acceptance: before blaming a fault on the "hardware", check which terminal the common control wire sits on. In the vast majority of "non-working buttons" the cause is exactly there.
FAQ
Can I use GND instead of COM if COM is occupied?
For digital inputs — no. GND is bonded to the chassis and picks up HF noise. If COM is physically single (AC01 or the smaller AC10), use it as the common point — that is exactly what it is for.
The buttons are on COM, but the input still does not trigger. What next?
Check the input logic: the drive may be in NPN while the signal arrives high-side (PNP) — then a PLC jumper is needed. And verify F01.01 = 1 — without it the terminal command is ignored.
Should the potentiometer also go to COM?
No. The potentiometer is analog: it is wired to +10V and GND (on the AC01 — to COM, because the "ground" there is single). The analog and digital ground must not be confused on the AC310/AC10.
