A main contactor ahead of an Active Line Module (ALM) provides physical disconnection of the three-phase AC input when the drive lineup must be electrically isolated. The EP enable circuit serves a different purpose: it commands the ALM output off before the power contacts open. These functions are complementary and must not be treated as interchangeable.
Main Contactor and EP Functions
| Element | Supported function | Engineering implication |
|---|---|---|
| Main contactor | Disconnects the drive lineup from the three-phase AC supply. | Use it when the required machine state includes electrical isolation of the lineup. |
| Leading auxiliary contact | Removes the EP enable before the main power contacts open. | Coordinate it so the ALM output switches off before supply disconnection. |
| EP enable circuit | Enables or disables ALM output. | It does not provide physical isolation from the incoming supply. |
Required Shutdown Sequence
The available equipment guidance requires disconnecting the EP supply at least 10 ms before opening the main contactor. This interval allows the ALM output to switch off before the three-phase input is interrupted.
- Remove the EP enable signal.
- Maintain a minimum 10 ms interval.
- Open the main contactor and disconnect the ALM input supply.
- Verify that the ALM output is off and that the contactor reaches its commanded state.
Risk of Permanently Enabling EP
Permanently wiring the stated +24 V and -24 V EP signals removes the coordinated EP-off command from the contactor sequence. Opening the contactor while the ALM remains enabled therefore does not follow the documented 10 ms shutdown sequence. The evidence does not establish whether this will damage parallel equipment, damage contactor contacts, or how regenerated energy will behave, so do not claim those outcomes without the applicable equipment manual and system measurements.
The notation “+24 V and -24 V” is also ambiguous without the terminal diagram. Confirm whether the manual specifies two polarities, a 24 V supply and its reference, or separate EP channels before changing the wiring.
Isolation and Safety Decision
If the drive lineup must be electrically isolated while parallel cabinet loads remain energized, place the contactor so it disconnects the ALM branch without unnecessarily removing the other loads. For emergency stopping, determine whether the required protective function calls for supply isolation, a safety drive function such as STO, or another architecture controlled by a safety relay or safety PLC. Verify that choice against the applicable machinery requirements and the exact drive manual; the available evidence does not establish a required protection level or prove that EP alone is a safety function.
Include loss of power in the design review. Because a supply shortage may prevent controlled auxiliary-contact timing, verify the actual contactor and EP states during undervoltage or complete control-power loss. Accept the design only when the observed sequence and resulting machine state meet the documented shutdown and safety requirements.
FAQ
Why is a main contactor installed before an Active Line Module?
It electrically disconnects the drive lineup from the three-phase AC supply. EP can switch the ALM output off, but it does not provide physical input isolation.
How long before opening the ALM contactor should EP be removed?
Remove the EP supply at least 10 ms before opening the main contactor so the ALM output switches off first.
Can the ALM EP enable remain permanently wired to 24 V?
Permanent enable prevents the contactor sequence from removing EP 10 ms before input disconnection. Confirm the EP terminal definitions and implement the documented sequence whenever a line contactor isolates the ALM.
