Video: How do you measure the SCRs on the ATS480, ATS48, ATS22, and ATS46, ATS490, ATS430 soft starters?

Before performing any testing, completely de-energize the soft starter by removing both mains and control power. Follow all applicable Lockout/Tagout (LOTO) procedures.

ATS46 Testing Procedure

When testing an ATS46, the control board must be removed before resistance measurements are taken.

The control board is the front section of the unit where the control terminals and keypad are connected. To remove it:

1. Remove the four screws securing the control board to the power section.
2. Disconnect all connectors from the rear of the control board.
3. Label each connector before removal to ensure correct reinstallation.
4. Do not pull on the wires directly, as this may damage the connector or wiring.

Resistance Measurements

Using a digital multimeter capable of measuring more than 50 kΩ (such as a Fluke meter or equivalent), measure the resistance between:

• L1 and T1
• L2 and T2
• L3 and T3

Take each measurement in both directions:

• Red probe on T1, Black probe on L1
• Red probe on L1, Black probe on T1

Repeat for all three phases.

Expected Results

• A healthy SCR circuit should typically measure 50 kΩ or higher.
• All three phases should provide similar resistance readings in both directions.
• Significantly lower readings may indicate a faulty SCR or a problem with the shorting/bypass contactor (if equipped).

Important Meter Limitation

The meter used must be capable of reading above 50 kΩ. Some clamp meters, such as the Fluke 323, have a resistance measurement limit of approximately 6 kΩ and cannot be used to properly verify SCR health.

ATS430 Note

On the ATS430, one phase does not contain an SCR. Therefore, it is normal for that phase not to produce the same resistance reading as the other two phases. The absence of a resistance measurement on that phase does not indicate a fault.