Applicable Systems
Okken
Symptoms
The ComPact NSX breaker trips on overload (L-curve). The Micrologic display shows OverLoad and the load current history. The downstream feeder is de-energized.
Possible Causes
- Sustained overload exceeding the breaker long-time pick-up setting
- New equipment added to the feeder without updating the breaker rating
- Motor load increased due to process changes (e.g., higher pump head)
- Incorrect breaker rating selected for the original design load
Troubleshooting Steps
- Step 1: Measure the actual load current with a clamp meter and compare with the breaker L-setting
Load current is <= breaker rated current or the L-setting is increased within cable limits - Step 2: Review any recent equipment additions or process changes that increased the load
All connected loads are documented and the total is within feeder capacity - Step 3: Verify the cable ampacity supports the breaker rating per IEC 60364-5-52
Cable ampacity >= breaker rating; if not, downgrade the breaker or upsize the cable - Step 4: Check for high-resistance joints or deteriorating terminations causing localized heating
All terminations are tight and thermal scan shows no hot spots >10C above ambient
How to Reset
Reset the Micrologic trip unit by pressing the reset button after the overload condition is cleared. Adjust the L-setting if the load has permanently increased, ensuring cable protection is maintained.
Common Replacement Parts
- LV430830: Schneider ComPact NSX400F with Micrologic 5.2 (Verify frame size and trip unit compatibility)
Frequently Asked Questions
- Q: What is the difference between L and S trips?
L (long-time) protects against sustained overloads with an inverse-time characteristic. S (short-time) protects against high overcurrents with a definite-time delay.
- Q: Can I increase the breaker rating without changing the cable?
No. The breaker must protect the cable. If the load increases, verify the cable can handle the new current or replace the cable.
Source: Schneider Electric ComPact NSX Catalog, DOCADOC-002
Category: Electrical