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ETC‐12Q Failed DINF Tests

The ETC‐12Q is manufactured and marketed by ETC Technologies of Milford Connecticut, USA.

ETC Technologies is associated with Satin American of Shelton Connecticut and RESA Power of Houston Texas.

What is DINF and why is it important

DINF is a “breaker protection function” that must be provided by the trip unit on the breaker. It provides the Instantaneous close‐on‐fault protection required to protect the breaker when closing on fault currents that are above its Close and Latch rating.

If the MasterPact M & MP circuit breaker closes on a fault current above its Close and Latch rating, the mechanism is unable to latch the breaker into the closed position due to the extremely large electromagnetic forces created by the fault current. Unless the breaker is instantly tripped open by the DINF function, the breaker will be severely damaged.

Without proper DINF protection, rapid breaker contact bounce causes breaker damage during the attempt to close into a fault above the Close and Latch rating. The contact bounce occurs when the mechanism is unsuccessfully trying to latch the breaker into the closed position against the electromagnetic forces of the fault. Additionally, interruption of the fault current will be delayed if the DINF function does not operate properly.

The DINF function in the trip unit is controlled by a DINF switch attached to the breaker mechanism and operates when the breaker closes. The purpose of the DINF switch is to temporarily turn on the DINF protection during closing, and turn off the DINF protection after the breaker is closed and latched. The DINF function is only turned on for about 10 milli‐Seconds during breaker closing.

Requirements for proper DINF protection on MasterPact M & MP breakers

There is a sequence of events that must rapidly occur for proper DINF operation on breaker closing. As the breaker contacts touch, the breaker current powers up the trip unit, the trip unit must determine if the breaker current is greater than the DINF value, and the trip unit must detect the DINF switch position. All of these items need to occur rapidly for the DINF feature to work correctly and trip the breaker in time. If any of these items do not occur rapidly, the DINF feature will not protect the breaker.

Based on Schneider/Merlin Gerin documentation and testing at a high‐power laboratory, the DINF feature on MasterPact M and MP breakers must cause the breaker to interrupt a fault in no longer than 30 milli‐seconds after closing onto the fault.

Test Setup

Testing was performed using the ETC12Q trip unit (Serial # S‐18962, Date of MFG: Mar 2017) on a MasterPact MP breaker.

The test setup included a primary injection high current test set. No auxiliary control power was applied to the ETC‐12Q. The breaker was closed onto the test set current which simulates a real condition where the breaker closes on a fault.

Summary of Results for DINF Tests

The ETC‐12Q tested for this report is a repackaged version of the original ETC‐12Q trip unit. The original version was also found to have DINF trip time issues and when tested on a MasterPact MP breaker at a high‐power laboratory, the breaker was destroyed.

ETC‐12Q DINF (close‐on‐fault) test results:

  1. Primary injection testing indicates that the ETC‐12Q does not provide reliable DINF protection.

    Out of ten (10) close‐on‐fault test operations with current sufficiently above the DINF pickup current tolerance, only one (1) DINF trip occurred. See Figure 1A for a scope trace demonstrating the lack of DINF trip.

  2. ETC‐12Q DINF trip times were excessive.

    Even when a DINF trip did occur, the total trip time was approximately 40‐42 milli‐seconds. This is considerably above the maximum allowed time of 30 milli‐second. With such a long DINF trip time, the breaker would sustain considerable damage due to the fault. See Figure 1B.

DINF test details and scope traces are included below.

Instantaneous and FlashSAFE Instantaneous Tests

In addition to the DINF tests, Instantaneous and FlashSAFE Instantaneous time tests were performed.

The FlashSAFE is a maintenance setting for arc flash reduction during downstream live maintenance.

  1. ETC‐12Q Instantaneous Trip Time is excessive.

    The Instantaneous trip time was approximately 42 milli‐seconds. This is considerably slower than the AMP‐SAFE‐PRO (and OEM Schneider STR) Instantaneous trip times of 30 milli‐seconds maximum.The Instantaneous protection function is also too slow to protect the breaker if it closes on a fault greater than its Close and Latch rating.

  2. ETC‐12Q FlashSAFE Instantaneous Trip Time is excessive.

    ETC‐12Q FlashSAFE Instantaneous protection total trip time was approximately 42 milli‐seconds. This is slower than the AMP‐SAFE‐PRO Quick‐Trip protection total trip time, which is 30 milli‐seconds maximum.


Therefore, due to the slow DINF trip time and unreliable DINF operation as well as the slow Instantaneous trip time, the ETC‐12Q is unattractive as a replacement trip unit for the MasterPact M & MP breakers.

ETC‐12Q Settings (for DINF testing) and Oscilloscope Traces

800A Frame
400A CT
LT: PU 440A, 480S Delay
ST: PU 4400A, I2T On, 0.50S Delay
I‐PU: 12320A
DINF I‐PU: approximately 4000A (confirmed by off‐breaker testing)


Figure 1A: Test current 6140A. DINF trip should have occurred to protect the breaker, but it did not.


Figure 1B: Test current 6440A. DINF trip occurred but total trip time was 41.6ms.


Experiencing Problems?

If you're experiencing problems with your breakers please call us directly. We operate a 24/7 emergency call out service in support of air circuit breakers, we carry spares for ABB, Terasaki, Mitsubishi, Schneider, Merlin Gerin, Square D & Moeller.

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