You're right to be suspicious. The settings you're seeing strongly suggest the breaker is operating far above the 400A rating someone marked on it. Let's break down why: Frame Size vs. Trip Plug

A 1600A frame size means the physical size of the breaker is designed to handle up to 1600A of fault current. However, the actual trip unit (the part that senses overcurrent and trips the breaker) determines the continuous current rating. These trip units can be interchangeable in many cases. Someone could have installed a smaller amp trip in a larger frame.

CT Rating

Your CT rating is 800A. Current Transformers (CTs) are used to measure the current flowing through the conductor and send a reduced current signal to the breaker's trip unit. Since your CTs are 800A, it is likely that the original trip rating was 800A.

LT Pick-Up (600A)

This is the Long Time pickup setting. It means the breaker will start timing towards a trip when the current exceeds 600A. It does not mean it trips instantly at 600A. The "LT Delay" setting determines how long the breaker will wait before tripping at that current level (or higher).

LT Delay (4.05)

This is the Long Time delay, usually measured in seconds or a time-current characteristic curve. At a current slightly above the 600A pickup, it will take approximately 4.05 seconds for the breaker to trip. If the current is much higher than 600A, the trip time will be faster, following the inverse-time characteristic curve.

ST Pick-Up (2400A) & ST Delay (0.205)

These are the Short Time settings. The breaker will trip (almost instantaneously) with a delay of 0.205 seconds when the current hits 2400A (which is 3x the CT rating). These settings are designed to quickly clear short-circuit faults while allowing motor inrush currents or other temporary overloads to pass.

I Pick-Up (4800A)

This is the Instantaneous pickup setting. The breaker will trip instantly (practically no intentional delay) when the current hits 4800A. This is to protect against severe short circuits with minimal damage.

Your Interpretation is Correct

Based on these settings, the breaker's current settings are configured to operate at a much higher level than 400A. The 600A long-time pickup is your first clue.

What to Do


Verify the Trip Unit

The most important step is to

carefully examine the actual trip unit itself. Look for a nameplate or label on the trip unit that indicates its continuous current rating (e.g., 800A, 1200A, etc.). This is the definitive answer. The continuous trip rating can be on the front face or along the sides. Turn the breaker off before examining the trip unit.2. Confirm the CT Ratio

Double-check the CT ratio. The breaker settings should correspond to the CT ratio. You mentioned the CT rating as 800A, make sure the CT is a 800:5 amp CT.3.

Investigate the "400A" Marking

Find out who marked the breaker as 400A and why. It could be: A mistake A misunderstanding A past modification that was not properly documented A temporary measure that was never corrected4.

Consult a Qualified Electrical Technician/Engineer

This is crucial. These settings control a powerful piece of equipment. Get a qualified professional to: Verify the trip unit rating. Confirm the accuracy of the settings based on the load it's protecting. Ensure the settings are appropriate for the application. Correct any errors or inconsistencies.

Potential Dangers

Operating a breaker with incorrect settings is dangerous. Here are some of the risks:

Overloading

If the breaker's settings are too high, the circuit it protects can become overloaded, leading to overheating, insulation damage, and potentially fires.

Nuisance Tripping

If the settings are too low, the breaker may trip unnecessarily, disrupting power to critical equipment.

Equipment Damage

Incorrect settings can prevent the breaker from properly protecting downstream equipment during faults, leading to damage or destruction.

In summary, your instincts are correct. The settings you provided indicate that the breaker is configured to operate much higher than a 400A rating. Do not* rely on the marked "400A" label. Immediately investigate the trip unit and consult a qualified electrician to ensure safe and proper operation. Flag for review