Okay, you're on the right track. Diagnosing intermittent breaker trips requires gathering solid data. Here's a breakdown of considerations and product options for installing a current meter to capture inrush and steady-state currents

Understanding the Problem:
Inrush Current

Motors, transformers, and even some electronic devices draw a significantly higher current when they first power on. This "inrush" can be 5-10 times (or more) the normal operating current. If the breaker's instantaneous trip curve is too close to the inrush current, it will trip.

Overload

A steady-state overload means the circuit is drawing more current than the breaker's rating for a sustained period. Breakers have thermal overload protection that trips after a delay (the delay depends on the overload).

Breaker Type

The type of breaker (e.g., thermal-magnetic, electronic trip) influences its tripping characteristics. Thermal-magnetic breakers are most common in residential/commercial settings. Electronic trip breakers are more common in industrial settings and offer more sophisticated protection settings.

TCC (Time-Current Curve)

Your statement about the TCC not making sense for the trip implies that either: The actual current is higher than you think. The breaker is faulty (degraded trip characteristics). The TCC you're looking at is for the wrong breaker. There is some other condition that is affecting the circuit.

Key Considerations for Selecting a Current Meter


Current Range

Crucially, estimate the maximum possible inrush current. Consider the current rating of the breaker you are monitoring. You need a meter that can measure well above the breaker's rating to capture inrush. For example, a 20A breaker could have inrush currents of 100A or more. A 100A breaker could have an inrush current of 500A or more.2.

Sampling Rate

To capture inrush, you need a fast sampling rate. Inrush events typically last milliseconds to a few seconds. A sampling rate of at least 1 kHz (1000 samples per second) is highly recommended. Higher is better, but there's a trade-off with data storage requirements.3.

Data Logging

Essential. You need to record the current over time to see the profile of the event leading to the trip. Look for sufficient memory to capture several events before needing to download the data.4.

Ease of Use



Clamp-on Ammeter

Generally the easiest to install. They clamp around a conductor without interrupting the circuit.

Display

A clear display (preferably with graphs) helps with immediate analysis.

Software

User-friendly software for downloading, analyzing, and visualizing the data is important.5.

Accuracy

For troubleshooting, good accuracy is important. Look for meters with accuracy specifications (e.g., ±1% of reading + ±2 counts).6.

True RMS

Ensure the meter measures "True RMS" (Root Mean Square) current. This is important for accurate readings of non-sinusoidal waveforms, which are common with electronic loads.7.

Safety

Choose a meter with appropriate safety ratings for the voltage level of the circuit you're measuring (e.g., CAT III 600V, CAT IV 600V).

Product Options (Examples)

Keep in mind I am an AI and cannot provide a recommendation on specific hardware. You need to ensure whatever hardware you purchase is tested and appropriate for your application.

Fluke 376 FC True-RMS AC/DC Clamp Meter with iFlex

A popular choice for industrial electricians.

Pros

True-RMS, measures up to 1000A AC/DC, flexible current probe (iFlex) for large conductors, data logging, Bluetooth connectivity for remote viewing and data logging.

Cons

Can be expensive.

Klein Tools CL800 Digital Clamp Meter

A more budget-friendly option.

Pros

Measures up to 600A AC, True-RMS, data hold, min/max, and relative mode.

Cons

May have lower sampling rate than Fluke.

Amprobe AMP-330 True-RMS Clamp Meter

Another mid-range option.

Pros

Measures up to 600A AC/DC, True-RMS, data logging, min/max, inrush current measurement.

Cons

Fewer features compared to the Fluke.

Drantez/BMI Power Analyzers

Higher-end power quality analyzers. These are more expensive but provide very detailed information about voltage, current, harmonics, power factor, and transient events. Suitable for complex troubleshooting and power system analysis.

General Guidance and Steps


Safety First

Always de-energize the circuit before working on electrical panels. Use proper PPE (Personal Protective Equipment). If you are not qualified to work with electricity, hire a licensed electrician.2.

Verify the Breaker

Double-check the breaker's rating, type, and that the TCC you have is actually for that breaker. Ensure the breaker is properly seated in the panel and making good contact.3.

Install the Clamp Meter

Clamp the meter around one conductor of the circuit you want to monitor (either the hot or neutral). Do not clamp it around the entire cable, as the magnetic fields will cancel each other out.4.

Set Up Data Logging

Configure the meter to log data continuously at a fast sampling rate (1 kHz or higher).5.

Monitor During Normal Operation

Let the system run normally and monitor the current. Look for the following:

Inrush Current

Observe the current spike when the equipment turns on. Is it exceeding the breaker's instantaneous trip current?

Steady-State Current

Is the average current close to the breaker's rating? Is it gradually increasing over time?

Spikes and Transients

Are there any other unusual current spikes or transients that could be contributing to the problem?6.

Simulate the Trip

If possible, try to recreate the conditions that cause the breaker to trip. This might involve turning on specific equipment at the same time, or increasing the load on the circuit.7.

Analyze the Data

Download the data from the meter and analyze the current waveform. Look for the following:

Inrush Duration

How long does the inrush last?

Peak Inrush Current

What is the maximum current reached during inrush?

RMS Current

What is the steady-state RMS current?

Harmonics

Are there significant harmonics present in the current waveform? (A power quality analyzer would be best for this).8.

Test the Breaker

If you suspect the breaker is faulty, have it professionally tested using a breaker test set. This will verify its tripping characteristics and ensure it meets specifications.

Troubleshooting Based on Data



High Inrush Current



Solution

Install a soft starter, inrush current limiter, or a time-delay fuse/breaker.

Steady-State Overload



Solution

Reduce the load on the circuit. Move some equipment to a different circuit. Upgrade the wiring and breaker to a higher rating (but only if the wiring is also rated for the higher current).

Breaker is faulty



Solution

Replace the breaker.

Harmonic Distortion



Solution: Install harmonic filters. Harmonics can cause breakers to overheat and trip prematurely.By gathering detailed current data, you'll be able to pinpoint the cause of the breaker trips and implement the appropriate solution. Remember safety first, and consult with a qualified electrician if you're not comfortable working with electrical equipment. Good luck! Flag for review