{"id":518,"date":"2026-06-06T21:59:30","date_gmt":"2026-06-06T21:59:30","guid":{"rendered":"https:\/\/khkrh7q1ur.wpdns.site\/?p=518"},"modified":"2026-06-06T21:59:32","modified_gmt":"2026-06-06T21:59:32","slug":"mccb-calibration-machine-tips-for-optimal-performance","status":"publish","type":"post","link":"https:\/\/benlongkj.com\/ko\/blog\/mccb-calibration-machine-tips-for-optimal-performance\/","title":{"rendered":"Ultimate Guide to MCCB Calibration Machine Tips for Optimal Performance"},"content":{"rendered":"

Real production problem:<\/strong> The production manager of a medium voltage switchgear manufacturer reported that they were experiencing inconsistent trip times on their MCCB long time calibration bench with regards to the morning and the afternoon. Upon investigation into the cause of this phenomenon, it was discovered that there was a temperature change of 12\u00b0C within the room that housed the calibration bench and the calibration bench itself did not have temperature compensation built into it. As a result, the production manager has been having to recalibrate the calibration bench every 2 hours.<\/p><\/blockquote>\n

A machine used to calibrate MCCB is not just a \u201cpass\/fail tester\u201d. It also functions as a highly precise device that can verify and adjust the thermal and magnetic trip characteristics of moulded case circuit breakers (from 100A through 1600A). If the user is going to achieve repeatable and compliant results in accordance to IEC 60947-2 and UL 489, it is necessary for the calibration machine to provide stable current sources, accurate timing measurements, proper fixturing and ideally some form of ambient compensation for temperature variations. This guide describes the critical components, the calibration process, the common mistakes that can arise in calibrating MCCB’s, and general recommendations on how to select a machine that will provide optimal performance for many years of operation.<\/p>\n

This guide covers:<\/h2>\n
    \n
  • What an MCCB calibration machine does (and what it does not do)<\/li>\n
  • Three essential subsystems: current source, timing\/measurement, fixturing<\/li>\n
  • Step\u2011by\u2011step calibration process for thermal and magnetic trips<\/li>\n
  • Key performance metrics: current accuracy, timing resolution, repeatability (Cpk)<\/li>\n
  • How to choose between manual, semi\u2011automatic, and fully automatic machines<\/li>\n
  • Common mistakes and how to avoid them<\/li>\n
  • FAQs answered by calibration engineers<\/li>\n<\/ul>\n

    \"Ultimate<\/p>\n

    1. What is an MCCB calibration machine and why is it different from a test bench?<\/h2>\n

    A test bench (e.g., go\/no\u2011go) typically tests circuit breakers against a wide-ranging calibration window to determine whether to pass or fail.<\/p>\n

    Conversely, a calibration device is usually more reliable and, in most cases, adjustable. For example, an MCCB (Molded Case Circuit Breaker) manual thermal calibration bench permits the operator to change the position of a bimetal while recording trip-time information; once complete, the operator can retest the MCCB for confirmation. In comparison, an MCCB long-time thermal calibration bench, designed for high-volume production applications, automatically tests at many current levels, stores trip-time information, and can be associated with a downstream adjustment station. Advanced test benches, such as the MCCB Semi-Automatic High Voltage Test Bench, fuse the calibration function into one testing cycle with the dielectric test function.<\/p>\n

    2. Three critical subsystems of a reliable MCCB calibration machine<\/h2>\n

    2.1 High\u2011accuracy, low\u2011ripple current source<\/h3>\n

    The Supply Current Source must supply stable, adjustable current to support testing e.g. thermal testing typically 10A to 2000A peak; magnetic\/instantaneous testing \u226410kA. The current ripple must not exceed 5% of rated value, and must have an accuracy \u00b11%. Directly correlated with poor supply current stability will be variations in trip time. For long-time current tests (i.e. 1 hour @ 100% In), the output current must remain within \u00b1 2% of set value and have no drift. Many manual test benches use variac based power supply; whereas most automated type test benches utilize thyristors or IGBTs with some form of closed loop.<\/p>\n

    2.2 High\u2011resolution timing and measurement system<\/h3>\n

    For thermal trip testing which takes longer than one second, the resolution will be 0.10 seconds. For instantaneous trip testing which takes place in milliseconds, the system must have a resolution of +\/- 1.0 millisecond. The machine should also be capable of measuring and displaying contact resistance and\/or micro-ohm meters for electronic trip units and should also have a secondary injection test capability for electronic trip units. MCCB long-time thermal calibration benches will generally have a multi-channel timer so that all three poles can be tested at the same time.<\/p>\n

    2.3 Robust, low\u2011resistance fixturing<\/h3>\n

    Most people underestimate the value of fixtures; however, connections between the calibration device and the MCCB terminals should have as little resistance as [less than 100 micro-ohms], because if there is too much resistance, there will be a voltage drop across the terminals, thus causing inaccurate readings of the actual current flowing through the circuit breaker. To avoid excessive resistance, it is best to use copper bus bars with silver plated contact pads and pneumatic clamps. The way an MCCB test bench is set up is also important. A manual magnetic trip testing bench usually uses simple screw clamps to hold the MCCB in place while tested. An automated test bench will utilize power operated clamps that include force sensors to accurately measure the clamping force and apply the required clamping force.<\/p>\n

    \"The<\/p>\n

    3. The calibration process: from raw breaker to verified product<\/h2>\n

    The following are the stages of calibrating a typical MCCB (thermal\u2011magnetic type), such as that used to calibrate the MCCB long time thermal calibration bench.<\/p>\n

      \n
    1. Fixture<\/span>: Operator places the MCCB, and pneumatic clamps close.<\/li>\n
    2. Contact resistance check<\/span>: A quick milliohm test ensures good connection.<\/li>\n
    3. Long\u2011time thermal calibration (overload)<\/span>:\n
        \n
      • Pass 100% of rated current for a specified time (typically 1 hour) \u2013 breaker must NOT trip.<\/li>\n
      • Then pass 135% of rated current \u2013 breaker MUST trip within 1 hour (for >100A frames).<\/li>\n
      • The adjustable breakers will receive an external command from the machine to move the bimetal in order to set the trip time in a precise range (that is, 45 – 55 seconds @ 135% of 100A).<\/li>\n<\/ul>\n<\/li>\n
      • Short\u2011time \/ Instantaneous (magnetic) test<\/span>:\n
          \n
        • Apply 5x, 7.5x, and 10x of rated current (depending on curve: C, D, K).<\/li>\n
        • Measure trip time \u2013 must be <100ms (typically 20\u201140ms).<\/li>\n
        • The machine checks the calibration of adjustable magnetic trips at both the dial’s maximum and minimum settings.<\/li>\n<\/ul>\n<\/li>\n
        • Dielectric withstand (optional)<\/span>: Examples of such test benches are the MCCB Semi Automatic Bench Test and high voltage test benches that perform a high potential (hi-pot) test to verify the insulation integrity of the product after performing electrical testing.<\/li>\n
        • Data logging and labeling<\/span>: An automated labeller or engraver prints an identifier onto the circuit breaker that includes test date and result; the information is sent to the MES.<\/li>\n<\/ol>\n

          4. Key performance metrics to evaluate a calibration machine<\/h2>\n

          When comparing machines, ask for documented evidence of these metrics:<\/p>\n

            \n
          • Current accuracy<\/span>: \u2264\u00b11% of reading over the full range, verified by a traceable ammeter.<\/li>\n
          • Current stability<\/span>: Drift less than 2% over 1 hour at full load.<\/li>\n
          • Timing resolution<\/span>: 0.01s for thermal tests, 0.1ms for instantaneous tests.<\/li>\n
          • Test repeatability<\/span>: Operation of the breaker for 10 trips is to have an average of <5% of the average trip time to be standard deviation (<5% of mean). 135% of the average time means 55 seconds; standard deviation must be <2.75 seconds for every trip in order to meet this goal.<\/li>\n
          • Changeover time<\/span>: When you’re getting a multi-frame electrical bench (like a bench with a 100A to 800A rating), check with the manufacturer to find out how long it will take to change out the busbars and clamps.<\/li>\n<\/ul>\n

            The high-quality MCCB Automatic Production Line has a built-in Calibration Module that achieves a Cpk \u2265 1.33 for all testing parameters.<\/p>\n

            \"How<\/p>\n

            5. How to choose the right calibration machine for your factory<\/h2>\n

            Based on your production volume and product mix, choose one of these three types:<\/p>\n

              \n
            • Manual calibration bench<\/span>: A manual thermal calibration bench (MCCB) is better suited for low volume (fewer than 50 units per day), research and development (R & D). An operator can set the desired current on a dial, use a stopwatch to time the test and record the results by hand. It usually has a low cost of $8,000-20,000 but is time-consuming and subject to human error.<\/li>\n
            • Semi\u2011automatic bench: For example<\/span>: The operator will load the breaker on its own, however, the current applied, timing of test, and whether the test passes or fails, is automated. At the end of the test, the results will be stored. This method is appropriate for both medium volume (50-500 units\/day) applications and will be relatively good priced at $25,000-$50,000.<\/li>\n
            • Fully automatic inline calibration system<\/span>: (Automatic production line for MCCB breakers.) The breaker is fed continuously by conveyor, loaded automatically, tested using thermal \/ magnetic \/ dielectric methods, sorted and unloaded. Suitable for high volume production of more than 500 units\/day. The estimated cost of a complete testing system is between $150,000 and $400,000, depending on how many test stations and how many are being processed at once.<\/li>\n<\/ul>\n

              6. Common calibration mistakes and how to avoid them<\/h2>\n
                \n
              • Mistake 1: Not allowing the breaker to cool between tests.<\/strong> Bimetal thermal trip test implies the heating of the bimetal by the tests. If a second test is conducted immediately after a first, the trip time will decrease. Solution: Always allow for a cool down period (3-5 minutes) after each thermal test before conducting another thermal test on the bimetal.<\/li>\n
              • Mistake 2: Using the same calibration parameters for all poles.<\/strong> Each pole of a 3-pole MCCB may experience slight variations regarding bimetal components. Solution: Test each of the three poles independently (or simultaneously, but with an independent trip detection method). A proper bench for long time thermal calibration of an MCCB will include three independent trip sensors.<\/li>\n
              • Mistake 3: Ignoring ambient temperature.<\/strong> The duration of a trip is affected by approximately 1\u20112% for every degree Celsius of temperature change. Therefore, either keep the temperature in the control room at 25 degrees Celsius plus or minus 3 degrees Celsius or utilize a calibration machine with real-time temperature compensation, which dynamically adjusts the testing current or acceptance window.<\/li>\n
              • Mistake 4: Not cleaning contact surfaces.<\/strong> Terminals that have oxidation introduce resistance which can impact distribution of current flow. To remediate the problem wipe the terminals of a MCCB prior to performing any test, using a lint-free wipe and isopropyl alcohol. For high-volume applications automatically cleaning the terminals prior to entering the calibration machine can be accomplished by establishing an automatic terminal cleaning system.<\/li>\n<\/ul>\n

                7. Real\u2011world performance improvement example<\/h2>\n

                Prior to upgrading their calibration bench, a company had difficult time achieving consistent success (87% first-pass), meaning that 13% of their circuit breakers would need to be reworked. After the upgrade was complete, the company achieved an impressive first-pass yield of 98.5% from the new thermal calibration bench that uses automatic adjustment and temperature compensation features. The savings from reduced labor costs and materials from reworked circuit breakers easily paid for the new bench within nine months. Additionally, during the next twelve months after the upgrade, a major customer reported zero returns due to thermal trip-related out-of-calibration conditions for the first time in the company’s history.<\/p>\n

                Frequently asked questions (FAQ)<\/h2>\n

                How does the design of a manual Thermal Calibration Bench differ from that of a Long Term Thermal Calibration Bench?<\/h3>\n

                An operator at a standard thermal calibration rack will typically only be able to apply current for testing, as well as when they read off a timer. The operator of this rack would be responsible for manually adjusting the bimetal screw of their breaker (if required), and will then have to determine when to stop testing. In comparison, in the case of a MCCB long time thermal calibration rack, it is semi- or fully-automatic. This means that multiple levels of current (usually 100%, 135% and sometimes 150%) are tested at the same time, with the results being logged. The time taken to trip each of these breakers would be recorded on the calibration rack and compared against pass and fail limits. Further to this, some of these racks even include an external stepper motor to automatically adjust the breaker.<\/p>\n

                How often should an MCCB calibration machine itself be calibrated?<\/h3>\n

                Calibration must be done a minimum of once per 12 month period and\/or more often than that if very high usage (> 2000 tests\/day). Calibration must be completed by an accredited laboratory using traceable standards. The process for this includes:<\/p>\n

                  \n
                • Current source verification at 5 points across the range (e.g., 50A, 100A, 500A, 1000A, 2000A).<\/li>\n
                • Timer accuracy check against a reference stopwatch.<\/li>\n
                • Contact resistance measurement verification using a known shunt.<\/li>\n<\/ul>\n

                  Keep the calibration certificate for at least 3 years for audit purposes.<\/p>\n

                  Can a calibration machine also test electronic trip units (MCCB with LSIG functions)?<\/h3>\n

                  However, there are additional functions that you will require. Electronic trip breakers require a secondary injection test set to test the sensing and logic of the electronic trip unit. Some all-in-one benches (e.g. those incorporated into an MCCB automatic production line) perform both primary injection (to test power contacts) and secondary injection (to test the trip unit) in one test cycle. Check with your supplier to ensure that the machine you are purchasing will work with your specific electronic trip model.<\/p>\n

                  What is the typical payback period for investing in an automatic calibration machine?<\/h3>\n

                  The industry reports record a typical payback period for a manufacturer producing more than 200 MCCB’s per day, to be between 6 and 14 months. Savings are produced from:<\/p>\n

                    \n
                  • Reduction of rework (on the average, a manual workstation has a first pass failure rate between 10-15%, while an automated workstation may have a first pass failure rate of only between 2-5%).<\/li>\n
                  • Lower labor cost (one operator can run two automatic benches).<\/li>\n
                  • Avoided field returns (automatic benches with data logging catch more defects).<\/li>\n<\/ul>\n

                    What standards must an MCCB calibration machine comply with?<\/h3>\n

                    Though there is no universal product standard for the machine, the machine must be able to carry out tests as defined by the standards IEC 60947\u20112 (Annex F – Routine test) and UL 489 (Clause 7 – Production test). Current accuracy, timing accuracy, and test capabilities of the specified multiplier of the rated current are the key requirements for the machine. Be sure to request a \u201cstandards compliance matrix\u201d from the manufacturer when you are purchasing the calibration machine listing all tests required by the standard and how the machine performs those tests.<\/p>\n

                    When looking to purchase a machine for calibrating MCCBs (molded case circuit breakers), it is important to make sure it will help with the overall quality of your MCCB products (i.e. first-pass yields, field reliability, etc.). To ensure that your calibration machine does what it’s intended to do, select one that has accurate current specifications (\u00b11%), accurate timing resolution (0.1 ms for instantaneous testing), and a fixture that will withstand the use of the calibration machine. The following are ideal selection criteria based on your expected volume of MCCB production:<\/p>\n

                    – A manual calibration bench will suffice for low-volume MCCB production and for research & development.
                    \n– A semi-automatic bench (e.g., a manual magnetic trip test bench) is ideal for medium-volume MCCB production.
                    \n– An automated bench will work well for high-volume MCCBs that are produced as part of an MCCB automatic production line.<\/p>\n

                    Some common mistakes that manufacturers make when calibrating MCCBs include:<\/p>\n

                    – Not taking the ambient temperature of the MCCB into consideration.
                    \n– Not allowing the MCCBs to cool down prior to testing them (this may affect their performance).
                    \n– Not cleaning the electrical contacts on the MCCBs (brass or gold plating).<\/p>\n

                    If you use a properly calibrated and maintained calibration machine, it will usually result in a payoff within 1 year through the reduction of product rework and scrap. Always request a demonstration on-site with your own MCCB samples and request documented repeatability data (Cpk \u22651.33).<\/p>\n","protected":false},"excerpt":{"rendered":"

                    Real production problem: The production manager of a medium voltage switchgear manufacturer reported that they were experiencing inconsistent trip times on their MCCB long time calibration bench with regards to the morning and the afternoon. Upon investigation into the cause of this phenomenon, it was discovered that there was a temperature change of 12\u00b0C within […]<\/p>\n","protected":false},"author":1,"featured_media":519,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-518","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"blocksy_meta":[],"acf":[],"_links":{"self":[{"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/posts\/518","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/comments?post=518"}],"version-history":[{"count":1,"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/posts\/518\/revisions"}],"predecessor-version":[{"id":522,"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/posts\/518\/revisions\/522"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/media\/519"}],"wp:attachment":[{"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/media?parent=518"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/categories?post=518"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/benlongkj.com\/ko\/wp-json\/wp\/v2\/tags?post=518"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}