Things you MUST know when commissioning low voltage switchgear and circuit breakers

Commissioning process for LV switchgear

Purchasing low voltage switchgear is not that easy, it’s not like purchasing a new TV or laptop. You have to be very experienced and deadly serious when specifying and ordering LV switchgear, but also during the commissioning and testing. This article is the guidance on the items that should be inspected, checked, and tested during the commissioning of an LV switchgear and associated circuit breakers.

The commissioning process for low voltage switchgear and circuit breakers involves evaluations, verifications, and checks that determine whether the proper switchgear and circuit breaker specifications and installation requirements are met.

Tests are also performed that determines whether the electric power distribution system will operate properly and safely after installation.

When the low voltage switchgear and circuit breakers are inspected and tested satisfactorily during the commissioning process, the system should operate in accordance with the manufacturer’s specifications for its maximum useful life.

Table of Content:

1. Evaluating LV switchgear and CBs upon receipt
   1. Visual Inspection
   2. Verification Against Specifications
      1. Low voltage Switchgear Nameplate
      2. Circuit Breaker Nameplate
2. Evaluating LV switchgear and CBs installation and testing
   1. Visual Inspection
      1. Suitability
      2. Physical damage
      3. Alignment
      4. Cleanliness
      5. Arc chute assembly
      6. Contacts
      7. Mechanism/Linkage
      8. Lubrication
   2. Mechanical Inspection
      1. Bolt Torque
      2. Door Operation
      3. Rack In – Rack Out
      4. Open/Close Operation
   3. Electrical inspection

1. Evaluating LV switchgear and CBs upon receipt

The installation of low voltage switchgear and circuit breakers is a process that occurs over a period of time. The installation begins with an identified need for a new low voltage power distribution installation (e.g., a new facility). Power is necessary for the new facility to function, so a switchgear and circuit breaker installation is designed. After the design is approved, the switchgear and circuit breakers are ordered.

Once the switchgear and circuit breakers are received from the manufacturer, they must be evaluated to ensure that they are proper for installation.

This section will describe how low voltage switchgear and circuit breakers are evaluated upon receipt.

1. Visual Inspection
2. Verification Against Specifications

1.1 Visual Inspection

When low voltage switchgear and circuit breakers are received from the manufacturer, a visual inspection should be performed. The purpose of the visual inspection is to verify that the switchgear and circuit breakers that were received from the manufacturer are in good physical condition and that all of the requested parts and accessories are present.

Because of the damage that can occur to the moving parts that are associated with low voltage switchgear and circuit breakers during installation, only a cursory inspection is performed at the receiving point.

A detailed inspection of the low voltage switchgear and circuit breakers is performed when they are completely installed at the site or facility.

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1.2 Verification Against Specifications

When a new facility or facility modification is at the equipment installation stage, the design of the installation has already been completed. The type of low voltage switchgear and circuit breakers that are selected for a specific power system should be shown in the drawings, prints, or specifications for the installation.

The purpose of verifying low voltage switchgear and circuit breakers against the specifications is to ensure that the equipment that is is being installed meets industry standards.

Generally, the verification against specifications consists of a determination of whether the type and rating of the equipment that is to be installed match the size and type of the equipment that is required for the installation. Usually, this determination is accomplished by reading an electrical plan that identifies the low voltage switchgear and circuit breaker sizes and types.

In some situations, the Electrical Engineer must rely on his knowledge of the correct application of switchgear and circuit breakers sizes and types to determine whether the correct equipment is being used. The data sheets that were used to order the switchgear from the manufacturer should also be consulted.

Take a look at the example of the LV switchgear datasheet:

Download Datasheet

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1.2.1 Low voltage Switchgear Nameplate

All low voltage switchgears should have a nameplate that is clearly visible on the front of the switchgear. The nameplate should contain manufacturer-type information. The information that describes the type of switchgear should consist of the manufacturer’s name, the type designation, and the serial number.

Because switchgear may contain different assemblies at various voltages, nameplates should be present at each switchgear segment.

LV switchgear is designed for and should be marked with the maximum voltage at which the switchgear can be applied. The rated maximum voltage level of the low voltage switchgear is the highest RMS voltage for which the switchgear is designed, and the rated maximum voltage is the upper limit for operation.

The rated insulation level of low voltage switchgear at each maximum voltage rating is equal to the low-frequency one-minute withstand voltage of 2.2 kV.

Low voltage switchgear is designed for and should be marked with the continuous current that the switchgear is capable of carrying and the fault current values that the switchgear is capable of interrupting without damage to the switchgear.

Specific current ratings for low voltage switchgear are as follows:

Rated Continuous Current at 50/60 Hz

The rated continuous current at 50/60 Hz is the amount of current that can be continuously carried by the switchgear primary circuit components (e.g., buses, bus connections) without exceeding switchgear equipment allowable temperature rise.

Examples of switchgear equipment are primary or secondary circuit components, insulation, and switchgear structural components.

The Rated Short-Time Current

The rated short-time current is the designated limit of available current at which the switchgear must interrupt the current within the required time at the rated maximum voltage.

The Rated Short-Circuit Current

The rated short circuit current of low voltage switchgear is the designated limit of available current at the rated maximum voltage that the switchgear must be required to withstand for a period of no less than four cycles.

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1.2.2 Circuit Breaker Nameplate

All circuit breakers must have a nameplate that is clearly visible on the front of the breaker. The nameplate should contain circuit breaker manufacturer-type information. The information that describes the type of circuit breaker should contain the manufacturer name, the type designation, and the serial number.

In accordance with ANSI C37, the manufacturer and rating information that should appear on the circuit breaker nameplate should contain the following rating information: