HVL/cc™ Grounding Switch Application

The HVL/cc switch may be equipped with an internally interlocked grounding switch that is formed as an integral part of the main power switch. The grounding switch feature is optional and must be specified at the time of order. The grounding switch is only effective on one side of the switch. The options are: (1) no grounding switch (see HVL/cc without Grounding Switch), (2) grounding switch located on the load side of the switch (see HVL/cc with Grounding Switch Ground on Load Side), or (3) grounding switch located on the line side of the switch (see HVL/cc with Grounding Switch Ground on Line Side).

The grounding switch is capable of trip-closing duty at the short-circuit current rating of the switch; however, this duty is not recommended.

Load Side Discharge Assembly (LDA) located on the load side of the power fuses is available as an additional accessory (see HVL/cc with Grounding Switch Ground on Load Side). The purpose of this device is to drain capacitive charges from disconnected circuits. The LDA is available as an option when the HVL/cc grounding switch is specified, and only with DIN-E style fuses. The LDA is not rated for fault current duty and is not to be considered a grounding switch.

Do not use a Load-side Discharge Assembly in the following situations:

• If there is any possible source of power on the load or downstream side of the LDA. For example, do not use LDAs on the load side of switches involved in double-ended or multiple feed applications.

• Power transformer applications where there is a possibility of backfeeding from a low voltage generator. An exception to this general rule is when the source of downstream power is a generator that utilizes a key interlock scheme to block the closing of the LDA when the generator is connected.

The following illustrations depict the grounding switch and LDA options available with the basic HVL/cc switching unit.

Load-side Discharge Assembly

HVL/cc without Grounding Switch	HVL/cc with Grounding Switch Ground on Load Side
HVL/cc with Grounding Switch Ground on Line Side	HVL/cc with Grounding Switch on Load Side and Load Discharge Assembly

The LDA should only be used where there is no possibility of power back-feed from alternative power sources such as commercial power, a downstream generator, and/or a charged capacitor bank. See the HVL/cc Metal Enclosed Switchgear instruction bulletin for more information about LDAs.

When an HVL/cc switch is provided with a grounding switch, an LLI unit is always provided on the grounding side of the HVL/cc switch to indicate the presence (see HVL/cc with Grounding Switch on Load Side and Live Line Indicators). In addition to indication lights, the LLI unit also has a provision for the use of a voltmeter or phase-testing devices.

• Grounding Switch on Load Side, With Power Fuses: When an HVL/cc switch is specified to have the grounding switch on the load side with power fuses, a LLI is provided as standard equipment with the voltage dividers located at the load end of the power fuses. A line-side LLI unit and voltage divider may also be used as an additional cost option (see HVL/cc with Grounding Switch on Load Side and Live Line Indicators).

• Grounding Switch on Load Side, Unfused Switch: An LLI unit and voltage divider are placed on the load side of the HVL/cc switch as standard. A line-side LLI unit and voltage divider may also be used as an additional cost option (see HVL/cc with Grounding Switch on Load Side and Live Line Indicators).

• Grounding Switch on Line Side, Unfused Switch:

  An LLI unit and voltage divider are placed on the line side of the HVL/cc switch as standard. A load-side LLI unit and voltage divider may also be used as an additional cost option (see HVL/cc with Grounding Switch on Line Side and Live Line Indicators).

• Test ports on the LLIs are suitable for testing voltage with a properly rated voltage sensing device. LLIs are not an indicator of the absence of voltage. Properly rated test equipment must be used to help ensure no voltage is present before performing any maintenance procedures.

Never use a grounding switch in a circuit for which the operator does not have full control of the circuit and is capable of locking out and tagging out the circuit on both ends. For example, do not use a grounding switch on the line side of an HVL/cc that is considered a service disconnect (in accordance with NEC) connecting to a commercial utility source (see HVL/cc with Both Load Side Grounding Switch and Load Discharge Assembly Acceptable). A utility customer does not have control over the source of power, thus a grounding switch for this service is prohibited. Within a utility power system or within a premise where the owner has control of both ends of the circuit, do not use a grounding switch unless the operator has exclusive control of all sources of power to the grounding switch.

See Application Diagrams.

Due to the popularity of the duplex switch (two services for a common fused load), mechanical interlocking is available between the two switches. The mechanical interlock is designed to prohibit paralleling of the two sources and requires the use of the stored energy mechanism. Key locks can be used for same functionality and are required for the over-toggle mechanism.

When duplex switches are equipped with load-side grounding, a single ground switch is incorporated on the duplex switch containing the fuse. This ground switch serves as the load-side grounding mechanism for both switches and is key interlocked with the two duplex mains. The duplex switch arrangement is designed so that both switches must be open to remove the load side panel. In addition, when equipped with the ground switch, the load-side panel cannot be removed until both switches are key-locked open, and the ground switch is key-locked closed.

Key interlocking is only shown as an alternative to mechanical interlocking for the duplex switch and to enable the use of the LDA for systems having a generator supply source downstream. Key Interlocking can be used as an additional application design feature and to assist in performing the proper operating sequence before switching operations. It is not the scope of this application section to cover all possible combinations of suitable key interlocking schemes. Each power system must be evaluated, and appropriate key interlocking specified to meet particular risks a system may have. This process is typically performed by the professional engineer of record for the facility. Key Interlocking may be applied considering the following general philosophy.