Interlock Application Schemes - Table of Contents

Interlock Application Schemes
Examples of typical interlock schemes to help you design your own schemes.

Application Schemes - Table Of Contents

Introduction
Symbols Legend
Scheme Book - Printable

Switch and Breaker

Scheme # 1
Prevents opening of switch when breaker is closed.

Scheme # 2
Prevents operation of switch when breaker is closed. Permits re-closing the breaker for servicing when switch is locked open.

Scheme # 3
Prevents operation of switch when breaker is closed. Circuit cannot be cleared until proper supervisory key is obtained.

Grounding Switch with Main Switch

Scheme # 4
Prevents closing of grounding switch when main switch is closed, and vice versa.

Isolating Switches and Breaker

Scheme # 5
Prevents operation of disconnect when breaker is closed. Prevents opening fuse compartment door when disconnect is closed.

Scheme # 6
Prevents operation of disconnect when any or all of a group of breakers are closed. Operates through transfer interlock, no sequence is required for breaker closing.

Scheme # 7
Prevents operation of disconnect when any or all of a group of breakers are closed. Breakers operated in prearranged sequence.

Scheme # 8
Prevents operation of disconnects when breaker is closed. Permits servicing of breaker when disconnects are locked open.

Scheme # 9
Prevents operation of disconnects when breaker is closed, and prevents access to breaker compartment with disconnects closed.

Isolating Switches and Breaker Isolating Switches and Breaker or Regulator with By-Pass Switch

Scheme # 10
Prevents operation of breaker disconnects and by-pass disconnect under load. Provides for closing of by-pass disconnect before circuit is opened, or permits circuit breaker to be opened with by-pass disconnect remaining open.

Scheme # 10A
Prevents operation of voltage regulator disconnects and by-pass disconnect under load. Permits by-pass disconnect to operate only when regulator is in neutral position. Permits isolating regulator for servicing.

Prevent Paralleling of Lines

Scheme # 11
Prevents paralleling of two lines - single load, fed from either source.

Scheme # 12
Prevents paralleling of two lines - single load, fed from either source - breaker on load side.

Scheme # 13
Prevents paralleling of two lines - two loads, fed from either source (one tie breaker).

Scheme # 14
Prevents paralleling of two lines - two loads, fed from either source (one tie breaker). Prevents operation of switch when breaker is closed (on either source).

Scheme # 15
Prevents paralleling of two lines - two loads fed from either source (one tie breaker). Prevents operation (open or closed) of disconnect when breaker is closed (on either source). Prevents access to fuses when disconnects and breakers are closed.

Scheme # 16
Prevents paralleling of three lines - three loads, fed from any source (two tie breakers).

Scheme # 17
Prevents paralleling of four lines - four loads fed from any source (three tie breakers).

Scheme # 17A
Prevents paralleling of four lines - four loads fed from any source (three tie breakers). Also prevents opening of rear access doors when breakers are energized.

Scheme # 18
Prevents paralleling of three lines - three loads fed from any source (three tie breakers).

Scheme # 19
Prevents paralleling of four lines - four loads fed from any source (four tie breakers).

Scheme # 20
Prevents paralleling of three power sources through a common tie bus not normally in service. Permits feeding any load bus from a second power source through the tie bus. Permits one power source to supply all three load buses through the tie bus.

Scheme # 21
Prevents paralleling three power sources through a common tie bus not normally in service. Permits feeding any load bus from a second power source through the tie bus only when authorized by a supervisor. Permits one power source to supply all three load buses through the tie bus only when authorized by a supervisor.

Scheme # 22
Prevents paralleling two incoming primary sources through primary tie bus disconnect. Prevents operation (open or closed) of the disconnects under load. Permits one power source to supply both loads through tie bus.

Scheme # 23
Prevents paralleling of two incoming primary sources through the primary tie bus disconnect or secondary tie bus breaker. Prevents operation (open or closed) of disconnects under load. Permits one power source to supply both loads through either the primary or secondary tie bus.

Scheme # 24
Prevents paralleling of two incoming primary sources. Prevents operation (open or closed) of disconnects under load. Permits the isolating of breakers for servicing. Permits one power source to supply both loads through tie bus.

Interrupter Switch

Scheme # 25
Prevents opening fuse compartment door when the interrupter switch is closed. Prevents closing interrupter switch until fuse compartment door is locked closed.

Scheme # 26
Prevents operation (open or closed) of interrupter switch when breaker is closed. Permits the breaker to be serviced and operated while the interrupter switch is locked open.

Scheme # 27
Prevents operation (open or closed) of interrupter switch when breaker is closed. Prevents opening fuse compartment door when interrupter switch is closed. Prevents closing interrupter switch until fuse compartment door is locked closed. Permits the breaker to be serviced and operated while the interrupter switch is locked open.

Scheme # 28
Prevents dropping load when shifting from one source to the other. Prevents opening both interrupter switches at the same time. Permits both interrupter switches to be closed at the same time.

Scheme # 29
Prevents paralleling two lines requires dropping load when shifting from one source to the other. Prevents closing both interrupter switches at the same time. Permits both interrupter switches to be opened at the same time.

Scheme # 30
Prevents paralleling two lines requires dropping load when shifting from one source to the other. Prevents closing both interrupter switches at the same time.Permits both interrupter switches to be open at the same time. Prevents operation (open or closed) of either interrupter switch when breaker is closed. Permits the breaker to be serviced and operated while both interrupter switches are locked open.

Scheme # 31
Prevents operation (closed, open or closed) of the a three position interrupter switch when the breaker is closed.Permits the breaker to be serviced and operated while the interrupter switch is locked open.

Scheme # 32
Prevents operation (closed, open or closed) of a three position interrupter switch when the breaker is closed. Prevents opening fuse compartment door when the interrupter switch is closed. Prevents closing interrupter switch until fuse compartment door is locked closed. Permits the breaker to be serviced and operated while the interrupter switch is locked open.

Motor or Machinery Guard

Scheme # 33
Prevents opening of guard when motor circuit is closed. Guard may be a door or fence gate that prevents access to moving parts, belts, cutters, or any dangerous equipment.

Motor or Machinery Guard with Time Delay

Scheme # 34
Prevents opening of guard (or door) for a predetermined time after removal of power (from motor, centrifuge, condensers, etc.).

Breakers and Generators

Scheme # 35
Prevents paralleling of two lines - two loads, fed from either source (one tie breaker). Allows switching loads to a generator.

Scheme # 35A
Prevents closing generator breaker when main breaker is closed.

Scheme # 36
Prevents paralleling of two lines - two loads, fed from either source (one tie breaker). Allows switching loads to two generators.

Capacitor Bank Access

Scheme # 37
Prevents access to capacitor bank enclosure until capacitors have been grounded and discharged.

Scheme # 38
Prevents access to capacitor bank enclosure until capacitors have been grounded and discharged - utilizing a Time Delay Key Release Unit (TDKRU).

Uninterrupted Power Sources

Scheme # 39
Prevents improper maintenance bypass of UPS equipment.

Scheme # 40
Prevents improper maintenance bypass of UPS equipment.

Precipitator Access

Scheme # 41
Prevents access to an electrostatic precipitator, scrubber, or baghouse until all power supplies have been de-energized and properly grounded.

Scheme # 42
To allow operation of dual output transformer rectifiers with one field removed from service and to prevent opening any access doors of an electrostatic precipitator until all power supplies are de-energized and properly grounded.

Scheme # 42A
To allow operation of dual output transformer rectifiers with one field removed from service and to prevent opening any access doors of an electrostatic precipitator until all power supplies are de-energized and properly grounded.

Scheme # 42B
To allow operation of dual output transformer rectifiers with one field removed from service and to prevent opening any access doors of an electrostatic precipitator until all power supplies are de-energized and properly grounded.

Rectifier Access

Scheme # 43
Prevents opening any rectifier enclosure door while the rectifier is operating.

Scheme # 43A
Prevents opening any rectifier enclosure door while the rectifier is operating.

Scheme # 44
Prevents opening any rectifier enclosure door while the rectifier is operating.

Scheme # 45
Prevents opening any rectifier enclosure door while the rectifier is operating and prevents opening the negative disconnect
switch under load.

Scheme # 45A
Prevents opening any rectifier enclosure door while the rectifier is operating and prevents opening the negative disconnect
switch under load.