Disconnect switch

FIG. 29-5 Siiiiplificd schciiiatic dia raiii of a coiiilunation line starter with a circuit lirciLker as the fault interrupter and disconnect. Alternative fuses and disconnect switch are shown as siilistitiites for the circuit lirciLker,... 

We can improve the starting performance of the above method by providing C in two parts, one for start Cl, of a much higher value, depending upon the requirement of 7, through a disconnect switch (Figures 1.25(fl2) and (bi)), and the other C, for a run of a much lower value (so that... 

ANSI C.37.47/1992 Specifications for distribution fuse disconnecting switches, fuse supports and current limiting fuses Motors and generators ratings, costruction. testing and performance... 

Batteries should normally be installed in an unclassified area. However, if installed in Division 2 areas, a suitable disconnect switch must be installed to disconnect the load prior to removing the battery leads and tlius avoid a spark if the battery leads are disconnected under load conditions. Batteries should not be installed in Division 1 areas. 

As with the single bus arrangement, each connection is linked to the main bus through a circuit breaker, but the breaker may be bypassed using disconnect switches through a transfer bus and another breaker to the main bus. This permits isolation of the circuit breaker for maintenance without loss of service to the connection. 

For every piece of equipment in a substation, manual switches—called disconnect switches—are provided to enforce complete electrical isolation from equipment before any service is pertornied. Disconnect switches are placed in clearly visible locations so maintenance personnel can continuously confirm that the equipment is isolated. The disconnect switch cannot interrupt current, so it is opened only when the current has already been interrupted by an automatic switch such as a circuit breaker. 

Figure 2.128 describes the main components of a photovoltaic solar collector system that is connected to the grid. These include the AC service entrance, the AC and DC disconnect switches, the inverter, and the two kWh meters, one tracking the total solar production and the other tracking the electricity flow to (and from) the grid. 

When a disconnect switch, circuit breaker, or set of fuses is included in the same enclosure as the contactor, the starter is then called a combination starter. In addition to the fault-current-interrupting function, the breaker or fuses serve as the disconnecting device. Figure 29-5 illustrates schematically combination starters of various types. The latch is arranged to open the disconnect before the door can be swung open. There are also provisions for padlocking the disconnect open with the door closed so that maintenance wonc on the motor may proceed in safety. 

Service entrance equipment should be installed in an indoor electrical room whenever possible. The equipment should include one to six main service entrance power circuit breakers or load break disconnect switches and feeder circuit breakers for loads within the plant. Circuit breakers and disconnect switches for 480/277 V systems that are rated at 1000 A or more must include groimd fault protection. Feeder circuit breakers will typically be molded case. Integrally fused circuit breakers are available with very high short circuit lAC ratings for both power and molded case circuit breakers. Fuses and current limiters for integrally fused circuit breakers must be stored within the electrical room. 

Fuses should not be used to protect secondary voltage feeders. The time current characteristics of fuses above 100 A will not coordinate with the groimd fault pickup currents and time delays of the main overcurrent protection (circuit breaker or fused disconnect switch) ground fault protection. A main load break disconnect switch can be equipped with current-limiting fuses to reduce the available short-circuit current from the utility and should have a three-phase voltage relay for single-phase protection. 

Two (2) to six (6) separate service entrance cables connected to the secondary side of one utility owned transformer can connect to separate main circuit breakers or main load brake fused disconnect switches that are mounted next to each other. The sum of the ampacity of all of the service entrance conductors must have a current rating equal to or greater than the present and future maximum demand for the plant. This approach can reduce the cost of the service entrance installation but will not provide the additional level of protection provided by having one main circuit breaker or one main fused disconnect switch. Therefore it is not as reliable. 

Unit substations, each consisting of a primary fused disconnect switch or circuit breaker, a dry transformer, and secondary switchgear should be in a central location near their loads. Unit substation transformers should be sized to carry at least 125% the maximum present and future connected load. 

Primary selective circuit arrangements utilize two primary selectable feeders for each transformer. These feeders are either connected to the line side of two interlocked primary non-fused disconnect switches that have a common load side fuse or to the line side of two interlocked primary fused disconnect switches. The latter configuration is shown in Fig. 2. Only one primary disconnect switch can be closed at any time. 

SERVICE SWITCH - Disconnect switches or circuit breakers. Purpose is to completely disconnect the building from the electric service. 

Application of LOTO devices to breakers and disconnect switches, valves, and energy isolating devices. 

Mains disconnect switch Fuses (internal and external)... 

Fixed power cords are common to machinery and household appliances, but care must be taken to ensure that the cord, strain relief, plug, and terminal block are type-approved and that the proper termination methods and makings are utilized. lEC-type terminal blocks (touch safe) are the preferred method for termination of the incoming power wiring. Other methods of termination are possible, such as for connection directly to circuit breakers, mains disconnect switch, PCBs and tabs/ screws on filters. Refer to the product standard for the alternative methods of input terminations. Solder connections shall not be the only method of fixing and in some cases are not allowed for high current connections. 

A hand-operated power disconnect device shall disconnect the whole equipment from main input supply power. There are several possibilities. A user-accessible disconnect switch located on the front of the product is preferred but not the only option. Some of the power disconnect methods are ... 

B. Mains Disconnect Switches Mains disconnect switches are required on all machines to isolate the entire electrical equipment. The OFF position must be lockable, lEC symbols for ON/OFF positions must be present and meet the relevant EU standards for construction and operation, which is assured if the device... 

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