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The Important safety devices fitted on main switch board are:
- Circuit breakers: A circuit breaker is an auto shut down device which activates during an abnormality in the electrical circuit. Especially during overloading or short circuit, the circuit breaker opens the supplied circuit from MSB and thus protects the same. Different circuit breakers are strategically installed at various locations.
- Fuses: Fuses are mainly used for short circuit protection and comes in various ratings. If the current passing through the circuit exceeds the safe value, the fuse material melts and isolates the MSB from the default system. Normally fuses are used with 1.5 times of full load current.
- Over current relay: OCR is used mainly on the local panel and MSB for protection from high current. They are installed where a low power signal is a controller. Normally relays are set equivalent to full load current with time delay.
- Dead front panel: It is another safety device provided on the Main switch board individual panels wherein you cannot open the panel until the power of that panel is switched off.
What are switchboard safety devices ?
- Overload trip
- Preferential trip
- Under voltage trip
- Over voltage trip
- Reverse power relay (No voltage trip)
- Reverse current trip
- Fuse
- A .C .B( Air circuit breaker )
- Earth lamps.
- Low frequency trip
- Meters
- Synchroscope
- Emergency synchronizing lamp
- Ebonite handrail and Rubber footstep
MSB Safeties
Minimum 3mm rubber mat (approved and certified) in front as well as back of switchboard.
Dead front-end switchboard.
Insulated door handles (Ebonite)
Panel doors are also earthed.
Can’t open door, if breaker is closed.
No pipeline to pass in vicinity.
Minimum 1m free air surrounding switchboard.
Short circuit protection (ACB gen.)
Preferential trip circuit breaker (110%, 115%)
Reverse power trip circuit breaker (ACB, Gen)
UV/OV trip circuit breaker (ACB, Gen – 50%)
OF/UF trip circuit breaker (ACB, Gen)
Single phasing alarm.
Over speed trip/relay (ACB, Gen)
Over Current trip/relay (ACB, Gen)
Over load trip (ACB, Gen)
No voltage trip (ACB)
Fuses, meter, synchroscope
Earth fault indication.Main Switch Board or MSB to be installed on a raised platform.
The location where Switch Board or MSB is installed should have good ventilation, illumination and affected by minimum vibration.
No water or oil pipes should pass above the Switch Board or MSB.
There should be adequate space around allowing comfortable operation ans maintenance.
The operating floor space in front and behind the Switch Board or MSB should be covered with anti skid, insulated rubber mats with a minimum thickness of 15 mm.
Panel doors should be in locked position.
Door opening mechanism should be interlocked with power supply.
The enclosure should be drip proof.
MSB should be dead front type. (i.e. All the live conductor should pass behind MSB)
Every equipment onboard must be properly earthed. Also MSB must be properly earthed.
Every incoming and outgoing feed must be protected by a switch fuse or circuit breaker.
Insulation resistance should not be less than 1 Mega Ohm in any case. Insulation Resistance (IR) to be checked and records are maintained.
All meters must be calibrated periodically and records are maintained.
All the meters, switches, fuses, push button, indicating lamps, etc. should be in working condition and identified with individual name plate or tag.
All the interlocks must be in working condition.
Operating switch gear, tools such as circuit breaker handle, fuse puller, lamp grip, etc. must be readily available and to be used.
Red tag / name plate indicating high voltage and danger sign should be fitted
Appropriate ready to use fire extinguishers should be positioned nearby. (CO2and DCP)
Charts indicating drill procedures in case of electric shocks must be displayed near MSB.
Wiring diagram laminated or framed indicating supply system must be displayed nearby.
All the appropriate spares should be properly preserved and protected, individually packed and identified, and should be readily available for use.
Earth fault indication should be fitted and displayed in front panel.
24 volt battery supply emergency light should be provided near MSB.
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