Explainer: Electrical components and ways to increase BESCOM sanctioned load

Here is an explainer on electrical system components and its maintenance, how to calculate sanction load and the process to increase it.

(Part 1 covered the components of BESCOM bill, tariff structure and sanction loads. Part 2 delves into electrical system maintenance)

With the adoption of electric vehicles, owners are tapping into their existing meters to charge their vehicles, leading to electrical mishaps. If you need to connect a 3.3 kw/7.2kw EV charger, your sanctioned load needs to be enhanced. This leads to cable/wire, MCB (miniature circuit breaker) and RCCB (residual current circuit breaker) replacement, possibly the energy meter too may need to be replaced. 

Overall, if every household enhances sanction load, this leads to constant tripping of the transformer and short circuits in the electrical panel room, etc.  

Electrical System of 2 Bhk flat with 3 Kw Sanction Load 

1. Electrical DB (distribution board): Also known as electric panel/fuse box is a component of an electricity supply system that divides an electrical power feed into subsidiary circuits while providing a protective fuse or circuit breaker for each circuit in a common enclosure. It comprises of:

  • RCCB rated for 25A – 100mA
  • MCB 2 pole, rated for 25 A  
  • MCBs, 1 Pole rated for 16A and 10 A as per design (say 10 to 12 numbers)

 

circuit board with multiple MCBs and an RCB
Inside of a Distribution Board – RCCB and MCBs. Pic: Gautam Kamath
RCCB – 25A/100mA, MCB -C25 amps, C16amps.
RCCB – 25A/100mA, MCB -C25 amps, C16amps. Pic: Gautam Kamath

Why is there a 25 AMPS rating? 

As per Standards, the RCCB/MCB should be rated for max 80% loading. Hence, for 13.05 Amps as 80%, we need a RCCB/MCB of 16.31 Amps. The nearest RCCB/MCB is 16 Amps, which is on  a lower side and so, the next available rating i.e., 25 Amps is installed.

  1. The RCCB/MCB should be rated for a 120% loading
  2. Given a load of 13.05 Amps, we calculate the required RCCB/MCB rating as follows:
    • 120% of 13.05 Amps is approximately 10.44 Amps
    • Therefore, we need an RCCB/MCB with a rating greater than or equal to 15.66 Amps
  3. The nearest available RCCB/MCB rating is 16 Amps, which is slightly higher than the required 15.66 Amps
  4. As a result, the next available rating, 25 Amps, is installed

In summary, the 25 Amps RCCB/MCB is chosen to ensure adequate protection for the given load.

Causes for RCCB tripping  

Why and when does your RCCB trip: RCCBs provide critical benefits in electrical systems. They  swiftly (in milli-seconds) disconnect circuits in the presence of residual currents, preventing  electric shocks and enhancing safety. RCCBs contribute to fire prevention by detecting and isolating faulty circuits. They also protect electrical equipment from damage caused by faulty  currents, ensuring device longevity. Compliance with safety standards, versatility across  various settings, and early detection of potential hazards are key advantages, making RCCBs  essential components for electrical safety. 

A 2 BHK apartment with 3 KW sanction load is provided with

  • 2 Pole 
  • 25 Amp /100 milli amp 
  • RCCB inside DB 

These are generally found at the entrance.

RCCB tripping problems mean trips that are not caused by normal electrical faults in the system. It usually indicates one of several underlying problems, such as:  

  1. Incorrect installation 
  2. Equipment failure – Faulty connected equipment
  3. Damaged supply wiring/ageing
  4. Dirt build-up on the trip unit  contacts 

One of the most common reasons for unexpected RCCB trips is moisture-creating resistance leaks in wiring, also called ground faults. This water intrusion happens more  frequently in bathrooms, kitchens, basements, and outdoor circuits.  

Causes for MCB tripping 

Why and when does your MCB trip: The primary function of a miniature circuit-breaker is to protect an installation or appliance against sustained overloading and short-circuit faults, but it will also give  protection against earth faults provided that the earth fault loop impedance is low enough. 

In a 2 BHK flat, there is a main 2 Pole MCB with 25A rating. This MCB is connected to: 

  • A number of individual MCBs of 16 A and 10A ratings
  • Each 15A socket is connected to a 16A MCB, where a number of switches in a circuit is connected to a 10A MCB

Wiring and sockets

wires inside a cable
Wires. Pic: Sunroom.com
cable size and power rating. Wire sizes and wattage
Cable sizes and power rating. Pic: Gautam Kamath
switch board
From Right to Left – 5A socket, 5 A Switch, 3 no’s 16A switches and 16A Socket. Pic: Gautam Kamath
  • Number of 5A switches are connected to the 10A MCB vide1.5 sq.mm wire circuit and can carry a combined load of 15A
  • Whereas, only one 16A switch is connected to the 16A MCB vide 2.5 sq.mm wire, which can carry a load of 20 A 

Safety instructions 

  1. Check equipment load before connecting:
  • Always assess the load of electrical equipment before plugging it into a socket. This ensures that the socket can handle the power demand without overloading
  • Consider factors such as the wattage, voltage, and current requirements of the device. If the load exceeds the socket’s capacity, it could lead to overheating, tripped circuit breakers, or even electrical hazards
  1. Avoid using Extension Cords for heavy equipment:
  • Extension cords are convenient, but they have limitations. Never use them to connect multiple heavy-rated appliances simultaneously
  • Heavy equipment (such as air conditioners, refrigerators, or high-power tools) should be directly plugged into a wall socket. Extension cords may not handle the load, leading to potential fire risks or damage

When we draw more current (measured in amperes) through a wire than its capacity allows, the wire heats up. As a consequence, the outer insulation begins to melt, and the individual strands of the wire may fuse together. This can lead to a short circuit, which in turn can cause a fire hazard.


Read more: A guide to fire safety in hospitals How should apartments and gated communities handle transformer maintenance?


How to increase your load (especially in apartment complexes)

  • Check your sanctioned load from the bill
  • Check the connected load by adding all common area lighting, water pumps, lifts, STP, WTP and any other load( do-not add standby pumps/equipment and fire pumps)
  • The connected load should be lower than the sanctioned load
  • Verify that the transformer capacity meets any additional demand due to enhancing the connected load
  • Check the incomer MCB rating for adequacy
  • Check for the cable sizing of incomer cable from transformer to the LT Panel in the electrical room
  • Check for the cable sizing from BusBar (A BusBar is an electrical junction used for collecting electric power from the incoming feeders and distributes them to the outgoing feeders. to the individual feeder)
  • Check the adequacy of the BusBar capacity too
  • Check for availability of spare feeder of adequate capacity the LT panel ( Any new load to be drawn only from the feeder)

These are basic checks before adding any load and requesting for enhancement of sanction load

If everything is fine then meet your area BESCOM AE/AEE for guidance on applying for enhancement of sanction load.

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