Continued from second part: Electrical Thumb Rules You MUST Follow (Part 2)
Size of Capacitor for Power Factor Correction
| For Motor | |
| Size of Capacitor = 1/3 Hp of Motor ( 0.12x KW of Motor) | |
| For Transformer | |
| < 315 KVA | 5% of KVA Rating |
| 315 KVA to 1000 KVA | 6% of KVA Rating |
| >1000 KVA | 8% of KVA Rating |
Earthing Resistance value
| Earthing Resistance Value | |
| Power Station | 0.5 Ω |
| Sub Station Major | 1.0 Ω |
| Sub Station Minor | 2.0 Ω |
| Distribution Transformer | 5.0 Ω |
| Transmission Line | 10 Ω |
| Single Isolate Earth Pit | 5.0 Ω |
| Earthing Grid | 0.5 Ω |
| As per NEC Earthing Resistance should be <5.0 Ω | |
Voltage Limit (As per CPWD & KEB)
| Voltage Limit (As Per CPWD) | |
| 240V | < 5 KW |
| 415V | <100 KVA |
| 11KV | <3 MVA |
| 22KV | <6 MVA |
| 33KV | <12 MVA |
| 66KV | <20 MVA |
| 110KV | <40 MVA |
| 220KV | >40 MVA |
Voltage Variation
| > 33 KV | (-) 12.5% to (+) 10% |
| < 33 KV | (-) 9% to (+) 6% |
| Low Voltage | (-) 6% to (+) 6% |
Insulation Class
| Insulation | Temperature |
| Class A | 105°C |
| Class E | 120°C |
| Class B | 130°C |
| Class F | 155°C |
| Class H | 180°C |
| Class N | 200°C |
Standard Voltage Limit
| Voltage | IEC (60038) | IEC (6100:3.6) | Indian Elect. Rule |
| ELV | < 50 V | ||
| LV | 50 V to 1 KV | <=1 KV | < 250 V |
| MV | <= 35 KV | 250 V to 650 V | |
| HV | > 1KV | <= 230 KV | 650 V to 33 KV |
| EHV | > 230 KV | > 33 KV |
Standard Electrical Connection (As per GERC)
| As per Type of Connection | |
| Connection | Voltage |
| LT Connection | <=440V |
| HT connection | 440V to 66KV |
| EHT connection | >= 66KV |
| As per Electrical Load Demand | |
| Up 6W Load demand | 1 Phase 230V Supply |
| 6W to 100KVA(100KW) | 3 Phase 440V Supply |
| 100KVA to 2500KVA | 11KV,22KV,33KV |
| Above 2500KVA | 66KV |
| HT Connection Earthing | |
| H.T Connection’s Earthing Strip | 20mmX4mm Cu. Strip |
| CT & PT bodies | 2Nos |
| PT Secondary | 1Nos |
| CT Secondary | 1Nos |
| I/C and O/G Cable+ Cubicle Body | 2Nos |
Standard Meter Room Size (As per GERC)
| Meter Box Height | Upper level does not beyond 1.7 meter and Lower level should not below 1.2 meter from ground. |
| Facing of Meter Box | Meter Box should be at front area of Building at Ground Floor. |
| Meter Room / Closed Shade | 4 meter square Size |
Electrical Load as per Sq.ft Area (As per DHBVN)
| Sq.ft Area | Required Load (Connected) |
| < 900 Sq.ft | 8 KW |
| 901 Sq.ft to 1600 Sq.ft | 16 KW |
| 1601 Sq.ft to 2500 Sq.ft | 20 KW |
| > 2500 Sq.ft | 24 KW |
| For Flats :100 Sq.ft / 1 KW | |
| For Flats USS /TC: 100 Sq.ft / 23 KVA | |
Contracted Load in case of High-rise Building
| For Domestic Load | 500 watt per 100 Sq. foot of the constructed area. |
| For Commercial | 1500 watt per 100 Sq. foot of the constructed area |
| Other Common Load | For lift, water lifting pump, streetlight if any, corridor/campus lighting and other common facilities, actual load shall be calculated |
| Staircase Light | 11KW/Flat Ex: 200Flat=200×11=2.2KW |
| Sanctioned Load for Building | |
| Up to 50 kW | The L.T. existing mains shall be strengthened. |
| 50 kW to 450 kW (500 kVA) | 11 kV existing feeders shall be extended if spare capacity is available otherwise, new 11 kV feeders shall be constructed. |
| 450 kW to 2550 kW (3000 kVA) | 11 kV feeder shall be constructed from the nearest 33 kV or 110 kV substation |
| 2550 kW to 8500 kW (10,000 kVA) | 33kV feeder from 33 kV or 110 kV sub station |
| 8500 kW (10,000 kVA) | 110 kV feeder from nearest 110 kV or 220 kV sub-station |
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Hello Sir,
Can you explain me that thumb rule for the selection of APFCR panel Capacity in LT distribution.
Hi Sir. Can you help me with the formula on calculating motor thermal overload