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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Hi Sir. Can you help me with the formula on calculating motor thermal overload