Electrical Thumb Rules-(Part 3)

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 & Kerala Elect.Board):

Voltage Limit (As Per CPWD)
240V	< 5 KW
415V	<100 KVA
11KV	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

 Approximate 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