cable route marker

CABLE ROUTE AND MARKER

cable route marker

Cable route

Before the cable laying work is undertaken, the route of the cable shall be decided by site/project Engineer considering the following-

(i) While the shortest practicable route should be preferred, the cable route shall generally follow fixed developments such as roads, foot paths etc. with proper offsets so that future maintenance, identification etc. are rendered easy. Cross country run merely to shorten the route length shall not be adopted.

(ii) Cable route shall be planned away from drains and near the property, especially in the case of LV/MV cables, subject to any special local requirements that may have to be necessarily complied with.

(iii) As far as possible, the alignment of the cable route shall be decided after taking into consideration the present and likely future requirements of other services including cables in route, possibility of widening of roads/lanes etc.

(iv) Corrosive soils, ground surrounding sewage effluent etc. shall be avoided for the routes.

Route of cables of different voltages.

(a) Whenever cables are laid along well demarcated or established roads, the LV/MV cables shall be laid farther from the kerb line than HV cables.

(b) Cables of different voltages, and also power and control cables shall be kept in different trenches with adequate separation. Where available space is restricted such that this   requirement cannot be met, LV/MV cables shall be laid above HV cables.

(c) Where cables cross one another, the cable of higher voltage shall be laid at a lower level than the cable of lower voltage.

(d) Cable Route Marker shall be min 0.5meter away from cable trench

Route markers

 Location: Route markers should be provided along with the runs of cable allocations approved by the site Engineer and generally at intervals not exceeding 30m. Markers shall also be provided to identify change in the direction of the cable route and locations of underground joints.

MATERIAL

·         Aluminium

·         Cast Iron Material with Standard or Custom design

·         Fibreglass Reinforced Plastic [FRP]

GREADE     : Fire Retardant

COLOUR    : Red/yellow /white

Typical Size:

Dia 150mm, thick -8mm, length 0.6m -1.5m

Dimensions: 150mm x 100mm x 1.5m long

Dimensions: 150mm x 75mm x 1.3m long

a) Plate type marker: Route markers shall be made out of 100 mm x 5 mm G.I./aluminium plate welded / bolted on 35 mm x 35 mm x 6 mm angel iron, 60 cm long. Such plate markers shall be mounted parallel to and at about 0.5 m away from the edge of the trench.

c) CC marker: Alternatively, cement concrete 1:2:4 (1 cement: 2 coarse sand: 4 graded stone aggregate of 20 mm in size) shall be laid flat and cantered over the cable. The concrete markers, unless otherwise instructed by the site engineer, shall project over the surrounding surface so as to make the cable route easily identifiable.

d) Inscription: The LT / HV CABLE as the case may be shall be inscribed on the marker.

Precast Concrete Markers and Protection Slabs

Precast Concrete Protectors are used on top of vulnerable cables, conduits, ducts and pipes to protect them against accidental mechanical damage. Concrete is maintenance free, inexpensive and strong, save the frustration of locating underground services or worse, accidental damage to service.

Book reference :
A practical guide to cable installation and tool box talk

Available with book shop and -

http://www.amazon.in

http://www.abebooks.com

www.discoverypublishinggroup.com

Price: Rs. 375/- excluding delivery charges

Electrical thumb rule

Cable current Capacity:

• For Copper  Wire Current Capacity (Up to 25 Sq.mm) = 5-6X Size of Wire in Sq.mm
• Ex. For 4 Sq.mm=6×4=24 Amp, 
• For Aluminum wire Current Capacity = 4X Size of Cable in Sq.mm ,upto 10sqmm
• Ex. For 1.5 Sq.mm=4×1.5=6 Amp.

Nomenclature for cable Rating 

Uo=Phase-Ground Voltage, U=Phase-Phase Voltage, Um=Highest Permissible Voltage
Current Capacity of Equipments:

• 1 Phase Motor draws Current=6-7Amp per HP.
• 3 Phase Motor draws Current=1.7Amp per KW.
• Full Load Current of 3 Phase Motor=HPx1.3 from 10 HP onward
• Full Load Current of 1 Phase Motor=5 to 6 times of HP
• No Load Current of 3 Phase Motor =25-30% of FLC
• KW Rating of Motor=HPx0.75
• Full Load Current of equipment =1.39xKVA (for 3 Phase 415Volt)
• Full Load Current of equipment =1.74xKw (for 3 Phase 415Volt)

Earthing Resistance:

• Earthing Resistance for Single Pit=5Ω ,
• Earthing Grid=0.5Ω
• As per NEC 1985 Earthing Resistance should be <5Ω.
• Voltage between Neutral and Earth <=2 Volts
• Resistance between Neutral and Earth <=1Ω
• Creepage Distance=18 to 22mm/KV (Moderate Polluted Air) or
• Creepage Distance=25 to 33mm/KV (Highly Polluted Air)

Insulation Resistance:

• IR Value for Rotating Machine= (KV+1) MΩ.
• IR Value for Motor (IS 732) = ((20xVoltage (L-L)) / (1000+ (2xKW)).
• IR Value for Equipment (<1KV) = Minimum 1 MΩ.
• IR Value for Equipment (>1KV) = KV 1 MΩ per 1KV.
• IR Value for Panel = 2 x KV rating of the panel.
• Min Insulation Resistance Value (Domestic) = 50 MΩ / No of Points. (All Electrical Points with Electrical fitting & Plugs). Should be less than 0.5 MΩ
• Min Insulation Resistance Value (Commercial) = 100 MΩ / No of Points. (All Electrical Points without fitting & Plugs).Should be less than 0.5 MΩ.
• Test Voltage (A.C) for Meggering = (2X Name Plate Voltage) +1000
• Test Voltage (D.C) for Meggering = (2X Name Plate Voltage).
• Submersible Pump Take 0.4 KWH of extra Energy at 1 meter drop of Water.

Lighting Arrestor:

• Arrestor have Two Rating=
• (1) MCOV=Max. Continuous Line to Ground Operating Voltage.
• (2) Duty Cycle Voltage. (Duty Cycle Voltage>MCOV).

Transformer:

• Current Rating of Transformer=KVAx1.35
• Short Circuit Current of Generator/transformer

= Current Rating / % Impedance

• No Load Current of Transformer=<2% of Transformer Rated current
• Capacitor Current (Ic)=KVAR / 1.732xVolt (Phase-Phase)
• Typically the local utility provides transformers rated up to 500kVA For maximum connected load of 99kW,
• Typically the local utility provides transformers rated up to 1250kVA For maximum connected load of 150kW.
• The diversity they would apply to apartments is around 60%
• Maximum HT (11kV) connected load will be around 4.5MVA per circuit.
• 4No. earth pits per transformer (2No. for body and 2No. for neutral earthing),
• Clearances, approx.1000mm around Transformer allow for transformer movement for replacement. 

Diesel Generator:

• Diesel Generator Set Produces=3.87 Units (KWH) in 1 Litter of Diesel.
• Requirement Area of Diesel Generator = for 25KW to 48KW=56 Sq.meter, 100KW=65 Sq.meter.
• DG less than or equal to 1000kVA must be in a canopy.
• DG greater 1000kVA can either be in a canopy or skid mounted in an acoustically treated room
• DG noise levels to be less than 75dBA @ 1meter.
• DG fuel storage tanks should be a maximum of 990 Litter per unit Storage tanks above this level will trigger more stringent explosion protection provision.

Current Transformer:
Nomenclature of CT:

• Ratio: input / output current ratio
• Burden (VA): total burden including pilot wires. (2.5, 5, 10, 15 and 30VA.)
• Class: Accuracy required for operation (Metering: 0.2, 0.5, 1 or 3, Protection: 5, 10, 15, 20, 30).
• Accuracy Limit Factor:
• Nomenclature of CT: Ratio, VA Burden, Accuracy Class, Accuracy Limit Factor.Example: 1600/5, 15VA 5P10  (Ratio: 1600/5, Burden: 15VA, Accuracy Class: 5P, ALF: 10)
• As per IEEE Metering CT: 0.3B0.1 rated Metering CT is accu­rate to 0.3 percent if the connected secondary burden if imped­ance does not exceed 0.1 ohms.
• As per IEEE Relaying (Protection) CT: 2.5C100 Relaying CT is accurate within 2.5 percent if the secondary burden is less than 1.0 ohm (100 volts/100A).

Relay code of pratice

Relay code of practice

Relay code of practice

1.        The entire wiring of circuitry for indications, alarms, metering and protection should be permanent wiring.

2.        The leads should be marked and identified by ferrules near terminals.

3.        Every lead should end at a terminal point and no junction by twisting is allowed.

4.        The wiring should be by copper leads for C.T secondary for all cores i.e. metering cores as well as protection cores and for PT secondary for protection core.

5.        The wiring should be by copper leads 1.07 The copper lead for 1.05 & 1.06 above should be stranded but not single lead type.

6.        Aluminium leads can be used for indication, alarms and PT secondary for metering but stranded wires only are to be used. But copper leads are always preferable for these said purposes.

7.        The terminations should be lugged by ring shape ‘O’ lugs. ‘U’ shape lugs should be avoided since ‘U’ shape lugs may slip if terminal is loosen.

8.        For CT Secondary terminations, two nuts with one spring washer and two flat washers to be compulsorily used.

9.        The CT terminal strips should be stud type with nuts and not screw-in-type.

10.    Wherever two sets of batteries are available, the primary protection and back-up protection should be from different batteries.

11.    Where there is only one battery at an Electrical Power Substation, the primary and back-up protections should be given D.C supply through two individual circuits with independent fuses run from D.C bus.

12.    When CBs have two trip coils, both main protection and backup protection will energize both the trip coils.

13.    D.C and A.C supplies should not be taken through different cores of the same cable. Totally different cables should be used for DC and AC supplies.

14.    Independent D.C cables should be run to each equipment in the yard and looping of D.C supply from one equipment to other is not permitted.

15.    The D.C emergency lighting in substation should be through independent cables and not mixed up with protection and other circuitry.

16.   Standard colour codes for wires in control circuit of different sizes should be as follows,

sr.	PURPOSE	SIZE	COLOR
1	Indication, Alarm, trip, close etc	1.5 mm2	Gray
2	Red Phase Metering PT Circuit	1.5 mm2	Red
3	Yellow Phase Metering PT Circuit	1.5 mm2	Yellow
4	Blue Phase Metering PT Circuit	1.5 mm2	Blue
5	Red Phase Protection PT Circuit	2.5 mm2	Red
6	Yellow Phase Protection PT Circuit	2.5 mm2	Yellow
7	Blue Phase Protection PT Circuit	2.5 mm2	Blue
8	Red Phase Metering and Protection CT Circuit	2.5 mm2	Red
9	Yellow Phase Metering and Protection CT Circuit	2.5 mm2	Yellow
10	Blue Phase Metering and Protection CT Circuit	2.5 mm2	Blue
11	Phase for auxiliary AC supply	2.5 mm2	Red
12	Neutral for auxiliary AC supply	2.5 mm2	Black
13	Common star point of CTs	2.5 mm2	Black
14	Common star point of Protection PTs	2.5 mm2	Black
15	Common star point of Metering PTs	1.5 mm2	Black
16	Earthing Connection	2.5 mm2	Green

17.   The lead numbers are also standardized as follows so that anyone can easily identify the purpose for which the lead is connected-

sr	Alphabet Series	Purpose	Example
1	J Series	D.C Incoming	J1, J2, etc.
2	K Series	Control – Closing, Tripping, etc.	K1, K2, K3 etc.
3	L Series	Alarms, indications and annunciations	L1, L2, L3, etc.
4	M Series	Motor Circuit	M1, M2, etc.
5	E Series	Potential transformer secondary	E1, E2, E3, etc.
6	H Series	LT A.C Supply	H1, H2, H3, etc..
7	A Series	C.T secondary for special protection	A1, A2, A3, etc.
8	B Series	Bus bar protection	B1, B2, B3, etc..
9	C Series	Protection Circuits	C1, C2, C3, etc.
10	D Series	Metering Circuit	D1, D2, D3, etc

18.   The CT ratios available and adopted with number of cores shall be displayed on each panel as follows: (with underlined position as adopted).

19.   400 – 200 – 100 / 1-1-1

20.   19 Wherever CT cores are not used “SHORTING LOOPS” should be provided in CT secondary terminals and not in marshalling boxes or at panels.

21.   20 The Cable entries in the equipment, marshalling boxes and panels should be through appropriate size of cable glands. No other means are allowed.

22.   21 PT secondary should have group MOCBs with D.C alarm.

23.   22 Few cells from a battery set should not be used for separate low voltage D.C circuits. Here D.C – D.C converters may be employed for utilizing full D.C voltage of the entire battery as input.

Standard lead numbers used in control circuit of protection of power system

Certain lead numbers are standardized as follows and should be compulsorily adopted with ferrules at terminations of leads.

Main DC Positive supply – J1

 Main DC Negative supply – J2

 DC Positive bus inside panel – K1

 DC Negative bus inside panel – K2

Remote Close - K15R

 Remote Trip - K5R

 Local Close - K15L

 Local Trip - K5L

 Metering CT secondary’s – D11, D31, D51, D71 etc.

 Protection CT secondary – C11, C31, C51, C71 etc.

 Special Protection CT secondary – A11, A31, A51, A71 etc.

 PT secondary – E11, E31, E51, E71 etc.