Thursday, October 26, 2017

Three power calculations from single phase and three phase loads

Three phase power calculations when you have Both Single and Three Phase loads in System:-
While calculating three phase loads where  there are both single phase and three phase loads there are so many confusions arises such as how single phase and three phase loads comes at same platform while calculating total load.

This is can be simplified in below stated article:-

In electrical systems power is always additive i.e. if we have connected load in each single phase of 20 KW then total three phase power requirement will be 60 KW. There is often confusion arises while studying that if you have Three phase power of 90 KW then it means power will be 90 KW in each phase but same is not true as it means power will be 30 KW in each phase.
This can be illustrated by doing calculations in reverse order also:-

Three Phase Power calculations for Line to Line Voltage:-
Three phase power(KW) = 3 × PF × I(A) × VL-L (V) / 1000
Where PF= Power Factor
I(A)= Phase current in Amperes
VL-L= Line to Line RMS Voltage

Three Phase Power calculations for Line to Neutral Voltage:-
Three phase power(KW) = 3 × PF × I(A) × VL-N (V) / 1000
Power factor is usually taken as 1 for Resistive loads
Power factor is usually taken as 0.85 for Induction motors at full loads and 0.35 for no loads.
Now lets take three phase load of 90 KW, now if you consider this load to be equal to 90 KW in each phase then current in each phase will be= 90000/(1.732 X230X0.8)= 282 A
So every-time if you have to calculate total power then  just add single phase load and three phase load then cumulative will be your three phase load requirement.
In a balanced power system if there is total P having power factor pf and line to line voltage as VL

Then single phase power will be P(Single Phase)= P/3

Single Phase apparent power will =P/(3Xpf)
Phase current= Apparent Power
Then Phase current(A) =
1.732=  which comes as VLN=VL/

While doing above calculations efficiency must also be taken care.

These calculations given above are done considering three phase balanced load, which means that there will be same current and power consumption in each phase.  This is mostly applicable for electrical motors and transmission lines but in domestic loads where most of load is single phase this may not be effective. But above calculations will hold good for any industry.

This can be further simplified by assuming three motor of 90 KW. Now if you assume that there is 90KW load in each phase then you will get 270 KW overall load (Adding 90 KW of each phase) then you will pay for only 90 KW electricity charges then this will be huge savings as by withdrawal of 270 KW you have to pay only for 90 KW.
This means if you have a motor which is consuming a given KW then KW per winding is to be divided by 3 which are similar for three phase transformers where transformer is supplying given KVA then KVA in each winding will be third of total power.

Advantages of Three Phase power Over single phase power
There are following advantages of three phase power above single phase power:-
1.     When we use three phase power than frame size of required machine of same rating get reduce in comparison to when we use single phase power. It means frame size of machine get reduced.
2.     Single phase motors are not self-starting and required auxiliary means of starting the same but three phase motors are self-starting.
3.     Three phase motors have higher power factor and higher efficiency in comparison to single phase motors.
4.     Three phase motors of same rating as of single phase motors are smaller in size which will leads to lower cost , lighter in weight, lower in maintenance cost.
5.     Even in transmission lines for same amount of power at same voltage three phase transmission line requires lesser conductor material in comparison to single phase transmission lines. Thus three phase transmission system becomes cheaper. This will also leads to reduction in cross-sectional area of conductor. Thus leads to lower installation cost.
6.     Single phase motors have pulsating torque whereas polyphase system has uniform torque.

7.       It is quite easier to have parallel operation of three phase generators in comparison to single phase system.

Saturday, September 23, 2017

Working spaces for 600 V equipments installations (NFPA 70)

National Electricity code (NFPA 70) for working spaces while installation of 600 V electrical equipments:-

In this article we will discuss about working spaces of electrical equipment’s for voltage level of 600 Volts, Nominal, or Less.

Spaces required for all Electrical Equipment:-
There should be sufficient Access and working space shall be provided as to do the maintenance and operation of electrical equipment safely.

(A)  Working Space:-
There should be due attention to be taken regarding working space of equipment working at 600 Volts or less. This should comply with working space requirement for examination , adjustment, servicing or maintenance. The working spaces requirement will be shown in table as below:-

(i)                 Depth requirement of Working Space:-

The depth requirement of working space in the direction of live parts shall not be less than that specified in table below unless the requirements of all conditions are met as stated below        . In These cases distances can be measured from the exposed live parts or from the enclosure or from the opening if the live parts are enclosed.

(a)   Dead-Front Assemblies:-
For dead front assemblies such as:-

à Motor control centers
à Switchboards

In these assemblies there will not be requirement of working space in back sides.
In these assemblies all changing parts or adjustable parts such as fuses or switches are accessible from other than back and back sides. Where rear access is required to work on nonelectrical parts on the back of enclosed equipment, a minimum horizontal working space of 762 mm (30 in.) shall be provided.

(b)   Low Voltage:-
When there are exposed live parts having voltages in ranges between 30 Volts RMS- 60 Volts RMS then working space requirement can be reduced only by taking special permission.

(c)    Existing Buildings
If there is requirement of replacement of electrical equipment’s in existing buildings then working space or clearance is per condition 2 mentioned in tables above for dead-front switchboards, panel-boards, or motor control centers located across the passage. Where conditions of maintenance and supervision ensure that written procedures have been adopted to prohibit equipment on both sides of the passage from being open at the same time and qualified persons who are authorized will service the installation.

(ii)               Working space requirement across Width :-
The working space requirement across width in front of the electrical equipment shall be the width of the equipment or 762 mm (30 in.), whichever is greater. In all cases, the work space shall permit at least a 90 degree opening of equipment doors or hinged panels; it is more advisable to have space sufficient enough for opening of whole equipment as much allowable by hinge of panel.

(iii)             Working space requirement across Height:-
The working space requirement across height shall be clear and extend from the grade, floor, or platform to a height of 2.0 m (612 ft) or the height of the equipment, whichever is greater. Within the height requirements of this section, other equipment that is associated with the electrical installation and is located above or below the electrical equipment shall be permitted to extend not more than 150 mm (6 in.) beyond the front of the electrical equipment.

Exception No. 1: In existing residence units, service equipment or panel-boards that do not exceed 200 amperes shall be permitted in spaces where the height of the working space is less than 2.0 m (612 ft).

Exception No. 2: Meters that are installed in meter sockets shall be permitted to extend beyond the other equipment. The meter socket shall be required to follow the rules of this section.

(B)  Clear Spaces:-

Working space required shall not be used for storage. When normally enclosed live parts are exposed for inspection or servicing, the working space, if in a passageway or general open space, shall be suitably guarded.

(C)  Entrance space requirement and Egress from Working Space:-

(i)                 Minimum Required:-

At least one entrance of sufficient area shall be provided to give access to and egress from working space about electrical equipment.

(ii)               Large Equipment:-

For an electrical equipment having ampere rating of 1200 amperes or more and over 1.8 m (6 ft) wide that contains overcurrent devices, switching devices, or control devices, there shall be one entrance to and egress from the required working space not less than 610 mm (24 in.) wide and 2.0 m (612 ft) high at each end of the working space. A single entrance to and egress from the required working space shall be permitted where either of conditions stated below are met:-

(a) Unobstructed Egress. Where the location permits a continuous and unobstructed way of egress travel, a single entrance to the working space shall be permitted.

(b) Extra Working Space. Where the depth of the working space is twice that required by table above, a single entrance shall be permitted. It shall be located such that the distance from the equipment to the nearest edge of the entrance is not less than the minimum clear distance specified in table above for equipment operating at that voltage and in that condition.

(iii)             Personnel Doors:-
When there are electrical equipment’s having rated current more than 1200 A or more and also contains overcurrent devices, switching devices, or control devices are installed and there is a personnel door(s) intended for entrance to and egress from the working space less than 7.6 m (25 ft) from the nearest edge of the working space, the door(s) shall open in the direction of egress and be equipped with panic bars, pressure plates, or other devices that are normally latched but open under simple pressure.

(iv)             Illumination:-
Illumination shall be provided for all working spaces about service equipment, switchboards, panel- boards, or motor control centers installed indoors and shall not be controlled by automatic means only.

(v)               Dedicated Equipment Space:-
All switchboards, panel-boards, and motor control centers shall be located in dedicated spaces and protected from damage.

Exception: Control equipment that by its very nature or because of other rules of the Code must be adjacent to or within sight of its operating machinery shall be permitted in those locations.

For indoor electrical equipment’s

(a)    Dedicated Electrical Space:-
The space equal to the width and depth of the equipment and extending from the floor to a height of 1.8 m (6 ft) above the equipment or to the structural ceiling, whichever is lower, shall be dedicated to the electrical installation. No piping, ducts, leak protection apparatus, or other equipment foreign to the electrical installation shall be located in this zone.
Exception: Suspended ceilings with removable panels shall be permitted within the 1.8-m (6-ft) zone.

(b)   Foreign Systems:-
The area above the dedicated space required shall be permitted to contain foreign systems, provided protection is installed to avoid damage to the electrical equipment from condensation, leaks, or breaks in such foreign systems.

(c)    Sprinkler Protection:-
Sprinkler protection shall be permitted for the dedicated space where the piping complies with this section.

(d)   Suspended Ceiling:-.
A dropped, suspended, or similar ceiling that does not add strength to the building structure shall not be considered a structural ceiling.

à Outdoor:-
 Outdoor electrical equipment shall be installed in suitable enclosures and shall be protected from accidental contact by unauthorized personnel, or by vehicular traffic, or by accidental spillage or leakage from piping systems. The working clearance space shall include the zone. No architectural appurtenance or other equipment shall be located in this zone.

(vi)             Locked Electrical Equipment Rooms or Enclosures:-

Electrical equipment rooms or enclosures housing electrical apparatus that are controlled by a lock(s) shall be considered accessible to qualified persons.

Saturday, September 16, 2017

National Electricity code,NFPA 70 for Examination, Identification, Installation, and Use of electrical Equipment

NFPA – National Fire protection association 70 is also known as National Electrical Code

Examination, Identification, Installation, and Use of Equipment as per NFPA 70:-

(i)                 Examination:-

In judging equipment, considerations such as the following shall be evaluated:

(1)   Equipment usage can be identified by an equipment description either marked on the product or by description provided with a product to identify the suitability of the product for a
(a)    Specific purpose,
(b)   Environment, or
(c)    Application
Conditions required for its usage and limitations or other pertinent information may be marked on the equipment, included in the product instructions, or included in the appropriate listing and labeling information. Suitability of equipment may be evidenced by listing or labeling.

(2)   Mechanical strength and durability, including, for parts designed to enclose and protect other equipment, the adequacy of the protection thus provided

(3)   Wire-bending and connection space

(4)   Electrical insulation

(5)   Heating effects under normal conditions of use and also under abnormal conditions likely to arise in service

(6)   Arcing effects

(7)   Classification by type, size, voltage, current capacity, and specific use

(8)   Other factors that contribute to the practical safeguarding of persons using or likely to come in contact with the equipment

(B) Installation and Use:-
Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

Throughout this Code, the voltage considered shall be that at which the circuit operates. The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.

Conductors normally used to carry current shall be of copper unless otherwise provided in this Code. Where the conductor material is not specified, the material and the sizes given in this Code shall apply to copper conductors. Where other materials are used, the size shall be changed accordingly.

Conductor Sizes:-
Conductor sizes are expressed in American Wire Gage (AWG) or in circular mils.

Wiring Integrity:-
Completed wiring installations shall be free from short circuits, ground faults, or any connections to ground other than as required or permitted elsewhere in this Code.

Wiring Methods:-
Only wiring methods recognized as suitable are included in this Code. The recognized methods of wiring shall be permitted to be installed in any type of building or occupancy, except as otherwise provided in this Code.

Interrupting Rating:-
Equipment intended to interrupt current at fault levels shall have an interrupting rating not less than the nominal circuit voltage and the current that is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage not less than the current that must be interrupted.

Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics:-

The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors or between any circuit conductor and the equipment grounding conductor.

Deteriorating Agents:-

Unless identified for use in the operating environment, no conductors or equipment shall be located in damp or wet locations; where exposed to gases, fumes, vapors, liquids, or other agents that have a deteriorating effect on the conductors or equipment; or where exposed to excessive temperatures.
Equipment not identified for outdoor use and equipment identified only for indoor use, such as “dry locations,” “indoor use only,” “damp locations,” or enclosure Types 1, 2, 5, 12, 12K, and/or 13, shall be protected against damage from the weather during construction.

Mechanical Execution of Work:-
Electrical equipment shall be installed in a neat and workmanlike manner.

 (A) Unused Openings. Unused openings, other than those intended for the operation of equipment, those intended for mounting purposes, or those permitted as part of the design for listed equipment, shall be closed to afford protection substantially equivalent to the wall of the equipment. Where metallic plugs or plates are used with nonmetallic enclosures, they shall be recessed at least 6 mm (14 in.) from the outer surface of the enclosure.

(B) Integrity of Electrical Equipment and Connections.
Internal parts of electrical equipment, including busbars, wiring terminals, insulators, and other surfaces, shall not be damaged or contaminated by foreign materials such as paint, plaster, cleaners, abrasives, or corrosive residues.
There shall be no damaged parts that may adversely affect safe operation or mechanical strength of the equipment such as parts that are broken; bent; cut; or deteriorated by corrosion, chemical action, or overheating.


(a) Mounting of electrical equipment’s:-

Electrical equipment shall be mounted firmly and secured on to the surface on which it is required to be mounted. There is an old practice of mounting electrical equipment’s using wooden plugs which were mounted in holes of masonry, Concrete, plaster or similar material this practice should not be used.

(b) Cooling of electrical equipment’s:-

The electrical equipment’s which required sufficient natural air circulation for not getting heated up should be installed in such a way that room airflow over such equipment’s could not get restricted either by wall or by adjacent equipment. The equipment’s which were designed for floor mounting i.e. that directly mounted on trenches should have clearance between top surface and adjacent surfaces so as to dissipate heat generated from equipment’s. 
There will be equipment’s which have ventilation openings shall be installed in such way that there will  not be any obstructions to free circulation of air through the equipment.

(ii)               Electrical Connections.
There are different characteristics of different metals and we should not mix conductors of dissimilar metals in a terminal or splicing connector where there is contact occurs between dissimilar conductors such as:-
(a)    Copper and aluminum
(b)   Copper and copper-clad aluminum
(c)    Aluminum and copper-clad aluminum

When there is requirement of using solder, Fluxes, Inhibitors and Compounds then it must be kept in mind that they may not cause adverse effect on conductors, Installations or equipment.

(A)   Terminals:-  

Connections of conductors to the terminal parts should ensure good connection. Connections should not cause damage to the conductors. Connections to the conductors should be done by means of :-
(i)                 Hydraulic punching machine
(ii)               Pressure connectors
(iii)             Solder lugs
(iv)             Splices to flexible leads.

(B)   Splices:-
Conductors shall be spliced or joined with splicing devices by means of

(i)                 Brazing,
(ii)               Welding, or
(iii)             Soldering with a fusible metal or alloy.
Soldered splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then be soldered.
All splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors or with an insulating device identified for the purpose.

(C)   Temperature Limitations:-
The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

Equipment Provisions:-

(i)     For Termination if there is circuit having rating 100 A or less , or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
(a)    Conductors rated 60°C (140°F).
(b)   Conductors with higher temperature ratings provided the ampacity of such conductors is determined based on the 60°C (140°F) ampacity of the conductor size used.
(c)    Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
(d)   For motors marked with design letters B, C, or D, conductors having an insulation rating of 75°C (167°F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity.

(ii)   Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for one of the following:
(a)    Conductors rated 75°C (167°F)
(b)   Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75°C (167°F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors

Separate Connector Provisions:-
Separately installed pressure connectors shall be used with conductors at the ampacities not exceeding the ampacity at the listed and identified temperature rating of the connector.

(ii)High-Leg Marking:-
On a 4-wire, delta-connected system where the midpoint of one phase winding is grounded, only the conductor or busbar having the higher phase voltage to ground shall be durably and permanently marked by an outer finish that is orange in color or by other effective means. Such identification shall be placed at each point on the system where a connection is made if the grounded conductor is also present.

(iii) Arc-Flash Hazard Warning:-
For electrical equipment’s such as:-
(a)    Switchboard’s
(b)   Panel-boards
(c)    Industrial Control Panels
(d)   Motor control centers
(e)    Panels
There is need of routine examination, Maintenance while these remains energized so there should be marking to warn the qualified person against electrical flash hazard. The marking shall be located at such a place that it should be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

(iv)  Arcing Parts
Parts of electrical equipment that in ordinary operation produce arcs, sparks, flames, or molten metal shall be enclosed or separated and isolated from all combustible material.

(v)   Light and Power from Railway Conductors:-

Circuits for lighting and power shall not be connected to any system that contains trolley wires with a ground return.

(vi) Marking:-
The manufacturer’s name, trademark, or other descriptive marking by which the organization responsible for the product can be identified shall be placed on all electrical equipment. Other markings that indicate voltage, current, wattage, or other ratings shall be provided as specified elsewhere in this Code. The marking shall be of sufficient durability to withstand the environment involved.

(vii)                       Identification of Disconnecting Means:-

(A)  General.
Each disconnecting means shall be legibly marked to indicate its purpose unless located and arranged so the purpose is evident. The marking shall be of sufficient durability to withstand the environment involved.

(B)  Engineered Series Combination Systems.
Equipment enclosures for circuit breakers or fuses applied in compliance with series combination ratings selected under engineering supervision in accordance with 240.86(A) shall be legibly marked in the field as directed by the engineer to indicate the equipment has been applied with a series combination rating. The marking shall be readily visible and state the following:

(C)  Tested Series Combination Systems:-
Equipment enclosures for circuit breakers or fuses applied in compliance with the series combination ratings marked on the equipment by the manufacturer in accordance with 240.86(B) shall be legibly marked in the field to indicate the equipment has been applied with a series combination rating. The marking shall be readily visible and state the following:

(viii)                     Current Transformers:-

 Unused current transformers associated with potentially energized circuits shall be short-circuited.

(ix) Available Fault Current:-

(A)  Field Marking:-
Service equipment in other than dwelling units shall be legibly marked in the field with the maximum available fault current. The field marking(s) shall include the date the fault current calculation was performed and be of sufficient durability to withstand the environment involved.

(B)   Modifications:-
When modifications to the electrical installation occur that affect the maximum available fault current at the service, the maximum available fault current shall be verified or recalculated as necessary to ensure the service equipment ratings are sufficient for the maximum available fault current at the line terminals of the equipment. The required field marking shall be adjusted to reflect the new level of maximum available fault current.