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
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 (61⁄2 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 (61⁄2 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 (61⁄2 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.
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.
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.