1d Appendix D Rack Build Standard.pdf

Engineering Division Electronic Equipment Build Standard Appendix D, Rack Build Standard V1 Revision 1

D.1 Scope

This document provides the requirements for racks installed at LBNL for R&D and experimental use. This document incorporates requirements commonly required to be applied from UL standards for electrical safety. Additional requirements may apply. Refer to section 7 for the references used in this document.

These standards provide requirements from the UL standards for Industrial Control Equipment (UL508) and Industrial Control Panels (UL508A). For grounding and bonding requirements refer to the LBNL Electrical Equipment Build Standard or the Electrical Standard for Industrial Machinery (NFPA 79).

D.2 Construction

D.2.1 General

D.2.1.1 An enclosure shall be constructed so as to reduce the risk of unintentional contact with enclosed electrical devices, and to provide internal devices with protection from external conditions.

D.2.1.2 A part of an enclosure, such as a door or a cover, shall be provided with a means (such as latches, locks, mechanical interlocks, or screws) for firmly securing it in place.

D.2.1.3 A door more than 48 inches (1.2 m) long on the hinged side shall be provided with one of the following:

a) A multipoint latch operated by a single knob or handle;

b) Two or more snap latches or captive fasteners; or

c) One knob-operated latch and one snap latch or captive fastener.

D.2.1.4 A door giving access to a fuse or any portion of a circuit breaker other than the operating handle shall shut closely against a 1/4-inch (6.4-mm) rabbet as illustrated in Figure 1 or the equivalent.

Figure 1, Overlapping rabbet

D.3 Power outlets

D.3.1 Power Outlets on the Equipment

D.3.1.1 Power outlets should be designed for the intended load plus a headroom factor of an additional 80%. The expected load, due to future changes to the system, should not exceed 80% of the design capacity.

D.3.1.2 A receptacle located inside a rack provided for the permanent connection of a load shall be oriented to reduce the risk of electric shock when removing or inserting plugs.

Power strips located inside a rack should be mounted at a right angle if this orientation does not obstruct the sight line and the ability for personnel to see exposed prongs.

D.3.1.3 If any standard power supply outlet in the equipment is accessible to personnel, a marking shall be placed in the vicinity of the outlet to show the maximum load that is permitted to be connected to it.

D.3.2 Receptacles

D.3.2.1 General-use grounding type receptacles and a multi-pin type receptacles shall be NRTL listed devices.

D.3.2.2 A multi-pin receptacle mounted through an enclosure wall shall additionally:

a) Be provided with a metal housing that is integral to the rack or is NRTL listed;

b) Be a female type;

c) Be oriented to reduce the risk of electric shock when removing or inserting plugs;

D.3.2.3 A general-use receptacle rated more than 20 amperes or a multi-pin type receptacle of any rating shall have mechanical means to secure the connection(s). The receptacle shall be marked “For disconnecting use only, not for current rupturing” or the equivalent.

D.3.2.4 Class A ground fault circuit interrupter protection which is NRTL listed, shall be provided for all 120-volt, single-phase, 15- or 20-ampere receptacles used in racks marked as having a Type 3R or 3RX enclosure or otherwise intended for outdoor use.

D.4 Access to Energized Parts

D.4.1 Operator Access Areas

D.4.1.1 The equipment shall be so constructed that in Operator Access Areas there is adequate protection against contact with bare parts at hazardous voltages.

D.4.2 Accessibility of Live Parts (Finger Safe)

D.4.2.1 To reduce the likelihood of unintentional contact that may involve a risk of electric shock from an uninsulated live part, electrical energy - high current levels, or injury to persons from a moving part, an opening that has a minor dimension of 1 inch or more, such a part or wire shall be spaced from the opening as specified in Table 1.

Table 1, Minimum acceptable distance from an opening to a part

D.5 Interlocks

D.5.1 General

D.5.1.1 Interlocks used to protect operators from hazards shall prevent an operator from being exposed to the hazard before the hazard is removed. Conformity is checked by inspection and by performing relevant tests to verify that the interlocks perform as required.

D.5.2 Prevention of Reactivating

D.5.2.1 Upon operation, an interlock shall prevent a hazard from reactivating until the interlock has been reset

D.5.2.2 Until the action which caused the interlock to operate has been reversed or cancelled, an interlock for the protection of an operator shall prevent the hazard from reactivating.

D.5.3 Reliability

D.5.3.1 An interlock system for the protection of operators shall ensure that a single fault in the interlock system is either unlikely to occur during the expected life of the equipment, or cannot cause a hazard.

D.5.3.2 Components used for an interlock system should be designed for use in a safety application or rated for 100,000 operations minimum.

D.5.3.3 Conformity is verified by assessment of the interlock system by the LBNL Interlock SME.

D.6 Ventilation

D.6.1 Ventilating Openings

D.6.1.1 A ventilation opening in the top of a rack shall be covered by a hood or protective shield spaced above the opening when there are uninsulated components below the opening.

D.6.1.2 Any ventilating opening in a rack shall be finger safe (section 4.2).

D.6.1.3 A louver shall not be more than 12 inches (305 mm) long.

D.6.1.4 The area of an opening covered by a louver, a perforated or an expanded-metal mesh panel that is thinner than the enclosure shall not exceed 200 square inches (0.129 m2).

D.6.1.5 The diameter of the wires of a screen shall be at least 0.051 inch (1.30 mm) if the screen openings are 0.500 square inch (32.3 mm2 ) or less in area, and shall be at least 0.081 inch (2.06 mm) for larger screen openings.

D.6.1.6 Perforated sheet steel and sheet steel employed for expanded-metal mesh shall be at least 0.042 inch (1.07 mm) thick uncoated steel for mesh openings or perforations

0.500 square inch (3.2 cm2) or less in area, and shall be at least 0.080 inch (2.03 mm) thick uncoated steel for larger openings.

D.6.2 Barriers Used With Ventilation Openings

D.6.2.1 A barrier shall be interposed between ventilation openings and power circuit switching devices to prevent the emission of flames or molten metal from an enclosure.

D.6.2.2 The barrier shall be of such dimensions and so located that any straight line drawn from any arcing part past the edge of the barrier intersects a point in the ventilating opening plane that is at least 0.25 inch (6.4 mm) outside of the edge of the ventilation opening. See Figure 2.

Figure 2, Barriers for ventilation openings

D.1.2.3 A sheet-metal barrier shall be at least 0.053 inch (1.35 mm) thick uncoated steel, or 0.075 inch (1.91 mm) thick aluminum.

D.1.2.4 Exception: A metal barrier may be of thinner metal provided its strength and rigidity are not less than that of a flat sheet of steel having the same dimensions as the barrier and of the specified thickness.

D.1.2.5 A nonmetallic barrier shall be at least 0.250 inch (6.35 mm) thick and shall be supported to provide mechanical strength and rigidity.

Exception: A nonmetallic material less than 0.250 inch thick shall be located so that it is not subjected to mechanical damage during installation, and supported to provide mechanical strength and rigidity.

D.6.3 Forced Ventilation

D.6.3.1 When ventilation is fan forced – that is, ventilation is accomplished by one or more blowers within the enclosure that provide a positive intake and exhaust – the ventilation openings shall be finger safe (see section 6.1.2).

D.6.3.2 When operator controls are provided on the enclosure, the air outlet shall not direct air at the area occupied by the operator. The area occupied by the operator shall be 30 inches wide (horizontal) centered on any operator control, display, or disconnect handle up to 6-1/2 feet above the floor.

D.6.4 Blower Motors

D.6.4.1 Each blower motor shall be capable of delivering its maximum normal load without introducing risk of fire, electric shock, or injury to persons. The motor winding shall resist the absorption of moisture.

D.6.4.2 Each blower motor shall be NRTL listed and incorporate one of the following forms of locked rotor protection:

a) Thermal protection;

b) Impedance protection; or

c) Other protection that is shown by test to be equivalent to the protection specified in the Standard for Overheating Protection for Motors, UL 2111.

D.6.5 Enclosure With Power Circuit Switching Devices

D.6.5.1 Ventilation openings in an enclosure that contains power circuit switching devices such as a disconnect switch, circuit breaker, motor controller or an overload relay shall comply with the following;

a) The construction shall comply with the requirements for Ventilating Openings, or;

b) The opening is located at least 12 inches (305 mm) from power circuit switching components; or

c) The opening shall be so constructed and located that flame or molten metal is not emitted during the operation of power-circuit switching devices while subjected to overload and short circuit test conditions.

D.7 References

LBNL. Electrical Safety Manual. Berkeley CA: Lawrence Berkeley National Laboratory, 2015.

Underwriters Laboratories. Industrial Control Panels, UL508A. Northbrook, IL: Underwriters Laboratories, 2001.

Underwriters Laboratories. Standard for Safety, Electrical Equipment for Measurement, Control and Laboratory Use, UL61010-1. Northbrook, IL: Underwriters Laboratories, 2012.

Underwriters Laboratories. Standard for Safety, Industrial Control Equipment, UL508.

Northbrook, IL: Underwriters Laboratories, 1994.

D.8 Revision Log

Date, Revision #

Brief Description of Revision / Changes Sec. #, Parag.

1/26/2016 Version 1

Initial version All

Document Information

DOCUMENT INFORMATION

Title: Rack Build Standard Document number Revision number 1 Publication date: 2/11/2016 Effective date: 2/11/2016 Next review date: 3/1/2017 Last Edited By: pbong@lbl.gov EPG Section (home) Electrical Engineering References EPG Section (cross-reference) Functional Division Engineering