Atch 04- Nellis-Creech IFS appendix Electrical Req.pdf

NELLIS AND CREECH AFB

INSTALLATION FACILITIES STANDARDS (IFS)

ELECTRICAL REQUIREMENTS

22 JAN 2019

This document is an appendix to Nellis & Creech Air Force Bases IFS which is located here:

https://www.wbdg.org/ffc/af-afcec/installation-facilities-standards-ifs/nellis-creech-afb-ifs

LOW VOLTAGE (50v-600v) SYSTEM REQUIREMENTS:

1. All electrical receptacles and panels shall be labeled. Receptacle Labels must include panel number, circuit number, and voltage. Labels shall be made of polyethylene printed tags and will be attached with High Tack Adhesive rated at 140degF if outdoors or Permanent Adhesive if indoors. Panel labels shall be laminated (with black lettering on a white background), engraved with 1/2" high letters. Attach to front exterior of enclosures. Labels shall match plan designations. Panel circuit directory label shall be engraved laminated plastic with black lettering on a white background. Outdoor panels will have circuit directory mounted on inside with screw and nuts, no rivets permitted. Indoor panels shall not have labels or circuit directory riveted to enclosure. No handwritten or typed paper labels will be accepted.

2. Electrical equipment, wires, cables etc. installed in non-air conditioned rooms, i.e., mechanical rooms, utility rooms, electrical rooms, and hangar bays shall be de-rated or re-rated based on ambient temperature. Mechanical and boiler rooms shall use 140 degrees F or 60degC. Hangar bays between 5ft below and up to the door openings and above door openings shall use 140 degrees F. Hangar bays below 5ft of the hangar door openings shall use 122degF if air circulation is present to keep the bay temperature below 122degF. or 131degF if not. Electrical rooms may use 50degC or 122degF if no large sources of heat are present. The use of HVAC in mechanical rooms, utility rooms, electrical rooms will specifically waivered by the base regardless of any UFC requirements to the contrary.

3. All electrical equipment, wires, cables etc. installed outdoors above ground in non-classified areas shall be de-rated or rerated based on the ambient temperature of 140 degrees F if in unshaded areas or 122degF if in shaded areas without direct sunlight impingement. Rooftop mounted equipment shall use a minimum of 140degF. Enclosures shall be NEMA 3R/12(meets both 3R and 12 ratings) or NEMA 3 or NEMA 4 minimum.

4. All Low Voltage Underground circuits other than Service Entrance cables shall be installed in conduits and encased in 300 PSI concrete slurry when routed under parking areas, roads, sidewalks and other traffic areas.

5. All exterior light fixtures including LED drivers shall be rated for ambient temperature of 120 Degrees F or greater. Photocells shall be rated for operation in 140degF ambient.

6. All standard normal computer workstations shall use 300 VA at continuous duty in the load calculations and shall be on dedicated receptacle circuit(s) different from general purpose https://www.wbdg.org/ffc/af-afcec/installation-facilities-standards-ifs/nellis-creech-afb-ifs receptacles. Install a maximum of four standard computer workstations with or without one 6-Amp printer on a single circuit. Heavy duty computer workstations have higher VA continuous duty requirements and less computers allowed per each dedicated circuit.

7. Large fax machines, large printer/copiers with or without an associated printer server computer, and large shredders shall have dedicated branch circuits for each unit.

8. All offices shall have at least one (1) general purpose duplex receptacle not used for computers or other loads. All areas within a building/facility i.e., offices, corridors, shall be within 15-feet of a general purpose receptacle.

9. Provide dedicated electrical circuits to each panel that serves ACS, IDS, CCTV, EMCS, Fire Alarm & MNS system and to other control systems.

10. Electrical circuits serving loads exterior of a facility must not be connected to loads inside of the facility. Exterior located ground fault receptacles shall not have downstream receptacles tied to ground fault load terminals. Mechanical yard receptacles used for servicing equipment shall be on dedicated circuits from all other ground fault receptacles.

11. Panelboards: Specify breakers, no fuses. Square D or GE are preferable.

12. Contactors: Specify magnetic contactors, not manual. Lighting contactor with photocell, locate photocell as high as possible. Photocells shall be rated for inductive load use and be rated for the ambient temperature seen at the location.

13. Motor Starters: Always specify thermal overload usually with class 20 protection. Use of electronic overloads in starters is generally not permitted due to ease that the overload settings may be adjusted too high. Specify with a hand-off-auto switch so that it can be manually started if necessary.

14. Wire: All wiring shall be copper. No aluminum is allowed. All wires larger than #10 shall be stranded copper. For indoor and general wiring, specify THHN-2 insulation. For outdoor underground wire, specify either THWN-2 or XHHW-2. Note that for all motors that over 1/4HP or larger at 208/240/480v and larger than 1/8HP at 115v, the final termination to motor junction boxes shall be made with stranded wire.

15. Dry Type Transformers mounted indoors: Specify copper windings, 115 Deg C rise over a 40 Deg C ambient. Outdoors: 105 DegC rise over a 50 DegC ambient.

16. Wiring Devices: Provide new devices whenever an area is renovated. All devices shall be recessed except in mechanical rooms, utility rooms, and secure areas. Provide devices rated at 20 amps minimum. Devices must be of internal copper construction unless waived in writing by Base Civil Engineer (BCE) office (99CES/CENMP) which waiver shall not assumed to be given.

17. Controllers: Provide battery backup for landscape irrigation system controllers having appropriate temperature ratings. Automatic setback thermostats shall use battery backup for backup memory only and shall generally be operated from line power or from power supplies for operation at 50v or less not from batteries.

18. Over-Current Protective Devices: The minimum sized over-current device for receptacle and lighting branch circuits is 20 amps. Ensure proper coordination and withstand ratings for all over-current protection devices. No Fuses allowed on panelboards and switchboards except for specialty applications.

19. No series rating of circuit breakers permitted.

20. Demonstrate coordination with first upstream existing protective device. Replace old circuit breakers with new when remodeling facilities or if no AIC rating is listed on circuit breakers.

If replacement breakers are unavailable, the replacement of entire panelboard is required.

21. Provide non-ferrous phase and circuit identification labels in all enclosures for feeder circuit conductors. Provide underground marker tapes for all underground conductors. If underground conductors are not in metallic conduit, provide marker tape with foiled backing to facilitate detection.

22. Add PF capacitors to induction motors (50 HP or larger) to correct PF to 0.95 (+ .00, - .05).

Switch PF capacitors with the motor with the capacitors connected before the overloads. Size capacitor IAW Institute of Electrical and Electronics Engineers (IEEE) 141, National Electrical Manufacturers Association (NEMA) MG2, and motor manufacturer recommendations. Not required if a VFD is to operate the motor.

23. Power requirements for buildings shall be either 480Y277 or 208Y120 for three phase or 240/120 for single phase. Selection of voltage depends on several criteria: If the building has large HVAC units(better energy efficiencies) or large UPSs(smaller footprint at 480v) or large amount of stationary or portable inverters for powering aircraft or a large amount of motors(better energy efficiencies) will tend to require the use of 480Y277. All buildings requiring more than 50KVA shall use 3phase. All buildings requiring 500KVA service transformer or larger will use 480Y277. It is base policy to have one service transformer and one main service entrance per building. If 208Y120 is required for a building that has 480v service, the 208Y120 will be supplied by one or more drypack stepdown transformer(s) located inside the building. Balance loads on phases within 10 percent at all panelboards.

24. All electrical penetrations through fire-resistance rated walls shall be fire stopped.

25. All meters shall comply with Nellis-Creech IFS Utility Meter Requirements document listed in IFS Appendix G. Meters shall generally be located inside building and near service entrance. Meters shall meet Energy Management (AMRS) requirements. Cat-6 data port shall be installed to support all meters and ran to the main comm. room. The preferred location for the meter CTs is immediately downstream of the main service circuit breaker and ahead of all feeder breakers. A 3pole feeder circuit breaker of 20A or less is to be furnished in the main switchgear to provide power to the meter and/or the meters’ PT leads. If photovoltaic arrays are supplied with or connected to a building then a second meter for the PV array shall be furnished. This meter’s CTs and PTs shall be connected immediately downstream of the main switchgear or panelboard’s feeder breaker that the PV array inverter(s) is connected to. Meters or their CTs are not to be mounted in or on service transformers.

26. Provide lightning protection system (LPS) as required. Reference Annex L of NFPA 780 (Lightning Protection Code) and complete risk assessment for project. If LPS is required, design and install per NFPA 780 and AFM 88-9, Chapter 3. Mission critical, mission support facilities, and facilities with extensive electrical and communications equipment shall have LPS. Note that if the lightning protection grounding ring or counterpoise also serves as the main electrical and communication grounding counterpoise, the lightning protection ring conductors and ground rods will be upgraded and installed to the base standards for grounding counterpoises.

27. All service entrance panels rated over 225A shall have all 100% rated breakers.

Service entrance panels rated 200 or 225A shall have the main panel circuit breaker rated at 100%.

28. Heaters and other similar resistive loads 5KWand over at 208v and 10KW and over at 480v shall have their voltage drop limited to 2% (4% power loss) or less as computed starting with 208.0v or 480.0v at the service transformer secondary terminals.

29. Service entrance conduits from transformer to service entrance panel shall be a minimum of 2” in diameter. There shall be 25% spares with at least one spare conduit with pull rope and #10 THWN Cu tracer.

30. Depth of Secondary Entrance conduit shall be a minimum of 24inches. These conduits will be concrete encased at 500 PSI concrete if the distance from transformer to building is greater than 10ft. These conduits shall be encased in 3000 PSI rated concrete if routed under traffic areas and 4,000 PSI if routed under heavy traffic areas; i.e. aircraft, Tractor Trailers and other loads greater than 26000lb.

31. Install a ground ring around the perimeter of new or renovated building/facilities.

Counterpoise ground ring shall consists of multiple (minimum of 4) 3/4” x 10 ft long ground rods interconnected with bare 4/0 copper wire for the ring. The counterpoise must be terminated either at the main service switchgear grounding buss bar or at a separate main grounding buss mounted in the main electrical room. Main service switchgear grounding buss bar shall be connected with 4/0 copper to the separate main grounding buss. The counterpoise serves as the primary grounding electrode for the building.

All other grounding systems (including ufer, water pipes, metal gas pipes, comm., building steel) shall be each separately connected to the main grounding buss with bolts for future testing of each ground. Note that 5 or 10 ohms to ground required by comm is more restrictive than the 25ohms required by NEC or the higher values required for lighting protection.

a. All grounding connections shall be cad welded and tested.

b. The main connections for all grounding systems shall be accessible and permanently labeled.

c. Ufer ground is always to be furnished on new construction. Additions to building will either connect to the existing ufer or run a separate 4/0 ufer ground to the main grounding buss bar.

d. Bldg. steel connections shall be made to the main grounding buss with 4/0 Cu, not directly to the counterpoise grounding ring.

e. Comm. room ground buss bars shall be made to the main grounding buss with 4/0 Cu, not directly to the counterpoise grounding ring.

f. A minimum of four (more on large buildings) inspection ports to be furnished.

g. Counterpoise grounding rings are necessary due to the high resistivity soils of 2k-

40kohm-cm seen in Southern Nevada and 40ft+ deep water tables.

32. Low voltage switchboards, panels, disconnect switches, VFD enclosures, and above ground junction boxes are not to be rated NEMA 3R due to the presence of wind blown dust in southern Nevada (see NEC section 110.28). All of these items are to be rated for NEMA 3 or NEMA 4 or NEMA 3R/12 (ie meets both NEMA 3R and NEMA 12 ratings). Conduits entering these enclosures are to be sealed to avoid dust and water infiltration. All gaskets and adhesives on enclosures are to be rated for 122degF (50degC) if shaded or 135deg F (56degC) if at or within 5ft of ground level. Non-shaded roof top items or located above 5ft.

above grade are to be rated for a minimum of 140degF (60degC).

33. Disconnect switches or other enclosures with disconnects are to be flange mounted or side mounted or similar and are not to be thru the door type. They are to have heavy duty HP ratings, not general purpose ratings.

34. Building drypack transformers are to be numbered 1T, 2T, 3T…Bldg. Service Transformers generally will be numbered as T-xxxxx where xxxxx is the building number of one of the buildings or main building served by this transformer.

35. All motors used outdoors and in non-HVAC mechanical rooms are to be rated or derated for use at 50 deg C (122 deg F) if in shaded areas. Motors mounted on rooftops and in non-shaded areas will require 60degC (140 deg F) ratings due to direct sunlight impingement.

ODP type of motors are prohibited outdoors and in non-conditioned mechanical rooms. Note that rooms utilizing swamp coolers do not make a space conditioned.

36. Security Systems: Provide all electrical service, conduits, and junction boxes for Access

Control System (ACS), Intrusion Detection System (IDS) and CCTV in secured facilities or special access areas. ACS, IDS, and CCTV will be installed as GFGI equipment by the building tenant unless otherwise stated. Design, layout, and construction shall be coordinated with building tenant and their security representative.

37. PLC control systems requirements: Drawings for PLC systems shall include a power schematic, control schematic that includes an PLC I/O schematic, a drawing that shows all cables between PLC processor and I/O racks and all dip switch settings(and their meanings) for processor, I/O cards, I/O racks. Other drawings required are pushbutton station layouts and detail wiring, main panel layout, main panel terminal block layout, and main panel detail wiring, interconnection drawings, and system conduit layouts.

a. E-Stop circuit shall be hardwired at 120v. PLC 120v inputs shall be controlled by NO contacts, PLC outputs shall be controlled by a NO timed contacts with timer set at a max. of 50 msec(3 AC cycles) allowing for the PLC to turn off outputs before the control power is interrupted.

b. The I/O power shall be at 120v wherever possible. Solenoid valves, starters, contactors, starter aux. contacts, circuit breaker aux. contacts, float switches, temp switches, photocells, pushbuttons, pilot lights, etc. shall be powered at 120v.

c. The base reserves the right to specify the manufacturer of the PLC processor to ones that the base is familiar with. Allen-Bradley or Modicon currently. Other ones may be proposed subject to BCE acceptance. No additional charge shall be incurred for this change. The contractor shall include in his contract the tuition price for 2 electrical personnel from BCE shops to attend sufficient programming /maintenance /documentation classes to gain experience on the PLC used. The contractor also shall reimburse the travel and per diem expenses (not salary costs incurred) to the government.

d. The PLC must be programmed in relay logic, and all logic must be viewable and editable. Logic shall not be password protected. I/O, storage coils and registers must have names associated with them in the logic documentation (printouts and on screen displays).

e. Contractor utilizing PLCs must furnish to the government, a laptop with all necessary licensed software including Windows, Excel, Word, antivirus software, PLC software with 5 years worth of prepaid software updates as part of the contract. The licenses shall be assigned to the government (BCE). The licenses shall not expire and shall be able to view, edit, and document the program at all times. All software shall be furnished on CD or CDRW and it shall not be required to have internet connection to activate the software as this laptop cannot be attached to the AF network.

38. Hangar bays. Disconnects switches, motor control centers, panelboards, control panels, junction boxes, and other similar electrical equipment located below top of hangar door opening(usually 22-25ft high) in non-classified electrical area (as defined in NEC) shall be rated Nema 4 or Nema 4X depending on corrosiveness and/or chemical composition of fire suppression foam used. Any dry type transformer used in hangar bays shall be of the sand-filled epoxy type, with rubber waterproof boots around the terminal connections including any voltage tap connections, and shall have all conduit entries to the transformer sealed to prevent water infiltration from transformer to conduit. Note that the first 18”AFF is considered in hangars to be a classified area per NEC 513.3(B).

39. Buildings containing rooms with fire pumps: Fire pumps shall be powered by one of the two methods listed below in a or b:

a. A separate service transformer whose full load rating exceeds the total of 150% of sum of all fire pumps and jockey pumps plus 100% of house load for the fire pump room if any. Contractor shall provide a MLO main switchboard in the fire pump room or in the main electric room containing 1 CB per fire pump controller and with 1 CB per jockey pump controller and 1CB for feeding a small house transformer if any.

Service entrance conductors to be sized at 625% of the first or largest fire pump plus 125% of the second fire pump plus 125% of the jockey pumps plus 100% of the house load.

b. The other scheme is one transformer with service conductors feeding a main switchgear having a center section with MLO connections feeding a horizontal buss sized at locked rotor amps of the largest fire pump plus the building main circuit breaker amps. The left vertical section will have 1 CB per fire pump controller and with 1 CB per jockey pump controller with vertical buss rated at twice the locked rotor amps of a fire pump. The right vertical section will have the main circuit breaker for the building with additional feeder sections extending to the right.

Service entrance conductors to be sized at 625% of the first or largest fire pump plus 125% of the second fire pump plus 125% of the jockey pumps plus 100% of the building main circuit breaker.

Service transformer to be sized at whose full load rating exceeds the total of 300% of the first or largest fire pump plus 125% of the second fire pump plus 125% of the jockey pumps plus 100% of the building main circuit breaker size. In this instance the house load for the fire pump room will be supplied from the regular building supply.

40. Buildings having an out building with fire pumps: Fire pumps shall be powered by the following method:

a. A separate service transformer whose full load rating exceeds the total of 150% of sum of all fire pumps and jockey pumps plus 100% of house load for the fire pump room if any. Contractor shall provide a MLO main switchboard in the fire pump room or in the main electric room containing 1 CB per fire pump controller and with 1 CB per jockey pump controller and 1CB for feeding a small house transformer if any.

Service entrance conductors to be sized at 625% of the first or largest fire pump plus 125% of the second fire pump plus 125% of the jockey pumps plus 100% of the house load.

41. Reference separate Nellis-Creech IFS appendix documents for Lighting, Fire Protection, Mechanical-Plumbing, Utility Meter, and Telecommunications Requirements.

MEDIUM VOLTAGE (4160v, 12.47Kv, 25Kv) SYSTEM REQUIREMENTS:

42. All High and Medium Voltage equipment and materials shall be submitted to the base electrical engineer in the Base Civil Engineer (BCE) office for approval before ordering.

43. It is base policy that medium voltage conductor sets contain a 100% neutral conductor equal in size to the phase conductors generally composed of 1/3 copper concentric neutral on each phase conductor for proper grounding of the base medium voltage electrical system.

44. All Medium Voltage Underground circuits shall be installed in conduits and encased in Red Dye 500PSI concrete if in unimproved area, 3000PSI if in light traffic roads and parking lots, and 4000 PSI in high traffic roads, parking lots, and aircraft areas.

a. The top of conduits/ducts shall be a minimum of 36 inches below grade.

45. The design of underground distribution systems shall be based on the calculated demand with sufficient electrical capacity for expansion and for crossties to other base circuits. Note that all main base circuit conductor sizes and major crossties between base circuits conductor size will be determined by the base electrical engineer in the BCE office (99CES/CENMP). Any required replacement of existing undersized conductors will be upgraded to the current required size.

46. Manholes shall only be installed if multiple medium voltage circuits are required and bending radius mandate their use. Use of manholes must be preapproved by the base EE before any use is contemplated. The base mandates that vaults be installed. Nevada Power Company (local utility dba NV Energy) Style RS-82A units are preferred. These units must contain torsion-assisted lids and a maximum depth of 5’9”.

a. Any manholes permitted shall contain drainage leech fields sized to allow all water to drain from manhole within 24hours. This is due to poor drainage of the soils.

This drainage shall be tested by contractors before energization of any primary circuit in the manhole.

Other measures must also be taken to prevent water infiltration.

b. Vaults or Manholes shall have racking systems to support all cables.

c. Each Underground enclosure shall contain its own grounding electrode system. Grounds shall be interconnected to the circuit/system ground.

47. No splices, Load-break or Dead-break junctions are permitted in manholes or vaults. T and Y splices are never allowed. If standard splices must be installed, the contractor must gain advance written permission from the base electrical engineer in BCE office. This will not normally be granted as the base will generally require the installation of a switch or a sectionalizer.

48. All Medium Voltage cables shall be tagged with labels that meet the Nellis Standard. Labels shall be installed on cables at all equipment and in all underground enclosures. Contractors must contact the base Electrical AHJ for an example of the approved labels.

49. All Medium Voltage cables installed shall be looped and racked in underground enclosures and where required for support. These cables shall also be wrapped in Fire Tape when installed in these areas.

50. All 15KV Medium Voltage 3phase UG cables shall be a set of three 133% EPR insulated Cu MV105 cables with 1/3 copper concentric neutrals. Standard 3 phase cable sizes are #2, 1/0, 2/0, 250MCM, 500MCM, 750MCM. Single phase cables shall be 133% EPR insulated Cu MV105 cables with 100% copper concentric neutrals. Standard single phase sizes are #2, 1/0, 2/0, and 250MCM.

51. All newly installed medium and high voltage cables shall be tested using a High-Potential- Pot or Very Low frequency (VLF) alternating voltage withstand method before being placed in service. Test results shall be submitted to the government immediately upon completion.

52. A counterpoise ground ring shall be installed around all Medium Voltage transformers, switches, sectionalizers, and other equipment. It consists of four (4) 3/4” x 10 ft deep ground rods at each corner interconnected with bare 4/0 copper wire ground ring.

a. Transformer secondary grounding electrode conductor will also be separately connected to the ground ring with 4/0 THWN.

b. Transformer primary grounding electrode conductor will be separately connected to the ground ring with 4/0 THWN.

c. MV switches will have two 4/0 THWN connections to ground ring (one on each side with 4/0 Cu)

d. One side of transformer counterpoise may be incorporated into building counterpoise if located close enough. Service transformer and building grounding counterpoises will tied together with 4/0 conductor if located within 10ft of the building. Location of crosstie will be shown and DIMENSIONED on drawings.

53. Sectionalizers(12.47KV) shall meet the following requirements:

a. Sectionalizer will have one 4/0 connection to ground ring.

b. Enclosures shall be constructed of mild steel and be factory painted Sierra Tan color or close equivalent. Use of fiberglass and other non-metal type of enclosures is prohibited.

c. Must have sufficient parking positions for all 15KV cables.

d. Sectionalizer mounting Pads are to have hand-holes underneath the pad openings. Pads are to be similar to Jensen precast pads used by Nevada Power with pad window openings to match the sectionalizer. Conduits shall not be grouted into the pad. All pads shall be detailed on drawings.

e. Provisions for anchoring top opening doors to prevent closing in 70MPH winds.

f. Sectionalizers shall have adequate working room. Use of compact type sectionalizers prohibited as the base considers these to have inadequate working room.

g. Cooper SpecTer type sectionalizers are the basis for comparison for all others.

54. All Medium Voltage Switches (4KV-25KV) shall meet the following requirements:

a. All switches shall be dead-front type construction, shall be double sided, and contain parking positions for each Load-break or Deadbreak Elbow. (No Pothead Terminations allowed).

b. Only these (Cooper) switch style configurations will be permitted:

Style 9 2 Mains, 2VFI laterals Style 10 4 Mains * Used at major switching points only.

Style 11 3 Mains, 1VFI lateral Style 12 1 Main, 3VFI laterals * Not usually permitted. Use 5W2 style.

Style 5W2 2 Mains, 3VFI laterals Style 6W2 2 Mains, 4VFI laterals Style 6W3 3 Mains, 3VFI laterals All other proposed styles (which are special cases) must be approved in advance in writing by the base electrical engineer in BCE office. Approval is typically not provided.

Note that the base has had several recent episodes of replacing styles 5, 6, and 7 switches with style 9.

c. All Loadbreak or Deadbreak Elbows shall be rated 15KV minimum.

d. All switch laterals shall be VFI type. (No fuse type switches are allowed).

e. VFI to be Triphase with Ground type having either EF or KF trip curves. All three phases shall trip on a fault.

f. Each switch section shall have an on-off switch and a viewable switch window.

g. All switches shall be oil insulated type. Oil shall be FR3 or biodegradable seed oil. No airbreak switches or gas insulated switches allowed.

h. Generally the main sections of all switches shall be 600Amp minimum with an occasional use of 900A in locations determined by the base. 200A may be allowed with advance approval of the base electrical engineer in BCE office.

i. The Lateral sections of all switches shall be 200 Amps minimum.

j. Terminate all grounds and neutral connections on NEMA ground pads or flat ground bars. Use of ½-13 single bolts not permitted due the number of connections required.

k. Oil filler and drain valves with oil sampler shall be provided.

l. No Air-break or SF6 switch sections permitted.

m. No key interlock type switches shall be permitted.

n. Switches shall be factory painted Sierra Tan color or close equivalent.

o. All switches are to have sideways opening doors with pentabolts and padlocking provisions for the doors. No main doors to open upwards. No low profile switches or clamshell type.

p. Switch mounting Pads are to have hand-holes underneath the pad openings. Pads are to be similar to Jensen precast pads used by Nevada Power with pad window openings to match the switch. Conduits are not to be grouted into the pad. All pads to be detailed on drawings. Use of precast pads is preferred.

q. Cooper Kyle switches are preferred. Others may be approved by BCE office if they have similar specifications and characteristics and have sufficient working room inside.

Use of so called compact switches is prohibited.

r. All switches shall have a 10KA (12KA preferred) minimum interrupting rating.

s. Switches shall not be installed on top of vaults or on Manholes.

55. All Medium Voltage Transformers(primary at 4160v or 12.47KV or 25Kv) shall meet the following requirements:

a. All Medium Voltage Transformers greater than 50KVA shall be 3-phase, not single phase. Buildings and trailers requiring 480v secondary voltage shall be only 3-phase, not single phase.

b. 3 phase primaries shall be 3 phase delta connected. 3 phase secondaries shall be wye connected. Use of 3 phase transformer secondaries having one phase centertapped to create 120v or 240v to ground is generally not permitted by the base.

c. All transformers shall be dead-front construction in the primary compartment and contain parking stands.

d. All transformers shall be pad mounted type only. No Clamshell type transformer allowed. Installation or use of any pole mounted transformer or transformer bank shall require advance written approval by the base electrical engineer.

e. Transformer mounting pads shall contain hand-holes underneath the pad openings. Pads are to be similar to Jensen precast pads used by Nevada Power with pad window openings to match the transformer. Conduits are not to be grouted into the pad. Note that use of precast pads is preferred.

f. Transformer shall be loop feed, with three (3) 2-position on-off 3phase oil immersed switches (one switch each for A, B, T). Use of four, five or six position switch is not permitted.

e) Provide 3-nominal 9KV (8.4KV actual) or nominal 10KV (9.0KV actual) MOV in 15KV elbows on B feed connected phase to ground on all transformers that are last on a lateral circuit.

f) Provide metal isolation between the Primary and secondary compartments of each transformer. Mild-steel construction shall be used.

g) Provide 5-Position oil immersed primary tap changer (+5.0%, +2.5%, 0%, -2.5%, -5.0%).

h) Provide parking positions for Loadbreak Elbows on A and B feeds.

Parking positions to be provided for A and B feeds. Note that 2 parking positions are to be provided between the two C phases. (total of 6 required)

i) Doors to swing out, not up. Pentabolts on doors. Doors to be padlockable. This is also true of any single phase transformer.

j) Fuses to be bayonet type oil immersed removable in primary compartment having cups below them in series with in-tank current limiters. No bolt-on fuses are allowed as these are considered to be non-dead-front connections.

k) Units shall have Copper primary and secondary windings only.

l) Units shall have Pressure-vacuum gauge, temperature gauge, oil filler and oil sampler.

m) NEMA ground pads in primary compartment for termination of 100% incoming and outgoing primary neutrals and grounds and 4/0 from ground ring.

n) NEMA ground pads in secondary compartment for termination of secondary connection (4/0) from ground ring.

o) Transformer to be oil filled. No SF6 or dry type permitted. Oil shall be seed type oil such as FR3 or other environmentally friendly oil.

p) Transformers shall be factory painted Sierra Tan color or close equivalent.

q) Transformers to be rated for operation at 45degC (113degF) average ambient and with

50degC winding rise instead of the normal ratings of 30degC ambient with 65degC rise, maintaining the average hot spot temperature rating of 95degC. Note that this transformer must be suitable for operating at 43degC (109.4degF) for 12 hours per day with included ambient peaks up to 117degF for 4 hours.

r) Transformers shall not be installed on top of vaults or on Manholes.

56. Designs shall include the size and impedance of the new or existing transformer. Minimum impedance shall be 2.50% for transformers up to 125KVA; 3.00% for 150, 225, and 300KVA; 4.00% for 500 and 750KVA and 5.00% for 1000KVA and larger. If impedance is greater than 5.00% the contractor shall receive written pre-approval from base electrical engineer in BCE office. Maximum impedance allowed is 6.5%. Transformer impedance must be shown on electrical single-line drawing.

57. Designs shall include the size and impedance of new or existing transformer(s). Minimum impedance shall be 2.50% for transformers up to 125KVA; 3.00% for 150, 225, and 300KVA; 4.00% for 500 and 750KVA and 5.00% for 1000KVA and larger. If impedance is greater than the maximum of 6.75% (greater than 6.75% is a specialty transformer) the contractor shall receive written pre-approval from the Base Electrical Engineer. MINIMUM transformer impedance must be shown on electrical single-line drawing.

58. Design shall include the short circuit calculations. Basis of short circuit calculations is that infinite primary utility current is always available on the primary when calculating secondary short circuit current. MINIMUM allowed impedance shall be shown on the singleline for all transformers. Downstream panels from all transformers shall have a maximum calculated short circuit of approximately 90% of panel AIC rating available per the following chart:

Panel AIC rating Maximum Calculated short circuit amps allowed.

10KAIC 9.0KA

14KAIC 12.5KA

18KAIC 16.0KA

22KAIC 20.0KA

28KAIC 25.0KA

35KAIC 31.5KA

42KAIC 38.0KA

65KAIC 59.5KA

59. The following shall be shown on the electrical drawings, not solely in the technical analysis or in calculation booklet:

a. Summary charts of short circuit calculations.

b. Summary charts of voltage drop calculations.

c. AIC Ratings of all panels.

END OF ELECTRICAL REQUIREMENTS