Section 13 — Electrical

Low Voltage Automatic Transfer Switches

IPE Engineering Practice IPE-EP-13-19-1

Document number: IPE-EP-13-19-1 · Section: 13 — Electrical

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SCOPE

This Practice covers the requirements for low voltage (600 volts or less) automatic transfer switches. Included as part of this Practice are Data Sheets (EP 13-19-1 DS) listing environmental information as well at the specific equipment requirements.

This Practice is appropriate for attachment to an inquiry or purchase document when accompanied by the referenced IPE Engineering Practices and completed Data Sheets.

Any deviation from this Practice must be approved by the procedure described in EP 1–1–3. A revision bar indicates all changes made to this Revision.

REFERENCES

All applicable sections of the latest standards and codes listed below are a part of this Practice for design, construction and testing unless amended herein.

STANDARDS AND PUBLICATIONS

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DEFINITIONS

Contractor – Company or business that agrees to furnish materials or perform specified services at a specified price and/or rate to the Owner.

Inspector – A Inflection Point Engineering, LLC appointed engineer or inspector.

Manufacturer – The recipient of a direct or indirect purchase order for materials and/or equipment. In this context, a direct order is one issued to a Manufacturer by a Contractor or the Owner. An indirect order is one issued to a Manufacturer by a vendor (recipient of a direct order) for materials, fabricated components, or subassemblies.

Owner – Inflection Point Engineering, LLC.

Owner’s Engineer – A Inflection Point Engineering, LLC appointed engineer.

Purchaser – The party placing a direct purchase order. The Purchaser is the Owner’s designated representative.

SERVICE CONDITIONS

The automatic transfer switch will be located indoors in a plant with maximum ambient temperature of 120ºF and minimum ambient temperature of –15ºF, and an elevation of 3,300 ft. ASL or below.

DESIGN, CONSTRUCTION AND MATERIALS

All transfer and bypass switches shall comply with UL–1008 in all matters concerning construction, operation and conformance to testing. In addition all transfer and bypass switches shall be UL listed and bear such listing on the equipment nameplate.

Enclosure

Unless specified otherwise, all components shall be contained in a metal enclosure constructed in accordance with NEMA Std ICS–6 and ICS–250 and UL Std 508.

All components shall require only front access for maintenance or trouble shooting.

Provide an enclosure ground with a connection lug suitable for Owners’ No. 2 AWG stranded copper ground wire.

Automatic Transfer Switch

ATS shall be of the linear actuator type. Molder case circuit breaker and contactor types are not acceptable.

The automatic transfer switch shall provide connections to source “A” and source “B” as specified in the Data Sheet.

The transfer switch load shall be as specified in the Data Sheet. The switch provided shall be fully capable of transferring the specified sources to the specified load without damage to the switch or the sources and load.

• The automatic transfer switch shall consist of a power transfer module and a control panel interconnected to provide complete automatic operation. The automatic transfer switch shall be mechanically held and electrically operated from the source to which the load is to be transferred. The switch shall be rated for continuous duty and be inherently double throw (break before make). The switch shall be mechanically interlocked to ensure only one of two possible positions - source ‘A’ or source ‘B’.
• All main contacts shall be of silver composition or silver plated copper and shall be protected by separate arcing contacts.
• The operating transfer time in either direction shall not exceed one–sixth (1/6) of a second. Inspection of all contacts (movable and stationary) shall be possible from the front of the switch without disassembly of operating linkages and without disconnection of power conductors. A manual operating handle shall be provided for maintenance purposes. The handle shall permit the operator to stop the contacts at any point throughout the entire travel to properly inspect and service the contacts when required.
• When specified in the Data Sheet, overlapping neutral transfer contacts shall be supplied on the automatic transfer switch. The neutrals of the ‘A’ and ‘B’ power sources shall be connected together only during the transfer and retransfer operation and remain connected together until power source contacts close on the source of which transfer or retransfer is being made. The overlapping neutral transfer contacts shall not overlap for a time duration greater than 100 milliseconds.
• The contacts shall be designed to tighten under faults.
• When neutral contacts and buswork are specified they shall have the same construction as the phase (main) contacts and bus and rated as indicated on the Data Sheet.
• Transfer switches shall be listed to UL Standard 1008. Certified laboratory test data on a switch of the same design and rating shall be available to the Owner upon request.
• Bypass–Isolation Switch
• When specified in the Data Sheet, a manually operated bypass–isolation switch shall be provided. The bypass switch shall be capable of bypassing the load to either source with complete isolation of the automatic transfer switch.
• The main contacts and operating linkage shall be identical to that of the automatic transfer switch except that operation shall be manual. The switch shall have the same electrical ratings of ampacity, voltage, short circuit withstand and temperature rise capability as the associated automatic transfer switch.
• If the automatic transfer switch and bypass switch are mounted in a common enclosure, each switch shall have separate doors and separate compartments isolated from each other with a metal barrier.
• The bypass–isolation switch shall provide manual bypass of the load and isolation of all service and load terminals of the automatic transfer switch to permit periodic testing, maintenance and service of the automatic transfer switch without interrupting power to the load and removing all power to the line/load stabs of the automatic transfer switch.

• The bypass–isolation switch shall be capable of bypassing the load to either source. Load bypass to the automatic transfer switch’s connected source shall be effected without load interruption. Provisions shall be made to assure continuity of auxiliary circuits necessary for the proper operation of the system.
• The bypass–isolation switch shall be manually operated and be provided with two (2) handles. One (1) for operation of the bypass contacts and one (1) for operation of the isolation contacts. The isolation handle shall provide three (3) positions: Closed, Test, and Open. The “Test” position shall permit electrical testing of the automatic transfer switch without disturbing the load. The “Open” position shall completely isolate the transfer switch from both lines and load without actual removal of the line or load conductors and allow its removal for inspection, adjustment and maintenance. Also, while in the “Test” or “Open” positions, the bypass switch shall function as a manual transfer switch to allow load transfer to either source of power regardless or the position or condition of the transfer switch, including the condition when the automatic transfer switch is removed and without reconnection the load terminals of the automatic transfer switch.
• A visual position indicator shall be provided to indicate bypass–isolation switch positions and availability of source ‘A’ and source ‘B’. A prominent and detailed instruction plate shall be furnished for convenient operation.
• The operating speed of the bypass switch contacts shall be the same as the automatic transfer switch and independent of the speed of operation of the bypass handle.
• Controls
• Control Relays and Devices: Control relays and devices shall be classified as heavy duty industrial and comply with NEMA ICS–1 and ICS–2. Relays shall be of the plug in type or front connected with dust covers. All relays, timers, and devices shall be UL listed and or approved for use with a transfer switch.
• Solid State Components
• All solid state controls shall be UL listed for the transfer switch application for which it is being applied.
• Shall be capable of meeting (surviving) the impulse withstand voltage test in accordance with NEMA ICS1–109.21.
• Shall be capable of meeting (surviving) the ANSI/IEEE C37.90 voltage surge withstand test.
• Buswork and Wiring
• The Automatic Transfer and Bypass–Isolation Switch shall be completely factory interconnected and tested so that only the service and load connections to the bypass–isolation switch are required for field installation. All interconnections between the transfer switch, bypass switch and isolation switch shall be copper bus bar with tin plating at all connections or splice points. The transfer switch shall be arranged for drawout operation to facilitate its removal.

• All wiring shall be flame retardant. Control wire shall be 600/300–volt insulation as applicable, stranded soft tinned copper, MTW, SIS Type, XHHW or XHHW2.
• Extra flexible cable shall be used between stationary and hinged panels.
• All wiring shall be suitably protected against contact with sharp edges, neatly bundled and secured with wire ties.
• A wiring identification system shall be provided to facilitate troubleshooting and maintenance. The system shall consist of permanently hot–stamped plastic sleeve wire markers mounted on both ends of the wire. Tape type wire markers are not acceptable. Preferred wire identification system shall be of the wire destination address type.
• Terminal lugs shall be supplied and shall be insulated barrel compression type with ring or spade tongues. Source and load cable sizes shall be given on the Data Sheet.
• Terminal blocks shall be suitable for holding spade type lugs.
• All alarm relay contacts and Purchasers connections shall be wired to terminal blocks that are clearly and uniquely marked.
• Conduit size and entrance locations shall be as shown on the Data Sheet. The Manufacturer shall ensure that adequate space is available for cable installation and bending.
• Standard Operation
• The automatic transfer switch control panel shall utilize solid–state sensing on source ‘A’ and source ‘B’ for automatic operation.
• Both power sources and the load shall have all phase voltages monitored line–to–line. Close differential voltage sensing shall be provided on all phases. The pickup voltage shall be adjustable from 85 percent (85%) to 100 percent (100%) of nominal and the dropout voltage shall be adjustable from 75 percent (75%) to 98 percent (98%) of the pickup value. The transfer will be initiated upon reduction of the connected source to the dropout voltage. Alarm contacts shall be provided from the voltage sensing system on both power sources and the load which will close on loss of voltage. Alarm contacts shall be rated 10 amps, 120 volts, 60 Hz.
• The transfer switch shall be capable of operation (transfer in either direction) down to a voltage level of 70% of rated voltage (nominal) applied to the switch terminals.
• The following shall be provided:
• Provide a time delay to override momentary connected source outages to delay all transfer switch signals and loss of voltage alarms. The time delay shall be field adjustable from 0.5 to 6 seconds and factory set at 1 second.
• Two amber lights shall be supplied to indicate the switch position. All indicating lights shall be of the type specified on the Data Sheet. Lights shall be installed on the enclosure door.
• Provide two (2) spare auxiliary contacts that are closed when the automatic transfer switch is connected to source ‘A’ and two (2) auxiliary contacts that are closed when the automatic transfer switch is connected to source ‘B’. Auxiliary contacts shall be rated 10–amps, 120– volts ,60 Hz AC.
• A test switch installed on the enclosure door to momentarily simulate connected source failure.
• Preferred Source Operation
• When “preferred source” operation is specified on the Data Sheet, the requirements of Section

5.6 of this Practice shall apply with the exception that there shall be the capability for automatic retransfer as described below.

• Provide a selector switch mounted on the enclosure door which will allow either source to be selected as the preferred source. This is to be deleted if the alternate source is an engine driven generator.
• Provide a selector switch and push–button mounted on the enclosure door which will allow “automatic” or “manual” operation.
• Automatic operation is as follows:
• Upon failure of the preferred source, transfer to the alternate source shall be initiated.(See Section 5.6 of this Practice.)
• Provide a time delay which will initiate retransfer back to the preferred source upon return of the preferred source. The time delay shall be field adjustable from 0 to 30 minutes and factory set at 30 minutes.
• The time delay shall be automatically bypassed if the alternate source fails and the preferred source is available.
• Manual operation is as follows: Upon depression of the push–button, the transfer switch shall operate. All other transfers shall be inhibited regardless of the condition of either source.
• Provide an alarm contact which shall be closed when the transfer switch is connected to the alternate source. Contact shall be rated 10 amps, 120 VAC.
• If the Data Sheet indicates that a standby engine driven generator is being used for the alternate source, the following shall be supplied:
• Frequency sensing with the pick up adjustable from 90 percent (90%) to 100 percent (100) of nominal frequency. Factory set to pick up at 95 percent (95%) of nominal frequency.
• Two auxiliary contacts that close upon normal source failure and two auxiliary contacts that open upon normal source failure shall be provided for initiating engine starting control and alarms for loss of source voltage. The contacts shall be rated 10 amperes, 125 volts D.C.
• A field adjustable (0–10 sec.) time delay relay shall be provided to delay engine starting signals during momentary normal source outages. This relay shall be factory set at 3 seconds.
• Nameplates

All equipment, indicating lights, switches etc., shall have plastic lamicoid tag nameplates. Nameplates shall have bold black letters on a white background. All nameplates shall be attached with screws or reusable plastic rivets.

TESTING

• Production testing shall include but not be limited to:
• Dielectric strength test or main power circuit with a 1000 volt D.C. megometer.
• Complete operational test of all components including sequence of operation, transfer time measurement, variation of voltage and time delay settings. These tests shall be carried out with rated voltage applied to the switch and with connection to a functional load circuit.
• When witness testing is specified the Owner shall witness the complete test as specified on the Data Sheets and the contract documents.

DRAWING AND DATA REQUIREMENTS

All drawings provided for this equipment shall show equipment as specified and ordered. Typical drawings are not acceptable, unless they are revised to show only the equipment being furnished. Information shall be provided in the quantities and format specified on the Data Sheet. Electronic format information shall be provided in CALS G4 Tiff (Compressed).

• Information to be Supplied with Quotation
• Manufacturer’s prints and other descriptive data, including dimensions as required for a complete description of the equipment proposed. Seller shall furnish heat loss for each unit.
• Complete lists of all equipment and accessories proposed. Major components not manufactured by the Switch Manufacturer submitting the proposal shall be so noted as well as the Manufacturer and type proposed.
• Standard warranty.
• Overall dimensions and weights.
• The Manufacturer shall state in the proposal all exceptions to this Practice or shall state that no exceptions are taken.
• The Manufacturer shall include in the proposal as a separate item the cost of providing a technician for on site check–out and start–up after equipment is installed by others.
• Information to be Submitted to Owner for Approval after Receipt of Order
• Complete certified drawings showing:
• Arrangement.
• Dimensional plan and elevation, front view and other elevations if pertinent.
• Conduit entrance location and dimensions for both top and bottom entrance.
• Incoming and outgoing power cable connections position.
• Grounding connections.
• Weight of equipment.
• Detail connection (wiring) diagrams showing:
• All wiring within the unit.
• All interconnecting wiring between units.
• Identification of all terminal and terminal blocks.
• Clear identification, some distinguishing method, of all wiring which is to be installed by the Owner.
• Priced lists of normally recommended spare parts for the specified equipment.
• Certified Information to be Submitted
• All information requested in Sections 6.0 and 7.0 of this Practice.
• Installation, maintenance, and operating instructions which cover all the equipment furnished by the Manufacturer.
• A material list shall be furnished listing the quantity, rating, type and manufacturer’s catalog number of all equipment in each unit.
• Certified test report shall be supplied to the Owner and the Owner’s Engineer before shipment.

SPARE PARTS

A complete spare parts recommendation based on the total purchase order is required within 60 days after the Manufacturer receives the purchase order. Spare parts recommendations shall include:

• A complete spare parts list, including parts location diagrams or drawings.
• Lists of priced spare parts as recommended by the Manufacturer to be on hand during plant start–up and the first year’s operation.

SHIPPING

• “Preparation for Shipment” shall be in accordance with the Manufacturer’s standards unless otherwise noted on the “Request for Quotation” and/or “Purchase Order”. The Manufacturer shall be solely responsible for the adequacy of the “Preparation for Shipment” provisions employed in respect of material and application, to provide materials to their destination in ex– works condition when handled by commercial carrier systems.
• Each shipping box shall be provided with a weatherproof tag stating the purchase order number.

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