USACE / NAVFAC / AFCESA / NASA UFGS-26 36 23.00 20 (April 2006)
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Preparing Activity: NAVFAC Replacing without change
UFGS-16410N (February 2003)
UNIFIED FACILITIES GUIDE SPECIFICATIONS
References are in agreement with UMRL dated January 2009
SECTION 26 36 23.00 20
AUTOMATIC TRANSFER SWITCHES
04/06
NOTE: This guide specification covers the requirements for automatic transfer
switches intended for use in Emergency Electrical Power Systems meeting requirements
of NFPA 70, NFPA 99, and MIL-HDBK-1191.
Edit this guide specification for project specific requirements by adding, deleting,
or revising text. For bracketed items, choose applicable items(s) or insert
appropriate information.
Remove information and requirements not required in respective project, whether
or not brackets are present.
Comments and suggestions on this guide specification are welcome and should
be directed to the technical proponent of the specification. A listing of technical
proponents, including their organization designation and telephone number, is
on the Internet.
Recommended changes to a UFGS should be submitted as a Criteria Change Request
(CCR).
NOTE: The following system design requirements shall be adhered to when providing
automatic transfer switches:
1. Provide four-pole transfer switches. The neutral conductor for each source
of supply, including the neutral on separately derived systems, shall be switched
by the transfer switch.
2. Do not install transfer switches on the supply side of service equipment.
When the transfer switch is to be located on the supply side of service loads,
provide an independent service overcurrent protection device on the supply side
of the transfer switch.
3. Do not use open type transfer switches installed in other equipment such
as switchboards, or as part of the service equipment.
NOTE: The following information shall be shown on the project drawings:
1. The available fault current at the bus feeding the automatic transfer switch.
2. The rating of the overcurrent device protecting the automatic transfer switch.
3. Identify automatic transfer switches to be provided with By-pass/Isolation
Switches, when applicable.
4. Identify control type, i.e., Utility-Generator, Preferred Utility Source,
or Generator-Generator, for each automatic transfer switch.
5. Identify automatic transfer switches to be provided with "transfer time
delay" and "time delay transition" or "in-phase monitor" features, where applicable.
6. Identify automatic transfer switches to be used for fire pump service, when
applicable.
PART 1 GENERAL
1.1 REFERENCES
NOTE: This paragraph is used to list the publications cited in the text of
the guide specification. The publications are referred to in the text by basic
designation only and listed in this paragraph by organization, designation,
date, and title.
Use the Reference Wizard's Check Reference feature when you add a RID outside
of the Section's Reference Article to automatically place the reference in the
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to update the issue dates.
References not used in the text will automatically be deleted from this section
of the project specification when you choose to reconcile references in the
publish print process.
The publications listed below form a part of this specification to the extent referenced. The publications are
referred to within the text by the basic designation only.
[INTERNATIONAL ELECTRICAL TESTING ASSOCIATION (NETA)NETA ATS(2003) Acceptance Testing Specifications][NATIONAL FIRE PROTECTION ASSOCIATION (NFPA)NFPA 70(2007; AMD 1 2008) National Electrical Code - 2008 Edition][UNDERWRITERS LABORATORIES (UL)UL 1008(1996; Rev thru Dec 2007) Standard for Transfer Switch EquipmentUL 508(1999; Rev thru Sep 2008) Standard for Industrial Control Equipment]1.2 RELATED REQUIREMENTS
Section 26 00 00.00 20 BASIC ELECTRICAL MATERIALS AND METHODS, and Section 26 08 00 APPARATUS INSPECTION AND
TESTING, apply to this section, with the additions and modifications specified herein.
1.3 SUBMITTALS
NOTE: Review submittal description (SD) definitions in Section 01 33 00 SUBMITTAL
PROCEDURES and edit the following list to reflect only the submittals required
for the project. Submittals should be kept to the minimum required for adequate
quality control.
A “G” following a submittal item indicates that the submittal requires Government
approval. Some submittals are already marked with a “G”. Only delete an existing
“G” if the submittal item is not complex and can be reviewed through the Contractor’s
Quality Control system. Only add a “G” if the submittal is sufficiently important
or complex in context of the project.
For submittals requiring Government approval on Army projects, a code of up
to three characters within the submittal tags may be used following the "G"
designation to indicate the approving authority. Codes for Army projects using
the Resident Management System (RMS) are: "AE" for Architect-Engineer; "DO"
for District Office (Engineering Division or other organization in the District
Office); "AO" for Area Office; "RO" for Resident Office; and "PO" for Project
Office. Codes following the "G" typically are not used for Navy, Air Force,
and NASA projects.
Choose the first bracketed item for Navy, Air Force and NASA projects, or choose
the second bracketed item for Army projects.
Government approval is required for submittals with a "G" designation; submittals not having a "G" designation
are [for Contractor Quality Control approval.][for information only. When used, a designation following the
"G" designation identifies the office that will review the submittal for the Government.] The following shall
be submitted in accordance with Section 01 33 00 SUBMITTAL PROCEDURES:
SD-02 Shop Drawings
Automatic Transfer Switch Drawings; G
SD-03 Product Data
Automatic Transfer Switches; G
SD-06 Test Reports
Acceptance Checks and Tests; G
Functional Acceptance Tests; G
SD-07 Certificates
Proof of Listing; G
SD-10 Operation and Maintenance Data
Automatic Transfer Switches, Data Package 5; G
Submit in accordance with Section 01 78 23 OPERATION AND MAINTENANCE DATA.
1.4 QUALITY ASSURANCE
1.4.1 Proof of Listing
Submit proof of listing by UL 1008.
1.4.2 Automatic Transfer Switch Drawings
Drawings shall include outline, arrangement, and detail drawings. Detail drawings shall include manufacturer's
name and catalog number, electrical ratings, total system transfer statement, reduced normal supply voltage at
which transfer to the alternate supply is initiated, transfer delay times, short-circuit current rating, wiring
diagram, description of interconnections, testing instructions, acceptable conductor type for terminals, tightening
torque for each wire connector, and other required UL 1008 markings.
PART 2 PRODUCTS
2.1 AUTOMATIC TRANSFER SWITCHES
NOTE: Select the following options for switches to be installed in facilities
complying with MIL-HDBK-1191, DOD Medical and Dental Treatment Facilities Design
and Construction Guide: (a) "Switches utilizing circuit breakers are not acceptable";
(b) "Automatic Transfer Switches provided with a by-pass/isolation switch shall
be mounted on a drawout mechanism so that the automatic transfer switch can
be removed from the enclosure".
Provide four-pole, automatic transfer switches for use in emergency systems in accordance with UL 1008. Each
automatic transfer switch shall be rated for total system transfer and have the current and voltage ratings as
indicated. The rating of the switch shall be adequate for withstanding the effects of the indicated RMS symmetrical
fault current when protected by the indicated overcurrent device without contact welding. The switch operating
mechanism shall be electrically operated from the source to which it is transferring, shall have quick-make,
quick-break, load break contacts, and shall be mechanically held in both positions. [Switches utilizing circuit
breakers are not acceptable.] Non-fire pump service transfer switches shall have manual operating means provided
for maintenance and servicing accessible only by opening the enclosure. [Transfer switches for fire pump service
shall have manual operating means externally operable without opening the enclosure.] The manual operating means
shall affect the opening and closing of the switch contacts at the same rate of speed as that caused by the automatic
operation of the switch. [Automatic transfer switches provided with by-pass/isolation switches shall be mounted
on a drawout mechanism so that the automatic transfer switch can be removed from the enclosure.] [The switch
enclosure shall comply with UL 508, NEMA Type [1], [12],[____], and shall be equipped with an equipment ground
lug.]
[2.1.1 By-Pass/Isolation Switches
NOTE: Include by-pass/isolation switches only where the nature of the loads
make continuance of power essential when the associated ATS switch is disconnected
for repairs, preventive maintenance, or testing. Provide by-pass/isolation
switches for automatic transfer switches to be installed in facilities complying
with MIL-HDBK-1191, DOD Medical and Dental treatment Facilities Design and Construction
Guide.
Include by-pass/isolation switches for the indicated automatic transfer switches. Provide by-pass/isolation
switches in accordance with UL 1008 that can be used to manually select an available power source to feed load
circuits and to permit total isolation of the automatic transfer switch. The by-pass/isolation switch shall
be rated for total system transfer and have the same current rating, voltage rating, number of poles, and withstand
and closing rating as the associated automatic transfer switch.
]2.1.2 Automatic Transfer Switch Controls
[2.1.2.1 Controls for Utility-Generator Automatic Transfer Switch
NOTE: The following paragraph is intended for use when the automatic transfer
switch is to be used for transferring loads to an emergency generator upon loss
of the normal (utility) source.
Provide all necessary controls to start the generator set upon loss of the normal (utility) source, transfer
the load to the generator set upon reaching rated voltage and frequency, re-transfer the load when the normal
(utility) source returns, and stop the generator set.
The switch shall include the following control features.
a. Three-phase normal source voltage sensing circuit with adjustable dropout, 75-93 percent of nominal,
and pickup, 85-100 percent of nominal.
b. Engine starting control contacts with adjustable commit-to-start delay circuit, 0.5-6.0 seconds.
c. Voltage/frequency sensing circuit, set for 80 percent of nominal, for enabling load transfer to emergency
source.
NOTE: Provide transfer to emergency source time delay for the transfer switches
requiring delayed-automatic operation.
[d. Transfer to emergency source time delay for transfer switches as indicated, adjustable 0-5 minutes.]
e. Re-transfer to normal source time delay, adjustable 1-30 minutes.
f. Programmable exerciser to allow automatic starting of the generator set and subsequent load transfer.
Exercise periods shall be selectable for 1 to 24 hours per day for 0 to 7 days a week.
NOTE: When the transferred load includes motors (over 50 HP or over 5 HP without
significant resistive loads), select the following option.
[g. Adjustable time delay transition or in-phase monitor feature for indicated transfer switches to
allow safe transfer of highly inductive loads between two non-synchronized sources.]
][2.1.2.2 Controls for Generator - Generator Source Automatic Transfer Switch
NOTE: The following paragraph is intended for use when a second automatic transfer
switch is to be used to select between two generators in a three source (utility-generator-generator)
system.
Provide all necessary controls to start both generator sets upon loss of the normal utility source, transfer
the load to the first generator set to reach rated voltage and frequency, shutdown the second generator set upon
transferring the load to the first generator set, restarting and transferring the load to the second generator
if at any time the first generator set fails, re-transfer the load when the normal (utility) source returns,
and shut down the generator set. The switch shall include the following control features;
a. Engine starting control contacts.
b. Voltage/frequency sensing circuit, set for 80 percent of nominal for enabling load transfer to emergency
source.
c. Programmable exerciser time to allow automatic starting of the generator sets and subsequent load
transfer to each generator set. Exercise periods shall be selectable for 1 to 24 hours per day for 0
to 7 days a week.
][2.1.2.3 Controls for Preferred Utility Source Automatic Transfer Switch
NOTE: The following paragraph is intended for use when the automatic transfer
switch is to be used for selecting between two utility sources (preferred and
alternate).
Provide all the necessary controls to transfer the load to the alternate utility source upon loss of the preferred
utility source and re-transfer the load to the preferred utility source when the preferred utility source returns.
The switch shall include the following control features.
a. Three-phase preferred and alternate source voltage sensing circuit with adjustable dropout, 75-98
percent of nominal, and pick-up, 85-100 percent of nominal.
b. Re-transfer to normal source time delay, adjustable 1-30 minutes.
NOTE: When the transferred load includes motors(over 50 HP or over 5 HP without
significant resistive loads) select the following option.
[c. Adjustable time delay transition or in-phase monitor feature for indicated transfer switches to
allow safe transfer of highly inductive loads between two non-synchronized sources.]
][2.1.2.4 Controls for Fire Pump Service Automatic Transfer Switch
NOTE: The following paragraph is intended for use when the automatic transfer
switch is to be used for fire pump service.
Provide the following additional controls features:
a. Phase reversal of the normal source shall initiate transfer to the emergency/alternate source.]
2.1.3 Front Panel Devices
Provide devices mounted on cabinet front consisting of:
a. Mode selector switch with the following positions and associated functions;
1. TEST - Simulates loss of normal/preferred source system operation.
2. NORMAL - Transfers system to normal/preferred source bypassing re-transfer time delay.
b. Lamps for indicating connected source and normal/preferred source is available.
c. Auxiliary contacts for indicating connected source and normal/preferred source available.
NOTE: Select option for preferred source selector switch when specifying preferred
utility source automatic transfer switches.
[d. Source selector switch with the following positions and associated functions.
1. Source 1 - Selects Source 1 as the source to which the automatic transfer switch will transfer
if that source is available.
2. Source 2 - Selects source 2 as the source to which the automatic transfer switch will transfer
if that source is available.]
NOTE: Select the following option when specifying by-pass/isolation switches.
[e. Lamps for indicating that the by-pass/isolation switch is in the "normal by-pass", "alternate by-pass",
or "isolated" position.
]PART 3 EXECUTION
3.1 INSTALLATION
Installation shall conform to the requirements of NFPA 70 and manufacturer's recommendation.
3.2 PREREQUISITES FOR FUNCTIONAL ACCEPTANCE TESTING
Completion of the following requirements is mandatory prior to scheduling functional acceptance tests for the
automatic transfer switch.
3.2.1 Performance of Acceptance Checks and tests
Complete as specified in paragraph entitled "Acceptance Checks and Tests". The Acceptance Checks and Tests shall
be accomplished by the Testing organization as described in Section 26 08 00 APPARATUS INSPECTION AND TESTING.
3.2.2 Manufacturers O&M Information
The manufacturers O&M information required by the paragraph entitled "SD-10 Operation and Maintenance Data",
shall have been submitted to and approved by the Contracting Officer.
3.2.3 Test Equipment
All test equipment and instruments shall be on hand prior to scheduling field tests, or subject to Contracting
Officer's approval, evidence shall be provided to show that arrangements have been made to have the necessary
equipment and instruments on site prior to field testing.
3.3 FIELD QUALITY CONTROL
Give Contracting Officer 15 days notice of dates and times scheduled for tests which require the presence of
the Contracting Officer. The Contracting Officer will coordinate with the using activity and schedule a time
that will eliminate or minimize interruptions and interference with the activity operations. The contractor
shall be responsible for costs associated with conducting tests outside of normal working hours and with incorporating
special arrangements and procedures, including temporary power conditions. The contractor shall provide labor,
equipment, apparatus, including test load, and consumables required for the specified tests. Calibration of
all measuring devices and indicating devices shall be certified. The test load shall be a cataloged product
in accordance with Section 26 00 00.00 20 BASIC ELECTRICAL MATERIALS AND METHODS. Perform the following field
tests in accordance with the manufacturer's recommendations and include the following visual and mechanical inspections
and electrical tests, performed in accordance with NETA ATS.
3.3.1 Automatic Transfer Switch Acceptance Checks and Tests
a. Visual and Mechanical Inspection
1. Compare equipment nameplate data with specifications and approved shop drawings.
2. Inspect physical and mechanical condition.
3. Confirm correct application of manufacturer's recommended lubricants.
4. Verify that manual transfer warnings are attached and visible.
5. Verify tightness of all control connections.
6. Verify tightness of accessible bolted connections by calibrated torque-wrench method. Thermographic
survey is not required.
7. Perform manual transfer operation.
8. Verify positive mechanical interlocking between normal and alternate sources.
b. Electrical Tests
1. Measure contact-resistance.
2. Perform insulation-resistance on each pole, phase-to-phase and phase-to-ground with switch
closed, and across each open pole for one minute. Perform tests in both source positions.
3. Verify settings and operations of control devices.
4. Calibrate and set all relays and timers.
3.3.2 Functional Acceptance Tests
Functional Acceptance Tests shall[ be coordinated with Section 26 32 13.00 20 SINGLE OPERATION GENERATOR SETS
and shall] include simulating power failure and demonstrating the following operations for each automatic transfer
switch. Contractor shall show by demonstration in service that the automatic transfer switches are in good operating
condition, and function not less than five times.
a. Perform automatic transfer tests:
1. Simulate loss of normal/preferred power.
2. Return to normal/preferred power.
3. Simulate loss of emergency power.
4. Simulate all forms of single-phase conditions.
b. Verify correct operation and timing of the following functions:
1. Normal source voltage-sensing relays.
2. Engine start sequence.
3. Time delay upon transfer.
4. Alternate source voltage-sensing relays.
5. Automatic transfer operation.
6. Interlocks and limit switch function.
7. Time delay and retransfer upon normal power restoration.