832571250 PWS Appendix I - SRG for Grounding.pdf

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APPENDIX I: MINIMUM TECHNICAL SPECIFICATION FOR

SIGNAL REFERENCE GRID FOR GROUNDING

HAW RAISED FLOOR AND CRAH UPGRADE

EFFECTIVE DATE: 12 JUL 2019

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1. PURPOSE

This specification details the requirements Signal Reference Grid (SRG) for grounding. All DISA data centers are required to utilize SRG systems in computer rooms.

2. SCOPE

Provide a complete SRG in accordance with applicable codes and standards by replacement of an existing

SRG.

3. REFERENCES

The publications listed below form a part of this specification to the extent referenced. The publications are referred within the text by the basic designation only. The current revision of the reference, including all issued updates, must be followed. The advisory provisions are mandatory. Substitute "must" for "should" wherever it appears.

DEFENSE INFORMATION SYSTEMS AGENCY (DISA)

DISA Facilities Engineering Circular

INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS (IEEE)

IEEE 81 Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System

IEEE 1100 Recommended Practice for Power and Grounding Electronic Equipment

INTERNATIONAL ELECTRICAL TESTING ASSOCIATION (NETA)

ANSI/NETA ATS Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems

NATIONAL FIRE PROTECTION AGENCY (NFPA)

NFPA 70 National Electric Code

U.S. DEPARTMENT OF DEFENSE (DOD)

MIL-HDBK-419 Grounding: Bonding, and Shielding for Electronic Equipments and Facilities; Volume 1 (Basic Theory) and Volume 2 (Application)

MIL-STD-188/124 Grounding, Bonding and Shielding

4. ACRONYMS

AWG. American Wire Gauge

CRAC/CRAH. Computer Room Air Conditioning/Handling

DISA. Defense Information Systems Agency, Facilities Engineering Denver.

IRC. In-Row Cooler.

PDU. Power Distribution Unit.

SRG. Signal Reference Grid.

5. REQUIREMENTS

All brackets and clamps used on the SRG shall be UL listed for the purpose for which it is used. All conductors shall be continuous, splices are not permitted.

SIGNAL REFERENCE GRID FOR GROUNDING

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5.1. EXISTING CONDITIONS

When modifying/replacing an existing SRG, update the SRG to meet the minimum requirements of this standard, where existing components meet the requirements of this standard and are in good condition, they may be reused. When access-floors are installed as part of the project installing or modifying the SRG, ensure the floor tile metallic underside is not galvanized by an electroplating process. Galvanized by a hot-dipped process is acceptable.

5.2. REFERENCE GROUNDING BOND GRID

A reference bonding grid shall be installed in accordance with Figure 1 and MIL-HDBK-419.

B u ild in g S te e l

Earth Electrode Subsystem/Counterpoise

IT Cable Tray Above Access Floor

First Floor Computer Room (1), with Access Floor

Access Floor

Pedestals

IT

Equip.

Racks

IT Cable Tray Above Access Floor

Access Floor

Pedestals

IT

Equip.

Racks

Dedicated ground bus bar for SRG use only.

Isolated and prominently labeled

IT Cable Tray

IT

Equip.

Racks

Isolated, Insulated Conductors, 600 KCMIL (typ)

Isolated, Insulated

Conductors 4/0 (typ). Bond

SRGs together when on the same floor

Perimeter 4/0 Bare Copper Conductor

Exterior Edges 1/0 Bare Copper

Conductor

750 KCMIL (typ)

Isolated, Insulated Conductors, 600 KCMIL (typ)

Isolated, Insulated

Conductors 4/0

Isolated, Insulated

Conductors 4/0

Isolated, Insulated Conductor 4/0

First Floor Computer Room (3), with Access Floor

First Floor Computer Room (2), without Access Floor

Figure 1: Reference Grounding Bond Grid

The SRGs of different computer rooms are only bonded together when the rooms are on the same floor.

All other connections as shown in Figure 1 apply to all SRGs in the building.

5.3. SRG CONFIGURATION FOR COMPUTER ROOMS WITH ACCESS FLOORS (NEW OR EXISTING)

Plan the layout of the SRG based on the exact layout of all computer room equipment (i.e., metal power conduits or raceways, equipment cables, floor pedestals, computer equipment). Use of an access-floor

SIGNAL REFERENCE GRID FOR GROUNDING

UNCLASSIFIED Page 3 of 4 itself to create the SRG is not acceptable. The incorporation of a separate SRG is required. The SRG shall be suspended by the access floor pedestals.

Configure a 2 foot by 2 foot grid arrangement in accordance with Figure 1 and the following:

a. Bond each #6 AWG concentric copper conductor to the 4/0 copper perimeter loop at each end.

b. Bond #6 AWG bare copper concentric conductors as follows:

(1) Create the grid by bonding conductors to floor pedestals. Attach each conductive floor pedestal clamp to bare metal just below the stanchion of the floor pedestal. Each clamp shall connect to the conductor in each direction (see Figure 2).

Sublfoor

Conductive Pedestal Bonding Clamp

The bonding clamp shall be located near the top of the floor pedestal, just below the stanchion (not shown)

Floor Pedestal SRG Copper Conductors

Figure 2: Bonding to Floor Pedestals

Every 3rd floor pedestal (minimum) shall be bonded to the SRG in each direction (see Figure 3).

2 Feet.

Figure 3: Grid Pattern Secured to Floor Pedestals, Perimeter Loop Not Shown

(2) Where conductors in the grid cross and are not bonded to the nearest pedestal, the conductors shall be bonded together with a clamp.

c. Install the SRG grounding bond system in accordance with Figure 1 and the following:

(1) Bond a #6 AWG concentric bare copper conductor (minimum) from the SRG to all ducts, metal pipes, metal conduits, and cable trays entering the computer room located below the access floor.

SIGNAL REFERENCE GRID FOR GROUNDING

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(2) Connect to the existing SRG bonding system (where applicable, see Figure 1).

(3) Bond a #6 AWG concentric bare copper conductor from the SRG to the interior of the frame of each IT rack enclosure. Use as short a length as possible, not to exceed 24 inches.

d. When the SRG is installed, bonded and grounded, ensure the continuity of the SRG by measuring the resistance, in accordance with the requirements in paragraph 5.4, Commissioning Requirements for the SRG. If the resistance exceeds 1 ohm, all connections must be rechecked (between floor pedestals, SRG conductors, and equipment enclosures) to ensure the connections are secure.

(1) Record all testing to certify connections are verified and less than 1 ohm.

5.4. COMMISSIONING REQUIREMENTS FOR THE SRG

All testing must be performed while the facility is operating. The Contractor shall ensure the integrity of the facility is not compromised while the SRG is tested. The sequence for testing the various portions of the system is described in general in this document and must be included in detail in the Contractor’s testing and commissioning plan.

All sections of the SRG must be tested back to the system ground to verify that the system does not exceed 1 ohm back to the system ground. To verify this the system shall be tested and each bonding point (at not more than 6’ centers for each conductor) is tested and verified for proper installation. Each reading shall be mapped on a floor layout and provided to the owner as a part of the as built documentation.

Additionally, the testing shall include a point between the perimeter loop and the SRG at the center of the floor. If the computer room is too large to test between these points, then test between the perimeter loop and a point on the SRG toward the center of the floor along each wall of the computer room.

5.4.1. Qualifications

All required grounding system tests shall be performed by a third-party, NETA-certified testing organization. The testing organization shall have a minimum of 5 years documented experience in the testing and commissioning of grounding systems.

5.4.2. Documentation

The Commissioning Plan and Test Report (including completed test forms) shall be completed and provided in accordance with the DISA Facility Engineering Project Commissioning, Close-Out, and Transition Standard. Approval of the Test Report by the Government is required prior to final acceptance of the SRG.

5.4.2.1. Test Methods

Earth Electrode Resistance Tests Perform the “fall of potential” method in accordance with MIL-HDBK-419

Bonding Resistance Tests Perform the “four wire” method utilizing a balanced DC resistance bridge in accordance with

MIL-HDBK-419.

5.4.3. Notification

Contractor shall notify the Government a minimum of 30 calendar days prior to performing ground system testing and commissioning. The Contractor shall notify the Government if any section or subsystem tested does not meet the requirements of this standard before proceeding further.

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