AC UPS System Grounding Installation | Grounding Earthing System

This article is about AC UPS System Grounding Installation, Checklist & Requirements of Grounding Earthing System as per International Codes and standards for Commercial Buildings, Plants and Refinery Projects.

AC UPS System Grounding Installation | Grounding Earthing System

1. AC UPS System Grounding shall be as per the requirements of NFPA 70.
2. Each enclosure shall be provided with an equipment grounding bus for connection to the ground grid. The enclosure ground and the signal ground shall be connected to this common bus. The UPS AC output neutral shall be isolated from the enclosure and shall be connected only to the ground bus.
3. The positive and negative DC buses shall be isolated from the earth ground.
4. The neutral terminal of an output receptacle supplied from separately derived a.c. source shall be bonded to the protective earthing means of the equipment. (UL 1778 Clause 2.6.10)
5. Verify if the a.c power circuit has to be grounded. (UL 1778 Annex EE, Part EE.1.1)
6. The conductors to be grounded shall be as follows:
   a) single-phase a.c. system, 2 wire: one conductor
   b) single-phase a.c. system, 3 wire: the neutral conductor
   c) multiphase a.c. system having one wire common to all phases: the common conductor; and d) multiphase a.c. system where one phase is used as single phase, 3 wire, a.c. system : the neutral conductor. (UL 1778 Annex EE, Part EE.1.2)
7. The grounding of the circuits shall be made by a bonding jumper connected between the grounded conductor and to
   a) The enclosure of a metal enclosed unit: or
   b) The metal chassis that is bonded to the equipment’s protective earthing means of a non-metallic enclosed unit. The size of the bonding jumper shall be as specified in column 4 of Table EE.1 (Attachment 1). (UL 1778 Annex EE, Part EE.1.3)
8. The circuit may be grounded in the field if the following provisions are implemented: a) A field-wiring terminal is connected to the circuit by a bonding jumper. The terminal and jumper shall not be less than that specified in column 4 of Table EE.1 (Attachment 1). b) The field-wiring terminal is identified as the neutral. (UL 1778 Annex EE, Part EE.1.4)
9. The grounding terminals provided is capable of securing the conductor and marked with the following words: “”Grounding Electrode Terminal. (UL 1778 Annex EE, Part EE.1.5)
10. Determine the neutral-to-ground potential shall not exceed 30V rms (42.4 V peak) at no-load and full-load conditions. (UL 1778 Annex EE, Part EE.1.6)

International Standard and Codes for AC UPS System Grounding

1. Non-Hazardous Indoor Enclosures, Installation and Pre-Commissioning
2. Boxes, Enclosures, and Accessories Materials Selection & Requirements
3. NFPA 70 — National Electrical Code (NEC), 2008 Edition
4. 17-SAMSS-516 — Uninterruptible Power Supply System.
5. UL-1778 — Uninterruptible Power Systems.

   ATTACHMENTS:
   1. Attachment 1 – UL 1778, Table EE.1 Size of circuit bonding, equipment-grounding, and grounding electrode conductors