Earth Reference And Bonding; Communications Signal Reference Requirements - S&C PureWave SMS-250 Installation Manual

Earth Reference and Bonding

Earth Reference Requirements:
A low-impedance earth reference connection is required
for the PureWave SMS-250 equipment. The earth (ground)
reference system should be tailored to reflect the char-
acteristics of the site and the requirements of the facility
and shall use a grounding interface that meets the needs
of the local electric utility's system and that complies with
all applicable national and local electrical codes and stan-
dards. The PureWave SMS-250 uses power converters that
switch at frequencies up to 5 kHz. For S&C PureWave SMS-
250 equipment and systems rated less than 1000 kVA, the
resistance of the SMS-250 earth reference connection to
earth is required to be 25 ohms or less at both the nominal
power frequency of 50 or 60 Hz, and at the 5-kHz switching
frequency of the SMS-250 power conversion system.
Any associated battery equipment must have its own
direct earth reference connection. It is not permitted to
only ground the battery equipment through the PureWave
SMS-250 earth reference connections.
Bonding Requirements:
Besides the importance of creating an earth reference,
bonding is required between interconnected electrical
equipment to establish a low impedance path that minimizes
the potential difference between two metallic objects,
minimizes electric shock hazards, provides lightning
protection, and establishes references for electronic signals.
All cable tray, conduit, and raceway systems installed to
interconnect power, control, and communications wiring to
and from the S&C PureWave SMS-250 shall be electrically
continuous by bonding together at each individual section.
Each individual cable tray, conduit, and raceway section,
including pull boxes, junction boxes, and outlet boxes,
shall be bonded to the facility earthing system within 2 feet
(600 mm) of each end and at intervals not exceeding
50 feet (15 meters) along the run. All cable trays, conduits,
and raceways shall be securely bonded to all brackets,
hangers, and structural members to which they are
attached. The resistance of each bonding connection
shall not exceed 5 milliohms. The total bonding resistance
between the PureWave SMS-250 cabinet and any battery
cabinet/enclosure shall be no more than 1 ohm.
Communications Signal
Reference Requirements
All communications systems that interface with the
PureWave SMS-250 equipment must be designed for
operation in a multipoint earth (ground) reference system.
See examples of ground plan diagrams in Figures 7 and 8.
Installation, Assembly, and Setup
AUTO
SMS-250
TRANSFORMER
MINIMUM 72"
OPTION
CLEARANCE
TO BATTERY
GROUND CONDUCTOR #4/0 AWG BARE 7
STRAND COPPER
10 FT. CU CLAD STEEL, 5/8 INCH DIA
#1 AWG CU TO #4/0 AWG CU EXOTHERMIC
CONN. OR APPROVED LISTED SWAGE
CONNECTION
Figure 7. Example of a ground plan diagram showing the
S&C PureWave SMS-250 cabinet, the SMS-250 autotrans-
former option, and a battery system.
SMS-250 SMS-250
GROUND CONDUCTOR #4/0 AWG BARE 7
STRAND COPPER
10 FT. CU CLAD STEEL, 5/8 INCH DIA
NEMA TWO HOLE PAD OR GROUND CLAMP
TO #4/0 CU CONNECTOR
#4/0 AWG CU TO #4/0 AWG CU
EXOTHERMIC CONN. OR APPROVED
LISTED SWAGE CONNECTION
Figure 8. Example of a ground plan diagram showing two
S&C PureWave SMS-250 cabinets and a pad-mount isola-
tion transformer (var-only application—no battery system).
S&C Instruction Sheet 659-525
BATTERY
SYSTEM
LEGEND
TERMINATION TO GROUND CONDUCTOR
(1 AWG MINIMUM) BARE COPPER, 10 MM
THREADED STUD, SINGLE HOLE, LISTED
SWAGE LUG
GROUND CONDUCTOR TO SMS-250
EQUIPMENT (#1 AWG MINIMUM) BARE 7
STRAND COPPER
PAD MOUNT
TRANSFORMER
LEGEND
#1 AWG CU TO #4/0 AWG CU EXOTHERMIC
CONNECTION OR APPROVED LISTED
SWAGE CONNECTION
TERMINATION TO GROUND CONDUCTOR
(1 AWG MINIMUM) BARE COPPER, 10 MM
THREADED STUD, SINGLE HOLE, LISTED
SWAGE LUG
GROUND CONDUCTOR TO SMS-250
EQUIPMENT (#1 AWG MINIMUM) BARE 7
STRAND COPPER
13