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2012 Magnum Energy, Inc. Page 34
Installation
2.10.1 Sizing the Grounding Electrode Conductors
AC Side – The size of the AC Grounding Electrode Conductor (GEC–AC) depends on the size of
the largest ungrounded conductor feeding the AC load center. One #8 AWG (8.4 mm
2
) copper
conductor will serve as an AC Grounding Electrode Conductor (GEC–AC) for AC power conductors
smaller than and including #2 AWG (33.6 mm
2
) copper. See Table 2-6 for additional values.
Table 2-6, AC Grounding Electrode Conductor Sizing
Size of Largest Ungrounded
Conductor
Minimum Size of Grounding
Electrode Conductor
#2 AWG or smaller
#8 AWG
(8.4 mm
2
)
#1 to #1/0 AWG #6 AWG
(13.3 mm
2
)
#2/0 or #3/0 AWG
#4 AWG
(21.1 mm
2
)
Over #3/0 AWG
through 350 kcmil
#2 AWG
(33.6 mm
2
)
DC Side – To size the DC grounding electrode conductor, you must fi rst determine which one of the
following three methods will be used to connect the DC and AC grounding points in the inverter’s
two electrical systems to the common “earth” ground.
Info: There are many variables to consider when choosing the size of the DC grounding
electrode conductor. The MMP enclosure provides the means to ground both the AC and
DC to a single ground, and when feasible, the Single Connection to Ground (Method
1) is recommended. In this method, the NEC allows a #6 AWG wire which makes the
overall installation simpler and less costly.
1. Single Connection to Ground (Method 1): The AC Grounding Electrode Conductor
(GEC–AC) is bonded to the DC ground point and the DC Grounding Electrode Conductor (GEC–DC)
is the only connection to the grounding electrode, which must be a rod, pipe, or plate electrode
(see Figure 2-17).
Normally the size of the DC Grounding Electrode Conductor (GEC–DC) must be no less than the size
of the Battery Bank Negative Cable. However, in this method, since there is only one connection
to the ground rod, the NEC allows an exception that the DC grounding electrode conductor is
not required to be larger than #6 AWG (13 mm
2
) copper. The reasoning for allowing this smaller
grounding electrode conductor is that it is only required to stabilize the system voltage with respect
to earth, and the other properly sized conductors in each electrical system will safely carry any
fault currents if they occur.
DC
S
OURCE
M
AIN
AC P
ANEL
H
OT
1
N
EUT
G
ND
H
OT
2
MMP
AC
S
OURCE
DC side dedicated
DC Electrical
System
AC Electrical
System
Grounding System
G
ND
P
OS
N
EG
GBB
SBJ
GEC-DC
GE
GBB
SBJ
M
AGNUM
I
NVERTER
GEC-AC
GC-DC
BAT
GC-AC
HOT 1
HOT 2
NEUT
BAT
E
NCLOSURE
Figure 2-17, Single Connection to DC Ground Rod (Method 1)