Magnum Energy MMS-E Series User Manual

Page 21

2.5.2 DC Overcurrent Protection

For safety and to comply with local electrical code regulations, you
must install a DC overcurrent protection device in the positive DC
cable line to protect your DC cables. This overcurrent device can be
a fuse or circuit-breaker, but must be DC rated. It must be correctly
sized according to the size of DC cables being used; which means it
is required to open before the cable reaches its max. current carrying
capability, thereby preventing a ﬁ re. See Table 2-1 to select the DC
overcurrent device based on the min. wire size for your inverter model.

Electrical systems in mobile installations typically do not require using
a DC disconnect, although an overcurrent protection device is still
required. A fuse is usually used as the disconnect device in these
installations. These installations also do not normally use conduit,
so the fuse must be installed in the ungrounded conductor (usually
the positive DC cable line) within 45.72 cm (18”) of the battery – to
protect the DC wiring system.

If using a fuse, we recommend using a Class-T type or equivalent.
This fuse type is rated for DC operation, can handle the high short-
circuit currents, and allows for momentary current surges from the
inverter without opening.

2.5.3 DC Grounding

The inverter/charger should always be connected to a permanent,
grounded wiring system. To reduce the possibility of electric shock,
connect the metallic chassis of the various enclosures together to have
them at the same voltage potential. For the majority of installations,
the inverter chassis and the negative battery conductor are connected
to the system’s ground bond via a safety-grounding conductor (bare
wire or green insulated wire) at only one point in the system. The
size for the grounding conductor is usually based on the size of the
overcurrent device used in the DC system. Refer to Table 2-1 to select
the appropriate DC ground wire based on the overcurrent device used
for your inverter model.

If the inverter is in a vehicle, DO NOT connect the battery negative
(-) cable to the vehicle’s safety ground. Only connect to the inverter’s
negative battery terminal. If there are any non-factory installed
appliances onboard the vehicle, DO NOT ground them at safety
ground. Only ground them at the negative bus of the DC load center
(as applicable).

Table 2-2, DC Wire Size For Increased Distance

2.0 Installation

67.40 mm²

(#2/0 AWG)

53.46 mm²

(#1/0 AWG)

42.39 mm²

(#1 AWG)

Minimum Recommended DC Wire Size (one way)

107.16 mm²

(#4/0 AWG)

≤ 1 m

(3 ft or less)

1 m to 1.5 m

(3 to 5 ft)

1.5 m to 3 m

(5 to 10 ft)

3 m to 4.5 m

(10 to 15 ft)