Magnum Energy Magnum Panel (MP Series) - Manual (Page 52)

© 2011 Magnum Energy, Inc. Page 45
3.0 Installation
3.7.2 Inverter DC Overcurrent Protection and DC Disconnect
In a battery-based inverter system, the NEC/CEC assumes that each ungrounded conductor is
connected to some source that supplies currents in excess of the ampacity rating of the conductor
and could potentially damage that conductor under fault conditions. Because of this, the NEC/
CEC requires that all ungrounded conductors in the inverter’s DC system be protected by an
overcurrent device, this can be either a circuit breaker or fuse. These breakers or fuses are not
intended to protect equipment from damage, but protect the conductor/wire from overheating
which may potentiality cause a fi re. This means the overcurrent device is required to open before
the conductor reaches its maximum current carrying capability, thereby preventing a fi re.
The NEC also requires the inverter system to have a DC disconnect switch to allow service providers
to isolate the inverter from the battery. The disconnect must be either a DC rated circuit breaker
or switch.
The MP enclosure is provided with a 250 amp UL listed, high interruption capacity, magnetic-
hydraulic, DC rated circuit breaker. These breakers are designed to interrupt the tremendous
amount of current a battery can deliver when short-circuited. They are also specifi cally designed
to have a long enough time delay to prevent the breaker from tripping, as the inverter requires
high current levels when powering heavy loads.
If the battery cables to the inverter are no longer than fi ve feet and the wire size is a minimum
#4/0 AWG
1 , the circuit breakers in the MP enclosure can provide the inverter system with both
the DC overcurrent protection device and a safety disconnect switch.
If your battery to inverter cable length is greater than fi ve feet, the DC wire size will need to be
increased. Longer distances cause an increase in resistance, which affects the performance of the
inverter.
If your battery to inverter cable size is smaller than the recommended minimum DC wire size (#4/0
AWG
1 ), you must install a fuse/circuit breaker close to the battery bank that is compatible with this
smaller cable to protect against a potential fi re.
CAUTION: In a low voltage/high amperage system, it is important to use the correct
DC wire to achieve maximum effi ciency and to reduce fi re hazards associated with
overheating. Always keep your wire runs as short as practical to help prevent low
voltage shutdowns.
Info: Circuit breakers or fuses that are used on the DC side must be UL listed and DC
rated for the application.
3.8.2.1 Optional DC Breakers/Disconnects
When installing multiple inverters, the MP enclosure provides the space to add a 250 amp breaker,
for each additional inverter. These breakers — along with all the wires and hardware — are provided
with the MPX Series Extension Kit.
All MP enclosures (except for the MPSH-30D) provide space to fi eld install additional DC breakers
for use as DC input/output breakers for PV, charge controllers, or DC loads. See Section A6 for
more information.
1
Note 1 - Wire must be copper with a minimum rating of 300V, 75°C at an ambient temperature of 30°C.