©
2017 Sensata Technologies
Page 26
Installation
2.6.3
Sizing the DC OverCurrent Protection Device (OCPD)
The
fi
nal step necessary in sizing the DC conductor is to verify that the selected conductor can
handle the current and is protected by the DC OverCurrent Protection Device (OCPD). Once you
have identi
fi
ed the conductor that will handle the maximum continuous current (described in
Section 2.6.2), ensure the continuous rating of the selected overcurrent protection device is not
less than the maximum current for the circuit it is protecting and no greater than the ampacity
of the conductor selected. Per code, the rating of the overcurrent protection device (OCPD) must
comply with all of the following:
Info:
Per the NEC: 690.9 (D) Photovoltaic Source and Output Circuits - Listed PV
overcurrent devices shall be required to provide overcurrent protection in PV source
and output circuits.
1. In a PV system which includes batteries, an OCPD is required for each PV source circuit.
To protect the internal connections of the module, the OCPD must not be sized larger than the
maximum series current/fuse rating speci
fi
ed on the PV module’s nameplate.
2. The OCPD must be sized to continuously carry the PV system’s maximum currents (I
MAX
)
.
Normally, OCPDs are only 80% continuous duty-rated; therefore, they must be multiplied by
125%
1
to handle PV circuit currents — which are considered continuous.
• To determine the minimum OCPD size required to protect the conductor in the PV circuit,
multiply I
MAX
for a given PV system circuit by 1.25 (I
MAX
for a given PV system circuit x 1.25 = I
CONT
).
Info:
The 125% multiplier for the OCPD (for continuous operation) is on top of the
125% multiplier to the module’s rated I
SC
value (for high irradiance conditions) when
sizing the PV source and PV output circuits for maximum circuit current.
Info:
If no temperature rating is marked on the terminals, then a 60°C limit is used
for circuits rated at 100 amps or less and for cables #14 to 1 AWG. For circuits rated
greater than 100 amps and for conductors greater than 1 AWG, a 75°C terminal
temperature limit is used.
3. When the OCPD is operated in environments where the temperature can reach 40°C (104°F)
or higher, use the manufacturer’s temperature correction factors to adjust the OCPD rating.
Info:
The DC circuit breakers (PN: BR-75 to BR-125) have a terminal temperature limit
of 75°C (for copper conductors) and a maximum operating temperature of 40°C.
4. Where the OCDP is rated at 800 amps or less, the following ratings are allowed:
a) You are allowed to use the next-higher standard OCPD above the ampacity of the conductors
being protected.
Note:
The PV module’s maximum series fuse rating is not allowed to be exceeded.
Standard ampere ratings are: 1, 3, 6, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90,
100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 601, 700, 800,
1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes.
b) After any correction factors for ambient temperature and number of conductors have been
applied,
the OCPD of copper conductors for the following ratings are not allowed to be
exceeded:
14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A.
Note 1: The NEC allows an exception to applying the 125% multiplier for continuous operation. It
states ”Circuits containing an assembly, together with its overcurrent device(s), that is listed for
continuous operation at 100 percent of its rating shall be permitted to be used at 100 percent of
its rating”.
