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©
2017 Sensata Technologies
Installation
Check the Terminal Temperature Rating
- Whether the conductor is sized to continuously
carry the maximum current or sized with conditions-of-use factors applied, the temperature
rating associated with the ampacity of a conductor must be coordinated so as not to exceed the
lowest temperature rating of any terminal, device, or conductor of the circuit.
Regardless of the insulation temperature rating of the selected conductor, it must continue to
provide the minimum ampacity required when rated at the temperature of the connected terminals.
It is common in a PV system to use a conductor that is rated at 90°C while connecting to a device
(e.g., fuse holder, circuit-breaker, etc.) that has terminals rated for only 75°C. When a conductor is
connected to a device with terminals rated at a lower temperature than the temperature rating of
the conductor’s insulation, the conductor’s ampacity is now based on the lower temperature rating.
This ensures a minimum amount of copper is provided to pull enough heat away from the terminal
to prevent overheating problems. Check the temperature ratings of all the terminals to which the
conductor is connected and ensure the ampacity associated with the lower terminal temperature
rating is equal to or greater than the minimum ampacity required.
Determine the minimum conductor size by
fi
nding the lowest terminal temperature rating of all
the devices to which the conductor is connected. Use Table 2-2 to select the temperature column
that is based on the terminal with the lowest temperature rating. Select the conductor size in the
proper terminal temperature rating column that has an ampacity rating equal to or greater than
the calculated continuous current (I
CONT
).
For example, with a conductor connected to a 60°C termination on one end and a 75°C termination
on the other, the conductor’s ampacity must not exceed the rating listed in the 60°C column—
because the lowest connection point is a 60°C rating.
Info:
Even though
conductors with a 90°C or 105°C insulation rating can’t be applied at
their higher ampacity ratings because the terminal temperature is lower, they do have
an advantage. T
heir
higher ampacity rating can be used when applying
derating factors
due to ambient conditions, or when exceeding more than 3 current carrying conductors
in conduit.
Info:
Remember to consider both ends of the conductor when derating. For example, if
one end of the conductor is connected to a circuit breaker with a 75°C terminal, and the
other end is connected to a receptacle with a 60°C terminal. The conductor must have
an insulation rating no less than the highest temperature rated terminal (75°C circuit
breaker), and the ampacity of the conductor must be sized no smaller than the lowest
temperature rated terminal (60°C receptacle).
Note:
The ampacity sizing is to ensure
no additional heat is created at the receptacle terminals by using wire that is too small.
Info:
The terminal temperature limits marked on the equipment must be used. If no
temperatures are marked, then a 60°C limit is used for circuits rated at 100 amps or less
or 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.
Check the Voltage Drop
- Excessive system voltage drops due to wire size, wire connections,
and fuse/circuit breakers can limit the charge current and affect battery charging performance. If
there is a long wire run between the PV array and the PT-100 controller, or between the PT-100
and the battery bank, larger wire should be used to reduce voltage drop and improve performance.
On the PV array to controller side, a derating multiplier is applied to take into account for low
voltage issues when calculating the module’s lower V
MP
Level (see Section 2.5.4).
From the controller to the battery, voltage drop will lower the charge voltage at the battery. Table
2-8 provides increased wires sizes when the distance from the controller to the battery is longer
than 5 feet.
The terminal block inside the PT controller is rated for a maximum 1 AWG. Wire sizes larger than
1 AWG (42.4mm²) that are used to reduce voltage drop cannot be installed directly into the
terminal block. To use a larger size wire, use a splicer block or a split-bolt kerney external to the
controller to allow the smaller wire size from the controller terminal block to be connected to the
larger wire that is used and routed to the batteries.
