Part 5 of 8 – Cable Sizing and System Protection

i) Length of the longest cable run for the DC side(one way from the furthest panel to the inverter): Fill in the blank 1 of 7 m (closest metre)

ii) Number of modules in the string: Fill in the blank 2 of 7

(This is what you selected in the configuration section. Please select the MPPT with the largest number of modules)

iii) What is the voltage flowing through your PV string cable (Vcable): Fill in the blank 3 of 7 V

iv) Minimum required size of the DC string cable according to CCC considerations: Fill in the blank 4 of 7 mm²

v) State the selected STRING cable size. Fill in the blank 5 of 7 mm²

vi) What is the actual voltage drop based on the selected string cable size you have chosen? Fill in the blank 6 of 7 V

vii) What is the percent voltage drop based on the voltage at the maximum power point? Fill in the blank 7 of 7 %

i) How many strings will you parallel to a single MPPT in your design (select the MPPT with the greatest number of strings)?  Fill in the blank 1 of 2

ii) Minimum ARRAY cable size:  Fill in the blank 2 of 2 mm²

Determine whether the following PV system devices are needed and size them. 

Is string overcurrent protection required for this installation? (Y/N) Fill in the blank 1 of 3

If string OCPD is required what would be the current trip limits of the overcurrent protection?

Fill in the blank 2 of 3 < String overcurrent protection fuse ≤: Fill in the blank 3 of 3

Rooftop DC Isolator: Fill in the blank 1 of 2 A

DC Isolator next to inverter:  Fill in the blank 2 of 2 A

ii) What is the voltage flowing through your AC cable cable (Vcable): Fill in the blank 1 of 4 V

Assume a 1% maximum permissible voltage rise from the inverter to MSB (specified by the NSW service and installation rules) and a conservative cable run of 3m.

iii)  What is the maximum permissible voltage rise on the AC cable? Fill in the blank 2 of 4 V

iv) What is the maximum single phase millivolt rise per amp-metre route length V_C of the AC cable?  Fill in the blank 3 of 4 mV/Am

v) What is the minimum area of the AC cable based on the minimum Vc calculated above assuming a multicore circular copper conductor was used? Fill in the blank 4 of 4 mm²

This response will be reviewed and graded after submission.

i) What is the minimum required CCC of your AC cable:  Fill in the blank 1 of 2 A 

ii) Minimum required size of the AC cable based only on CCC considerations and standards. For CCC use the nominal current. Do not oversize this answer.  Fill in the blank 2 of 2 mm²

This response will be reviewed and graded after submission.

i)  Based on the above voltage rise and CCC sizing constraints, as well as the standards and overcurrent protection state the cable size you will use in your design for the AC cable.  Fill in the blank 1 of 3 mm²

ii) What is the actual voltage rise calculated based on the selected cable size you have chosen? (2 decimal places) Fill in the blank 2 of 3 V

iii) What is the percent voltage rise? (2 decimal places) Fill in the blank 3 of 3 %

This response will be reviewed and graded after submission.

ii) State the rating of the in-built battery protection device. Fill in the blank 1 of 4 A

iii) State the battery maximum continuous output current: Fill in the blank 2 of 4 A

iv) State the battery nominal voltage, this will be the minimum rating of the battery protection device. Fill in the blank 3 of 4 V

v) State the fault current rating of the battery protection device. Fill in the blank 4 of 4 kA

i) Length of the cable run: Fill in the blank 1 of 3 m

ii) Minimum required size of the cable according to CCC and overcurrent protection considerations: Fill in the blank 2 of 3 mm² 

iii) Exact minimum required size of the cable due to fault current (answer to two decimal places): Fill in the blank 3 of 3 mm²

Assume the duration of the short circuit is t = 0.1s before the circuit breaker trips (a significant buffer). Refer to fault current sizing in the balance of system online book. Please provide the exact value to 2 decimal places, do NOT round up to next largest cable size. 

This response will be reviewed and graded after submission.

iv) State the SELECTED cable size:  Fill in the blank 1 of 3 mm²

v) Calculate the voltage drop for the selected cable size:  Fill in the blank 2 of 3 V

vi) Calculate the percent voltage drop: Fill in the blank 3 of 3 %

This response will be reviewed and graded after submission.

State a suitable earth conductor cable size: Fill in the blank 1 of 1

i) Calculate the arc flash energy for the battery: Fill in the blank 1 of 7 cal/cm²

Hint: For the arc flash boundary distance use the “nominal” working distance. Refer to Preliminary System Design Chapter -> site-specific Hazards and Risks -> Energy Hazards.

ii) Based on the arc flash energy (cal/cm²) what PPE level is required? Fill in the blank 2 of 7

This response will be reviewed and graded after submission.