how to calculate circuit breakers in solar pv system
i'm trying to make a small pv kit. I'm blocked on circuit breakers and fuses. Where to use, what to use. And also about sizing..
could any one help.
thanks
Comments
Thavin, can you tell me more about your kit? Module type and string sizes, Inverter type (string or micro), whether you require there to be a separate AC disconnect between the inverter and the point of interconnection and the service panel's bus bar rating & main breaker size.
I will give you an example of the OCPD's between the major components below to help you get the basics:
Let's say we're using a SolarWorld 315 Watt module with an ISC rationg of 9.12. To calculate the fuse size required between the string and the inverter's DC input you take 9.12 x 1.56 = 14.7 and round up to the next trade size of 15A. Now, these are often included with some inverters but it's a good idea to check. So manufactures do not supply these with their inverters.
Next, let's assume this is a 7.5kW inverter with an AC output of 35.5A max. Take 35.5A x 1.25 = 44.4A, round up to the next standard trade size which will be 50A. Now... if the utility requires a disconnect between the inverter and main panel board this could be a 60A fused or non-fused disconnect dependig on their requirements. From there you'd land your inverter's output into a 50A breaker and your done. The main purpose of the fuses and breakers are to protect the wiring. So you always want to be sure your sizing your wire to handle the output of each circuit in the system.
Thank you for your comment. We can only recommend reviewing the NEC code for this particular request, NEC 690.9 may be particularly relevant. If you need design support we would be happy to help but please complete this engineering form request form. Thanks again.
Hello
I have 3x 150 watts mono crystal panels
3x100AH 12v battery
1x 50 amps controller PWM
Inverter 12v 2000 watts
(Connection is in parallel)
I want to add the breakers in between the connections.
I Have 4 Rich Solar panels 100W 5.41A Not a Big system by far , I have a Mars Charge Controller 1.200W Wind Solar 1,000W so-post to be auto censoring inverter 3KW 24v Hybrid inverter , my battery bank is Lithium Phosphate 280Ah in series 3.2v x 7 , I need to fuse everything panels to inverter , batteries to inverter , Inverter to breaker box North America 100A / 120v Grid any help welcoming, websites , stores etc.
To calculate the overcurrent protection for the DC conductors in the photovoltaic (PV) system shown in the image, we need to follow the guidelines provided by the National Electrical Code (NEC). Here is a step-by-step process you can follow - using your picture as a reference - we are estimating the values based on your image - we do not guarantee that we are viewing your image correctly, so we do not offer these calculations for actual construction:
### Step 1: Collect the Necessary Data
From the image, we have the following information:
- **Panel Voltage (Voc):** 39.3 V
- **Panel Wattage:** 300 W
- **Panel Short Circuit Current (Isc):** 9.65 A
- **Max Series Fuse Rating:** 30 A
- **Battery Bank Voltage:** 24 V
- **Panels in Series:** 2
- **Panels in Parallel:** 2
### Step 2: Calculate the Maximum System Voltage
For the panels in series, the maximum system voltage (Vsys) is:
\[ V_{sys} = Voc \times \text{Panels in Series} \]
\[ V_{sys} = 39.3 \times 2 = 78.6 \, V \]
### Step 3: Calculate the Total Current
For the panels in parallel, the total short-circuit current (Isc_total) is:
\[ I_{sc_{total}} = Isc \times \text{Panels in Parallel} \]
\[ I_{sc_{total}} = 9.65 \times 2 = 19.3 \, A \]
### Step 4: Apply NEC 690.8(A)(1) Overcurrent Protection
According to NEC 690.8(A)(1), the overcurrent protection device (OCPD) rating must be at least 125% of the short-circuit current:
\[ I_{OCPD} = Isc_{total} \times 1.25 \]
\[ I_{OCPD} = 19.3 \times 1.25 = 24.125 \, A \]
### Step 5: Select the Overcurrent Protection Device
The next standard size for OCPD above 24.125 A is 25 A. Therefore, a 25 A fuse or breaker would be appropriate.
### Step 6: Confirm with Max Series Fuse Rating
Ensure the selected OCPD does not exceed the maximum series fuse rating of the panels (30 A). In this case, 25 A is within the limit.
### Summary
For your PV system picture's configuration, the appropriate overcurrent protection device for the DC conductors should be rated at **25 A**. This ensures compliance with NEC guidelines while providing adequate protection for the system components.
If you have any further questions or need additional assistance with other aspects of your PV system, feel free to ask!
Comments
Thavin, can you tell me more about your kit? Module type and string sizes, Inverter type (string or micro), whether you require there to be a separate AC disconnect between the inverter and the point of interconnection and the service panel's bus bar rating & main breaker size.
I will give you an example of the OCPD's between the major components below to help you get the basics:
Let's say we're using a SolarWorld 315 Watt module with an ISC rationg of 9.12. To calculate the fuse size required between the string and the inverter's DC input you take 9.12 x 1.56 = 14.7 and round up to the next trade size of 15A. Now, these are often included with some inverters but it's a good idea to check. So manufactures do not supply these with their inverters.
Next, let's assume this is a 7.5kW inverter with an AC output of 35.5A max. Take 35.5A x 1.25 = 44.4A, round up to the next standard trade size which will be 50A. Now... if the utility requires a disconnect between the inverter and main panel board this could be a 60A fused or non-fused disconnect dependig on their requirements. From there you'd land your inverter's output into a 50A breaker and your done. The main purpose of the fuses and breakers are to protect the wiring. So you always want to be sure your sizing your wire to handle the output of each circuit in the system.
Hi, can u help me out in selecting dc circuit breaker between solar and inverter, Battery bank and inverter?
Thank you for your comment. We can only recommend reviewing the NEC code for this particular request, NEC 690.9 may be particularly relevant. If you need design support we would be happy to help but please complete this engineering form request form. Thanks again.
Hello
I have 3x 150 watts mono crystal panels
3x100AH 12v battery
1x 50 amps controller PWM
Inverter 12v 2000 watts
(Connection is in parallel)
I want to add the breakers in between the connections.
Can anyone give me the correct size please.
I Have 4 Rich Solar panels 100W 5.41A Not a Big system by far , I have a Mars Charge Controller 1.200W Wind Solar 1,000W so-post to be auto censoring inverter 3KW 24v Hybrid inverter , my battery bank is Lithium Phosphate 280Ah in series 3.2v x 7 , I need to fuse everything panels to inverter , batteries to inverter , Inverter to breaker box North America 100A / 120v Grid any help welcoming, websites , stores etc.
Hi i would like to know what size dc breaker to put on PLZ
Thank you for your comment.
To calculate the overcurrent protection for the DC conductors in the photovoltaic (PV) system shown in the image, we need to follow the guidelines provided by the National Electrical Code (NEC). Here is a step-by-step process you can follow - using your picture as a reference - we are estimating the values based on your image - we do not guarantee that we are viewing your image correctly, so we do not offer these calculations for actual construction:
### Step 1: Collect the Necessary Data
From the image, we have the following information:
- **Panel Voltage (Voc):** 39.3 V
- **Panel Wattage:** 300 W
- **Panel Short Circuit Current (Isc):** 9.65 A
- **Max Series Fuse Rating:** 30 A
- **Battery Bank Voltage:** 24 V
- **Panels in Series:** 2
- **Panels in Parallel:** 2
### Step 2: Calculate the Maximum System Voltage
For the panels in series, the maximum system voltage (Vsys) is:
\[ V_{sys} = Voc \times \text{Panels in Series} \]
\[ V_{sys} = 39.3 \times 2 = 78.6 \, V \]
### Step 3: Calculate the Total Current
For the panels in parallel, the total short-circuit current (Isc_total) is:
\[ I_{sc_{total}} = Isc \times \text{Panels in Parallel} \]
\[ I_{sc_{total}} = 9.65 \times 2 = 19.3 \, A \]
### Step 4: Apply NEC 690.8(A)(1) Overcurrent Protection
According to NEC 690.8(A)(1), the overcurrent protection device (OCPD) rating must be at least 125% of the short-circuit current:
\[ I_{OCPD} = Isc_{total} \times 1.25 \]
\[ I_{OCPD} = 19.3 \times 1.25 = 24.125 \, A \]
### Step 5: Select the Overcurrent Protection Device
The next standard size for OCPD above 24.125 A is 25 A. Therefore, a 25 A fuse or breaker would be appropriate.
### Step 6: Confirm with Max Series Fuse Rating
Ensure the selected OCPD does not exceed the maximum series fuse rating of the panels (30 A). In this case, 25 A is within the limit.
### Summary
For your PV system picture's configuration, the appropriate overcurrent protection device for the DC conductors should be rated at **25 A**. This ensures compliance with NEC guidelines while providing adequate protection for the system components.
If you have any further questions or need additional assistance with other aspects of your PV system, feel free to ask!