### What is Array Junction Box (AJB) in Solar PV Modules?

Posted January 30, 2021 by ACCUPANELS

Array junction box, AJB, is used to connect photovoltaic wires in parallel. The combined DC power is supplied to the photovoltaic inverter.

Array junction B, X, AJB, is used to connect photovoltaic wires in parallel. The combined DC power is supplied to the photovoltaic inverter. These include photovoltaic string protection, overvoltage protection and a DC output switch isolator. AJB is often customized for a variety of configurations, supporting the wire amount of solar array junction box modules used in the layout. AJB has a subsequent component
1. Connection
2. PV fuse
3. Surge protection device
4. DC disconnector / isolator
5. Cable glands / connectors
1. Attachment: Combiner bolts are usually made of thermoset (eg GRP or polyester) or thermoplastic (polycarbonate) material, and are available with IP65 protection. Holdings are available in a variety of sizes, supporting the amount of input strings. The essential features of the defence also contribute to changes in the enclosure required. Must be fire-resistant with external self-extinguishing property. It should be UV resistant and halogen free and will also have honest mechanical impact resistance, which will be higher than IK08.
2. PV Fuse: PV fuse or photovoltaic fuse, in the range of 1A to 32A, is readily available in the market. PV fuses are used for over-protection.
PV Fuse Selection: -
P.S. NSR per string = P.V. Serial NPL of modules. = Number of PV strings in a parallel PV subarray
ECC = short-circuit current of 1 module on standard test condition (STC), circuit voltage of 1 pv module in STC
Volt and Amps Testing Calculations: Fuse Voltage Rating? 1.20 x Voc x Nsr • Fuse amp rating? 1.56 x E.S.C.
For example: -
Let's assume
The number of PV modules in strings is as follows: - 20 nos. (NSR) Parallel PV Sub Array = 16 (NPL) ISC = 8.6 MP Walk = 37.2 V Number of PV strings in parallel
Fuse amp rating? 1.56 * 8.6A? 13.41a
According to the quality fuses available in the market, 15A fuses should be used here.
Fuse voltage rating? 1.2 * 37.2 * 20V? 892.8 V
According to the quality fuses available in the market, 1000V DC fuses should be lacking to meet this requirement.

3. Surge Protection Device: The SPD or Surge Protection Device operates within the AJB / SCB. That feature protects electrical and appliances from surges and voltage spikes. SPD converts surplus voltage and current transient or from surge to ground through an airing system.
Voltage protection level Selection of SPD compatible with VP: Each SPD has a maximum voltage protection level specified for operation and diverts ground surplus energy. The protection voltage level of the SPD is usually kept at 20% but the dielectric strength and voltage of the PV system are higher than the operating voltage.
4. DC Disconnector / Isolator: The DC disconnector / isolator can be a switch tap between the PV string and the inverter to disconnect the facility supply. To disconnect the DC side of the system when necessary, it is recommended to place the inverter first.
Selection criteria for PV isolator
Preliminary conditions for specifying PV disconnectors: N.S.R. = P.V. PV per string. The number of module serials is NPL. = P.V. Number of strings parallel pv. Sub Array E.Sc. = 1 pv. Module's short-circuit current Walk on standard condition conditions = 1 PV module in circuit voltage STC
• Breaker voltage rating? 1.20 x Voc x Nsr Volt • PV output current rating? 1.56 x ISC x NPL amp
For example: - Let's assume
The number of PV modules in strings is = 20 nos. (NSR) Parallel PV Sub Array = 16 (NPL) ISC = 8.6 MP Walk = 37.2 V Number of PV strings in parallel
Circuit breaker voltage? 1.20 * 37.2 * 20 volts? 892.8 volts
According to the standard circuit breakers available in the market, it should be a 1000V DC disconnector.
Current rating of isolator? 1.56 x ISC x NPL amp? 1.56 * 8.6 * 16 amp? 214.65 amp
According to the standard circuit breakers available in the market, it should be a 225-amp isolator.
5. Cable Glands / Connectors: Each system is of the outdoor type, so the AGB component should be IP65 protected and UV protected. AJB has two options with cable access.
1. Cable gland
2. MC4 connector.
Arrangements are needed to seal the cable glands once the connection to systems outside the AJB is complete. MC4 connectors have a male-female socket for connection, and therefore do not require a seal to take care of IP protection. MC4 connectors have a current capacity limit. At a low rating, 30A is the best choice for string level MC4. Only in the case of AJB, the output rating of the 30Amp cable gland is quite appropriate.
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