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A topic that always requires a lot of attention when executing photovoltaic projects, and which often ends up going unnoticed by integrators, are the peculiarities of installing stringboxes.
One incorrect installation or outside of the standards required by the NBR 16,690 can cause several problems in energy generation, and also risks during system operation. In this article we will talk about some of the problems that can be caused due to poor stringbox installation.
Electric arc
O electric arc may be caused in the stringbox due to poor cable connection of the photovoltaic string or by the use of cables that have the compromised insulation.
This type of design flaw can lead to fires, as the creation of an electric arc occurs by offering a current path between the connections through the air, which creates a plasma channel with very high temperatures, intensely heating the components around it. .
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https://canalsolar.com.br/riscos-do-arco-eletrico-em-sistemas-fotovoltaicos-e-solucoes-de-seguranca/
Polarity inversion
Another problem that frequently occurs in installations is the inversion of polarities of photovoltaic cables. This occurs due to the inattention of integrators when making project connections.
This mistake is caused simply by inverting the poles of the connections, such as the input and output connections within a stringbox.
Despite being a problem that is theoretically easy to solve, just having to reconnect the connections, many integrators attribute the error to other components of the project due to the loss of time that occurred during the installation of the project.
Therefore, it is worth highlighting the importance of checking connections with a multimeter so that problems like this do not occur, or at least they can be discovered as soon as possible.
Stringbox exposed to the weather
A common error when installing a stringbox is undue exposure of the device to the weather, as there are different categories of stringboxes, with different degrees of protection in relation to the penetration of water and solid bodies.
This classification is called protection index (IP), which serves to define the equipment's ability to resist the ingress of water and solid bodies without affecting operational safety.
This issue often goes unnoticed when designing the project. Below is a table that illustrates the specifications of the protection indices.
According to the table and according to section 6.5.2.1 of the “NBR 16690 – Electrical installations of photovoltaic arrays – Project requirements” it is necessary that for external environments, the minimum IP grade for the enclosure is the IP55, as shown in Table 1, while for indoor environments it is IP 2X, with X being any index in the table referring to the 2nd digit.
Below we have an example of a stringbox that can be used both outdoors and indoors, as its protection index is IP 65.
Another important point in this topic is the sealing of the conduits and the device's input terminals, since incorrect sealing allows the entry of insects, snakes and rodents, compromising the safety of electrical circuits and invalidating its degree of IP protection. The following figure illustrates entry/exit points of a stringbox where there is no cabling passage and there is no protective seal.
Therefore, integrators must pay maximum attention when installing the project, especially because a simple error in connection or sealing of the stringboxes can lead to significant problems in energy generation and in the photovoltaic system.
One Response
I always give these recommendations. Often the chosen location for installing string boxes is in a utility room. And, I always recommend that the owner leave free spaces around, avoiding metallic and flammable parts due to the possibility of the action of the electric arc.