Diversity Factor Bs 7671.pdf
Jaiker Edouard
Circuit-breakers serving continuous loads from a consumer unit may require derating when grouped together. This is due to the thermal interaction between the circuit-breakers when serving continuous loads. In a similar manner to derating cables installed in a group, designers should apply derating factors to grouped circuit-breakers when continuously loaded.
It is the consumer unit manufacturers who will specify the derating factor, which is referred to as the rated diversity factor (RDF). The rated diversity factor is generally applied to thermal-magnetic circuit-breakers that are continuously loaded and that are placed adjacent to other circuit-breakers that are also continuously loaded. The rated diversity factor is applied to ensure that the heat emitted from the circuit-breaker stays within a tolerable value when under continuous load.
As the demand increases for electrical equipment that has a sustained load, such as electric vehicle charging points and heat pumps, it is crucial for designers to recognize the thermal impact these circuits can have. It is important to determine and apply the appropriate rated diversity factor to circuit-breakers in order to accommodate these loads effectively.
The rated diversity factor is assigned by the manufacturer of the consumer unit, which is then used by the designer when determining the size of the protective device. The manufacturer can assign the rated diversity factor to a consumer unit as a whole or may choose to specify it in relation to a group of circuits within the consumer unit.
Rated diversity factors are generally only applicable to continuously and simultaneously loaded circuits. A continuous load is not defined in the BS EN 61439 series, although examples of what may be interpreted as continuous loads and what may be interpreted as intermittent loads are given below.
A calculation can be carried out to determine the root mean square (RMS) (average) current for an intermittent circuit, which can then be used to determine the rated diversity factor, although this is out of the scope of this article. For further reading see Annex E of BS EN 61439-1:2011.
The relevant design current shall not exceed the rated current of an assembly (InA) or rated current of a circuit (Inc) of the associated assembly, having taken any applicable diversity/loading factors into account.
The rated diversity factor enables manufacturers to design consumer units that account for the practical loading conditions of circuits, ensuring efficient and safe operation while maintaining cost-effectiveness.
Manufacturers of consumer units may apply a rated diversity factor derived from testing or may use the table below from BS EN 61439-3:2012, which states the assumed loading factor and is based on the number of outgoing circuits of the consumer unit. The assumed loading factor is the maximum permitted rated diversity factor to be applied by the user.
It is the responsibility of the manufacturer of the consumer unit to agree with the user (designer) on the required rated diversity factor of their equipment. Installation instructions may take the place of an agreement.
A selection of consumer unit installation instructions were downloaded from various websites. A summary of the assigned rated diversity factors is reported below. Where text accompanied the ratings, it has been included.
Adjacent thermal-magnetic MCBs should not be continuously loaded at their nominal rated currents when mounted in enclosures. We recommend a 60% derating factor is applied to the MCBs nominal rated current where it is intended to load the MCBs continuously.
Adjacent thermal magnetic MCBs/RCBOs should not be continuously loaded at their nominal rated currents when mounted in enclosures. We recommend a diversity factor (RDF) is applied to the MCB/RCBO nominal rated current where it is intended to load circuits continuously and simultaneously.
Adjacent Thermal Magnetic MCBs should not be continuously loaded or approach their nominal rated currents when mounted in enclosures. It is recommended that a 60% diversity factor be applied to the MCBs nominal rated current where it is intended to load the MCB continuously.
Adjacent thermal-magnetic MCBs should not be continuously loaded or approaching their nominal rated current when mounted in the enclosure. Therefore, we recommended 60% diversity factor is applied to the MCBs nominal rated current where it is intended to load the MCBs continuously.
Adjacent thermal-magnetic MCBs should not be continuously loaded or approaching their nominal rated currents when mounted in enclosures. It is good engineering practice to apply generous derating factors or make provision for adequate free air between devices.
In these situations, and in common with other manufacturers, we recommend a 60% diversity factor is applied to the MCB nominal rated current where it is intended to load the MCBs continuously (in excess of 1 hour).
The rated diversity factor is to be assigned to thermal-magnetic devices and not devices such as switch disconnectors and residual current circuit-breakers (RCCBs). The principal workings of the thermal part of a thermal-magnetic device is that the current from the load heats a bi-metallic strip that releases and opens the circuit in the event of an overload.
To avoid the need to apply the rated diversity factor to circuit-breakers, certain measures can be taken to enhance cooling. One approach is to strategically arrange the circuit-breakers to facilitate cooling. This can be accomplished by introducing blanks between circuit-breakers where they are continuously loaded.
By carefully planning the arrangement of circuits within the consumer unit during the design phase and breaking the conventional practice of grouping circuit-breakers based on their rating, it is possible to improve cooling efficiency. This strategic placement of circuits may eliminate the need for a rated diversity factor.
*Circuits that experience continuous but light loads tend to have a low rated diversity factor. For instance, consider a lighting circuit in a domestic premises that carries a load of 1 A (equivalent to 230 W) and is protected by a 6 A circuit-breaker, resulting in a rated diversity factor of 0.17. Since this circuit is lightly loaded, it is possible to position the circuit-breaker serving this particular circuit adjacent to a circuit with a higher continuous load, eliminating the necessity for applying a rated diversity factor to the larger loaded circuit.
As the nature of loads connected to consumer units in domestic electrical systems are changing, the significance of the rated diversity factor is becoming more evident for designers. Traditional domestic loads were often intermittent or lightly loaded, however, designers now face the challenge of incorporating loads, such as electric vehicle charging points and heat pumps, into their designs.
In either case, designers must consider the rated diversity factor and be mindful of the thermal interaction between circuit-breakers. This consideration is also important when adding a new circuit to an existing consumer unit.
For the past few decades, enormous efforts have been made to understand the neurobiology of schizophrenia, as its genetics and epigenetic factors can shed light on the pathology of the disease [5,6,7]. Only 4% of known genetic variances associated with schizophrenia has been mapped to distinct loci that has failed to highlight the potent genetic risk factors in the pathogenesis of SCZ. The identification of rare-loss-of-function in histone H3 methyltransferase SETD1A [8], missense variants in γ-aminobutyric acid (GABA) transporter protein type 1 (GAT1) encoding gene SLC6A1 [9] variations in Disrupted-in-Schizophrenia 1 (DISC1) gene [10,11], and transcriptional changes in 157 genes [12] also implicate epigenetic and some other mechanisms in this disease.
Symptoms, factors involved, and current therapeutics in schizophrenia. A combination of genetics, epigenetics, environmental factors, including gut microbiota, resulting in the prognosis of the illness. Schizophrenia involves variable symptoms having limited therapeutic options. On the left side of the figure, solid arrows indicate the potential etiology (genetics, epigenetics and gut microbiota dysbiosis) of schizophrenia and the dotted arrows are representing bi-directional relation of gut microbiota in health and disease.
(ii) A second important conclusion that has been drawn from the research is that these genetic risks are also pleiotropic, meaning that one gene may influence multiple phenotypic traits. Pleiotropy has been observed for common variants at the single risk allele level and whole-body level. Studies have shown the distribution of some common variant (risk alleles) overlaps between major mental disorders such as depression and schizophrenia within attention deficit hyperactivity disorder (ADHD) and depression, and also within autism and schizophrenia [38]. Other studies have indicated a connection of some common risk variants between schizophrenia and ADHD [38,39,40]. Pleiotropy is observed in a few rare variants as well. Copy number variants (CNVs), which hold a potential threat to schizophrenia are also found to affect epilepsy and other childhood neurodevelopmental disorders, including autism, ADHD, and intellectual disability (mental retardation) [32,41,42,43]. All of these make it difficult to differentiate the disorder based on risk alleles. Therefore, it is proposed that alleles with non-specific risk factors are easier to diagnose [44,45].
Several studies have suggested that the vagus nerve drives communication between gut microbes and the central nervous system through the immune system or neuroactive compounds produced by gut microbes. The most common neuroactive compounds produced by gut microbes are neurotransmitters such as gamma-aminobutyric acid (GABA), dopamine, serotonin, and norepinephrine [140,141,142]. Since the development of a healthy microbiome is essential for brain plasticity through the expression of N-methyl-D-aspartate (NMDA) and brain-derived neurotrophic factor (BDNF)/glial-cell derived neurotrophic factor (GDNF) receptors, it has been found that alteration in gut microbiota results in hypoactivity of these receptors, which have been studied in the schizophrenia patients [143,144].
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