UL 60079-25-2015 pdf download

UL 60079-25-2015 pdf download.Explosive Atmospheres – Part 25: Intrinsically Safe Electrical Systems.
The data needed for the Interconnection can be obtained from the Information given In the documentation cortificato. It there is no data in tho pldor cprtif,cptpc, the values should be obtained from the manufacturer of the apparatus.
In designing intrinsically safe circuits, an attempt should be made always to keep the interconnections and number of combined sub-assemblies low. This objective cannot always be achieved in practice, because it is also necessary to consider fault conditions. This means that some apparatus which are not acting in normal operation as sources have to be regarded as sources in the case of failures.
The passive Inputs of devices, for example, measurement transducers, plotters etc.. can, from the safely point of view, also act as active sources. Therefore the maximum values indicated In the documentation cortificatoc should be referred to. As a result, the operational characteristics of a circuit may deviate substantially from the safety characteristic. The values given in the documentation certificates for open circuit voltage and short-circuit current 10 for the circuit concerned are stated only for transient conditions in some cases. On the other hand, the power value applies for steady-state conditions which have to be considered for the temperature rise of connected components.
C.3 Interconnection of intrinsically safe circuits with more than one source
C.3.1 Determination of a resultant output characteristic
It Is assumed that the output characteristics of the circuits making up the combination, and which are to be regarded as sources, are known (see Clause C.2). It is then necessary to ascertain from the type of interconnection whether, in normal operation and under fault conditions, it is necessary to consider the voltage sum, the current sum, or both current and voltage sums.
If the combined sources are connected In series and are not bonded, for example, to earth (Figure C.2a). then, irrespective of the polarity of the sources, voltage addition only is possible. The resultant output characteristic is conveniently found by graphical addition. Thus for each current value, the voltages of the individual sources are added. The dotted-line curve in Figure C.2 shows the resultant characteristics in the ditferent cases.
In the series circuit shown in Figure C.2b, where there is a common connection of both voltage sources at the load, current addition can be excluded only if the polarity of both sources in the direction shown here is fixed with respect to safety (for example, for certain safety barriers). With sources which can change the polarity operationally or under fault conditions, both voltage and current addition should be considered (see Figure C.2e).
In the parallel arrangement of Figure C.2c, current addition is only possible if. with bipolar sources, two poles are connected in each case. Voltage addition is not possible in this case and the resultant characteristic is generated by graphical addition of individual current values.
If only one pole of each source is connected to that of the other (Figure C.2d), then voltage addition can be excluded only it the polarity of the sources as shown here is fixed regarding all circumstances (for example. with safety barriers). Otherwise, both voltage and current addition should be considered (see Figure C.2e).
If several circuits are connected to a circuitry In which arbitrary Interconnections should be assumed (Figure C.2e), then, depending on the fault conditions considered, a parallel or series connection may be set up. so that both current and voltage addition, should be considered. Because both cases are not possible at the same time, the resultant characteristic for current addition and that for voltage addition should be constructed separately. This procedure Is necessary also In all cases of doubt for the circuits In Figures C.2b and C.2d as well as with circuits with more than two conductors. The result so obtained will always be on the safe side.