DSH 582 Supply protection characteristics during abnormal operation

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DSH 582 # V* C- K9 N9 G: K% z2 @8 W9 [

Supply protection characteristics during abnormal operation 0 D" X6 g" q' K, K# u9 P

H27.1.2 and H27.1.3 ' b. K# h- M5 j& j/ ]* w

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Question:
+ I2 q5 m$ Y$ C8 n$ ASub-clause H27.1.2 item d) prescribes that for abnormal operation the electrical supply shall have a fuse rating such that the result of the test is not influenced by the operation of the fuse. The evaluation of compliance given in sub-clause H27.1.3 item f) states that “A fuse in the supply, external to the control under test and as described in item d) of H27.1.2, shall not rupture unless an internal protective device also operates that is accessible only after the use of a tool”.
1) There is an apparently inconsistency between H27.1.2 and H27.1.3. On one hand the fuse shall have such characteristics (e.g. high rated current or rated short-circuit capacity) in order to not limit the effects of the test; in the other the operation of the fuse is considered as a test failure. Which criteria shall be followed during the selection of the fuse.
/ ~7 _8 k: S/ v9 b) I( i% y. v8 N2) The use of fuse as protective device in the fixed wiring is not a common practice in several countries. Is it accepted the use of other protective devices such as circuit breakers?
Decision:
It was agreed that the intent of Clauses H.27.1.2 and H.27.1.3 is that the size of the supply fuse be large enough so that it allows the Equipment Under Test (EUT) to see the most onerous conditions (note that the “fuse in the supply” referenced in Clause H.27.1.3.f is the same fuse described in Clause H.27.1.2.d). That is, the EUT should be tested without the supply fuse opening. In this way, faults introduced to the EUT stress the EUT and its inherent protection (if any) without the EUT becoming protected by opening of the supply fuse
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