DHS-492中SELV电路接地的要求如何满足？

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Question:7

Is functional earthing for the secondarycircuit of SELV transformers permitted?

Decision:5

1) Earthing of secondary circuits of SELVtransformers (PELV circuits) is acceptable in general except when SELV is specifically required bythe standard for a specific circuit (for example in whirlpool baths), in which case earthing of the secondarycircuits are acceptable.

if:

a) the accessible parts of the secondarycircuits are separated from the protective earthingcircuit by at least protective impedance, or

b) the accessible parts of the secondarycircuits are either directly connected to the protectiveearthing circuit or are protected againstaccidental contact by insulation as specified for Class III appliances or constructions, in particular theinsulation shall be capable of withstanding a test voltage of 500 V AC for 1 min.7

Accessible parts directly connected to theprotective earthing circuit shall comply with therequirements for protective earthing (seesub-clause 27.5) or shall be separated from live; parts of the supply withinsulation as specified for Class II construction

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按照决议，SELV电路假如接地，也应该满足保护接地27.5的要求？

其他的都是用II类结构？III类部件？或保护阻抗与保护接地区分开吗？

那么PELV电路具体是怎么样的？

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