有效接地系统的电力设备的接地电阻约为（）。

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='34163' and id < 2737640 and id<>'2737640' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='34163' and id > 2737640 and id<>'2737640' order by id asc limit 5