British Rail Class 315
They operate on the 25 kV overhead line and work inner-suburban Transport for London-run services on the Shenfield Metro for TfL Rail , on weekdays only . 
<triplet> Transport for London <subj> TfL Rail <obj> owner of <triplet> Shenfield Metro <subj> overhead line <obj> type of electrification <triplet> TfL Rail <subj> overhead line <obj> type of electrification <subj> suburban <obj> instance of <subj> Transport for London <obj> owned by