Thieves attempting to steal copper in North Roanoke County knocked out electricity to around 3,400 Appalachian Power customers for about three hours.  Apco spokesperson Todd Burns tells WFIR that around 2:00 a.m. Apco lost service to a transformer. Burns says someone broke into the Barren Heights substation and stole some of the equipment in an attempt to steal copper. That substation serves the northern part of Roanoke and Roanoke County.  Most of the service was restored by 5:00 a.m.