We have several old schools in our district, which have panelboards distributed around the building. When the schools were built the conduit served as the equipment grounding conductor. I'm told the earth in this area of the country is rather corrosive and that the conduit may no longer be intact. I'm thinking that if I just test at the panelboards the interconnections would indicate an adequate ground, but I fear it would not be one originating at the service. Would it be adviseable to run a supplementary grounding conductor from the service, in a new conduit, to each panel? It would not be with the circuit conductors, but would guarantee an equipment grounding conductor at the panel. I appreceiate your thoughts on the matter.