existing 3 wire services

[codeworks]

we ( and I'm sure you all) have a lot of old houses out there with existing 3 wire services, and a 3 wire feeder to a subpanel. in the subpanel (i know what the code is for new work. this is a how would you/ do you deal with it question) the neutral and grounds are tied together. a local electrician called and asked what the best way to deal with this ? can he run a ground from the main to the subpanel , routed through the attic or some otherway, to provide the seperated ground. should it be "in the raceway with the feeding conductors" ( misquote , i know) and impossible in and old romex or ragwire feeder, right. is it best to "leave it alone". it may have been ok years ago, it's not now, for new work, but this is an existing condition that gets written alot by area real estate inspectors, who are looking at old buildings, under new building codes. (weird way of doing something, but , i quess tha's how it's done here) any input is greatly appreciated. if i (personnely) was going to do anything, i run a new 4 wire feeder, but , in an old house, thats going to cost bunches and probably disrupt walls, ceilings etc. i told him i'd probaly leave it alone, but would try to get opinions. thanks::beatdhrsitty

 

[Span]

Existing sub-panel leave it along. Any newly installed circuits pull from main panel will be fine.

 

[Dennis]

You cannot run a ground wire separate from the cable that is there. If the existing panel was fed with metal conduit, as often is the case, then the conduit may be used as a grounding conductor. It was never legal to run a 3 wire to a sub panel. Imo, if a new service was added and the old panel only had 3 wires then it would make the new install non compliant. My guess is that the sub panel may have been a main panel at one time and never got upgraded properly