High Voltage Duct Bank Locating

[A-1Sparky]

We had the electrical distribution system upgraded on campus last year, and there are new concrete-encased duct banks buried all over the place. I was recently asked to locate/mark out the duct bank in a certain area so that a contractor could safely dig for a water main repair. I informed my boss that the locator we have cannot be used on high voltage lines (12,470v). I was wondering if anyone's had luck using a locator to induce a signal in the EGC to track duct banks. I haven't tried it yet, but would like to to see if it works. Are there special high voltage locators out there that can determine location and depth of energized high voltage conductors? It seems to me that a tracer wire or something similar should have been run with the HV conduits for locating/marking these lines out. Was this a bad EE oversight?

 

[ohmhead]

Well we do lots new construction work only and lots of underground work normally our duck banks are encased in red dye concrete and steel reinforced the top is normally 4 foot below finished grade and we run a bare 3/0 and each 50 foot attached is a ground rod the length of duck bank on top of the encased duck bank is the 3/0 bare copper ground attached to the grounding system which can also serve as a tracer wire if needed on your common low freq wire tracer we also run one foot below grade on top a metal danger high voltage tape which can also be found with your common tracers . We attach the wire tracer to the ground of the transformer or switchgear ground or frame and locate any duck bank . take care

 

[cmanningjr]

You can connect a subsite type locator to the concentric neutral to pick up a signal from that or some locators have a 60hz "Power Sweep" Mode.

 

[A-1Sparky]

Thanks guys. I think I'll try using the ground with the inductive coupling to see if I can pick up a signal.

 

[zbang]

Perhaps this may be a stupid question, but are there any as-built drawings that show where the duct banks ought to be? I realize that they're not a substitute for proper tracing/locating, but they should be a good starting point.

 

[A-1Sparky]

There are as-builts, but they only give general locations. I wouldn't rely on them in terms of giving someone a green light to excavate in certain areas.

 

[zee-cbs]

Thumper

Thumper

You can use a thumper to locate the wire in the ground and i do belieave Ditch Witch make it... You can rent them from sunbelt rental or any place like that...