here is the problom. in an old building that we work in there is a 200a sub panel. It is being feed w/ 3 hot conductors (120/208) there is no grounded or grounding conductors w/ the feed. Coming off the sub panal to a water pipe is a number 10awg, it is terminated under a ground clamp. this number 10 is being used as both the gounded and the grounding conductor. this sub panel feeds a/c units as well as sensitive sound equipment(which periodically hums and buzzes). HOw do i explain to the customer the proploms here and what exactly are my probloms?
no grounded conductor
- Thread starter nedberg
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: no grounded conductor
There is really only one problem. The pipe and all other metal objects throughout the building will be carrying current. The amount of current flowing along the pipes at any given moment will depend on what loads are turned on, and on how well the loads are balanced among the three phases.
BUT HEAR THIS: Anybody who touches any metal object will be receiving a shock. No if, ands, or buts. It will happen, every time. It might be a small current, but it will not be "zero amps." You might get lucky most of the time, and years might go by before the amount of the shock is high enough to be felt. Decades might even go by before the shock is fatal to some unlucky person. But every time anyone touches a pipe, some amount of current will be flowing through their heart.
There is really only one problem. The pipe and all other metal objects throughout the building will be carrying current. The amount of current flowing along the pipes at any given moment will depend on what loads are turned on, and on how well the loads are balanced among the three phases.
BUT HEAR THIS: Anybody who touches any metal object will be receiving a shock. No if, ands, or buts. It will happen, every time. It might be a small current, but it will not be "zero amps." You might get lucky most of the time, and years might go by before the amount of the shock is high enough to be felt. Decades might even go by before the shock is fatal to some unlucky person. But every time anyone touches a pipe, some amount of current will be flowing through their heart.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Re: no grounded conductor
Ned, short of re-pulling the feeders, the best compromise might be to use one of the conductors as a neutral, and change it to single-phase, as long as you don't need the total capacity.
You could possibly derive a neutral from a grounding transformer. In any case, your existing installation is definitely not suitable for phase-to-neutral loads.
Ned, short of re-pulling the feeders, the best compromise might be to use one of the conductors as a neutral, and change it to single-phase, as long as you don't need the total capacity.
You could possibly derive a neutral from a grounding transformer. In any case, your existing installation is definitely not suitable for phase-to-neutral loads.
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