I have kind of a weird one. There are these portable power stations used for connected welders and drills in an industrial outdoor environment. Each of them have a 480-208/120V step down transformer. My thought is to provide a ground rod in a well where they can set up the grounding electrode system for the separately derived 208V system. The 480V connection is done with a pigtail connection at a 480V disconnect and the intent is for them to bring the equipment ground along with this feed to this "substation". I know that what will inevitably happed is they will try to ground the 480V side to the driven ground rods. Fundamentally, it just seems like a ground fault would just use the earth as a path back to the service GES. I can't see anything wrong with it. What code issues would disallow this?
Unique Grounding Situation
- Thread starter strap89
- Start date
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Earth would make a terrible return path, besides, the EGC ( from the 480 volt side) should also be terminated to XO, along with the GEC. If you have building steel available, it would be a better grounding electrode than a ground rod, providing it is bonded to the main grounding electrode at the service.
I agree, but there aren't any other options. I might be able to get some rebar. We actually get pretty good grounds here with just a rod. What I'm concerned with is when they don't route the equipment ground with the 480V side from the service. I think the obvious answer is they need to run the equipment ground, that's obviously a code issue.
- Occupation
- Licensed Electrician
So there are just 480V wires going into a transformer and 208V wires coming out? No secondary disconnect? Even without a disconnect or breakers on the 208V power the fault path is from the 208V conductor to the XO on the transformer which should be bonded to the 480V equipment ground and back to the 480V disconnect. Earth does not enter into the discussion.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Grounded system, with switchboard feeding fused 480V disconnect. There is an equipment ground bus in the disconnect. Feeds one of those Larson portable substations. There is a breaker on the transformer secondary feeding the 208V side. Ideally they route EG from disconnect and land on X0, but they may just land it on a ground rod or effectively grounded steel without proper supervision. Agree equipment ground needs to be present to get back to service grounding electrode system. I think I understand, thanks everyone.
- Occupation
- Licensed Electrician
The XO is the destination for the EGC on the 208V power side. The 480V power should have an EGC run with it. Nobody should need to route an extra equipment ground from anywhere to anywhere.
My mistake, I meant the ground bus in the transformer. Where everything comes to one node.
Meant to say "Ideally they route EG from disconnect and land on ground bus, but they may just land a connection on the ground bus to a nearby ground rod or effectively grounded steel without proper supervision"
Last edited:
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Happens a lot, usually ends up as a “floating” neutral, as the grounding electrode is too high of a resistance to be effective.