remote 240V AC site has no ground wire

[TheRocketScientist]

Test wall outside the building was wired by others before me. From the building come 5 wires- 3 are L1 L2 L3 of 3-phase 240V AC, a 4th wire serves as a Neutral for the 240V AC which gives 125V AC off 2 legs and 210V AC off the 3rd "crazy" leg. These come from a known breaker panel in the building.

The other 2 feed wires appear to be unused and show no voltage.

I am using the 240V AC 3-phase to run a 1/2 HP test motor mounted to a wood wall some 20 ft from the building. The 125V leg runs the timer and relay.

The lack of earth ground wire worried me, so I ran a green wire from DUT [Device Under Test] housing to the feed conduit, which enters the earth for feed from the building- just in case something bad happens to the motor. At least the errant voltage would have a path to earth other than thru me.

Does this seem adequate? Kosher? Exceedingly inadequate?

the goal is to prevent death/ injury in the unlikely event that something goes horribly awry with the motor or its wiring.

 

[dpc]

Assuming this is rigid steel or aluminum conduit? You are probably OK provided the other end of the conduit is properly bonded to ground.

The neutral should also be bonded to ground at the service panel.

 

[itsmoked]

You can add a ground stake to the ground for a local, less kludgey ground.

You can get them at most hardware stores. Often they are a steel rod about 8 feet long with a pointed end and are copper plated. They're not expensive. While there pick up an appropriate ground rod clamp that will make for easy connection to the rod.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TheRocketScientist]

Yes, the conduit that enters the earth is steel. It runs from a plastic enclosure on the wood wall down into the ground to an undetermined depth. Here in Michigan [USA], the soil is always quite moist, so it should have great earth contact. Interestingly, the conduit that arises from the ground at the building is plastic- so at some point underground, it must have a steel to plastic joint.

I'll see if I can get a store-bought earthing rod installed to reduce the kludge factor, though that might preclude me from attaining fame at thereifixedit.com.

I checked, and indeed, the Neutral and various other Neutral Whites and Grounding Greens are all tied to a bus bar in the breaker box in the building.

One of my L1 L2 L3 feeds is a white wire, but this is nothing some black tape won't fix.

Thanks for your input, folks. I feel much better about this setup now. I'll be much happier with a "real" ground wire. Typically, test samples are provided 240V 1-phase, just the two black HOT wires; no neutral required and and no safety ground provided.

 

[wareagle]

You can't just grab a green wire form anywhere and make a connection. The required EGC is taken from table 250.66.
The conduit may be used as an EGC but it must run from the ckt panel to the A/C unit. If the is plastic in between it won't work. Also driving a ground rod at the A/C is not adequate to consider the unit grounded. I am not sure if that is what Ismoked was suggesting or not. You must have a
EGC installed from the service panel to the A/C unit for it to be grounded.

 

[dpc]

Actually, even if you put a ground rod in, I would still strongly recommend running the green ground wire back to the conduit. This will represent a much lower impedance path for any ground return current compared with the earth path.