I've got a 3ton AC condenser unit on my roof, with a blower system nearby in attic space supplied by 20A 240v circuit.
- The condenser unit is supplied by a 40A 240v circuit, 2 8ga wires
- The blower unity is supplied by a 20A 240v circuit, 2 12ga wires
- Both circuits are run through the same steel conduit from my outdoor breaker panel.
- There are no ground wires in the conduit.
- The conduit is a little corroded in places
- The total span is about 45'
- Measuring voltage in the panel, I get 118v to the ground bar on each wire and 236v wire to wire on each circuit.
- Measuring voltage on the roof (with the conduit completely disconnected from the AC unit, so only connected to the panel), I get 95v between the wire and the conduit on each of the 4 wires, but I still get 236v wire to wire on
each circuit.
Why would there be so much voltage drop? It's like the conduit at the roof is at a higher potential than at the panel. Do I need to replace the whole run with new conduit, and circuits with a shared 8ga ground wire? Or run a new ground through the conduit? I can't see being able to easily do that. What size conduit do I need to carry those wires? Thanks
Best Answer
If you think the conduit is not providing an adequate ground-fault current path, you can run a separate grounding conductor from the panel to the A/C unit. Current code no longer requires you to run the grounding conductor with the other circuit conductors. So you can run an appropriately sized grounding conductor any way you'd like.
If it's easy enough to do, you could run the grounding conductor along the outside of the conduit. If that's not possible, you could simply run it up the side of the building (providing protection if necessary) .