[abcsalem]

I am in the process of replacing our AC condenser's wires which powers the outside unit
From main breaker. The existing 25+ years old wore out and damaged wire is romex 8/3 with ground on a 40A 240v dual-breaker. The AC guys when installed the unit,
Connected the BLACK and RED to the 40A breaker, WHITE to the ground bar,
And then cut-off ground on entry to the main breaker, i.e. they used the WHITE wire
(which is size#8) for the ground.

I was planning on buying a romex 8/2 with ground. But I noticed that the ground
Is like #10 or #12 solid wire.

Questions (reminder circuit is 240v, 40A):

1- is there an advantage of buying a romex 8/3 w ground, and then use the WHITE
(which is #8) for ground, and cut-off the ground like they did 25+ years ago?

2-if I decide to use THHN wire and 3/4 inch PVC conduit, then I need to buy
#8 BLACK and #8 RED for HOT wires. What size and color I should buy for my ground wire?

Thanks
-Ab

[KISS]

Well first you'll need an AC disconnect outside. From there you will run Sealtite to the unit. Kits are available with all of this together.

You have an option to buy a disconnect with a convience outlet where you would need to run a separate circuit too.

If the location is considered wet, then you need THWN. Usually THHN is dual marked THWN.

PVC conduit is acceptable.

You can also buy all black wires and tape the ends of the wire with electrical tape the proper color.

Come back with some further questions based on what you want to do.

They used 8/3 and cut off the ground because they wanted a larger gauge ground wire.

[stanfortyman]

1- is there an advantage of buying a romex 8/3 w ground, and then use the WHITE
(which is #8) for ground, and cut-off the ground like they did 25+ years ago?

NONE. 8/2NM is fine. The bare ground is #10.

2-if I decide to use THHN wire and 3/4 inch PVC conduit, then I need to buy
#8 BLACK and #8 RED for HOT wires. What size and color I should buy for my ground wire?

#10 or #8 green. Re-marking #10 or #8 is a violation. A technical violation, but a violation nonetheless. Same goes for using white for a ground.

[abcsalem]

Well first you'll need an AC disconnect outside. From there you will run Sealtite to the unit. Kits are available with all of this together.

Thank you for mentioning this; I am well aware of disconnect requirements.

You can also buy all black wires and tape the ends of the wire with electrical tape the proper color.

The reason I mentioned color was because small wires cannot be marked
For this type of installation, and therefore they need to be in their respective colors.

They used 8/3 and cut off the ground because they wanted a larger gauge ground wire.

That is understood what the original installer was trying to do. My question is
Why? Why did the original installer buy romex 8/3 with ground wire (which costs more)
Rather than buying 8/2 with ground (which is cheaper). Cutting off the bare copper
Wire at breaker and disconnect box in my opinion is a dangerous and bad practice.
My reason is, what if one of the HOT wire's insulation within the cable gets damaged
And the HOT wire comes in contact with the bare copper wire inside the cable.
Then the bare copper wire become HOT. For safety, I would have grounded
Both the bare copper wire and the WHITE (marked green) wire. Or better yet,
Buy 8/2 NM with #10 ground or buy black/red/green #8 THHN/THWN wire. Right?

[stanfortyman]

That is understood what the original installer was trying to do. My question is
why? Why did the original installer buy romex 8/3 with ground wire (which costs more)
rather than buying 8/2 with ground (which is cheaper). Cutting off the bare copper
wire at breaker and disconnect box in my opinion is a dangerous and bad practice.
My reason is, what if one of the HOT wire's insulation within the cable gets damaged
and the HOT wire comes in contact with the bare copper wire inside the cable.
Then the bare copper wire become HOT. For safety, I would have grounded
both the bare copper wire and the WHITE (marked green) wire. Or better yet,
buy 8/2 NM with #10 ground or buy black/red/green #8 THHN/THWN wire. Right?

Right.

IF a ground wire is present it must be terminated.