How do I ground conduit assemblies?

[NM_Shooter]

I'm pulling wire through hard conduit for an AC unit.  I have a j-box mid way that I am using to splice wires, and it is all terminating in safety disconnect near the condensor.

This is a 240V service.  3 individual 8AWG wires.  Two hot legs and a ground.   

Where should I bond that ground to the conduit?  My gut feel is that I attach ground where ever I splice or terminate.  So I ground the midway j-box, and I ground the terminal disconnect box too.

Thoughts?

[ChuckinVa]

I would think you would have 4 wires. 2 Hots a neutral and a ground. The ground would be bonded to the conduit via a ground bushing on the ends of the conduit from the ground bar. The neutral you would pull strait through to the unit safety switch. You should have a neutral bar and a ground bar in both the panel you are feeding from and the safety switch.

CHUCK

[UK4X4]

Normally you try to ground things in a star configuration

ie all parts , equipment, steel fixtures all ground back to the same point

usually at the distribution board

You can daisy chain - but the idea is that you don't build any loops- equipment in the same room on diferent ground circuits for example is a no no

Any failure of any equipment on the system should have a direct route to earth, so equipment that fails prefers to send the charge down the wire and not through you !

Usually I would ground the conduit where it connects to the distribution box
and run a seperate ground from the distribution box to the AC directly.

[NM_Shooter]

None of my 240AC appliances have a way to attach a neutral.  I'm pretty sure that when running wiring for only 240VAC, you don't need a neutral.  Both mains are 180 degrees out of phase to one another, and they serve as the return as well as the source.  For 120V, you have to have a neutral leg to return to ground. 

Both my A/C condensor and the air handler are 240V, and the 60A disconnect is for 240V, and they only have three bonding lugs.  One for each phase, and the ground.

I'm certain that I bond out the ground on the disconnect to the actual ground bond lug in the disconnect at the end of the line.  I am just not sure if I am supposed to ground bond the intermediate junction box where I made the splice.  I have done so, but it would be easy enough to remove. 

[NM_Shooter]

Normally you try to ground things in a star configuration

ie all parts , equipment, steel fixtures all ground back to the same point

usually at the distribution board

Usually I would ground the conduit where it connects to the distribution box
and run a seperate ground from the distribution box to the AC directly.

Yup.. .the conduit is grounded at the sub panel, which is grounded to earth.  The conduit further is grounded at the far end, at the disconnect box. 

Mid way is a junction box that is splicing all wires.  Trying to figure out if I should ground bond that j-box to the ground wire.  Sort of feels like I should.  If any of those splices fail, and one leg of the hot hits the box, I want it to return through the ground wire right there, and not through the conduit all the way back.  Dunno though.... and I can't find the answer online. 

[Dave Sparks]

Think of it this way. If it were a plastic J box you would not have to ground it. If it is out in the open where someone could be shocked by a fault then ground it. If it can't easily attract lightning (under ground) then it is not an issue.

[NM_Shooter]

Thanks Dave. 

I decided to ground it this past weekend thinking that I could easily change it if necessary.  I decided to err on the side of caution and ground it.

I also saw an example online of conduit based receptacles for basement wiring.  Every metal box that had an outlet in it was grounded.  I figured that was proof enough for me.