70 ft run to ground rod

[Spgtwn]

We're going to install an antenna mast on the roof of a MDU. The radio equipment will be powered from an existing outdoor electric outlet box on the side of the MDU (hard wired inside the box).

The electrical outlet is not part of the MDU's electric service (it is not tied into the MDU resident's electric service ground rod), rather it connects to the management office's electric service breaker box via 50 ft. buried PVC with 16 ga. hot lead, neutral and ground. Obviously bonding the mast to the that 16 ga. ground wire that connects to the breaker box isn't going to be adequate for lightning protection.

I think the answer will be to drop my own 8 ft. ground rod near the mast and bury 70 ft. of #6 gauge copper wire back to the management office's electric meter's ground rod. Is this adequate for safety?

 

[Smart $]

While your proposed grounding scenario sounds good, I find myself questioning the #16 branch circuit. I believe it is in violation, needing to be at least #14 [ref: 210.19(A)(4)]

EDIT to ADD
Perhaps the #16 was predominating my thoughts. Now having after thoughts, the outlet on the side of the MDU can be and likely will be considered as suppltying power to the MDU, especially since the powered radio equipment has an associated antenna located on the roof of the MDU. As such, the circuit needs a disconnecting means at the MDU, and also must be bonded to the grounding electrode system of the MDU. Running the #6 back to the manager's office is optional, if not excessive. Start at Article 225, Part II...

 

[Spgtwn]

As I was saying, the electric service to the MDU has no connection whatsoever to the outdoor electric outlet attached to the outside wall of the MDU structure. The MDU has completely different electric meters for the residents and ground rod, in fact it's fed off a power transformer on the other side of the complex.

So bonding my equipment to the MDU's ground rod would be effectively isolated from the electrical outlet's ground that is 70 feet away at the management office.

The outlet might be #14, instead of #16. I'll look again. My total load is less than 3 amps on a 70 foot run of line back to the management office breaker panel.

 

[Smart $]

As I was saying, the electric service to the MDU has no connection whatsoever to the outdoor electric outlet attached to the outside wall of the MDU structure. The MDU has completely different electric meters for the residents and ground rod, in fact it's fed off a power transformer on the other side of the complex.

So what does this have to do with the following:

• a disconnecting means at the MDU is required
• the MDU's grounding electrode system (GES) must be connected to the supply circuit's grounding conductor (EGC) at the disco'

So bonding my equipment to the MDU's ground rod would be effectively isolated from the electrical outlet's ground that is 70 feet away at the management office.

Running an EGC with the circuit conductors is required. This would tie the two GES's together. As such, your equipment would be connected to both.

 

[Spgtwn]

I can understand the recommendation to have a disconnect box at the point where the buried electric line comes up out of the ground.

Going forward, perhaps I'm not understanding the significance of the other building being an MDU versus an empty barn.

Let me back up and suggest that I were to have my own 30 foot wood pole next to (but not physically attached) to the MDU:

1) The buried electric line comes up out of the ground and instead of having it physically attached to the MDU's outside brick wall, I attached to the wood pole (and have a disconnect box on the wood pole).

2) Place my antenna on the 30 foot pole that is next to the MDU.

In the above scenario, the MDU does not even enter into the picture.

Now, lets say that instead of my antenna sitting on the top of my own wood pole, I have the antenna sitting on top of the MDU. Does the mere fact I moved the antenna from my pole to the roof of the MDU make a difference? What if my disconnect box was physically attached to the MDU's brick wall, instead of my wood pole?