Article 810 Tower Gonding Question

[dereckbc]

Pretty sure I know the answer, but wanna a sanity check.

Assume amateur radio transmitting tower operating @ VHF frequencies @ 1500 watts. 150 foot tower located 200 feet from house. Each tower leg is bonded to a dedicated ground rod and structural steel in the concrete peers. Coax runs underground in Schedule 80 PVC.

Me says there is no requirement and out of NEC scope to run a Bonding Jumper to connect the house GES where AC Service is located to the Tower Leg GES. Am I right or wrong.

Even if you did. I do not think it would be of any value from either a safety or operational POV. The Coax Shield would provide a bond in addition to having a larger cross-sectional area of any 10 AWG copper. What is throwing me off is table 810.52

 

[grich]

Pretty sure I know the answer, but wanna a sanity check.

Assume amateur radio transmitting tower operating @ VHF frequencies @ 1500 watts. 150 foot tower located 200 feet from house. Each tower leg is bonded to a dedicated ground rod and structural steel in the concrete peers. Coax runs underground in Schedule 80 PVC.

Me says there is no requirement and out of NEC scope to run a Bonding Jumper to connect the house GES where AC Service is located to the Tower Leg GES. Am I right or wrong.

Even if you did. I do not think it would be of any value from either a safety or operational POV. The Coax Shield would provide a bond in addition to having a larger cross-sectional area of any 10 AWG copper. What is throwing me off is table 810.52

The broadcast towers I work at are bonded to the building ground with wide copper strap. Coax shields are bonded to the tower steel at the lowest point they reach on the tower, and bonded to the ground system at the building entrance.

I believe 810.52 refers to antenna wires strung out in free-air to receive low-frequency signals, and doesn't apply to your situation.

 

[dereckbc]

Thanks for our comments Gregg, I am very familiar with commercial towers as I have worked in Telecom my whole career. Commercial does a lot of things that exceed NEC requirements. One example I know of is many commercial AM broadcast towers are not bonded to anything except the center conductor of the coax. The Tower itself is the radiating element and the tower is physically isloated from making contact from the concrete piers or anything around that that might conduct current. However they have barriers around them and a commercial application. They do have extensive RF Ground Radials, but only the coax shield is bonded to ground.

Reason I am asking is I am helping a friend with building a tower for amateur radio use and it is 200 feet from the house and he is trying to save a few dollars. The tower itself is properly bonded. coax shield will be bonded at the top and at the bottom where it exits the tower and goes underground. So via the Coax it is bonded. There is no lighting or rotors used on the tower so other than the transmitter located 200 feet away, there is no electrical on the tower.

IMHO I do not think there is any requirement or benefit from bonding the tower GES to house GES. Never built a tower 200 feet away from shelter or house in my 40 years in telecom. I do agree with your 810.52 interpretation.

Thx again.

 

[LarryFine]

Wouldn't bonding be necessary to minimize (the effects of) lightning-induced voltage gradients?

 

[hbiss]

So via the Coax it is bonded.

You can't rely on the coax shield to bond anything. Further, if there were no metallic path back to the house I would say OK but since you do have the coax I would bond it and with larger than #6.

The broadcast towers I work at are bonded to the building ground with wide copper strap. Coax shields are bonded to the tower steel at the lowest point they reach on the tower, and bonded to the ground system at the building entrance.

Good advice.

-Hal