Grounding steps before concrete pour

RFI-EMI-GUY

Member
Joined
Dec 22, 2013
Messages
3,827
Got it all in and bonded in the concrete, which was the timely part. I’ll figure out the other ground rods later. Thank you both for all your help!

is it a dumb idea to have the roofer add a vent type port in the roof for bringing in coax to run down the inside of the rafters, out the eves, down to the ground rod, and then back up to the eves and over to the radio (straight line down and back, all over the same interior wall)? It would be a neater/tidier result, wouldn’t have to negotiate bending around gutters, and wouldn’t make a dam for leaves to and such from the overhanging trees to get caught on on the roof.
Glad to hear you got your wiring in before the pour.

Personally, I wouldn't do a roof penetration, but I have the option of a gable end. My concern with any sort of roof penetration you have a chance for failure. Then if you change your mind, move or whatever you have that "stack". It sounds like you are doing roof antennas' so maybe thats not a problem.

You might look at products used for solar panel wiring to see if any make sense. You might look at cable trays that come in all sorts of sizes and shapes. You could do a "U" turn from the wall, over the gutter and lay in your cables over it.
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
12,835
Location
SNCZCA01DS0
I've had roof jacks put in for us on some buildings. Makes life easier to run cable straight down to where you need it. But in a commercial install, we can do things you wouldn't want on your home. And then you still gotta get to your ground rod.

Too late to put in a tower????
 

Firekite

Member
Premium Subscriber
Joined
Apr 2, 2019
Messages
346
Too late to put in a tower????
A tower doesn’t work for this location. I’ve already got the neighborhood power lines across the back fence line, no easy way to run the coax to the shack without taking a long route or causing a tripping hazard, and none of it will pass the wife test. She said she’s cool with antennas on the roof, though, so I’m hoping to hold her to it :)
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
12,835
Location
SNCZCA01DS0
none of it will pass the wife test.
Yep, gotta keep the Minister of War and Finance happy.

Like I said, I've had roof jacks put in with a weather head on top. If you get some rigid conduit and properly mount it to the rafters, you can mount an antenna or a short mast to it. Any reputable roofer can seal the flashing and you won't have issues. Heck, even I added some roof vents when I installed fans in the two bathrooms about 10 years ago, and no leaks. So easy even a radio guy can do it.
 

K4RBT

Member
Joined
May 12, 2011
Messages
63
If you run the coax through the attic before taking it to the grounding point, a lightening strike will travel through the attic, not good.
The rule for ground rods is the sphere of influence (think that is the right word). rods right next to the house 1/2 of this sphere. The sphere circle has a radius of the length of the rod. Eight foot rod, will have a 16 foot sphere. The next rods sphere con overlap the others, but not more that 1/2. I have not found how the sphere is shaped when you drive the rod horizontal, That was not in Motorola's publican R56 (518 pages!).
 

prcguy

Member
Joined
Jun 30, 2006
Messages
9,529
Location
So Cal - Richardson, TX - Tewksbury, MA
A service entry weather head is a great way to bring coax into the attic from the outside. Some of the punch out holes in the rubber or plastic gasket thing are a good size for RG-8 or LMR-400. Problem is you have to pull back some roof shingles and install a sheet metal something or other, I forget what its called but it properly seals off the hole in the roof and weather proofs everything.

Got it all in and bonded in the concrete, which was the timely part. I’ll figure out the other ground rods later. Thank you both for all your help!

is it a dumb idea to have the roofer add a vent type port in the roof for bringing in coax to run down the inside of the rafters, out the eves, down to the ground rod, and then back up to the eves and over to the radio (straight line down and back, all over the same interior wall)? It would be a neater/tidier result, wouldn’t have to negotiate bending around gutters, and wouldn’t make a dam for leaves to and such from the overhanging trees to get caught on on the roof.
 

RFI-EMI-GUY

Member
Joined
Dec 22, 2013
Messages
3,827
If you run the coax through the attic before taking it to the grounding point, a lightening strike will travel through the attic, not good.
The rule for ground rods is the sphere of influence (think that is the right word). rods right next to the house 1/2 of this sphere. The sphere circle has a radius of the length of the rod. Eight foot rod, will have a 16 foot sphere. The next rods sphere con overlap the others, but not more that 1/2. I have not found how the sphere is shaped when you drive the rod horizontal, That was not in Motorola's publican R56 (518 pages!).
There are so many variables and difficulties in effective grounding and bonding. No wonder R56 is so lengthy. Residential homes are a more difficult situation due to aesthetics and differences in construction.

With so much of residential wiring being attic placed Romex , introducing an antenna conductor into an attic situation would make me nervous unless it is entirely vertical (orthogonal to existing Romex wiring) and far from other vertical wiring to minimize mutual inductance. For example if all the lines are run down outside of an exterior wall in a frame construction before grounding, how is that different from an interior wall?

My house has a metal chimney that extends from floor through a frame chimney stack. I am sure it is not intentionally grounded to anything. It does make me nervous that it exists. Our fire code here in FL does not require lightning rods. It should, we had a new apartment building burn down last month due to an attic fire from lightning.

As far as minimum spacing for ground rods. If you drive two ground rods right next to each other you would have essentially one ground rod with twice the surface area. If you move them one, two, four, six feet apart it would be interesting to measure their impedance. Could there be a "sour spot" where the currents cancel out for a specific lightning waveform? I think industry needs to study this. Until then my rule of thumb is that you can never have enough ground rods so if the distance requires 6 feet spacing, I have gone with it. Also over time, ground rods tend to corrode away. How does this affect the sphere of influence and effectiveness? In a Ufer system, the re-bar is spaced closely together, the conductors considered to be homogeneous.

In my opinion, the best ground system is the one that breaks your wallet.
 
Top