DIYbanter - View Single Post - Retrofit-Grounding Fifties-Era House?

Bud--

On 11/20/2012 3:08 PM, wrote:
On Nov 20, 3:46 pm, wrote:
Per bud--:

I agree. There should also be a ground block where the coax enters the
house. That allows the coax shield to be earthed. That connection, in
particular, plus the ground wire from the TV antenna, should connect to
the earthing system near the service panel. ...
That requires a short wire
from entry protectors to a common connection point on the earthing
system. The distance from the service N-G bond to the common connection
point also has to be short.

Is there a conflict there for a TV antenna mounted on the North
end of the house with coax running down the North wall and
entering the crawl space there - and a service panel on the
opposite end of the house?
--
Pete Cresswell

In that situation the technically correct thing to do would
be to have another ground rod on the end of the house
with the antenna and have that ground rod bonded to the ground rod at
the main panel. However there are plenty of houses out there that
just have the antenna ground on one end and the panel grounded on the
other. This common
ground is one reason utilities, ie electric, phone, cable,
etc come in at the same place.

I agree again.

The NEC wants a 20 ft max ground wire from the coax entry ground block
to the power earthing system. If the wire is over 20 ft the NEC wants a
ground rod near the coax entry point (connected to the entry ground
block) and a #6 min bond wire from that ground rod to the power earthing
system.

During an "event" that rod can be thousands of volts different from the
building 'ground'. Because of the inductance of the bond wire and
relatively high frequency current components of a surge, the bond wire
does not necessarily reduce the voltage to a reasonable level.

IMHO the 20 ft limit is more reasonable for cable, where you have
significant risk of surge entry. There should be little surge risk from
a TV antenna. (The protection in the NEC is not for a direct lightning
strike to the antenna - far more elaborate protection would be required.)

1 I might use a ground wire somewhat longer than 20 ft

2 If a rod is added at the cable entry you could run the coax near the
power service and add a second ground block. (That adds coax length and
signal loss.)

3 Just add a rod and bond wire.

Particularly for 1 and 3 (or leaving it the way it is) a plug-in
protector at the TV would add protection. The coax must run through the
protector. (All external wires go through the protector, and all
interconnected equipment connects to the same protector.)