[aprssig] Whole house suppressors

Perry Chamberlain canoeman at qnet.com
Tue May 31 02:35:21 EDT 2011

Any device like a suppressor, disconnect, sub panel,  ground conductor to ground rod,  should have ground bushings installed at both ends of a ferrous  metal conduit,  so the conduit is grounded at both ends, and grounded to the Can, panel, etc. with a  mechanical lug.
For a ground rod run,  the pipe must also be bonded to the ground rod as well as the ground connector inside the conduit  when running grounds. ( they make a connector for that)
This action of bonding both ends of a conduit nipple or pipe, eliminates the choking effect of having an unbonded ferrous  pipe act as a choke, which they will definitly do.
This is very critical on the ferrous rigid pipe going to the ground rod.
Or explained like this :

"Here's another way to understand the "choking" of a GEC in a ferrous raceway.
The current in the GEC is alternating, so the magnetic field created by the current is expanding and intensifying, then weakening and collapsing 120 times a second (each half cycle). 120 times a second there is no magnetic field.

The field moves out through the stationary metal raceway. The raceway, being also a conductor, in the presence of a moving magnetic field is a generator and has a current generated in it. This current is commonly called an eddy current.

The eddy current, flowing in the raceway metal, creates its own magnetic field, which is in the opposite direction of the magnetic field that creates the eddy current in the first place. This is the "choke".

As a side note: if the current in the GEC is DC, the magnetic field around the GEC is not changing (not moving) so it doesn't generate eddy current in the raceway, and is not choked.

The ferrous raceway concentrates the magnetic field that passes into it, as compared to aluminum or other non-magnetic conductive material. Because of the higher magnetic field density inside the ferrous metal, the eddy current created by AC is great enough to really be a problem for GECs. When the GEC is bonded to both ends of the ferrous raceway that houses it, as the choking effect increases on the GEC, the current shifts more and more to the raceway itself. The fact that the raceway becomes a large part of the active path in a fault condition, underscores the importance of making all the raceway joints tight, as well as bonding to both ends."
But I would never run a suppressor in a pvc pipe.
The added  ability of the GEC, and the metal nipple to carry the dumped surge, is multiplied, by the metal conduit, acts as a safe path.
Aluminum pipe will act like pvc.

I am a DSA inspector and a master electrician.

Mike holt publishes an excellent book on grounding and bonding, available on amazon.

He said:

"Ensure that you connect the surge panel to the 
breaker box wit PVC or similar non metallic conduit.
Metallic conduit will act as a choke preventing 
the surge from getting into the surge suppressor.
Most surges will be lightning induced and lightning is a high frequency event.
All grounds should be as short as possible, 
number 6 or larger inside the building.
Do NOT use braid for a lightning ground as the 
high frequency event does not like the bends back 
ad forth that make up the braid."

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