[aprssig] Whole house suppressors

Ray Wells vk2tv at exemail.com.au
Tue May 31 03:23:17 EDT 2011


I'm a licenced electrician and a licenced electrical contractor in 
Australia. It's very interesting to see how different the electrical 
codes are in diametrically opposed parts of the world.

Ray vk2tv

On 31/05/11 16:35, Perry Chamberlain wrote:
> 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.
> Ke6anm
> 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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