[Elecraft] [OT} Whole House Surge Protection

[Jim Brown]

On 1/31/2013 4:26 PM, Don Wilhelm wrote:
> We had a close lightning event last summer and there were no 
> incidences of damage on the AC side, although all the GFCI breakers 
> tripped.
>
> The wired Ethernet devices were not so fortunate, I lost a router, 2 8 
> port switches, an access point, a NAS storage device, and 4 computers 
> after that event, that did not mention the Ethernet connected network 
> printer that lost its Ethernet capability, but still worked with a USB 
> connection - all apparently due to the surge coming in over the 
> Ethernet cables.  Fortunately, no data was lost, the devices did not 
> work due to damaged network ports.
>
> So the AC protection did work, but the unprotected Ethernet devices 
> did not survive. 

The so-called surge protectors on your computers is what CAUSED your 
Ethernet devices to fry.  Shunt mode (MOV) protectors on branch circuits 
are a REALLY bad idea.

MOVs at the service entrance are a very GOOD thing -- IF the house is 
properly grounded.

The "high leg delta" is simply three Delta-connected transfomers on the 
pole, one of which is center-tapped.  There's 240V between legs, and if 
you have 3-phase service from high-leg Delta, you get all three phases. 
Customers who buy single-phase service (99.9% of homes) get both sides 
of the center-tapped transformer and the neutral.

The (really) bad  part of this is that ALL 3-phase systems have lots of 
harmonic current, AND the single-phase get a super heavy dose of that 
harmonic current on their neutral, which is the only path to ground for 
it. THAT'S where "ground buzz" comes from.

A "whole house" surge protector has two BIG MOVs, one connected from the 
two sides of the 120-0-120 to neutral, which is bonded to ground in the 
entrance panel. For a 3-phase system, you simply need a protector with 
one more MOV.

BTW -- the system I've described is called "high leg Delta" (also "wild 
leg" or "red leg") because the terminal of the 3-phase system opposite 
the transformer is 277V to neutral.

There's a discussion of all of this in the Power and Grounding tutorial 
on my website. http://audiosystemsgroup.com/publish.htm Although it's 
written for audio and video professionals, everything in it applies 
equally to installations of all sorts, including radio.

73, Jim K9YC