Joe of NJ, please consider these items.
1. According IEEE 95% of all surges happen on the primary side of a transformer in the common mode. If that is the case then the surge appears on the secondary as a differental or transvers mode (L-L & L-N
2. At the service entrance the neutral and ground are bonded together. There is no SPD that can equal that short circuit. If you were to add a SPD between L-G or N-G would only parallel the L-N device. Therefore adding devices L-G and N-G anywhere there is a N-G would be waisted material and ineffective. You get more bang for the buck by using a larger SPD device than adding multiples in parallel.
3. When you bond the N-G you essentially make the differential mode and common mode one in the same becuase they are both the same point electrically at the N-G bond. I never implied that transverse and common were the same, only at the service entrance. Please go back to my first post where I sated all-modes were usefull downstream of the N-G bonds, about 80-feet to be exact.
4. Common modes does become important downstream from the entrance and downstream from SDS for the Class B and A units (sometimes called Point of Use). But earth in no way has anything to do with the operation of a TVSS which was my original point. Joe test, that should address your concerns as of the induced strike.
