Regarding the TVSS discussion taking place:
As mentioned previously, the intents of many TVSS devices installed on the Load side of the Main Disconnect, are to "Divert" Surge(s) from the "Active Circuit", with hopes that the devices connected to the normal Active Circuit (L-N) will not have to deal with any surges.
The idea is to attempt to pass surges, which originate from sources both external and internal to the system, around the sensitive load item(s), and back to the Power Supply.
Except for Lightning surges and RFI (or even line charging...but that's stretching it!), the surges will be between Source and Load - or Transformer and Equipment.
This would mean that any TVSS component connected to the "Grounding Conductor", outside of the
Point Of Physical System Earth Bonding, is simply shunting the surge load around the normal active circuit, back to the
Point Of Physical System Earth Bonding - and eventually returning to the Power Supply of origin.
BTW,
Point Of Physical System Earth Bonding is in reference to the location on a given AC Power System, where the System's Grounded Conductor is Bonded to the local Grounding Electrode System - via the Grounding Electrode Conductor(s); along with the Metallic Enclosures and Equipment Grounding Conductors being Bonded to the same "Star Point".
Surge Protection Devices (SPDs) on the "Line" side of the
Point Of Physical System Earth Bonding, will still - in effect - be connected the same as others - unless they are not connected to the same Electrode as the AC System - and this Earthed side is isolated from any physical connection to the Bonded AC System's "Grounding System" (GES and Enclosures).
In our field, the term "Grounding" and "Grounded" are very misleading - and at times downright confusing; to the point of pending disaster!
I encourage using terms like "Bonded", "Bonding" and "Equipment Ground Bonding", in the field, so the idea of a physical connection to the AC system is made - instead of the notion of several mysterious connections of wires to the Earth.
There is (typically) only one connection of the AC system to the "Earth Ground", and this is only to establish a "Neutral Point" - not for any system performance reasons.
The system will work exactly the same with no physical Earth connection - and this includes TVSS devices (as long as the EGCs still terminate to a given Conductor of the referenced AC system).
I need to create an easy to follow seminar of basic system grounding principles - how, what, where, when and why scenarios to describe the ideas of AC System Grounding, and submit this to the Technical Reference section.
This is really important, and once again, I have had to resolve some major confusion of Grounding Techniques in the Field - between Clients, Contractors and our own Employees.
Per a part of "Joe Testengineer's" last message
Scott posted several drawings of surge arrestors that were just pi-type LC input filters with MOVs in parallel with the caps.
This is 100% correct! And goes along with the first part of my reply.
The TVSS designs I submitted on-line (posted in the Technical Reference section), are - by the most part, simple PI filters - with MOVs in Parallel (between L-G and N-G).
The intent of these TVSS devices are to shunt surges away from the Load devices, by "Dumping" the surges into the Equipment Grounding Conductor, and "Sending Them" back to the Source / Supply via the connection of the system's Grounded Conductor to the Bonded Equipment / GES Star point.
On Ungrounded AC Systems, the termination of TVSS devices, along with Low Pass / Band Pass filtering terminating to an Equipment Grounding Conductor, will still eventually result in flows returning to the Power Supply (Transformer).
They will be limited to the level of flow which would be Capacitively Coupled to the System.
Or in the cases where the Secondary side of the PoCo's Transformer is Earth Grounded via a Center Tap point only (and there is no system Grounded Conductor), there will be a flow through the Earth Ground, between the local Grounding Electrode System(s) and the PoCo's Transformer Earthing Conductor point of connection to the actual Ground.
I will include a few drawings and examples + explanations of this type of Ungrounded AC System.
OK, time to leave the soapbox!
Scott35
