Carl Denk wrote: > On 2/13/2011 9:35 AM, Gerhard Fiedler wrote: >> We get our share of thunderstorms and lightnings around here, and I'd >> like to protect the electric supply of our home -- somewhere near >> the entry. The=20 >>=20 >> The supply is a three-phase system with a neutral wire (four wires) >> and the neutral wire is grounded (typically a grounding rod) at each >> connection point.=20 >>=20 >> Our connection point is at the property boundary, where the four >> wires come in from the street. As required, the neutral is grounded >> there and there is a master circuit breaker. This would be the first >> possibility to place overvoltage protectors, between the three >> phases and the ground rod (which is connected to the neutral).=20 >>=20 >> My question with this is whether this makes sense, considering that >> the neutral is connected to the same ground rod where I'd connect >> the protection devices -- and the neutral comes from the same >> "problem zone" where the 3 phases come from. But OTOH it's >> supposedly well grounded and probably already reasonably clean when >> it reaches my property. (I don't expect to have good protection if a >> lightning strikes within a few meters... :)=20 >>=20 >> From there, the four wires go through some 20 m underground to reach >> the house. There I have a ground rod for the protective earth wire >> in the installation inside the house (separate neutral and PE). This >> would be another place to put the protection devices (and I've seen >> quite a few installations that do this).=20 >>=20 >> However, I don't think I'd like to connect the protection devices to >> the protective earth grounding rod; after all, it's directly >> connected to many exposed surfaces all over the house. Connecting >> them to the neutral there would beg the same question as in the >> first option, with few if any advantages. (If a lightning strikes >> directly on the property, I don't think there's much that these >> protection devices can do anyway.)=20 >>=20 >> It's not easily possible to use a third ground rod that is far >> enough away from the other two. I'm tending to prefer the first >> option, placing the protective devices right at the entry point, and >> connect them to the neutral/ground connection there.=20 >>=20 >> Does anybody have any ideas what is the best solution here? What do >> you guys do for lightning protection?=20 >>=20 >>=20 >> BTW, how would this earthing scheme be called? It seems it is a >> mixture between TN-C-S and TT. AIUI, it would be TN-C-S if I hadn't >> used a separate ground rod for PE and connected PE to the same >> ground rod where the incoming neutral is connected to, and it would >> be TT if the incoming neutral weren't grounded at each connection to >> the grid.=20 >>=20 >> The overvoltage protectors they sell for TN-S and TT systems have >> four protection devices, and the ones they sell for TN-C systems >> have three. Another question I have is how many overvoltage >> protection devices I need. I figure I only need three... no use >> trying to protect the combined neutral/PE wire that comes from the >> pole, since it is grounded anyway. Right? > > I'm no expert in this area, but have got into the topic a bit. I > thought that basically one ground rod, and on a single phase system, > the neutral is also grounded there for all loads supplied by that > supply.=20 There are different ground(PE)/neutral connection schemes. This is one. In another one, separate PE and neutral wires are provided by the supply system. In yet another one, the PE is "private" for each installation. > This minimizes ground loops.=20 I think as long as you have a common point for PE, all of the common PE/neutral connection schemes minimize ground loops in the same way; they don't differ in this. The difference is in the way ground and neutral are connected -- and neutral shouldn't be involved in ground loops anyway, as you say with the next phrase: > Then important not to tie together anywhere else the neutral and > ground. That also might create weird issues with GFCI's.=20 Agreed. > I assume the 3 phase is for heavy motors, etc., and a normal 110/220 > single phase is derived from that.=20 No. AFAIK, the "normal" 110/220 V US-style two-phase power supply is not widely known outside the USA. Most places I've seen have 3-phase systems, and where fewer phases are needed, you just take one or two from the 3-phase system.=20 In Germany, I don't think there are installations with fewer than 3 phases in modern houses, and phase to phase connections are not used (other than in real 3-phase equipment); phase to ground is 230 V anyway. In Brazil, installations of simple houses sometimes have only one or two phases, but all from the same 3-phase system. In my area it's 127 V phase to neutral and 220 V phase to phase, and phase to phase is commonly used for power equipment that's not 3-phase (electric grass mower and similar machinery). The advantage is that neither the consumer nor the power supply company have to do anything special if for some reason the consumer needs a 3-phase supply -- you just have it in front of your property, in the normal end user supply wires. And I don't see a disadvantage. > Could you not then treat the 110/220 single phase in the normal > manner, providing surge suppressor at main breaker box.=20 Well, yes... I can treat the 3 phases in the normal manner.=20 But my question was about where it is best to place it -- and where it is best to ground it. I have an entry breaker box with the meter and a main breaker (3 x 60 A) where the wires enter the property from the street and a "detail" breaker box inside the house where the wires from the entry breaker box enter the house. > For the whole house, I have had one of these for maybe 5 years, and we > are in an open area with lightning. > http://www.google.com/products/catalog?q=3Dwhole+house+surge+suppression&= oe=3Dutf-8&rls=3Dorg.mozilla:en-US:official&client=3Dfirefox-a&um=3D1&ie=3D= UTF-8&cid=3D2095718605650227831&ei=3Dc_JXTe2YHMKftgfZ2YXsDA&sa=3DX&oi=3Dpro= duct_catalog_result&ct=3Dimage&resnum=3D1&ved=3D0CCsQ8gIwAA# I'm thinking along these lines: http://www.buildingtechnologies.siemens.com/bt/low-voltage/EN/product-portf= olio/protection-devices/overvoltage-protection-devices/Pages/surge_protecti= on_devices_electrical_installation.aspx Probably similar, internally. Thanks, Gerhard --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .