How protect high voltage coming from ground using SPD  - Page 1
Forum section: electronics / beginners

author: NASK
author_rank: Contributor
timestamp: March 12, 2020, 10:54:28 am
content: Due to the lighting high voltage coming through ground terminal to the house according to below diagram , at that time how spd work protect the devices.

author: madires
author_rank: Super Contributor
timestamp: March 12, 2020, 12:27:41 pm
content: SPDs won't help much in that situation. In most cases mains is referenced to earth, i.e. the potential difference between earth/PE and line stays the same even when the earth' potential changes because of a lightning strike. But there will be a potential difference in the earth based on the distance to the point where the lightning strike hit the soil. So the earth/PE potential at your neighbors house would hugely different from the one at your house for a very short period. SPDs help when the voltage difference between earth/PE and line exceeds some specific limit, not if the potential of the whole system is raised.

author: AVGresponding
author_rank: Super Contributor
timestamp: March 12, 2020, 12:45:24 pm
content: Neutral will be referenced to earth either at a nearby substation/transformer or at the house incomer, but the effective referencing of the line occurs at the substation/transformer only.Why do I make this distinction?Because a lightning strike near your house may alter the potential of the earth and/or neutral in your house, but unless the substation/transformer is equidistant to the strike wrt your house, the line will not be changed to the same degree, and will exceed the level at which your spd activates.

author: madires
author_rank: Super Contributor
timestamp: March 12, 2020, 03:03:39 pm
content: Yep, this topic is more complex. So I've started with a simple model to explain things.Quote from: ThickPhilM on March 12, 2020, 12:45:24 pm... or at both which is the usual setup. The latter regarding line is correct. The complexity comes from the multiple current paths, i.e. neutral in the mains distribution from the substation and the multiple connections between neutral and earth, and earth/soil itself. Then add the distributed potential difference of the earth/soil during the lightning strike and time. As a result you have both, a system with a raised potential and an overvoltage. It depends on the details if one prevails or not.

author: AVGresponding
author_rank: Super Contributor
timestamp: March 12, 2020, 08:18:18 pm
content: Line is not referenced in the home, unless you have a very large house and merit your own substation/transformer.It's correct to point out the complexities of the current path, though you could draw a much simplified version which would give you a general idea.In the broadest possible terms, earth and neutral are normally referenced to earth ground at the substation/transformer by means of a grounding stake forced up to several metres into the ground.Depending on local regulations, you might have a grounding stake at your property, but this is by no means certain.The line is generated at the substation/transformer, and this is where it is referenced to neutral and earth ground. After that, it's just a straight connection to your consumer unit/fuseboard/distribution board. The greater the distance between this reference point and your house the more likely you are to see a big difference between earth ground and line in the event of a lightning strike, as the line is referenced to an earth ground with a different potential than the local earth ground.Having a supply not locally referenced won't necessarily save you though, most lightning damage afaik happens due to induced current when a strike tracks down the outside of the property and causes big spikes on the internal wiring.

author: NASK
author_rank: Contributor
timestamp: March 13, 2020, 03:13:17 am
content: Thank you all for support. I got thing SPD does not work in this situation. Because line and earth potential difference not effective to SPD to active in this situation. Am I correct?Other thing is. It is necessary to install in parallel to load it is work like varistor, when high voltage live neutral short and it will burn then huge current flow to ground , is it correct?How does it installed to circuit 1 way or 2 way in diagramWhat is type A type B SPD ? How choose it ?Thank you

author: AVGresponding
author_rank: Super Contributor
timestamp: March 13, 2020, 01:15:47 pm
content: Drawing 1 is the correct method.There are 3 types of SPD, type 1/A is used at the substation/transformer, type 2/B is used at the distribution board/consumer unit/fuseboard, and type 3/C is used at the equipment to be protected (ie a surge protection socket strip).The one in your drawing would therefore be a type 2/B.

author: madires
author_rank: Super Contributor
timestamp: March 13, 2020, 01:52:40 pm
content: And the best way to wire an SPD is in-line with neutral and phases. Avoid stubs because of the inductance of the stub wire.