Can anyone explain how it is that a lightening strike close to a home can wipe out only a selection of electronic equipment in the home and not affect other items. Also this home is on the same xfmr as its neighbor and the neighbor was not affected at all. The strike was not a direct hit to the home. I have been asked to replace the damaged equipment and survey the rest of the house for possible damage. What have you all done when asked to perform such a survey and how do you ensure the integrity of the wiring in the walls? What type of protection have you all installed and have found adequate? Thank you!!
Lightening strikes
- Thread starter patc
- Start date
- Status
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Lightening strikes
One important rule is all the TVSS devices for power, phone, coax, antenna be located very close together, and bonded togehter and to the same grounding electrode system. A lighting stike creates a voltage gradient in the earth, the the dvevices are grounded but not bonded together, the distance between will creat a voltag drop, which causes a current flow.
When I install radio coax protectors they are mounted on a common copper buss bar, which is grounded per art 810 and 820.
A rule of thumb on TVSS is more is better. You want a really big robust unit on the outside for the power, and smaller ones sprinkled through out the house.
Thats non technical I admit. But it should get you started.
One important rule is all the TVSS devices for power, phone, coax, antenna be located very close together, and bonded togehter and to the same grounding electrode system. A lighting stike creates a voltage gradient in the earth, the the dvevices are grounded but not bonded together, the distance between will creat a voltag drop, which causes a current flow.
When I install radio coax protectors they are mounted on a common copper buss bar, which is grounded per art 810 and 820.
A rule of thumb on TVSS is more is better. You want a really big robust unit on the outside for the power, and smaller ones sprinkled through out the house.
Thats non technical I admit. But it should get you started.
Re: Lightening strikes
Tom, I guess what you are saying is to put whole house protection at the service and then put additional devices at each recepticle location as needed.I dont see how it will be possible to bond all of these throughout someones house though. Is there also any way to improve on the sevice grounding to assist in dissipating the voltages?
Tom, I guess what you are saying is to put whole house protection at the service and then put additional devices at each recepticle location as needed.I dont see how it will be possible to bond all of these throughout someones house though. Is there also any way to improve on the sevice grounding to assist in dissipating the voltages?
Re: Lightening strikes
Pat, Tom is refering to the entrance of your various services like CATV, electric, and telephone. They should all enter at approxiametly the same point into the building or a window if you will. This allows all bonding to be short and directly to the GEC.
The best advice I can give for a residential installation is to call your electric company and have them install a TVSS in the meter base. In my area the utility charges $35 to install and $5 per month. They come with a gaurantee to protect large appliances only like AC refrrig, etc. They also offer point of service devices for sensitive equipment that also comes with a gaurantee. I wouldn't use the point of use devices. The meter devices employ "Kelvin Clamp" methods which cannot be equaled by any add on device in parallel. For the most part TVSS devices are rendered useless by the installation. The reason is it is not possible to keep your leads shorter than 6 inches. The other method that is effective is from new construction or replace the main panel with one that has TVSS built in using a series "Kelvin Clamp".
Pat, Tom is refering to the entrance of your various services like CATV, electric, and telephone. They should all enter at approxiametly the same point into the building or a window if you will. This allows all bonding to be short and directly to the GEC.
The best advice I can give for a residential installation is to call your electric company and have them install a TVSS in the meter base. In my area the utility charges $35 to install and $5 per month. They come with a gaurantee to protect large appliances only like AC refrrig, etc. They also offer point of service devices for sensitive equipment that also comes with a gaurantee. I wouldn't use the point of use devices. The meter devices employ "Kelvin Clamp" methods which cannot be equaled by any add on device in parallel. For the most part TVSS devices are rendered useless by the installation. The reason is it is not possible to keep your leads shorter than 6 inches. The other method that is effective is from new construction or replace the main panel with one that has TVSS built in using a series "Kelvin Clamp".
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Lightening strikes
Dekek is correct all the LV TVSS's are placed close together. In fact for a residential application if its over 20 ft a ground rod is required at the telecom network interface, and 6 awg run to the power system grounding electrode, see section 800.40(A) , new for the 2002 NEC
Dekek is correct all the LV TVSS's are placed close together. In fact for a residential application if its over 20 ft a ground rod is required at the telecom network interface, and 6 awg run to the power system grounding electrode, see section 800.40(A) , new for the 2002 NEC
Re: Lightening strikes
The best bet is to install a TVSS device at the entrance, bond all other surge arrestors (CATV, Telco, etc.) to the GEC. Choose an AC service entrance device that only has protection modules between L-N, avoid all mode devices that have protection modules from L-G and N-G, there is no reason for them and only add cost. Put your money into the L-N modules, and make them as large as you can afford.
Then at each sensitive device install a point of use TVSS device to aid in arresting any let through at the service device. Don't worry about ground at the point of service devices, the EGC impedance is to high to offer any protection. Besides 99% of lightning strikes occur ahead of the transformer and the surge is in the differential mode so ground is not involved. The service entrance device will take care of the surge in common mode in residential applications. However a TVSS device made for computers that have connections for phone and cable act as a surge reference equalizer and are useful to limit common mode disturbances at the device. Hope that helps.
Dereck
[ September 06, 2003, 12:19 AM: Message edited by: dereckbc ]
Pat I missed this question first time around. There is no point in trying to lower the impedance of the ground electroce impedance as lightning has a very high frequency content and the impedance of the GEC will be many times higher than the electrode impedance. For example the typical impedance of a # 6 AWG copper coductor of 10 feet in lenth will exhibit 2.6K ohms of impedance at 10 Mhz. You add that in series with a 100 ohm electrode you still have 2.6K ohms. So if you lowered the electrode impedance to 5 ohms you have not gained anything 2.6K + 5 is still 2.6K.
The best bet is to install a TVSS device at the entrance, bond all other surge arrestors (CATV, Telco, etc.) to the GEC. Choose an AC service entrance device that only has protection modules between L-N, avoid all mode devices that have protection modules from L-G and N-G, there is no reason for them and only add cost. Put your money into the L-N modules, and make them as large as you can afford.
Then at each sensitive device install a point of use TVSS device to aid in arresting any let through at the service device. Don't worry about ground at the point of service devices, the EGC impedance is to high to offer any protection. Besides 99% of lightning strikes occur ahead of the transformer and the surge is in the differential mode so ground is not involved. The service entrance device will take care of the surge in common mode in residential applications. However a TVSS device made for computers that have connections for phone and cable act as a surge reference equalizer and are useful to limit common mode disturbances at the device. Hope that helps.
Dereck
[ September 06, 2003, 12:19 AM: Message edited by: dereckbc ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Lightening strikes
Dereck
Somthing that I never would of expected happened about three months ago.
We had a high surge from the power company power lines. I recorded it at 972 volts for a duration of 12.6 seconds. We got slamed with service call for the next few days and since I do most of the service calls I was able to get a first hand view at how surge protection was able to handle it.
the first thing I noticed was the in all the cases of the houses that had some point of use protection the MOV,s had shorted or blown open. This depended on sevral circumestances. in houses with only one surge device I found it blown open and or the circuit breaker on that circuit was triped, In houses with two devices on the same leg of the service they would be shorted but held agaist the surge by tripping the breaker and even tripping the main on houses with only 100 amp main's,
On the houses that had four or more with at least two accross each leg of the sevice and each on a different circuit in the panel even 200 amp main breakers were triped these people lost not one piece of equipment or the surge protectors. this was telling me that with good name brand point of use surge protectors installed to at least have two on each leg of the panel and each on a differant circuit they will protect the whole house. now there was some house that had one or two cheep no name types that just blew wide open and these people lost everything. but it was a great eyeopener Even right here with the six that I have and the four line conditioners the only thing that happen was I woke up to no power but I was able to just reset my main and everything was fine.
After some denial by the power company I was able to find out that a tree had fallen on a 56kv line and droped it down on a 12kv line of course they clam act of god but it would seem that there should of been some kind of protection from this?
as it happened at 5:06 a.m. and there wasnt a cloud in the sky or any wind.
Of course this was not a lightning strike but it did give me an idea that it could do a little good maybe for a lost neutral. as it should open a breaker or keep the balance without the neutral. as soon as I can I'm going to do some research into this and see just how much it will protect against a neutral loss.
Dereck
Somthing that I never would of expected happened about three months ago.
We had a high surge from the power company power lines. I recorded it at 972 volts for a duration of 12.6 seconds. We got slamed with service call for the next few days and since I do most of the service calls I was able to get a first hand view at how surge protection was able to handle it.
the first thing I noticed was the in all the cases of the houses that had some point of use protection the MOV,s had shorted or blown open. This depended on sevral circumestances. in houses with only one surge device I found it blown open and or the circuit breaker on that circuit was triped, In houses with two devices on the same leg of the service they would be shorted but held agaist the surge by tripping the breaker and even tripping the main on houses with only 100 amp main's,
On the houses that had four or more with at least two accross each leg of the sevice and each on a different circuit in the panel even 200 amp main breakers were triped these people lost not one piece of equipment or the surge protectors. this was telling me that with good name brand point of use surge protectors installed to at least have two on each leg of the panel and each on a differant circuit they will protect the whole house. now there was some house that had one or two cheep no name types that just blew wide open and these people lost everything. but it was a great eyeopener Even right here with the six that I have and the four line conditioners the only thing that happen was I woke up to no power but I was able to just reset my main and everything was fine.
After some denial by the power company I was able to find out that a tree had fallen on a 56kv line and droped it down on a 12kv line of course they clam act of god but it would seem that there should of been some kind of protection from this?
as it happened at 5:06 a.m. and there wasnt a cloud in the sky or any wind.
Of course this was not a lightning strike but it did give me an idea that it could do a little good maybe for a lost neutral. as it should open a breaker or keep the balance without the neutral. as soon as I can I'm going to do some research into this and see just how much it will protect against a neutral loss.
G
Guest
Guest
Re: Lightening strikes
Hurk27 said:
../Wayne
Hurk27 said:
I will be very interested in hearing the results of your research. This is very good stuff!
../Wayne
Re: Lightening strikes
Wayne what you are describing are things I have witnissed. I was fortunate to work for MCI. They had thousands of technical facilities located all throughout the country. My group was responsible for all power QA issues and investigations, and each year we had on average about 20 lightning strikes. The damage ranged from none to blowing out every TVSS device in the building. It all depends on the amount of energy in the event.
The case you are describing would be a high energy event and not typical. TVSS devices are designed for short milli-second events. I suspect what you were seeing with the tripped breakers is the MOV's shorted out, and had the capacity to trip breakers. While others gave thier life and tripped the main breakers.
I would like to point out that if you use enough point of use devices (class A) they can offer modest protection where used. However upstrem toward the main they cannot limit the voltage of a lightning strike because of the high impedance of the circuit conductors. What you are describing was accidental contact with MV over a long duration. The frequency was low 60Hz so the downstream units were able to offer some protection upstream.
I still stand by my oppinion and the engineering community oppinion that effective surge protection starts at the entrance, then work you way down through the system.
While you are doing some research I suggest you look into hybrid devices that use SAD as primary with MOV secondary protectors. The SAD provide speed, and MOV's provide bulk. Look into UL-1499 and ANSI C62.41 documents if you can obtain them. There is a wealth of information in those documents.
Dereck
[ September 06, 2003, 01:48 PM: Message edited by: dereckbc ]
Wayne what you are describing are things I have witnissed. I was fortunate to work for MCI. They had thousands of technical facilities located all throughout the country. My group was responsible for all power QA issues and investigations, and each year we had on average about 20 lightning strikes. The damage ranged from none to blowing out every TVSS device in the building. It all depends on the amount of energy in the event.
The case you are describing would be a high energy event and not typical. TVSS devices are designed for short milli-second events. I suspect what you were seeing with the tripped breakers is the MOV's shorted out, and had the capacity to trip breakers. While others gave thier life and tripped the main breakers.
I would like to point out that if you use enough point of use devices (class A) they can offer modest protection where used. However upstrem toward the main they cannot limit the voltage of a lightning strike because of the high impedance of the circuit conductors. What you are describing was accidental contact with MV over a long duration. The frequency was low 60Hz so the downstream units were able to offer some protection upstream.
I still stand by my oppinion and the engineering community oppinion that effective surge protection starts at the entrance, then work you way down through the system.
While you are doing some research I suggest you look into hybrid devices that use SAD as primary with MOV secondary protectors. The SAD provide speed, and MOV's provide bulk. Look into UL-1499 and ANSI C62.41 documents if you can obtain them. There is a wealth of information in those documents.
Dereck
[ September 06, 2003, 01:48 PM: Message edited by: dereckbc ]
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Lightening strikes
Great tech! Thanks Dereck.
Great tech! Thanks Dereck.
- Status