lightning protection circuit for set top box

[nel]

Hi everyone,

Pl. let me know wheather my circuit is correct for lightning protection. As i have connected it to my STB and is working fine i mean the picture is fine. As i could not draw i would like to describe it as follows:
first 100mA fuse and PTC c980 both in series connected between the LNB and STB.

the GDT(230 79 0)
the MOV 150v
the filter cap (0.010/K 250v/PPC)
All the 3 GDT, MOV, Filter cap are connected after the 100mA fuse and before the PTC in between the center wire and the outer wire of the coaxial cable and the outer wire of the coaxial is then grounded to earth.

 

[cmsajith]

A circuit for lightning protection? How will you protect this circuit from frying due to lightning?

 

[nel]

I think the 100ma fuse which is before the circuit will blow off due to execess current thus saveing the circuit from burning as the same circuit is used in my telephone lightning protection and it is working fine and atleast more then 10 time my EPEBX has been saved from burning it, as the fuse blow off every time when there is a thunder storm protecting the circuit and the EPEBX. As before installing this circuit on my telephone twice the EPEBX had burnt and the tech. told me to install it and till today there is no problem as far as i know this time even the wired broadband equipment on their centre had been burnt and was down for 2 days. So hope this circuit should also work for my DTH. What you say?

 

[shredder]

All steps taken by you are good and should contribute to your peace of mind. However, there is no real protection against lightning. All you can do is make sure to unplug everything at the first sign of an electrical storm.

 

[gobble]

But why do you want to protect lightning??! It will be gone in a flash anyways!!! Better you do something to protect your house and gear instead hyeah:

Cheers

 

[captrajesh]

AFAIK, all telephone lines coming to EPABX use GD (Gas Discharge) tubes which blow off in case of lightning etc. But I'm not sure how the GD tube would affect the PQ & SQ.

 

[nel]

But why do you want to protect lightning??! It will be gone in a flash anyways!!! Better you do something to protect your house and gear instead hyeah:

Cheers

i am not protecting the lightning, how can anybody prevent/protect lightning from happening i did this circuit only to protect the STB/tv from the charge which can induce in the RG6 cable if any lightning strike takes place in and around my house and i very well know if at all it strikes directly on the dish for that also i used some earthing to the dish so the extent of damage might be less and still i am thinking to install lightning arrester.

 

[cmsajith]

i am not protecting the lightning, how can anybody prevent/protect lightning from happening i did this circuit only to protect the STB/tv from the charge which can induce in the RG6 cable if any lightning strike takes place in and around my house and i very well know if at all it strikes directly on the dish for that also i used some earthing to the dish so the extent of damage might be less and still i am thinking to install lightning arrester.

If the line / cable catches the lightning supply, there is no way to protect your equipments except unplugging.

 

[nel]

AFAIK, all telephone lines coming to EPABX use GD (Gas Discharge) tubes which blow off in case of lightning etc. But I'm not sure how the GD tube would affect the PQ & SQ.

Yes i have the same. no i did not say the GD would effect the PQ & SQ but i meant that both are fine when i used it. As i checked in the market and i found one lightning protection which the shopkeeper told me that "when you use it the PQ gets effected and it has to be used only when the lightning is there and then remove it and keep it aside." I checked it by opening i found some small circuit in it with some MOV type components that too between the outer and inner wire and did not have any contect to connect the earth wire so i was wondering as to how it can ground the spike from the cable to the ground when there is no ground connection to it neither to the STB and TV.

 

[nel]

If the line / cable catches the lightning supply, there is no way to protect your equipments except unplugging.

Then how the same circuit has protecting the EPABX for more then ten times. Can you please explain it when even the neighbours EPABX are burnt when we are on the same telephone exchange. By the way do you know what is MOV and GDT and what are its function?

 

[nel]

Can any body tell as to how my EPABX is 100% safe and not even 99.999%. when there is thunder and lightning storm and the only thing i loose is 100ma fuse that cost me Rs. 5for the 5 fuses to replace it every time there is a storm?
i would like to thank for the correct answer.

 

[cmsajith]

Then how the same circuit has protecting the EPABX for more then ten times. Can you please explain it when even the neighbours EPABX are burnt when we are on the same telephone exchange. By the way do you know what is MOV and GDT and what are its function?

Please, go ahead with your circuit. If the circuit really protects an equipment from lightning, it can be a nomination for Nobel prize or one of the greatest invention of our century... Please inform us once you get, good luck...

@All, Please dont ever use any landline during thunderstorms, it can be life threatening..

 

[digitalv]

There is a reason why most equipment manufacturers don't cover lightning damages as part of standard warranty.

GDT's, MOV's etc work great in most cases but they cannot assure 100% protection and most importantly, their performance degrade over time and hence such protection cannot be taken for granted.

Due to lower capacitance, GDT's are better suited for high frequency lines but they are a bit slow in action meaning that the equipment might see higher voltage for a few hundred nanoseconds (and might get damaged too).

It's common sense to have some protection than none at all, but due to the very nature of lightning, no protection is as good as physical disconnect (but don't try to do so in the midst of a storm).

 

[nel]

Please, go ahead with your circuit. If the circuit really protects an equipment from lightning, it can be a nomination for Nobel prize or one of the greatest invention of our century... Please inform us once you get, good luck...

@All, Please dont ever use any landline during thunderstorms, it can be life threatening..

i can't understand why are you smelling like as if you are jalous i did not say i invented i only asked wheather my circuit is correct for lightning protection since i copied it of the EPABX lightning protection circuit and i didn't ask for a noble prize from you if you dont like the topic well i didnt force you to reply.
well i dont want to argue with you
thank you.
cmsajith

 

[nel]

There is a reason why most equipment manufacturers don't cover lightning damages as part of standard warranty.

GDT's, MOV's etc work great in most cases but they cannot assure 100% protection and most importantly, their performance degrade over time and hence such protection cannot be taken for granted.

Due to lower capacitance, GDT's are better suited for high frequency lines but they are a bit slow in action meaning that the equipment might see higher voltage for a few hundred nanoseconds (and might get damaged too).

It's common sense to have some protection than none at all, but due to the very nature of lightning, no protection is as good as physical disconnect (but don't try to do so in the midst of a storm).

Well for the first para you said it correct but they only give some protection from the 230volt supply side with MOV and Y & X type capacitorfor spike suppression and noise filter.

For the second para you rightly said it but i did this circuit just for the sake as there is a say "something better then nothing. Well i will be testing it whenever there is a storm by disconnecting the output cable from the circuit and see if the 100ma fuse blow off as i will not be disconnecting the input cable from the circuit.

For your 3rd para i thing you said a lot so can you pl. give some details as you are wanting to say something about the frequency and voltage. i want to know more about it as i know there is a difference between the 2 as tele has some 48v and DTH has 13/18v as far as frequency is conserned i dont know much so pl. through some light on it. i would be very greatfull to you.

In you last para you very well said it.

Thanks for you reply

Awaiting for you further reply soon.

thanks once again.

 

[StanleyB]

Can any body tell as to how my EPABX is 100% safe and not even 99.999%. when there is thunder and lightning storm and the only thing i loose is 100ma fuse that cost me Rs. 5for the 5 fuses to replace it every time there is a storm?
i would like to thank for the correct answer.

A fuse won't protect you. The fuse takes at least one mains cycle before it will blow. In a 50Hz mains system that is 20ms. Lighting strikes at a far quicker speed. Also, lighting can arc across VERY long distances.

For equipment that is not connected to any outdoor aerials or dish you can fit a mains fuse box with those resettable fuse. They trip far quicker than the traditional wire fuses.

But 100% safety is never guaranteed when it comes to lighting.

 

[borg]

A fuse won't protect you. The fuse takes at least one mains cycle before it will blow. In a 50Hz mains system that is 20ms. Lighting strikes at a far quicker speed. Also, lighting can arc across VERY long distances.

For equipment that is not connected to any outdoor aerials or dish you can fit a mains fuse box with those resettable fuse. They trip far quicker than the traditional wire fuses.

But 100% safety is never guaranteed when it comes to lighting.

fuse is not protecting the equipment but the MOV, it is a voltage dependent resistor. mov clamps down the voltage to safelimits instantly by absorbing the energy (but it has a limited capacity to do so, say 20j),so the fuse blows to protect the mov

 

[nel]

fuse is not protecting the equipment but the MOV, it is a voltage dependent resistor. mov clamps down the voltage to safelimits instantly by absorbing the energy (but it has a limited capacity to do so, say 20j),so the fuse blows to protect the mov

This is what i wanted to say. Also i have put tha PTC in series so that if the mov heats up the the PTC will blow off.

You said it 100% correct leave apart that we cant get 100% guarantee from the lightning but atleast something better then nothing.

Instead of opening the tv for repair or replacing the PCB of the tv atleast the fuse will blow off as you said it.

Thank you for it as i read it before doing the circuit but could not explain it as you did.

Thanks once again

 

[suri]

Surge Protection FAQ's

 

[StanleyB]

The fuse or MOW won't protect you. Lighting will jump across a blown fuse. Do you know how many KV lighting is? The fuse is designed for 250V, and many MOV are designed for 1KV. That is well below the lighting voltage ability.