Phone line hit by lightning

[Carlosfandango]

Customer phoned on Friday looking for a few jobs done, he says his BT line has been struck by lightning twice this year wiping out phones and routers etc. Is there anything can be done to protect his gear other than maybe one of those surge protection extension thingys??

 

[Marvo]

There should be lightning protection in the main phone jack already. Surge protection on the electrical installation won't make any difference to the outcome if the phone line gets struck by lightning.

 

[Darkwood]

Get a mobile instead

 

[Carlosfandango]

Sorry I meant one of the extension things that have phone jacks on them too?

 

[Darkwood]

Is their cable available in the area as opposed to overhead bt lines?

 

[Marvo]

UK Telephone Wiring

The first photo on that linked page shows the spark gap surge arrestor in the main socket. I'm sure you can purchase supplementary in-line protection from RS Components or Farnell but if the direct strike is very close to the customer's installation it would still be a lottery whether the protection is going to prevent failures.

Another option would be to investigate optical isolation for the phone line but I think it might be expensive.

 

[Farmelectrics]

Do away with land line and just youse your mobile you don't get any cold callers either

 

[Burnt Fingers]

You might find that any supplementary protection other than that incorporated within some older NTE's (master Socket) may interfere with ADSL Broadband. However replacing the master is up to BT in cases of lightning strike and you can use a gas-discharge tube type protector before the router without a significant speed or signal quality loss - we used to routinely fit them. Farnells is the place to buy. Usually though, if even a near strike catches a phone line, the router is the cheapest thing they will need to replace. Marvo is right - that's a gas discharge tube and they are effective - but absent from modern NTE.

 

[Carlosfandango]

BT are going to look next week. I was up today and it had blown the master off the wall, but the armoured bt cable looked fine. What size of GDT would you fit and where?

 

[Burnt Fingers]

ADSL Broadband Surge Protector: Amazon.co.uk: Electronics seem similar to the ones we used to use, and for the price I think they are worth a go. Trouble with lightning is its big in volts, and sometimes, even a copper lightning band wont cope!

We tend to use these CITEL surge protectors, protection against transient overvoltages where we install multiline systems. One thing to remember though - you can spend a fortune but lightning will still be lightning...lotsa volts and not a clue where to put it. Like kitchen fitters.

 

[westom]

What size of GDT would you fit and where?

A discussion requires numbers. A surge may even be hundreds of thousands of joules. A protector that only claims to absorb hundreds of joules does what? Protection is always about where hundreds of thousands of joules are absorbed.

Will a 2 cm part inside a protector stop what 3 kilometers of sky could not? Of course not. Will that part somehow absorb hundreds of thousands of joules? Of course not. Those other protectors are only for a completely different transient that also does not harm modems and routers. Modems and routers already contain superior protection.

A surge that actually does damage must be absorbed by earth. Just like a lightning rod. Does the rod do protection? Of course not. The rod is effective (for structure protection) because it connects a surge harmlessly to earth. A protector is effective (for appliances) because it connects a surge harmlessly to earth.

Master sockets once contained these well proven solution. No longer because surges are so rare in the UK. Many are willing to just replaced damaged parts. And believe hearsay that nothing can protection from such events.

BT's switching computer is threatened by about 100 surges with each storm. How often is your town without phone and DSL service for four days? Never? Because BT installs this earthed protector on every wired BEFORE it enters the building. You need same on the master socket.

Classic examples are on page 10 of:
http://bourns.com/data/global/pdfs/bourns_osp_product_guide.pdf
Unfortunately even it is useless if not properly earthed. And best installed as far as possible from electronics (ie in the master socket). Unfortunately, rules say only BT can install it.

Protection is never provided by a protector. Either a protector connects low impedance (ie 'less than 3 meters, no sharp wire bends, etc) to single point earth ground. Or that protector only protects from another type surge that typically causes no damage. This rule applies to every incoming wire - not just telephone / DSL. Every wire must connect to earth either directly or via a protector before entering the structure.

These concepts have been proven by over 100 years of science and experience. And is why BT's $multi-quid switches remain unharmed with every storm.

 

[Burnt Fingers]

Which I think, is longhand for "One thing to remember though - you can spend a fortune but lightning will still be lightning...lotsa volts and not a clue where to put it. Like kitchen fitters."

 

[westom]

Which I think, is longhand for "One thing to remember though - you can spend a fortune but lightning will still be lightning...

Spend about £1 per protected appliance for a superior 'whole house' solution. Or spend tens times more money for other devices (ie ADSL Broadband Surge Protector: Amazon.co.uk: Electronics) that do not even claim to perform such protection. A less expensive solution diverts even direct lightning strikes to earth. Remains functional. And costs less. Because protection was always about earth ground.

 

[DPG]

'Diverts even direct lightning strikes to earth' - really??? Daz

 

[westom]

'Diverts even direct lightning strikes to earth' - really???

Why does BT suffer maybe 100 surges per storm without damage? Either lightning is connected harmlessly to earth. Or it hunts for destructive paths to earth via appliances. You make that choice. Earthing lightning without protector failure was routine for over 100 years. Today, even better devices accomplish that.

A lightning rod connects lightning harmlessly to earth to avert structure damage. An effective protector connects lightning low impedance (ie 'less than 3 meters') to earth to avert appliance damage. If not earthed before entering, then lightning will hunt for destructive paths to earth via appliances. Protection is always about a path for hundreds of thousands of joules to get to earth. Harmlessly outside or destructively inside.