Telephone linebox question (NTE5)

[Chris Hogg]

We had a thunderstorm on Sunday night. Spectacular lightening all around us. I saw it approaching and disconnected the TV and computer etc. Fully expected a power cut, but it didn't. But on reconnecting the computer after the storm had passed, no broadband connection, no dialing tone, no nothing. Quite dead. Even the test socket in the linebox was dead. However, ringing neighbours on our mobile showed we were the only ones without a land line connection. Engineer duly arrived yesterday; linebox had blown. Replaced it, and all now OK.

But what is it in the linebox that blows? A quick internet search talks about spark gaps and the like, but I haven't found anything that suggests a fuse. So what blows, and why is it so integral to the box that the whole box has to be replaced?

[Mike Tomlinson]

En el artículo , Bob Eager escribió:

Seems likely. If it did, it would short the line and render it inop (it would give 'busy/engaged' if called from another line.)

[Bob Eager]

There's a 'lightning arrester' (they probably call it something else) across the line. I suppose it could be a MOV but I've no idea really.

I would guess that could go short circuit. As for replacing it, that would involve soldering, and more effort 'cost' than a new box.

[Chris Hogg]

That makes sense. I tried dialing our land line number with our mobile, and got a recorded message that the line was engaged. So the surge suppressor was blown; presumably not a direct hit on the telephone line (overhead, hereabouts), as I would have expected our neighbours to be knocked out as well, but enough of an EMP to blow the suppressor.

Thanks both.

[Dave Liquorice]

Spark gap and it is what it says not a MOV.

Did the message use the word "engaged" or "unavailable". A line actually making a call would normally return engaged tone not a recorded message unless the line has a provider based answering service.

Or vapourise the tracks from the socket pins to components. Replacing the whole NTE is simply quicker and cheaper than the time taken to diagnose and fix a fault with it.

[Andy Wade]

Neither of those, it's a gas discharge tube (GDT).

Think of it as a butch neon tube, or for more info try

[Chris Hogg]

So how does it blow into an unrecoverable state? Or would it be DL's vaporised tracks that crippled the box?

[Graham.]

Just shows that the lightning arrester across the pair can work, I still think you are lucky there wasn't damage done to your router and phones.

[The Natural Philosopher]

well you haven't had a direct strike on an overhead telephone line so count yourself lucky. The whole cable disappeared . And that was just the start..

What blows is almost anything depending on how many induced votlts and amps there were. Thank you lucky stars your ADSL modem still works

There are all over the place spark gaps capacitors and varistors all designed to absorb surges, or, failing that, to blow.

I'd guess either a crimp blew open or a shunt protector blew closed.

[The Natural Philosopher]

[Graham.]

Years ago I used to maintain a Philips office phone system in rural Wales. It got zapped frequently, and each time the whole unit had to be replaced. So when it happened again we took a closer look, and one of the BT lines feeding it ran very close to a long run of wire fencing. After re-routing this dropwire, it never again caused trouble.

[Dave Liquorice]

Posh name for a spark gap. B-)

[Johnny B Good]

Is exactly right! :-)

On a BT exchange, you'd expect to receive an unavailable announcement or NUT when calling a number that has a loop fault (unless called within 60 seconds of the fault developing or after the S&Z cycle period if the fault occurred whilst on an outgoing call and the called number hung up on the call).

Getting PET for hours/days/weeks of such an "off hook" fault is typically the case with Talktalk exchange equipment (and possibly also the case with all of BT's competitor telco exchange equipment).