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[burakkucat]

Perhaps the self-install 'kits' of the future will contain instructions how to identify and remove a SP26 from the NTE5/A . . . 

[neilius]

A question for the knowledgeable sages of this forum - would there be any risk if one of these happened to 'fall' out or are they more of a hangover from the past and what's the point of them? I've heard a few reasons, like lightning protection (which I am doubtful of, unless it's very far away), or spikes caused by mains powered things in the end user's home somehow bridging over the phone wiring, to protect BT's wiring and its staff from a nasty surprise.

[roseway]

It certainly wouldn't protect the modem against a nearby lightning strike. I've seen a modem fry when connected to an NTE5 during a thunderstorm. The device glowed briefly with a rather attractive blue light...

[burakkucat]

Without looking up the relevant information, I believe that the SP26 or SP26/A is a 'throw back' to years gone by and is not that much use . . . especially when there is no dedicated earth connection made to the relevant terminal of the NTE5. For example my NTE5/A, an original with the 'T in circle' Beattie logo dating from the early 1980s, has screw terminals for the B-, the A- and a dedicated earth wire.

Does anyone else remember the original (pre-1959) block terminals? The service cable brought the B- & A-wires to dedicated line terminals, a bare copper wire running from an earthing rod was connected to a third dedicated terminal, there were shellac-coated carbon blocks between both the B- & A-wires and the earth and, finally, fuses in series with the B- & A-wires of the pair before the dedicated instrument connection terminals. How much 'protection' that gave to: (a) the local instrument (b) the exchange equipment (c) an engineer 'up a pole' or 'down a hole' is anybody's guess. 

[ColinS]

Does anyone else remember the original (pre-1959) block terminals? The service cable brought the B- & A-wires to dedicated line terminals, a bare copper wire running from an earthing rod was connected to a third dedicated terminal, there were shellac-coated carbon blocks between both the B- & A-wires and the earth and, finally, fuses in series with the B- & A-wires of the pair before the dedicated instrument connection terminals. How much 'protection' that gave to: (a) the local instrument (b) the exchange equipment (c) an engineer 'up a pole' or 'down a hole' is anybody's guess. 

Yes, the line of a friend of mine nearby is still connected via one of them! 

[Black Sheep]

I'm with B*cat on this. The 'protector' in the NTE5 is not a lightning protector, it is only a 2-terminal device and as such there is no path to earth. If additional protection is required to the circuit, a 3-terminal device should be installed at the DP.

ALL circuits are 3-terminal protected at the Exchange.

[burakkucat]

The 'protector' in the NTE5 is not a lightning protector, it is only a 2-terminal device and as such there is no path to earth.

That got me thinking.   

Knowing that I had, stashed away in my grotto, a cardboard box containing various gubbins I decided to look at the contents. Yes, there was an identical NTE5/A to that installed in The Cattery with the original 'T in a circle' Beattie logo. Looking at the rear, the plastic shroud is green and there are three screw terminals, for B-, A- and earth-wires. Being of the era when all six connections were expected to be made between the NTE5/A lower-front faceplate and any extension sockets, it has six IDCs on the former. Careful checking showed that the earth terminal is connected through to IDC4.

[Black Sheep]

Hmmm ?? You've now got me thinking ??

The full 6-wire connection scenario was only for 'Business Systems'. From memory, as it was a hell of a long time ago I last 'faulted' one ............ T1 and T6 were used to power the LCD displays on the system phones. T2 and T5 were the 'feed'. T3 and T4 were used to pass the call from extention to extention, IE: From the receptionist to the relevant caller. They were also used for the employees to get an outside line.

Therefore, my guess, and it's only a guess, is that T4 would be connected to Earth for old 'Earth Calling' systems ?? Please don't shoot me down in flames if I'm wrong  .

[c6em]

I Think BS is correct.
I still have the telephone earth connection here - it goes to a dedicated earthing stake in the ground outside the house. I also have the older NTE5/b with screwed connections and an earth screw point which is not connected to my earth wire

I thought the 'A26' unit was a simple surge arrestor such that if the voltage between A and B exceed its flashover point then it broke down and became a full short, thence 'taking the spike' back to the exchange and ground. Obviously not intended to protect against full lightning strikes.
Maybe at the higher frequencies of VSDL it is starting to react as a circuit component.

[burakkucat]

Earth recall . . . Yes, absolutely correct. 

And it was even specified for domestic circuits before all the public exchange equipment was standardised onto the current 'timed break' recall. One old telephone, of 1980s vintage, that I have given to my brother in law for use as his bedside phone has a recessed switch underneath to select the recall method which will be used.

c6em's NTE5/B clearly has the same back-plate as my NTE5/A . . . after all, the only difference between a /A and a /B is just the EU's lower front face-plate.

Maybe at the higher frequencies of VSDL it is starting to react as a circuit component.

Yes, that is the reasoning behind the latest revision of the NTE5.

Here is a page entitled Lightning and Telephone Equipment.

Some pictures of surge arrestors.

[snadge]

Sorry I'm late in keeping up with this convo, computer problems...  I would like to have clarified that someone previously said the bellwire/rf3 filter was on the nte5 faceplate, they are 2 different things here... And not one and the same thing.. 

Sent from my Sony Xperia Miro on Tapatalk

[asbokid]

I can confirm that on new NTE5/A's...the most recent ones, there is no surge arrestor, apparently omitted by Pressac on BT's request because they say it has an effect on the VDSL signal. Now it's just the cap and resistor on BT's side.

Perhaps the self-install 'kits' of the future will contain instructions how to identify and remove a SP26 from the NTE5/A . . . 

I'll give it a go (on a private circuit) to see how it fairs!

cheers, a

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[burakkucat]

I'll give it a go (on a private circuit) to see how it fairs!

Thank you, It will be interesting to see if you can measure any change in circuit performance. 

[snadge]

asbo - isnt that a new Openreach NTE5..?  Ive had that installed by an SFI just late last year when I had my problems, he said its new one as my other one was old and no good? (i still have it) and I thought it was just older ones that has this surge arrestor and new ones didnt?

also, a filtered faceplate or SSFP would not remove that from the connection would it? so why the talk about self installs being an issue with this surge arrestor? when the BT OR engineer comes and pops on an SSFP..any NTE5 he puts it on that has a Surge Arrestor is still gunna be affected by it (if it has an effect) - or is it in the Engineers remit to install a new NTE5 that doesnt have a SA on?

sorry but Iam confused lol...

ive been looking at the NTE5 on RunITdirect and doesnt seem to have any mention of RF3 filter built into the faceplate? only the bellwire choke
http://www.run-it-direct.co.uk/nte5-nte5a-bt-openreach-socket.html

[neilius]

Here's what the newest PCB looks like:



And compared rears with the previous (note that the numbers are the same?)...