Why do phone sockets have a separate faceplate and test socket?

[#1]

This might be a silly question, but it seems worth asking. After all, it doesn't seem like sound engineering to add unnecessary points of failure.

My line terminates at a test socket, into which a faceplate is intended to be plugged, feeding the signal to another identical socket on the faceplate. I see no point in this arrangement. Why not just put the socket in the middle of the box and cut a hole in the faceplate to enable the phone/filter to be plugged directly in?

I used the word "intended" above because I just have my microfilter plugged into the test socket all the time and see no point removing it to refit the faceplate since that would just be a cosmetic change on a socket in a corner of the room where it's not normally visible anyway.

It seems a rather pointless design. Is there a reason for it?

[#2]

This is done to isolate the user (home) wiring for testing purposes thus eliminating problems caused by internal wiring.

[#3]

The Test Socket is the interface between BT and your home. Properly terminated extension cables are isolated when the faceplate is removed, hence when fault finding the probability that internal wiring, which is your responsibility, is causing the problem can be discounted. Obviously if you have no extension cabling then this is not a factor.

The other advantage is that a filtered faceplate can be fitted, eliminating the nead for a microfilter (and it's additional connections). 

[#4]

Different types of socket box could be manufactured just as easily to meet these different needs. It's no harder to make a different box than a different faceplate. There are no terminals to attach extensions on the faceplate I have, nor in the part of the box exposed when it's removed. It's not as if faceplates are regularly changed.

On my box, nothing is isolated when the faceplate is removed, except the replacement socket which appears unnecessary, since everything works without it.

I don't think that's much of an explanation.

[#5]

From your respose I assume that you have the latest type of box with the extension cable wired to the back box. These are quite clever in that removing the front panel isolates the extension wiring. As you have no extension cables then I agree that it adds nothing to your set up. However if you fitted a filtered faceplate and scrapped the microfilter you would have a neater arrangement with the same number of connections.

[#6]

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@kjpetrie wrote:

There are no terminals to attach extensions on the faceplate I have, nor in the part of the box exposed when it's removed.

Either this can't be correct, or you have something unusual. Can you show us a photo of it?

[#7]

@ejs 

The NTE5C lets you connect extensions without the insertion tool 

here's a link

https://www.ispreview.co.uk/index.php/2016/02/a-quick-look-at-bt-openreachs-new-nte5c-master-socket....

[#8]

Yes, and with the NTE5C, there's a bit to attach extension wiring to, accessible after removing the faceplate.

[#9]

I posted the link, because I believe this is the type of socket the OP is referring to.  

[#10]

I have just retrieved the faceplate from behind the cupboard where it had fallen. I have no idea where the screws have gone. I now see it does have three ID terminals to which extension wiring could be connected.

However, that still strikes me as poor design. Given that the current arrangement needs two sockets in series, wouldn't it be better to have two sockets in parallel - one for the main phone/filter and the second for extensions. Then the same effect could be achieved by unplugging the extension plug and there'd be no need to remove the faceplate to reach the "test" socket.

And yes, the main socket could be filtered into phone and ADSL sockets if desired, but then the microfilter would be part of the socket which makes it harder to test by swapping, which is why built in microfilters (even in the faceplate) might not be a good idea.

[#11]

You're just not listening. A filtered faceplate, which doesn't require the dangly microfilter, uses exactly the same number of in line connectors as plugging a dangly filter into the test socket.

The latest design is much simpler in that the extension wiring is connected to the rear section but is disconnected when the faceplate is taken off and a microfilter plugged in. Connection wise the faceplate is identical to having no faceplate plus a dangly filter, it's just that the microfilter is built in to the faceplate rather than hanging on a short length of cable..

Consequently in line connection wise your current arrangement is identical to fitting a filtered faceplate. I agree that using your original non filtered faceplate inserts another connector pair in line, which is undesirable.

[#12]

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@kjpetrie wrote:

However, that still strikes me as poor design. Given that the current arrangement needs two sockets in series, wouldn't it be better to have two sockets in parallel - one for the main phone/filter and the second for extensions. Then the same effect could be achieved by unplugging the extension plug and there'd be no need to remove the faceplate to reach the "test" socket.

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I, for one, disagree.  Just like many people don't want 'dangly' micro-filters and prefer to use a faceplate type, so there are many people who don't want extension cable(s) dangling either.  Some people actually prefer to have (completely) concealed wiring which would not be possible using your suggestion.

[#13]

I have a filtered faceplate but unfortunately I lost those dangly filter things ages ago.

Result:- the modem/router connector (RJ45) won't fit the RJ11 test socket - so its totally useless for testing.

[#14]

My understanding was that the idea of the removable face plate was not so much that the consumer can test the line himself, but that Plusnet can test the line remotely without the fear that there would be any interference from the house wiring, as the house wiring would be connected either directly to the removable faceplate or by means of cables plugged into the RJ11 socket on the removeable faceplate using a simple double or triple adapter.  I cannot really see what all the fuss is about, if the purpose is to allow remote testing of a virgin master socket.

[#15]

@shermans

I think your understanding is fundamentally incorrect. The remote test can't disconnect your extension wiring. It needs to be physically disconnected first. Who's doing the testing is not so important.