Does polarity matter when wiring an RJ11 jack ?

Usjes

Hi,

The main phone line coming into my house is ancient, see photo attached. It is simply a single twisted pair of grey/white wires which dates from the 70's or maybe a few decades earlier. Anyway, the white wire is at +52V relative to the grey one and I am wondering does the polarity matter when I connect these to the central two pins on an RJ11 ? Could I damage a phone/fax/ADSL modem by wiring it incorrectly. Also, there are 3 different connections radiating from this main line in a star topology, would it matter if the polarity was different on some of the connections eg:
- Connection1: Grey -> pin2, White -> pin3
- Connection2: White -> pin2, Grey -> pin3
- Connection3: White -> pin2, Grey -> pin3

Thanks,

Usjes

ED E

Jaysus, hope you arent running DSL over that mess....

NB: Not an electrician, dont take electrical advice from strangers over the net

The irish two wire system doesnt care. As long as you dont short em out you're golden. If you're doing a rewire and plan on using DSL I'd strongly advise trying to get your hands on a proper filtered NTU from eircom or a similar generic.

Usjes

ED E wrote: »

Jaysus, hope you arent running DSL over that mess....

NB: Not an electrician, dont take electrical advice from strangers over the net

The irish two wire system doesnt care. As long as you dont short em out you're golden. If you're doing a rewire and plan on using DSL I'd strongly advise trying to get your hands on a proper filtered NTU from eircom or a similar generic.

Yes, it may look pre-historic but I've been running ADSL over it for about 10years now, largely without problems. I changed the modem recently and moved its location and that seems to be when the problems started so I've just been fiddling around with all the connections noting their polarity etc. and changing the ADSL filters to try to see if I can get to the bottom of the problems. I seem to have a stable broadband connection again now but there is a lot of intermittent noise on the phone receiver so I was wondering if wrong polarity on one of the links could be the culprit. My line dates back to the Teilecom Eireann days so no proper NTU but the broadband modem measures SNR at 17dB and above which is well beyond the 6dB min. required by ADSL.
This 'proper filtered NTU' you suggest, is this something I could buy in any electrical store or should my phone provider supply one ? Since the problems started I have been considering calling out my phone provider but I am confused as to whose responsibility these connections are. Consulting the Eircom interface doc (http://www.reci.ie/Portals/0/Documents/eircominterface.pdf) I see that it defines the NTU as the termination point of the Eircom network and => anything beyond it is the customer's problem but given that they failed to supply me with an NTU does that mean that everything is their problem ? Indeed even the interface doc is ambiguous; it says 'The NTU 2001 is the termination point of the eircom network' . So does that mean the NTU itself is part of the Eircom network or not ? Because I suppose the circular junction in my previous attached photo could be considered an NTU, albeit an anchient one.

ED E

Theres a few terms related to this kinda stuff:

ETU: External Termination Unit - Pothead or box on the outside wall, if present.
NTU: Network Termination Unit - The "Master Socket" essentially. Where eircoms responsibility stops.

New NTUs have two parts, the NTU itself and the CCU which incorporates a DSL filter. When this faceplate is removed it disconnects the entire internals of the premises, so you or they can test the eircom portion of the line by itself and nothing else. If these tests are clean but theres problems when the CCU is re-inserted, the problem is yours to fix, if not its eircoms fault to find. Theres BT style ones on amazon, but havent seen eircoms one. Presumably its a standard part if you found out the number.

If the phone is noisy put a handset directly onto the line at the point picture and disconnect your internals for a few minutes. See if its still noisy. If so get your provider to log a fault.

Also, if your SNR is that high theres room for improvement, but you may be limited by package or the exchange.

SpaceTime

Polarity isn't an issue on the eircom network - as long as the line is on the centre two contacts, it should work fine either way.

Equipment shouldn't care either at your end or their end.