BT Master Sockets - ring capacitor

Hi,

I currently run a very old in house BT Ultimate 106 6 extension PABX.

This device uses a pair of cables (2 wire) per extension with BT Master sockets which include a ring capacitor fitted as terminators.

I have two of these BT 106 units and they are both showing signs of failure ( one unit was a replacement for the other which needed repair)

If I fit Grandstream ATA units with FXO and FXS ports such as a HT813 and a separate HT814 can I just connect to the master sockets in a junction box and then take a lead to the RJ11 connector on the ATA's?

I know the PSTN is being shutdown but I do not have access to FTTP and I have not yet ported the number which the FTTC is also running on to SOGEA so I still need an FXO port.

Any issues with leaving the ring capacitor in place at the wall sockets?

If this is OK then I would convert to FreePBX.

Thanks

Edited by dlucas46 (Tue 10-Sep-24 23:22:39)

The master socket ring capacitor is a peculiarly British feature. Products intended for an international market which require a ring capacitor will in general provide their own, This includes ATAs.

The ring capacitor itself is in series with a high value resistor [see this: https://www.britishtelephones.com/pictures/ljumast.gif ] and if it is not used pin 3 remains open circuit and the exchange effectively sees just the resistor which is of no consequence. So you need do nothing about it, but if you are feeling bold, you can cut the capacitor leads, or just change the socket to a secondary.

Edited by DFScale (Wed 11-Sep-24 08:43:35)

In reply to a post by dlucas46:

If I fit Grandstream ATA units with FXO and FXS ports such as a HT813 and a separate HT814 can I just connect to the master sockets in a junction box and then take a lead to the RJ11 connector on the ATA's?

I know the PSTN is being shutdown but I do not have access to FTTP and I have not yet ported the number which the FTTC is also running on to SOGEA so I still need an FXO port.

Any issues with leaving the ring capacitor in place at the wall sockets?

If this is OK then I would convert to FreePBX.

Thanks

SOGEA - does not provided any voice service, so if you port the number to SIp you will only require a ATA with a FXS port, you can then connect the ATA to internal house wiring, but be sure to remove the cable going to the openreach's network.

You don't actually need the ring Cap in the socket, and it has not been required for some years unless you have a ancient telephone, as the ring cap is not used in Europe most telephones have a ring cap built in to the phones so you can leave them or remove them.

What are you trying to do? The Grandstream devices you have listed have enough physical ports but I am not aware of any PBX functionality that they have.

Hi,

I plan to install FreePBX instead and replace the Analog and failing BT Ultimate 106 PBX.

I was hoping to reuse the existing cable drops and sockets from the old PBX.

The plan was to install the Grandstream units where the current PBX is and using a junction box to connect the old CW1308 cable drops to RJ11 cables, these will then be connected to the FXS ports on the Grandstream units.

The sockets on the wall are all BT 2/2A Master sockets (not NTE type) with a ring capacitor.

Eventually when I can port the phone number to voipfone.co.uk and after I have updated my alarm auto dialler as well, I will be able to ditch the FXO port.

At some point I also intend to convert the majority of phones to IP phones and ditch the ATA devices.

I was going to have to use two units because I can no longer find an 6-8 port FXS unit which still have an FXO port to take the BT land line.

Unless you know of such a device still being around?

Thanks

This what you are looking for https://www.netxl.com/voip-phone-adapters/grandstrea... ?

In reply to a post by iannewson:

This what you are looking for https://www.netxl.com/voip-phone-adapters/grandstrea... ?

I was always under the impression that FXO ports were for Foreign Exchanges and that FXS ports were for local telephones.

Surely that device supports 4/8 FXO ports for connecting incoming PSTN Lines but only 1 FXS port for connecting an analogue telephone.

What I would need is 1 FXO port with 8 FXS ports to replicate my current setup. Or have I got this backwards?

According to this https://www.3cx.com/pbx/fxs-fxo/ you have it backwards. I think, LOL

In reply to a post by iannewson:

According to this https://www.3cx.com/pbx/fxs-fxo/ you have it backwards. I think, LOL

Well,

The setup documents for the HT841 linked above says this :

FXO ports to be connected to physical PSTN line from a traditional PSTN PBX or PSTN Central Office.
HT841 supports 4 FXO ports and HT881 supports 8 FXO Ports.

and

FXS port to connect analog phone / fax machine to HT841/HT881 using RJ11 telephone cable.

That would seem to support my view rather than the 3CX definition.

I think some of the older Panasonic units would do this for you.

For instance, the TEA-308
I see a few on ebay this morning.

I've installed some of these in the past. Old hat technology nowadays but I know of at least 2 systems still in operation in offices.

They will handle "ordinary" telephone handsets. There are proprietary Panasonic handsets but they are not obligatory.

I'm not sure about them handling DECT phones.