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GradeShift UDL Instruction Manual

Last updated 22/03/2018

3.1 PSTN Connection

Telephone Line Connection

There are several different types of telephone line available from different service providers.

GradeShift requires an analogue telephone line connection. ‘Earth Loop Calling’ or ‘Earth Calling’ types of analogue telephone line cannot be used.

GradeShift cannot be directly connected to any type of digital telephone line.

Earth connection

In accordance with EN regulations GradeShift does not require an Earth connection at the telephone line terminals.

Analogue PSTN Telephone Line

The analogue PSTN is a communication network where the line from the exchange equipment and the service supplied to the subscriber is ‘analogue’, i.e. not ‘digital’.

A telephone line is always terminated at the user’s premises by an NTP (Network Termination Point) which is provided by the Telecoms Service Provider. This is a socket or connection where the user’s equipment can be connected. Some NTPs provide a socket and terminals for connection.  In many cases, the NTP operates using power supplied from the exchange equipment via the telephone line.


Figure 1 Analogue PSTN Telephone Line

PSTN Line Connection Options

GradeShift’s PSTN connection requires an analogue telephone line (also called a POTS line).  Analogue telephone lines often carry ADSL (Broadband) signals as well. Refer to ADSL later in this section.

Connecting other telecoms equipment in parallel to the analogue telephone line used by GradeShift can stop the unit sending polling calls and alarm calls to an Alarm Receiving Centre.  Parallel connection should not be used for GradeShift when it is used in a security system.

There are several ways that a GradeShift may be connected to a PSTN telephone line particularly when other equipment needs to share the same telephone line.  Some require that your Telecom Service Provider supplies particular line features. Some require GradeShift NVM programming options.

The highest security PSTN line for GradeShift (Recommended):

A PSTN line supplied as ‘outgoing calls only’, i.e. Incoming Ringing Barred,

AND the PSTN line is ex-directory,

AND the PSTN line goes to the GradeShift ONLY.

Other equipment can be connected to the GradeShift A1 & B1 terminals (i.e. series connection) to make outgoing calls only. See Figure 3.

The next best security option for a PSTN line (Recommended):

A PSTN line supplied with the ‘3-way calling’ feature,

AND the GradeShift NVM is programmed for ‘3-way calling’,

AND the PSTN line goes to the GradeShift ONLY.

Other equipment can be connected to the GradeShift A1 & B1 terminals (i.e. series connection) for incoming and outgoing calls. See Figure 3.

The ‘no security’ option ( NOT Recommended )

A PSTN line supplied without ‘outgoing calls only’ or the ‘3-way calling’ feature. This option cannot cancel or ‘hold’ incoming calls and these will inhibit the GradeShift from making a telephone call to the Alarm Receiving Centre.

Parallel Connection ( Do NOT use )

The GradeShift A & B terminals connect to the telephone line, and other equipment connects directly to the same telephone line. See Fig 2. This connection option can not cancel or ‘hold’ incoming or outgoing calls to other telephone equipment on the same line, and these will inhibit GradeShift from making polling & alarm calls to the ARC.

Figure 2

PSTN Line Connection (GradeShift ALONE on line)

Your Telecom Service Provider should be asked to supply and fit an analogue line and an NTP with terminals near the alarm system. The alarm installer should then follow steps 1 & 2 below.

Series Connection (GradeShift & OTHER EQUIPMENT on line)

Your Telecom Service Provider should be asked to supply and fit an analogue line and an NTP with terminals near the alarm system. The alarm installer should then follow steps 1 to 3 below.

1.  Connect 2 wires to the GradeShift’s PSTN A & B terminals.

2.  Connect the other end of the wires to the NTP connections for the incoming telephone line, marked A & B, or 2 & 5.

3.  If the PSTN line used by GradeShift is shared with other customer apparatus (e.g. telephone, fax or answer machine) connect the GradeShift’s terminals marked A1 and B1 to a new PSTN Master Socket. The customer may then plug their phone, fax etc, into that socket. See Fig 3.

A PSTN Master Socket type LJU2/4A is suitable and has screw terminals for connection. These can be obtained from many electrical distributors including:

CPC                Part Number:  TE 05285

Maplin             Part Number:  FT48C

RS                  Part Number:  472-534


Where the GradeShift’s telephone line is shared with the customer’s phone/fax etc. you can avoid GradeShift’s polling calls interfering with the customer’s calls.


Setup a programmable output on the panel to operate when the panel is set/unset. (When unset, the customer is likely to be in the premises and using the phone.) Connect this panel output to GradeShift’s ‘pin triggering’ terminal 4.

In this way, GradeShift will know when the telephone line is likely to be used and can avoid making polling calls that clash with the customer’s calls.

PABX (Private Automatic Branch Exchange)

A PABX is a telephone exchange in one business or building (where a dial 9 is needed for an outside line). It connects to one or more outside telephone lines and has two or more extensions within the business or building.  See Figure 4.

GradeShift may be connected to one of the outside telephone lines where they are the analogue PSTN type. See Figure 4.

The extensions within the building may be analogue or digital.  Where an extension is analogue, a normal phone or fax machine may be connected. GradeShift may be connected to this analogue extension. See Figure 4.

Where the PABX is mains powered and it is not battery backed-up then the extension line to the GradeShift may fail in the event of a mains failure. This may make this type of telephone connection unsuitable for GradeShift in alarm applications.

Where the extension is a digital line then a special ‘feature phone’ is usually required, provided by the manufacturer of the PABX equipment.  GradeShift cannot be directly connected to any type of digital telephone line.


Figure 4 PABX with connection to Analogue PSTN Line

ADSL (Asynchronous Digital Subscriber Line) or ‘Broadband’

When an analogue PSTN telephone line also carries ADSL (Broadband) signals and it is used by a security system e.g. GradeShift, then an ADSL (Broadband) filter MUST be used.

A filter is used to separate the analogue telephone signals from the Broadband digital data signals because the phone or security system may be disrupted or completely inhibited if Broadband digital data is allowed into them from the telephone line.

The CSL CS0720 Broadband Filter is designed specifically for use with security systems.

This item meets all of the requirements of the British and European telephone and security standards. See Figure 5.

Other types of filter and plug-in filters should not be used for Series Connection of a security system to the telephone line.

The installer must ensure that the Broadband Filter is fitted in the wiring between the NTP and the GradeShift’s A&B terminals.

Other items connected to the GradeShift’s A1 and B1 terminals must be analogue equipment, i.e. phone, fax. Note that a computer or broadband modem will not work if connected here because the Broadband Filter will stop the entire broadband signal from reaching the GradeShift.       

Figure 5


Q. Why is a Broadband Filter necessary?

A. When ADSL (Broadband) digital data is supplied on a normal PSTN telephone line then an ADSL (Broadband) Filter must be fitted between that telephone line and each item of ‘non digital’ equipment because:

1).  The operation of ‘non digital’ equipment may be disrupted or completely inhibited if ADSL (Broadband) digital data is allowed into it from the telephone line.

2).  The operation of  the ADSL (Broadband) equipment may be disrupted or completely inhibited by the connection of unfiltered ‘non digital’ equipment to the telephone line.

‘Non digital’ equipment means anything that can be used on a normal analogue PSTN telephone line, e.g. a Phone, Fax, GradeShift, Control Panel Digi-Modem.

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