PROVISION OF POWER PLANT FOR
SUBSCRIBERS' INSTALLATIONS

This page brings together all the GPO documents on power requirements and plant required at subscribers' premises.  The requirements change depending on the equipment installed and is based on power consumption.

Once the power requirements are known, the documents required can be referenced by the links below.

For information on Power apparatus - follow this link.

ENGINEERING INSTRUCTIONS
POWER
GENERAL
S1001
Issue 5, 25.4.66

PROVISION OF POWER PLANT FOR SUBSCRIBERS' INSTALLATIONS

1. General
This Instruction gives brief details of the methods to be used for providing power plant at subscribers' installations.  These methods include all-mains power units, primary cells, power leads and secondary cells charged by a power lead or by a mains-energized rectifier.

2. Choice of method of providing power supply
The most economical means of power supply (see annual charges in S0901) should normally be used.  Where a power lead would normally be the cheapest method a self-contained power plant may, however, be provided if justified by the size of the installation, line plant shortage, or service considerations.

Table 1 lists the E.I. references for the various methods of providing a power supply against the range of sizes of installations.

Neither a power lead nor a power-unit should be used for either a PA 450 police telephone and signal system or an installation using switchboards which have divided-feed cord circuits.

TABLE I
Installation requirement Methods of supply - E.I. references

Emergency services, e.g. Civil Defence, police, fire stations, ambulance centres and hospitals should not be served by a power-unit, without first inquiring whether standby battery-power to carry on full extension-to-extension service during mains failure is needed. They should never be served by a power lead.

When the public supply is to be used and is d.c. or other than 200 - 250V 50 c/s ac. the supply authority should be asked if any change of supply characteristic is under consideration unless it has recently been confirmed that a change is not contemplated in the near future.

3. D.C. mains areas
When it is desired to provide mains-operated power plant where only a d.c. mains supply is available, one of the following methods may be used:-

1. A Dynamotor No. 22 in conjunction with equipment suitable for ac. mains.
    

2. A static d.c./a.c. converter in conjunction with equipment suitable for a.c. mains. If this method is used reference should be made to the
   Eng. Dept. (S2/4) quoting the information as in par. 5.

4. Standby power supply
The power units available are for use without batteries, hence there is no standby if the mains supply fails.

If standby power plant is provided at the subscriber's request an additional rental is charged.

Any request for a reserve greater than that provided by the methods listed in columns 5-7 of Table 1 should be referred to the Eng. Dept. (S2/4)

5. Non-standard power plants
Power plant for any installation not referred to in pars. 2 to 4 will be specified by the Eng. Dept. (S2/4) and the following information should be submitted:-

1. Busy-hour load and daily load in ampere-hours.
    
2. Working voltage (nominal, also upper and lower limits).
    
3. Mains supply characteristics.
    
4. Accommodation and existing power plant (if any).