CALL BELLS AND SIMPLE FIRE ALARM SYSTEMS


P.O. ENGINEERING DEPT.
ENGINEERING INSTRUCTIONS
MISCELLANEOUS
Fire Alarms
B 1010
Issue 1, 1938

CALL BELLS AND SIMPLE FIRE ALARM SYSTEMS
Description of Apparatus commonly used

1. General
This Instruction describes the apparatus commonly used for call bells and simple fire-alarm system. The annual rental charges are specified in T.S.I. B2 and B4.

2. Bells (battery operated)
The operating data indicated below are applicable when the bells are used for fire-alarm purposes only.

(a) “Bell No. 17C”. 500 ohms, 3in. gong; used indoors on omnibus call-bell systems when a moderate ring is required.

  Nominal current Minimum current Maximum No. of cells
Operating Data 50mA 35Ma 18

(b) “Bells, Nos. 40A and 40B”. 50 + 50 ohms and 500 ohms, 4in, gongs; used indoors when a loud ring is required.

(i) “Bell No. 40A” with coils in parallel (25 ohms); is usually connected in the local alarm contacts of an indicator for continuously-ringing bell systems.

Operating Data Nominal current Minimum current Maximum No. of cells
Coils in Series 90mA 70mA 6
Coils in parallel 170mA 120Ma 3

(ii) “Bell, No. 40B”. 500 ohms; is specified for omnibus call-bell systems in indoor locations.
      Operating data As for “Bell No. 17C.”

(c) ”Bell No. 41A“. 50 + 50 ohms, 3in. gong; used similarly to “Bell No. 40A,” when a moderate ring is required.
    Operating data As per “Bell No. 40A.”


3. Bells (Magneto)

  1. Bell No. 53A”. 1,000 ohms, 6in. gong. Used indoors or outdoors on generator call bell systems when a loud ring is required. A 2uF condenser to be fitted in series and charge for this is included in the bell rental. Shown to right.

  2. Bell-set No. 26”. 1,000 ohms, 2.5in. gongs. Used indoors on generator call-bell systems. The bell is connected with the 2uF. condenser in the earth lead. This bell-set is invariably specified on magneto systems, unless a renter asks for a loud sounding bell.

4. “Boydell Head” (Birmingham pattern)
This cast-iron head, together with a post, if required, is designed to house a “Telephone, No. 97 or 99” and should be purchased as necessary, through the Stores Department, from Messrs. Boydell, Leigh, Lancs. 

Boydell Box exterior Boydell Box interior with Telephone No. 99

Boxes, F.A.

5. “Box, F.A., No. 7”
This is a weatherproof box (shown right) designed to house a press button or switch and is suitable for mounting out of doors on walls outside fire stations and other places, as public operated call-points. The public gain access to the switch by breaking the glass. This door is secured by a simple catch, which can be released by pressing button A, or locked as desired by a “Key, Telephone, No. 47.”

6. “Box, F.A., No. 8”
The pictures below show the outside view of the box and the code signalling and trip mechanism inside. The box can be mounted on a wall or on a “Pedestal, Box, F.A., No. 8”; its operation is as follows:

  1. To operate the alarm, the glass inset on the outside of the door is broken and the handle is pulled down. This action winds the mechanism, which commences to transmit its code number immediately the pull handle is fully depressed (whereupon the engaging gear trips) or when the handle is released.

  2. The hinged trigger-arm (A) engages with the winding lever (B) and depresses
    it. A toothed sector (C) attached to the other end of the winding-lever axle, meshes with the spring winding mechanism and winds the spring. The code wheel (D) revolves anti-clockwise and the projections cause contacts E to make and break, thereby earthing the line intermittently.

  3. The code is transmitted four times, and the mechanism then comes to rest ready for the next pull. It is arranged that the code-signalling mechanism cannot be operated until the spring has been wound sufficiently to revolve the code wheel at least once.

  4. On the sub plate is mounted a Morse signalling key (F) and a telephone jack (G), for testing purposes by the fire brigade staff.

NOTE: When ordering these boxes it is necessary to quote the code number of the wheel, which is requisitioned separately. The code numbers should preferably be two digits, and 6 should be the highest digit. The first digit of a code number should preferably not be less than 2.

Box, FA, No. 8 closed Box, FA, No. 8 open


7. “Box, F.A., No. 9”
This box is designed to house a “Switch, 2-way, No. 1,” or “Press Button, G, Black, indoors,” and was introduced in connexion with the operation of power sirens (see A 3003). The glazed door is secured by a single ball catch. A recess in the side of the case enables the door to be readily opened by finger pressure. It is not intended that the glass be broken, although it may be readily replaced should this occur. The broad surround may be sign written locally with suitable instructions to open.

Box, FA, No. 9 Case, Switch, Fire Telephone, FA, No. 176


8. “Cases, Switch.”—”
Case, Switch, Fire Telephone, F.A., 176”

This case was specially designed for use with “Telephones No. 47“ (private fire telephone) but can be most effectively associated at fire stations with “Telephones No. 97” (public fire telephones). With 18 “Cells, Leclanché, Air-tight, No. 2,” a direct telephone line up to 800 ohms resistance can be satisfactorily worked ; alternatively, a power lead may be provided from the nearest exchange if the voltage of the exchange battery is not less than 40v., if this would be more economical in annual charges. A minimum of 24v is necessary at the terminals on the “Case, Switch”.

9. “Case, Switch and Indicator, D 9735”
This offers a convenient method of mounting indicators, keys, jacks, etc., used at a fire station or ring out point on simple fire alarm systems. A microtelephone can be added if required.

10. “Cells, Leclanché, Air-tight, No. 2”
This cell, which is specified exclusively on simple fire-alarm systems, differs from other Leclanché type cells in that it is air-tight, and its satisfactory operation is dependent upon this. Evaporation is prevented by closing the jar with a glass lid fitted with a rubber gasket, which rests upon the ground edge of the jar and is held down firmly by the weight of the central element. When properly set up, the cells may be left untouched, so far as the inside is concerned, throughout the life of the elements. The following points should be carefully observed when installing these cells:

  1. Strength of electrolyte. Thirty-two fluid ounces of saturated solution per cell is required, i.e. 10 oz. of Chloride of Ammonia (Sal-ammoniac) dissolved in 22 oz. (1.1 pints) of water. Chloride of Ammonia in solid form should not be placed within the cell, but should always be added as a saturated solution.

  2. Chloride of Manganese should not be used.

  3. The ground edge, lid, gasket and outside of the jar should be carefully wiped dry of all traces of the solution before the lid is placed in position.

  4. It may be necessary to add a little solution to the cell after a few hours, to make up for the liquid absorbed by the sack element, and to bring the electrolyte up to the proper level.

  5. The bottom of the zinc and the sack element should be at the same level. The blackened top of the zinc should be approximately half submerged in electrolyte.

11. Generators

  1. “Generator No. 8 AN” will ring up to 10 “Bell-sets No. 26.”

  2. “Generator No. 13 FN” will ring up to 15 “Bell-sets No. 26.”

  3. “Generator No. 106” will successfully ring 30 or more bell-sets.

Generator No. 13FN Generator No. 106

12. Indicators

(a) Indicator 400-type
”Indicators No. 401 DN “ (8 ohms) are connected in series with bell groups on battery-operated omnibus call-bell circuits, and on magneto systems when the number of magneto bells in a group exceeds 5. Groups of five (or fewer) magneto bells should be rung through an “Indicator No. 401 HN”(50 ohms).  These are an eyeball type indicator in a wooden box.

(b) “Indicator No. 2201 AP”
This indicator (1,000 ohms) is used in conjunction with continuous-ringing call-bells or for terminating lines to call-points and for operating an alarm bell.  These are a drop flap style indicator in a wooden box.

13. Keys and mounting
The illustration shows a “Key No. 212 “in a “Key-mounting, NV.” This is a very convenient way of mounting single keys. The keys commonly used on call-bell systems are “Keys, Nos. 68, 72 and 212.”

14. “Posts, ‘Brown,’ F.A., large”
This post is used to house a “Press Button, Locking, F.A., No. 1 or 2,” or” Press Button, F.A., with glass front” (non-locking) when a non-code-signalling public call point is required. It is the post used by the London Fire Brigade with the “Brown” system.  The post is shown to the right.

15. Press buttons

  1. (a) “Press Buttons, Locking, F.A., No. 1 and 2”
    These press buttons “make” one and two sets of independent spring contacts, respectively, and are used for fire-alarm purposes when a “break glass before operation” and a locking press button is required. They are housed, with the glass removed in “Posts, Brown, F.A.,” or “Boxes, F.A., No. 7" as public call-points and they also are the standard fire-alarm press buttons in P.O. buildings. The alarm usually continues until released by the fire-fighting personnel.

  2. (b) “Press Button, F.A., with glass front”
    This press button is non-locking and is used similarly to the locking type.

Press Button, Locking, FA, No. 1 & 2 Press Button FA, with Glass Front

16. Relays

  1. “Relay No. 4354 “ - make 3, 50 ohms, operating current 50 mA - is the relay specified on multiple group call-bell circuits operated from public callpoints or duplicate ring-out points. The relay is associated with a “ Mounting No. 151.”

  2. “Relay No. 3034“ - make 4, 30 ohms, operating current 75 mA - has been specified when there has been four bell-groups.

17. Switches

  1. “Switch, Housebell. F.A. 145 “
    Used for controlling house-bells at fire stations, or call-bells, independently or in groups. The bells can be commoned by strapping the appropriate connexion plates. The two meters act as indicators when ringing out. The front of the cabinet and the case are protected by a glazed cover.

  2. “ Switch, Housebell, F.A. 154“
    Similar to the “ Switch, Housebell. F.A. 145,” provides for an acknowledgment signal from each call bell rung. The reply signal is received at the station on the indicators.

  3. “ Switch, Time, Mechanical, No. 2 “
    This switch enables three battery-operated bell groups to be rung simultaneously in one operation, the ring ceasing automatically after an interval of one minute. A spring mechanism is wound when the ring-handle projecting below the case is pulled down. The code wheel revolves to the lower stop and when the handle is released, rotates slowly back to its original position. At the same time, the projections oil the periphery cause the three sets of contacts to make and break and re-actuate the call bells.

18. “Telephones, Nos. 97 and 99“
These are used on simple direct public telephone fire alarm circuits and are housed in Boydell heads mounted on posts on the pavement or attached to convenient walls. They employ C.B. and magneto signalling respectively. They are rented at ‘Tariff I)‘ rates.

Telephone No. 97 Telephone No. 99

 

BACK Home page BT/GPO Telephones A - Z Index Glossary of Telecom Terminology Quick Find All Telephone Systems

Last revised: September 08, 2003

FM