Protection Equipment for Open Wire

Protection Equipment for Open Wire Systems and Equipment


Early rural 1900-1910 Kellogg Magneto wall phone set. These were protected on farmer mutual open wire lines by the station protector shown below.

Early 1919 Station Protector. The red tubes were series fuses and the black Bakelite twist knob below housed the carbon for lightning protection.

Close-up of interior of lightning protection feature under Bakelite twist cover. Note copper ground below lower porcelain hardware.

From an early guide to mutual telephone company practices, this primative–but effective–station protector, was the first line of defense against errant power and current surges over open wire party lines.

These protectors were also used in railway stations, depots and at exposed call box locations along a route.

Early 1900s AT&T No. 61 Protector at junction between lead cable and aerial wire.

Distributing box and terminal with lightning arrester schematic, non-railway.

Wiring diagram for long-distance distributing boxes with room for lightning protection.

Open wire was exposed to lots of nuisences, some man-made and many acts of God and nature.  To combat these threats to its proper and continued existence, openwire lines were built with adequate grounding, proper bonding, overcurrent as well as overvoltage protection.

In the collection are a number of Bell System protective devices, which correspond neatly to associated similar protection apparatus of the REA/RUS and Independent Telcos.  Lets discuss a few of them and how they functioned to protect an open wire line from man and nature.

118B Protectors on 10-pin arm, bonded and grounded.

Western Electric’s 104-Type Protector (capacitance-resistance type)

104B Western Electric Protector. Internal view. Rubber grommets at bottom (right) allow for bridle wire entrance and exit. Hinged snap cover pulled.

Here the culprit to an openwire line’s satisfactory operation is man.  By building a.c. power distribution and transmission lines, either crossing the path of the openwire line or paralleling it closely for many miles, induced voltages occur along its length. These induced voltages can become quite high and this 104B Protector balances “drainage” from both sides of a telephone circuit (tip and ring) to ground.  


It is very good at what it is designed for, because it is important that the device not interfere with the standard operation of an energized pair.  Some protectors were designed for only one pair, others two pairs, which allowed them to be hung by a strap to a crossarm and connected with bridle wire runs to the energized pair and one firmly bonded ground wire to the common neutral of a joint-use pole, or the telephone ground furnished by the telco on the pole.  


In both cases, the connection to ground must be made not with merely a “butt ground,” which is stapling a concentric spiral of ground wire around and beneath the pole butt.  But, must be accomplished with a lengthy 6′ or 8′ ground rod driven deep into the soil.  


At the conductor attachment points, using bridging sleeves, the bridle wire is crimped and tightened with a tool.  Sometimes, it is necessary to use a special connector such as the one shown below:

104B Wiring diagram on hinged snap type cover interior.

Western Electric’s 108 Type Protectors (inductive-capacitance type)

Open wire again is fighting man’s civilized streak, so the various communications companie have perfected another type of protector to combat induced nearby power line voltages.  In the Bell Culture, this was the 108-Type unit, which was used where voice and carrier frequencies were applied to the line wire pairs.  Again, proper bonding and grounding is necessary to ensure a proper follow-through path to ground from induced a.c. currents.


It is always important to use a Voltage Tester on the multi-grounded neutral, if joint-use poles’ ground is used.  That confirms the grounded portion of the plant will accept this drainage current safely by the use of the 108 Protector.

Western Electric’s 116 Type Protector for Openwire Lines

In the application of a 116 Type Protector (or similar REA-acceptable apparatus), the problem isn’t man–it is nature.  It is vital that lightning exposed above ground openwire lines don’t carry high voltages down to both aerial and buried cables and damaging them.  Indeed, these protectors are vital when you have a meeting of openwire to cable, multiple burred wire or subscriber drops.  


The 116 Protector can easily be mounted on the strand of a multi-pair cable or self-supporting aerial sheathed cable, typically at the point of junction between the media.  It can also be directly mounted on crossarm faces or lag screws can join it to the pole surface directly, if needed.


In the unit, open it and find a connecting block with binding posts arrayed in a row of six pairs.  There are two grounding terminals and twelve associated protector units.

Internal wiring of Western Electric 104B Protector for open wire lines. 1960s vintage.

Western Electric’s 118A Protector for Openwire Lines

The 118A is a small encapsulated device composed of a mounting bracket by which two screws fasten it to the crossarm, a round metal can-type cover and a base where the three leads enter and exit.  One lead is for grounding; the other two are for direct connection to the openwire pair.  This unit can only serve one pair on an openwire line.  


This device is different from the others because it protects against man’s accidental nature; in the event of an accidental power contact between high voltage secondaries or primary circuits and the telephone conductors, the protector will protect the openwire pair from damage.


The equipment is simple to understand.  By connecting the openwire leads to the pair and then grounding it, the only path for high tension power to follow through is through separated carbon blocks inside the protector’s aluminum cover.  The carbon acts as an insulator to typical telephone currents but allows power-follow-through when accidental contact with high voltages is made.

REA 2-pin Sidearm with Lightning Arrester installation.

The 108C Protector

The 108-Type Protector for induced voltages from neighboring a. c. power circuits.

Internal view of the unit illustrating inductors and capacitors.

Protector for railway open wire communications circuits, c. 1940s. External view with hanger bracket for crossarm..

Internal view of protector for railway communications. Note white porcelain bushings on left end instead of rubber grommets.

Base of protector with porcelain entrance and exit bushings.

Western Railway & Supply Terminal (unprotected) mounted directly to pole below lowest double arm for insertion of signal connections to control hut. Some terminals were equipped with protected terminal blocks; some not.

Open Wire polarity diagram: to residential drop customer

Protection where open wire and aerial/buried cable interface

Open wire to cable junction protection

Drainage units for power contact protection

Open wire power contact protection from a.c. neighboring lines

Bonding and grounding of protector units

Five pair crossarm style protection unit grounding

Power distribution contact protection units for REA open wire

Bracket lead protection devices for REA and independent lines

American Railway Association/Communications Section Protective Equipment

McGraw-Edison Pyrex Valve Arresters on signal circuits below 750 volt a.c. American Railway Association/Communications Section specification.

Protection of open wire railway communications and signal systems required higher voltage and current-rated equipment.  Here are some of the most commonly seen lightning arresters and fuse cutouts typical of the period from 1912 up to the 1950s.

Overvoltage Protective Equipment for Railway Use

Crystal Valve Lightning Arrester for under 1,000-volt service. Note the base ground has been cut, but the lead in to the primary circuit is intact.

Crystal Valve Lightning Arrester for signal circuit protection with railway companies.

Pyrex glass lightning arrester housing on this 3-kV valve-type Line Material Industries unit. Placed on signal circuits for lightning protection. 1933-1950s. Called a “Granulon Arrester.”

Hubbard & Co (later Joslyn Mfg. & Supply Company) Autograp 3-kV lightning arresters, c. 1950s. Dual gapped. An external and one internal (expulsion) gapped arrangement

This is a Hubbard & Company (having later merged into Joslyn Mfg. & Supply in the 1940s) Autogap expulsion arrester. Possessing two arcing gaps (one external and one internal) the overvoltage would simply be extinguished by powerful gas explosive action.

3-kV General Electric 1950s version of a dual gapped arrester. However, this unit had both an initial external air gap and a valve-action combined to arrest surge voltages.

Westinghouse Autovalve 151-500-volt lighting arrester, 1930-1940s. Top view. Taken from Cottonwood Falls, Kansas Santa-Fe Railroad installation.

Two Westinghouse Autovalve Lightning Arresters installed on a pair of signal circuit leads. Note the heavy current conductor used and large heavy duty dead-end insulators. From rural Chase County, Kansas Santa Fe (deceased) lead in 2004.

Joslyn Manufacturing & Supply 3-kV valve type lightning arrester with mounting bracket, c. post 1966. Primary terminal at top and ground at bottom.

McGraw-Edison 3-kV E6 valve arrester for crossarm mounting.

Westinghouse Magnavalve 3-kV arrester, 1970s.

Overcurrent Protective Equipment for Railway Use

2.-kV Westinghouse unit left; General Electric Plug-type cutout on right. 1912 vintage.

Line Material Industries (McGraw-Edison/Cooper) style fused cutout for 750-volt circuits or less. 1940s period.

Side view of same L.M. Cutout. Holes in housing allowed it to be mounted in parallel with the crossarm by lag screws.

James R. Kearney Company 1940s Enclosed Cutout (5-kV). Door assembly with hot stick hook is to the left containing the internal fuse. When fuse element blew, door dropped indicating failed link.

Door open exposing the internal fiber tube (barrel) containing the fusable element. Elements can be either single or dual. The links are kept on hand for various current amounts. 20-amp is very common.

Early 1930s General Electric Enclosed (door type) cutout. Action similar to the Kearney model above. Note non-standard hanger bracket. Pre-NEMA standards.

General Electric 5-kV Enclosed fuse cutout (expulsion type) with door and porcelain housing. ANSI Gray color indicates it was manufactured after 1966. Door on this model was made of fiberglass resin materials.

While the porcelain cutout holders are equipped with 100-amp switch blades, these units more often carried a fiber fuse tube or barrel. Inside the barrel was the single or dual element fuse link. UPRR installation.