1920’ish Pole Transformers

A model railroad often will have pole mounted transformers since they are a detail that are ubiquitous in the “real world” .. are often a detail that helps to add authenticity to a scene. In smaller scales a simple cylinder with a couple of beads glued on is fine if any distance from the viewer. When the transformer is closer to the viewer then the simple transformers may be problematic. Larger scales simply make that more obvious. In the following I will be focusing on a reasonable representation of transformers on a model layout … attempting to make sense (from a modeler’s perspective) how to model and wire them. Reality sometimes pokes it’s head in .. most times not so much.

For now I am going to focus on “Distribution Transformer which provides a final voltage transformation in the electric power distribution system, stepping down the the voltage used in the distribution lines to the level used by the customer.” – Wikipedia

Wikipedia classifies distribution transformers into different categories based on factors such as – (I am striking through items I am not concerned with as a modeler)

• Mounting location – pole, pad, underground vault: Pole yes, pad perhaps .. underground vault transformers are used in urban areas where above-ground space is at a premium. is not really useful for a layout I think.
• Type of insulation – liquid-immersed or dry type: Important to modeling only if it affects the visible outside design
• Number of phases – single phase or three phase: This is important for our modeling since this tells us how we wire the primary and secondary lines.
• Voltage class – Transformer voltage classes, generally, are categorized based on the voltage level of the high-voltage windings, with Class I transformers having 69 kV and below, and Class II transformers having 115 kV to 765 kV.
• Basic impulse level (BIL): The breakdown voltage of an insulator is the minimum voltage that causes a portion of an insulator to experience electrical breakdown and become electrically conductive.

I model in the early part of the 20th century so I am using the October 10, 1914 issue of the Journal of Electricity, Power and Gas “Sketches for Hanging Transformers” to get a handle on poles, transformers etc. Having great fun .. these things can be a complete model all in itself. 1914 was 111 years ago and the tech used then has constantly changed and things like utility poles have evolved greatly.

“The notes on transformer hanging do not represent hard and fast rules . The construction foreman will use his best judgment to secure the best results , but where no distinct benefit will be derived by deviation from these rules , then they should be followed exactly.” (ahh .. “Modeler’s License”)

“The sketches shown apply to single phase 2300 or 11,000 volt transformers of 50 k.v.a. or less (for modeling purposes a 50 kVA transformer can on average power 5 homes), and open delta banks of 30 k.v.a. or less (An open delta transformer uses only two single-phase transformers to provide three-phase power. This is less expensive than a full three-phase setup but has reduced capacity. Open delta systems are often used in rural areas where the load is small and widely spread out, or for motor loads. Here’s a nice video showing how this works and how to wire it – Open Delta-Open Delta) “For banks of larger transformers two -pole transformer racks are built . These are known as Class A or B substations ; the former has a 10 ft. x 20 ft. platform surrounded by a railing for the convenience of trouble men , while the latter contains footboards only.“

It’s important to note that these arrangements for hanging transformers is only from a single source. The era was a time that technology was evolving rapidly so what we have is a single “Snapshot” from that time. For me the fun part is making a model that is interesting and mostly looks correct for the time period.

Single Phase – 2,300 Primary and 440 Volt Secondary (TH1)

Transformer Hanging for single-phase – 2300 and 440 Volt transformer poles.

Single Phase – 11,000 Volt Primary (TH2)

Transformer Hanging for single-phase – 11,000 Volt transformer poles.

Three Phase – 2,300 Primary and 440 Volt Secondary (TH3)

Transformer hanging for three-phase 2,300 and 440 Volt transformer poles.

Three Phase – 11,000 Volt Primary (TH4)

Transformer hanging for three-phase 2,300 and 440 Volt transformer poles.

This is like being an archaeologist .. these poles are long gone and I am sifting through this old magazine instead of sand to understand how they were constructed. The complicated arrangement to me means that modeling this will be quite fun. Below I am summarizing what I get from examining these transformer hanging drawings TH1-TH4.

• The crossarms are all the same length except for the 4-pin arm on TH1.
• The secondary arm and 4-pin arm on TH1 and the secondary arm and double 6-pin arms on TH3 are Green.
• The double 6-pin arm on TH1 is Yellow (from Bill of Materials/BOM).
• The BOM for TH2 lists 2 “4x6x8 Special Transformer Arms”. These are labeled simply “Double Arm” on the drawing. I can’t read this well but suspect it is 4″x6″ x8′ dimensions.
• The “Cut out boxes and fuses” on TH2 “Styles 1&2” and “Cut out boxes and fuses” on TH4 “Styles 1-2-4” refer to how the wire enters.
• Crossarm braces on TH2 are listed in the BOM as 28″

When I saw the crossarms painted yellow and green I was curious. Color photography was still quite rare in 1914 .. I suspect that a color photo of a transformer pole would be like finding a chicken with teeth. Note that these painted crossarms appear on the 2300 & 440 drawings, both Single and Three phase.

The drawing shows the ground wire, ground wire molding and straps. In the Bill of Materials a Ground Cone is mentioned. From the same magazine I found a diagram showing “Standard Grounding for transformers, lightning arresters or metallic pins at railroad crossings. Clear redwood is used for molding, there being 1-1/2 inches of wood around the conductor at all points“.

The molding is 3-3/4″ dia redwood with 4 ft. between the straps.

Pole Sizes: I am using the Pole Dimension calculator from WoodPoles.org to dimension my poles. In my world will be 40′ Class 4 made from Yellow Pine. Class 4 Wood Poles are suitable for secondary power lines. The 40′ is simply because of the visual look for placement of the crossarms (see Crossarm Position lower down).

O scale:
Class 4 Yellow Pine, Pole Height – 40 ft = 10″, Base Diameter 6′ from ground – 10.6″ = 0.22″, Top Diameter – 6.7″ = 0.14″. Nice .. taper a 1/4″ wood dowel.

Timber Color: I “assume” that the primary arms and pole are creosoted for modeling purposes. In 1913 the US consumed 108 million gallons of creosote oil, 26 million pounds of dry zinc chloride and 4 million gallons of other liquid preservatives. Interestingly less than 30 percent of the 135 million cross-ties annually consumed were treated and further that “The proper treatment of an annual consumption of 4 million poles may to be said to have scarcely commenced“. Creosoted timber is initially a dark green or brown color, timber preserved with zinc chloride or chromated zinc chloride, can impart a dark reddish color to the treated timber. Naturally over time this changes to a gray or silver-gray due to sunlight exposure and weathering. For my own purposes I think that for a c.1920’ish scene any preservative use would not have faded that much … but some .. so say .. brown’ish rather than black.

Crossarm Sizes: My source for this is from “The Song of the Open Wire” . The drawing shows 6-pin and 4-pin cross-arms. From a General Electric Supply Catalog published in the late 1920’s a 4-pin “Power Arm” is 5’6″ and 6-pin is 7’9″ in length. The crossarm itself varies but seems to be ~ 3’x4″ +/- ½”. Again .. this link goes into insane detail. Looks like everything else pin spacing varies widely but a ptin 4″ from the end and pins spaced 16″ apart seems fine.

O scale (1:48) :
3″ W x 4½” H = 0.0625″ W x 0.094″ H … 1/16″ W x 3/32″
6 Pin – 1.94″ Long, 4-Pin – 1.375″ Long

Crossarm Position: The 1914 source says –
for 2,300 and 440 Primary –

– One secondary and two primary arms on transformer pole-
On 35 ft. poles transformers are hung directly on the secondary arm instead of on a separate arm.
On 40 ft. poles the transformer arm is placed 2 ft. below the secondary arm. (O scale .5″)
On 45 ft. poles and over the transformers arm is placed 6 ft below secondary arm. (O scale 1.5″)

– One secondary arm and one primary arm on transformer pole-
On 35 ft. poles the transformer arm is placed 2 ft. below the secondary arm. (O scale .5″)
On 40 ft. poles the transformer arm is placed 4 ft. below the secondary arm. (O scale 1″)
On 45 ft. poles and over the transformer arm is placed 6 ft. below the secondary arm. (O scale 1.5″)

– for 11,000 Primary –
On 40 ft. poles the transformer arms are placed 4 ft. below the 11,000 volt arm. (O scale 1″)
On 45 ft. poles , 7 ft. (O scale 1.75″)
On 50 ft. poles , 10 ft. (O scale 2.5″)

This 1958 video shows attaching the crossarms and erecting the poles. They use 5/8″ bolts and I am guessing a 3″ square washer – Tichy #8082 with a 4″ washer and 2″ square nut will work. This was really interesting information and a fun watch. Simple crossarm braces can be flat 30″ long 1/4″ x 1-1/4″ .. in O scale that would be 0.625″ x 0.005″ x 0.026″. You can get Evergreen strip #101 at 0.010″ x 030″. 1/2″ bolts/lag screws – Tichy #8034 with a 1″ bolt, 1-1/2″ nut and 3″ washer will be oversized a bit but will work fine.

Gains or equivalent means shall be provided for increasing surface contact of crossarms with round wood poles. Where gains are cut, the depth shall be not less than 1/2 inch or more than one inch. _{Original General Order 95}

Crossarm Color: Same as the timber color unless we follow the 1914 direction to paint the double 6-pin arm yellow and the secondary and 4-pin arms green ¹. Why are only the 2300 and 440 volt Single and Three Phase crossarm painted? I’ll have to consider that .. I don’t want my brain to explode. On a side not .. Roman statues were not white marble but painted, often in garish colors.

Found a California Code from 1915 – “Crossarms to be painted yellow – … any wire or cable which shall conduct … more than 600 volts .. painted a bright yellow ..” <sup>2

3</sup> Discussion about painting all high voltage crossarms green rather than yellow because the yellow would meet with disapproval by the public and green blending in more. Apparently, this was a “thing” for a short wile.

So. Early in the 1900’s that was some thought/use of green and yellow painted crossarms, reflected in two of the drawings, TH1 and TH3 which appear to me to be by the same draftsman/source. TH2 and TH4 look like a different draftsman/source.

1 – Journal of Electricity, Power and Gas” Volume 33 published 1914
2 – The Statues of California and Amendments to the Code: Page 1060 – 1915
3 – Paper by J.E. Macdonald 1912 from the Journal of Electricity, Power and Gas 1913

Grounding: In O scale that 3-3/4″ molding (ground wire cover) would be ~ 0.078″ – Evergreen #212 rod is 0.080″ … in HO ~0.043″ dia.