Duncan Electric (Manufacturing) Co. (1901-1975)

Duncan Model A (DC)                                                  

Model A (1902 to 1908)                                                                                                          
This was the first model made by Duncan Electric Mfg. Co. and was similar in design to the Thomson Recording Wattmeter. The bearing was different from the other meters as the pivot was retained in the disk shaft by magnetism. Also, the jewel could be lowered for shipping to prevent damage to the jewel and the jewel post had a window that allowed inspection without having to take out the post. This model also incorporated a cover sealing arrangement similar to the one incorporated in the Fort Wayne K series of meters. This was also one of only two early Duncan models that incorporated a 5-dial kilowatthour register (5-dial registers at the time typically registered in watthours). 
Photo credit: Electrical Meterman’s Handbook. 

Duncan Model D (DC)

Model D (ca. 1905 to ca. 1911)
The Model D was a special version of the Model A made for those who did not care for a high-priced meter or require a high-torque meter. This meter has two unique features: It has a carrying handle built into the top and the cover slides on from and is fastened on the bottom. Although this was a commutator-type meter, many of this model were marked, calibrated, and sold for use on AC circuits.
Photo credit: Electrical Meterman’s Handbook.  

Duncan Model E, EA (DC)                                           

E, large version (1908 to 1930s?), E, small version (1910 to 1922), EA (1912 to 1930s?)
In 1908, the Model A meter was replaced by an improved version, the Model E. The Model E incorporated a more compact case, a 4-dial register, and a redesigned starting coil (light-load adjustment). Model E meters with serial numbers beyond 150,000 have no additional information printed on the register except for "Kilowatt Hours" in conformance with industry standards going into effect around this time. The EA meter was an improved version of the E with the coils arranged astatically to make the meter immune to external stray electrical fields. In 1910, the 2.5, 5, and 10 ampere ratings were replaced with a more compact version that fit better to the smaller DC services these were built for.
Photo credits: TOP – Electrical Meterman’s Handbook; BOTTOM: Phil Shelley  

Duncan Model ER (DC)

(1912 to 1930s?)
The Duncan ER meter consisted of a Type R switchboard meter element mounted on a Type E base. This shunt-type DC meter was for use on DC circuits from 100 to 10,000 amperes.
Photo credit: Handbook for Electrical Metermen  

Duncan Model EK (DC)                                                

(1922 to 1930s?)
In 1922, the Model EK replaced the low-capacity version of the Model E. The only difference between the two versions is the EK has a terminal chamber at the bottom to fit meter service cabinets which were coming into use around this time. 
Photo credit: Handbook for Electrical Metermen 

Duncan Model D (Single Phase)

Model D (ca. 1905 to ca. 1911)
Although this was a DC meter by design, many units were calibrated and sold for use on AC circuits. This was likely an attempt to get around a patent lawsuit brought by Westinghouse that prevented Duncan and Sangamo from selling induction-type meters (GE had a license agreement and was unaffected) until Tesla's patent expired at the end of 1910. This is also the only known North American model with a carrying handle built in, and the method of fastening the sheet zinc cover from the bottom is also unique to this model. 
Photo credit: Electrical Meterman’s Handbook. 

Duncan Model M (Single Phase)

Model M (1912, 1913)
   This model had all the major base pieces made from punched steel (base, terminal chamber, mounting frame, inner frame, etc.). Unlike other AC meters, the 90 degree lag of the Model M's voltage coil was accomplished by using a second air gap on the voltage coil and utilizing the reactance of the disk. The light load adjustment was also unconventional, as it consisted of small iron cores on sliders in front of the potential coil cores that were positioned to obtain the light load adjustment. The full load adjustment was a little more conventional, consisting of an iron disk that could be adjusted relative to the retarding magnet air gap. 
Photo credit: Electrical Meterman’s Handbook. 

Duncan Model M1 (Single Phase)

Model M1 (1913 to 1915)
As with the previous M, the M1's body parts were made out of punched steel. The lag load adjustment was changed to a plate that surrounded the voltage coil tips and could be adjusted up and down as needed. The light load adjustment was replaced with a system that used a hollow square of copper that was operated by a lever to move it left or right. The full-load adjustment was the same as on the M, and remained unchanged until the MF series meters were introduced in 1934. 
Photo credit: Electrical Meterman’s Handbook. 

Duncan Model M2 (Single Phase)

Model M2 (1915 to 1926)
The M2 meter was of a new design and easier to work with than the M and M1 meters. The enclosure and internal frame were now made of cast iron instead of punched steel. The potential coil on this meter was the same as used on the previous M1 meter, the coil having 2 sections connected in series on a U-shaped core. The light load adjustment was changed to a screw-type adjuster that allowed for more precise adjustment. The M2 used the same lag-load adjustment plate as the M1. The M2 came in three sizes, depending on capacity: 5-25A, 50A-75A, and 100-400A. The mid-size style exists in 2 versions - the earlier one shown below and a later style where the sides taper outward an inch towards the bottom.
Photo credits: TOP: David Turner Collection; RIGHT: Handbook for Electrical Metermen; BOTTOM LEFT: Watertown Municipal Utilities Collection. 

Duncan Model MD (Single Phase)

Model MD (1926 to 1934)
In the late 1920's as the meter companies incorporated improved compensations into meters to retain accuracy over wider temperature and overload ranges, Duncan revised their M2 meter to incorporate these improvements. This version is known with embossed or plain glass covers as well as a metal cover (similar to the M2's but without the DUNCAN embossing). In 1929, several changes were made to the MD's design. The power factor adjustment was changed from the adjustable plate to a closed loop of wire. The cover was changed to a studless version with a pair of twist-lock bayonet joints (similar to the arrangement used on the later Sangamo HC meters). One version of the later MD was also made with a terminal box that could accept conduit fittings for a more secure installation. 
Photo credit: David Dahle Collection 

Duncan Model MFS and MFA (Single Phase)

With standardization of meters in 1934, Duncan chose to replace the MD meter with a new meter design. Early MF meters had a large chrome-steel magnet assembly, but this was replaced in 1938 (S/N #2,650,000) with an Alnico magnet assembly which was less susceptible to loss of strength from lightning and power surges. The first MFS and MFA meters had painted register faces but these were replaced in 1936 with aluminum faces which were far less susceptible to fading and peeling from constant exposure to the sun. With S/N 2,600,000, the MFS and MFA meters were redesigned to increase the overload capacity from 300% to 400%. Earlier MFS meters have an insert-type base that allowed Duncan to use the same stator for the MFS and MFA, but this was eventually abandoned. MFA meters made during WWII used a base made of porcelain instead of aluminum. In 1949, the MF-SE was introduced and is the first socket meter to have a capacity of 200 amps.
Photo credits: TOP LEFT: Don Price Collection; BOTTOM LEFT: David Dahle; BOTTOM RIGHT: Watertown Municipal Utilities Collection. 

Duncan Models MKS and MKA (Single Phase)

Models MKS and MKA (1954 to 1960)
The MF single phase meter was superseded in 1954 by the MK single phase meter. This model was an entirely new design that took advantage of advances in meter design, including a new Alnico V brake magnet (the MF series of meters used an Alnico I magnet) and an increase in overload capacity from 400% to 667%. Interestingly, the 3-wire self-contained version is labeled 30 amperes but the current coils were rated at 50 amperes (the Kh of these meters is 12 instead of 7.2). The baseplate of the socket version was changed from metal to a compression-molded material. The MKS had an interesting choice of sealing methods - the cover could be sealed with the aluminum breakaway "T" seal coming into use at that time OR by using a small locking bar, it could also be secured with the more traditional screw and lead-wire seal used on the MFS. 
Photo credit: Austin International 

Duncan Model M2P (Polyphase)

Model M2P (1915 to 1927)
This meter had 2 M2 single phase elements in one case and resembles the GE D-6 and the Sangamo H polyphase meters. However, this model can instantly be identified at a distance by the prominent LINE and LOAD lettering on the two terminal chamber covers. 
Photo credit: Watertown Municipal Utilities Collection 

Duncan Model MD (Polyphase)

Model MD (1927 to 1934)
This model consisted of 2 or 3 MD single phase elements in a tall case with a common shaft and register, and like other polyphase meters of the late 1920s, the terminal chambers were moved from the sides to the bottom for easier and more secure wiring.
Photo credit: Watertown Municipal Utilities Collection

Duncan Model MF (Polyphase)

Model MF (1934 to 1936)
Along with the single phase version, Duncan introduced a redesigned polyphase meter in 1934. One unique feature introduced on this series of meters was an electromechanical device connected in series with the voltage coil (instead of the normal low-wattage bulb operated from a winding on the voltage coil) that indicated whether or not that voltage coil was energized. This series of polyphase meters was only available in A-base (like the Sangamo HF polyphase).
Photo credit: Watertown Municipal Utilities Collection  

Duncan Model MG (Polyphase)

Model MG (1936 to 1950)
In 1936, the MG series superseded the MF series, with two important changes: The retarding magnet was now made of Alnico and the sealing studs for the cover were eliminated. This was also the first model by Duncan to use a laminated disk which allowed for a reduction in the meter's size. This allowed the two-stator network and polyphase meters to be produced in a socket-type version (the 3 stator versions were only made in A-base). However, the stators were arranged front and back and not side by side like the other manufacturers' models, and problems from this design may have been a reason Duncan went back to a multi-disk meter with the following MH line of meters. The MG series now had a clearer designation which included the type of service and the type of base on these meters: socket, A-base (network only), and polyphase A-base ('P' designation). The 'reinforced' terminal cover used on the polyphase A-base meters is unique to Duncan.
Photo credits: LEFT: Marlow Galbraith; RIGHT: Watertown Municipal Utilities Collection. 

Duncan Model MH (Polyphase)

Model MH (1950 to 1963)
The MH series of meters was a simplification of the MG meter design by reverting to a multiple-disk design last used with the MF polyphase. However, the stators were made much more compact so the two-stator models could be produced in socket-type versions (and these models were the same size as the MFS single-phase model). A three-stator socket model was made using an oval cover and an adapter-type base that allowed it to plug into a standard socket. Also introduced at this time was the 'B' base (the forerunner of the 400-amp K-base meters) which brought the current coils directly outside the meter base to form terminals that slid into special clamps in a special enclosure for these meters, permitting a full 200 ampere capacity with a bottom-connected installation (but with the enclosure required, a socket meter would have sufficed). Incidentally, Sangamo did gear up to produce a line of 'B' base meters but only 4 units were built before production was abruptly halted! The self-contained MH meters were replaced by the ML series of meters in 1958, and the transformer-rated models continued until 1963. 
Photo credits: Electrical Metermen’s Handbook 

Duncan Model ML (Polyphase)

Model ML (1958 to 1963)
The ML series of meters were simply updated versions of the corresponding self-contained MH meters. Of the changes, these were the most noteworthy: The full-load speed was halved for more accuracy and the nameplate was changed to show the test and class amperes instead of the former full-load ampere rating. 

Duncan Model C, F (Switchboard)

Models C and F Switchboard (1909 to 1912)
The Model C was built self-contained in ratings from 100 to 3000 amps. The field coils were wound astatically from strip copper in ratings up to 600 amps. Higher ratings used copper castings for the field coils. In all other details, it was similar to the Model E DC meter. Because of the high full-load amperage rating of the C, a special feature was built into this model to make calibration easier: A second set of current coils rated for 10 amps was placed within a gap on each side of the main current coils. The Model F meter was identical to the Model C except for the cover which was metal with a glass front. Unlike the Model C, it was only offered for circuits rated between 100 and 600 amperes. 
Photo Credits: TOP LEFT: Electrical Meterman’s Handbook; BOTTOM RIGHT: unknown collection (photo found on eBay). 

Duncan Model R, FR (Switchboard)

Models R and FR DC Switchboard (1911 to 1930s)
The Model R was a shunt-type meter that was similar to the Model E DC meter. There were a few differences including large armature and field coils (astatically wound), gold commutator, and a diamond jewel bearing. This model was offered for use (with shunts) on circuits from 100 to 20,000 amperes, with larger shunts available on request. The Model FR replaced the Model F meter and consisted of the Model R meter element on the Model F base. This model was offered for circuits from 800 to 20,000 amperes (with appropriate shunts). .
Photo Credit: Electrical Meterman’s Handbook; No picture of the FR.  

Duncan Model MS (Switchboard)

Model MS Switchboard (1913 to 1915)
Not to be confused with the later MS single phase socket meter, this single phase switchboard meter was simply a back-connected version of the M1 meter. All the internal parts (nickel and copper) were polished as with other switchboard meters of its time. 
Photo Credit: Electrical Meterman’s Handbook 

Duncan Model M2 (Switchboard)

Model M2 Switchboard (1915 to 1926)
These switchboard models were based on the M2 single phase and M2P polyphase meters. The 'S' versions had a rectangular glass case and all the internal parts were either polished or lacquered. The 'A' version was the "poor man's" version of the 'S' version with a pressed glass cover and unfinished internal parts.
Photo Credit: Electrical Meterman’s Handbook; Clockwise from Top Left: M2S; M2A, M2PA, M2PS 

Duncan Model MD (Switchboard)

Model MD Switchboard (1926 to 1934)
The Type MD in both single phase and polyphase versions were also offered in switchboard construction but no pictures or construction details are available at this time. However, it would most likely have been similar to the M2 "S" style of switchboard case. 

Duncan Model MF-W (Switchboard)

Model MF-W Switchboard (1934 to 1936)
There were three versions of the MF switchboard meter, depending on the number of elements: (single phase - round, 2-element - oval, 3-element - rectangular).
Photo Credit: Electrical Meterman’s Handbook 

Duncan Model MG-W (Switchboard)

Model MG-W Switchboard (1936 to 1950)
As with the MG series of polyphase meters, the switchboard meters were more compact than preceding types, and came in various configurations depending on the circuit to be metered. 
Photo Credit: Electrical Meterman’s Handbook 

Duncan Model MH-W (Switchboard)

Model MH-W Switchboard (1950 to 1963)
The MH-W series of switchboard incorporated the same stator design as the MH polyphase meters, and these models were available in either surface-mount or semi-flush mount cases.
 Photo Credit: Electrical Meterman’s Handbook