Northwestern Electric

10 HP 3-Phase Siren Motor

Cleaning/Restoration

The original motor for my Federal STH-10 was a 220V (low voltage) / 440V (high voltage) 3-phase Valley Electric motor, which burned out and was thrown out, so I found and obtained this late 1950s / 1960s Northwestern 10 HP 3-phase motor from a Federal SD-10 siren. On this page, I cover the motor's restoration.

When I brought the siren/motor home from SirenCon, I tried to attach a box to the motor. However, the thread of the connector (1/2" to 3/4" compression connector meant for EMT conduit) was a fine thread instead of the coarse thread required for the box. As a result, all I kept doing was spinning the connector until the nut on it became loose. This meant that I needed to open the motor end bell up to access the connector.

I tried to remove the screws with the screwdrivers I had and sprayed the bolts daily for about a week, but was unsuccessful. So, I paused and waited until one day when I was at the hardware store (unrelated). There, I found the biggest screwdriver I could find and bought it, although I had some doubts that it would work.

With the help of a propane torch and the screwdriver with a vice grip attached for more leverage, each screw started coming out (FINALLY!). After that, I removed the end bell with the armature on it because I could not get the washer off the shaft. However, everything looked good inside, which I already knew because I had opened the end bell on the top of the motor before just to take a look.

Here is the motor before I started taking the screws off the bottom end

Here are the screws that were stuck

(2x are in use at the time of this photo to keep the end cap on while I move the motor for painting)

Here is that 1/2" to 3/4" compression connector. Not sure why they used that, considering that the hole where the wires are is threaded for a 3/4" coarse thread.

Here is the inside of the motor, the windings are in pretty good shape.

Restoration Photos:

Here is the end bell back on the motor casing.

Photos of the completed painting.

Here in this photo, you can see I finally got an electrical junction box installed. SD-10s generally didn't have a junction box on the motor because the siren had a housing that covered it, unlike the STH/STL-10. I added a 90° connector which allows more clearance for the stator since adding a box right onto that spot would have issues with the box hitting the stator.

Federal STH-10 siren back together after motor restoration.