Wiring a Lionel 1033 transformer

When it comes to wiring a Lionel 1033 transformer or its brothers, the Lionel 1044 and 4090, there’s more to consider than just which posts to use. The size of the wires also matters. If you derail a train 4 amps of power can run through the wire for 10-15 seconds before the circuit breaker kicks in. Although this is less of an issue than with Lionel’s larger transformers, a 1033, 1044 or 4090 still has enough power to melt wire and make it smoke or even catch fire.

Proper wiring for the 1033 transformer is a bit of a safety issue. It’s not just about preventing voltage drop to keep your train running smoothly. A smooth running train is nice, but safety is a must.

Pinouts for wiring a Lionel 1033 transformer

Wiring a Lionel 1033 transformer
With the Lionel 1033, the U post goes to the center rail, and either the A or B post goes to the outer rail. The convention is the same for the later 1044 or 4090, they just use a different styled case. These transformers are extremely common, having been in nearly nonstop production from 1948 to 1984.

The throttle corresponds to either the A-U and B-U posts. The U post goes to the center rail of your track. The A or B post go to the outer rail. Using the B post gives you better low speed control and a lower top speed. The A post gives a higher top speed, while sacrificing lower speeds.

If you’re going to power accessories off the 1033/1044/4090, you probably want the A-C posts for 16 volts. The B-C posts provide a less useful 11 volts. The undocumented A-B combination gives you 5 volts, but bypasses the internal circuit breaker. Use an external circuit breaker if you use the 5 volt connection.

Proper wire sizing

If your wire runs are no more than 10 feet long, you can get by with #18 gauge wire for your track. This will keep voltage drop at an acceptable level and sufficiently carry the current. If you have a larger layout requiring runs of 10-15 feet, step up to #16 gauge wire. For longer than 15 feet, use #14 gauge wire.

For your accessories, you can generally use thinner wire. The draw will be lower and there is much lower risk of short circuits. For lights, #18 gauge wire is usually sufficient. For switches, some people drop even lower, using phone cable.

In this application, there’s no difference electrically between solid and stranded wire. Stranded wire is more flexible and less likely to break. Breaks in wire are hard to troubleshoot, so it’s better to go with stranded wire if you can.

Be sure to get more than one color. It’s much easier when you come back years later to splice in another wire if it’s color-coded.

Bus wiring or star wiring

There are two ways to run wires throughout your layout. Both have advantages.

The old-fashioned way is to use bus wiring. With bus wiring, you make loops of wire all the way around the underside of your layout. For a 1033/1044/4090, you would make a loop for the A or B terminals, and a second loop for the U terminal. Also, when you figure your wire lengths for your wire gauge, only half of it counts, since it’s a loop. The electricity will take the shortest route. If you have more than one transformer and you phase them, the other transformer can share the loop that goes to the outer rail.

Then, at every point where you need feeder wires to your track, drill holes in the table, run wires up to the track, and splice those wires into the loop. I like to just cut the wire, strip back a bit of insulation, then twist all three wires together and secure them with a wire nut. There are special connectors for splicing without stripping wires, but I don’t find them as reliable as wire nuts. You’ll need yellow or red wire nuts due to the size and quantity of wires involved. You can use thinner 18-gauge wire for the short distance between the track and your bus, since the bus does the heavy lifting.

For star wiring, you run pairs of wires all the way from the transformer posts to the points on the track where you need a connection. Some modern electronics require this method to work properly. The downside to this method is it uses more wire.

Regardless of the style of wiring you use, you need feeder wires every 3-4 track joints to minimize voltage drop. Start over with your counting at each switch or crossing, as switches and crossings cause more voltage drop than regular track sections.

I prefer bus wiring, but if you run newer trains with sound and command control, you may have to use star wiring.

Adding protective circuit breakers

The 1033/1044/4090 has an internal circuit breaker, but it can take several seconds to trip. To protect your wiring and your layout, it’s best to add additional circuit breakers. Lionel’s 91 and 92 circuit breakers were each rated at 3 amps. Alternatively, you can use an American Flyer 1275 or Marx 420 circuit breaker. I like the American Flyer 1275 because it has an adjustment knob. Here’s how to use the Flyer 1275.

Normally a single train will not draw 3 amps, and a 3 amp breaker trips instantly in the case of a derailment.

To protect your wiring, install a breaker between your transformer’s U post and the track. If you use the A-B posts for an accessory that runs on 5 volts, install a breaker between one of those posts and the accessory. Install the breaker on the post that isn’t going to the track. That way, if a breaker trips, you can tell whether it was the train or the accessory that tripped it.

Some people use modern-production resetable miniature circuit breakers rated at 3 amps, but I haven’t been able to find one that even a ZW can trip. Until I can identify one that works reliably, I’ll continue to recommend the old Lionel ones.

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