American Flyer 1275 circuit breaker instructions

Last Updated on April 9, 2017 by Dave Farquhar

In spite of being older and rarer than the Lionel 92 circuit breaker, the American Flyer 1275 circuit breaker usually sells for less. It performs essentially the same function and is easy to adjust.

Here’s how to hook it up.

The American Flyer 1275 is a red box with an on/off switch, a thumbscrew for adjustment, and two wires. If the insulation on the wires is frayed, shore it up with some heat shrink tubing.

The thumbscrew is labeled high and low. This refers to voltage, not sensitivity, so setting it “low” actually increases sensitivity. You want to loosen the screw, then tighten it back just enough to avoid nuisance trips. If you tighten the screw all the way, the breaker is too tolerant to work safely. In the event of a short circuit, you want it to trip almost instantly.


Most transformers have built-in circuit breakers. When you use it to protect an accessory line, simply run the circuit breaker between your transformer and the accessory on one of the posts. If you don’t have the transformer’s accessory output phased with any other transformers, it doesn’t matter which post you use. But if you do have it phased, it’s best to use the hot post, not the common or base post.

If your transformer’s circuit breaker doesn’t trip after 12 seconds after you short two terminals together, using an external circuit breaker is a safe alternative to opening the transformer and replacing a breaker.

When connecting the circuit breaker between your transformer and your track, use the hot post, not the base (or common) post. American Flyer’s instructions said to use the common post, but the problem with this is that if you have a large setup with multiple phased transformers, leakage can occur and you can still have some voltage present if the breaker trips. If you use the hot post, this condition can’t occur.

The other advantage to using the hot post is that it makes it easier to find the fault when the breaker trips. If you put the circuit breaker on the common, more than one thing can stop working depending on where the breaker is in the circuit.

Marx transformers don’t have their posts labeled. Generally speaking, on Marx transformers that have two terminals the base post is on the left and the hot post is on the right. On Marx transformers that have four terminals, the base post will be the post on the top, and the hot post will be the one on the bottom.

Lionel was inconsistent in what post did what. So I collected a chart to help you figure out which post is hot and which is common or base.


The circuit breaker has a sliding on/off switch. When the switch is on, the trains or accessories operate. When the switch is off, they don’t. In the event of a short circuit, the breaker will buzz, then click, and the switch automatically flips. Fix the condition, then flip the switch again to restore power.

You can tighten the thumbscrew in the back to reduce nuisance trips. Sometimes a Flyer link coupler or Marx tilt coupler contacts the center rail for an instant and you don’t want that condition to trip it. But when it comes to a true derailment, the faster it reacts, the better.

Historical information

The 1275 circuit breaker isn’t in any of my guides. The instruction sheet I’ve seen bore a date of June 1932 and William Ogden Coleman’s initials. Its brass plate bears the address of 2219 South Halsted Street in Chicago. That building still stands, but they stopped making trains there in 1938.

It’s an interesting artifact and it functions just fine if you want some extra protection for your trains. It costs less than Lionel’s equivalents. And if Lionel isn’t your favorite brand, you’ll appreciate having something that doesn’t say Lionel on it.

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