Testing circuit breaker...Stumped!

You're going to have to be more specific on your hookups, as there really isn't a dedicated "hot" or "common on the Type R:

Going out the C and back in at A.

7 amps is too much. The internal breaker will trip first, especially since these "R" models are known to have weakened/sensitive breakers w/ age(or it won't trip at all). The "R" transformer is rated for an output of about 3-3.5 amps at 24 volts.

Turtlelinez,

Looking at the Breaker in your picture is rated for 10 amps and above.

You need a lower amp Breaker.

Hope that help you out here.

Any idea how I can test the breaker and make it trip?  My main transformer is a postwar ZW but I kind of want to bench test the breaker some how.

I just want the thing to  trip if I have a derail short.

I have the 7 amp version of the breaker.

Connect the breaker to A-U of the ZW and crank it up.

If you want to see at what amperage the breaker trips, put an ammeter in line(series) with the breaker and raise the voltage more gradually watching the meter.

I have a 1941 Type R.  The internal breaker does not protect every combination of binding posts.  I used it for a bench supply also, having retired it when my parents gave me a ZW in early 50's.  I recently re-retired it, and went to an MTH Z500 for the bench.  It's adequate, cheap, and has a reliable breaker.

ON the ZW, do be aware that the internal breaker is in the line from one end of the secondary winding to the U terminals, so it would not protect against a short between any of the A-D terminals, which can occur is a train stops with rollers bridging a gap between power districts.  For complete protection, I'd put a 10-amp external breaker in the Line from U, and a 7 or 5 in the ABCD lines.

FWIW, you can normally use a considerably lower value thermal breaker than the maximum rating of the transformer.  For my test bench, I have a 2 amp breaker, and I've yet to have a normally operating locomotive on the rollers trip the breaker.

For tracks, I like something in the 6-7 amp range.  A 10 amp thermal breaker requires considerably more than 10 amps for a significant period of time to trip.

Here's a chart for the TE Connectivity Potter & Brumfield Relays W28 series, a very popular type that is used on a number of transformers.  If you look at the 3-20 amp models, for a 135% overload, it'll trip only after one hour!  That being the case, you have 10amp capability using the 7 amp breaker unless you have continuous power draw at the 10 amp range.  The 10 amp breaker won't trip for a loooooooong time with over 13 amps of current.

Fast-blow fuse blow times are also prolonged.  Tables can be found on the manufacturers' web sites.

The times GRJ points out are why I use smaller breakers.

Magnetic or electronic breakers should be faster.

The Lionel PH180 breakers are nice and fast, one of the primary reasons I'm so high on that transformer.  They also have sort of a two-speed sensor where they recognize the difference between a gradual slight overload and a quick spike that indicates a short.

Given the breaker I have, how can I test it.  Will the 7 amp breaker I have on the track trip before my ZW breaker will?

Do I have the wrong size breaker?  All I want is for it to trip in derailments.  Some added or faster protection for the trains as compared to the ZW.

Almost any breaker 10 amps or less will open before the one in the ZW.  How many trains and lighted cars do you run on the circuit. A good rule of thumb is to use the smallest that handles the trains you run.

Among my layout's transformers are 2 old ZWs, each powering 2 TIU channels.  I use 5 amp breakers on these, which are adequate for running 2 trains each (smoke off). I have 2 more circuits powered by a Z4000, and on that I use a 7 amp because I frequently run 3 trains.

If you run one train, I'd drop to a 5.

Test:

Connect the breaker to A-U of the ZW and crank it up.

If you want to see at what amperage the breaker trips, put an ammeter in line(series) with the breaker and raise the voltage more gradually watching the meter.

This is a common misconception - the breakers were not / are not intended to protect the trains, they are to protect the transformer and wiring.

Crap....OK I will lower the breaker.  I run one train.

Ok thanks.  It looks like I need a 5 amp breaker as typically I only run one train.

They're cheap enough.  FYI, on a circuit powered by a Z4000, which has a fast breaker, on a derailment the 5-amp usually opens before the Z4000.  I wanted to protect the fine gauge wiring in cars, and pickup roller springs, from overheating.

I have the zw hooked up.  With the 7 amp breaker in series.  I put a screw driver across the rails.  I get a spark.  However the breaker never trips.  I am only holding the screw driver down for a second or so for fear of frying the zw.

It seems at this point that I have no circuit protection.  I am trying to have a modern breaker trip before the old zw one.

A brief short, especially with any resistance in the loop, won't trip a thermal breaker.