Correct Amperage for Circuit Breaker/Fuse for Postwar ZW?

Turn it up to 11.

Well, kind of...  if you don't have the voltage turned up enough then you may not be delivering 4 or 5 amps to the circuit... tou have to be bold when testing these breakers.

Circuit protection can be complicated.  There are two common types of circuit breakers used on older trains.  There is the thermal breaker and the magnetic breaker.  The thermal breaker opens where there is enough wattage to get it hot. If the voltage is low and the current is high it may take some time to open the breaker.  The Lionel specs. for the testing the breaker in the ZW, which is a thermal breaker, states it may take 30 amps for 11 to 60 seconds to open the breaker.  The magnetic breaker actually measures the current and opens when the current reaches the preset limit.  The Lionel #91 circuit breaker is a magnetic breaker and opens very quickly. Thermal breakers were popular because in the old days most electrical equipment was damaged by excessive heat.  Short time overloads would not damage equipment and allowed for starting inrush current to occur without tripping the breaker. This would be typical for starting a motor, where the instant the contractor closed the current could be hundreds amps, but with in a fraction of a second it would drop off to a normal operating current.  A magnetic breaker would have blown, a thermal breaker would taken the short time over current and allowed the motor to start.

The fuse is a thermal device.  The element opens when the voltage and current have produced enough heat to melt the element.   Fuses come with a chart showing the current vs time for when it is going to blow.

The other issue is the wiring on your layout.  If it is small it could be limiting the current and not providing enough power to trip a thermal device.

There are some issues with the ZW itself.  First is the circuit breaker in the ZW is there to protect the transformer windings, not you trains, wiring or house.  There is only one circuit breaker and it is in the “U” leg of the transformer. Since the A, B, C, and D posts are transformer taps, there can be a high current condition when there is contact between these four legs.  Lionel provides no circuit protection for this condition.

My recommendation for circuit protection for a ZW is as follows:

1) Provide a 10 amp thermal protective device, fuse or circuit breaker, on each of the A, B, C, and D outputs.

2) Provide a single 15 amp magnetic circuit breaker on the “U” post outputs.

3) Always plug the ZW into a GFI protected outlet.

4) Plug the ZW, and all other transformers on the layout,  into a single power strip equipped with an switch.  Never unplug any of the transformers until the power strip is turned off.

5) Never leave the train room with the power strip turned on.

David,

Great explanation, very enlightening.

What would you suggest I get (and where) in order to accomplish your recommendations #1 and #2?

Thank you very much!

Richard

It has been several years since I set up the wiring on my layout so my experience in purchasing these protective devices is not current. If you use the search function on this web site  I think you will find current recommendations for sources of protective devices. 

On my layout I use the Lionel postwar 91 magnetic circuit breakers. Their maximum rating is 6 amps. I can run a two motor loco without any unwanted trips, but if I run 2 two motor locos I get into trouble. On the 15 amp breaker this is a common breaker used to protect household circuits. The only problem with using these is they are usually designed for one end to snap into a bus bar. Another good sources of circuit protective devices is an auto parts store.   Lots of fuses and circuit breakers used in cars. Same with RV supply outlets. eBay is always a good source as is Amazon. 

I saw this posting and found the recommendation very informative and enlightening.

Are there any other recommendations from the OGR community that should be considered e.g. a specific product line?