I am hoping someone can fill in a lack of product information for me regarding Bussman breakers.
As a test I put a 10 amp fast blow glass fuse in line with a Bussman CBU-06 (6 amp) Type I breaker. The fuse always blows before the breaker trips.
Bussman sells the following:
UCB-XX Type I auto reset thin blade breakers
CBU-XX Type I auto reset rectangular breakers
CB174-XX Type III manual reset breakers (used by Scott’s Odds and Ends)
(XX refers to the number of amps. So UCB-06 would be a 6 amp breaker)
Bussman does not refer to these fuses as either “fast blow” or “slow blow”. Their website does not provide any technical information regarding the reaction time of the UCB and CBU series breakers. They do provide trip curves for the CB174 series breakers.
Does anyone know how fast the UCB and CBU series breakers should trip? Even though they are different styles, should they all have the same reaction time?
I would have thought a 6 amp breaker would respond before a 10 amp fuse.
I suspect the Type 1’s are similar in reaction to the Type 3. They probably are thermal breakers. These types can handle 200% load for a longer time than a 10 amp fast blow or standard fuse. The ONLY type of breaker I would use is the magnetic ones. They WILL trip at 125% of rated load-- no ifs ands or buts.
Thank you for the reply. They are thermal breakers.
The trip curve for the CB174-XX series (Scott’s Odds and Ends “Fast” breakers) says they can handle 200% of the load for 40 seconds, and 400% for 6 seconds. Here is the link.
If I understand this correctly it means that a 10 amp breaker can carry 20 amps of current for 40 seconds before tripping, and it can carry 40 amps for 6 seconds before tripping.
One of the magnetic breakers I was looking at carries 200% for about 15 seconds, and 400% for about 1.8 seconds. Here is the link.
On a 10 amp breaker I interpret this to mean it would carry 20 amps for 15 seconds, and 40 amps for 1.8 seconds.
As the curves go up the magnetic continues to trip more rapidly than the thermal breaker.
However, neither of them react as fast as a fuse. At 200% it appears a fuse blows in about .5 seconds. At 400% it appears it blows in about .09 seconds. Here is the link.
If I understand these curves correctly then I see why even a higher rated (higher number of amps) amp fuse blows faster than a lower rated (lower number of amps) thermal breaker.
The fuse trip curve I linked in the post above was for ATC blade style automotive fuses. These trip faster than the AGC glass fuses, but they are also more expensive.
Here is a link to the trip curve for AGC glass fuses from Bussman’s website.
The AGC fuses still blow faster than thermal and magnetic breakers, but slower than ATC blade fuses. However they are less expensive than ATC blade fuses.
Thermal circuit breakers are the appropriate type for protecting transformer windings and layout wiring from overcurrent. They do a reasonable job of modeling the thermal behavior of those circuit components and trip appropriately when the wire is in danger of being damaged by overheating. Neither circuit breakers nor fuses do an adequate job of protecting train electronics from overvoltage. The best they can do is to disconnect the transformer from the track before all the many voltage spikes that result from a derailment or other short circuit have happened. But even fuses will not do this until some have occurred.
The surest overvoltage protection is one designed for that purpose, which is to say, a transient voltage suppressor (TVS). They do a thorough job; they are very much cheaper than circuit breakers; and they don’t need to be replaced like fuses.
I understand and agree about TVSs. I use them. I am not saying fuses/breakers replace a TVS.
I see a secondary purpose for fuses/breakers besides proctecting the wiring and transformer. To me that secondary purpose is breaking the circuit during a short so that power to the engine is killed as quick as possible. This is not to protect the engine’s electronics. This is to protect the track, and engine/car wheels and rollers as much as possible.
I was having a series of derailments and the CBU-6 (6 amp) thermal breakers I have were not tripping fast enough. My reaction time with a throttle isn’t instantaneous. The result, even with a TVS on each block, was an engine that continued to drag sparking derailed cars around the layout. This caused damage to the rails before I could shut the transformer off.
So while I understand that thermal breakers may be the right application for protecting the wires and coil, I also see a breaker/fuse serving a secondary purpose of breaking the circuit as quickly as possible. The faster the circuit is broken the less time there is for something like a derailed car to be dragged around sparking and pitting the rails, wheels, and rollers.
Birds, I think you are right. I now have resetting automotive breakers inside my post war transformers [removed the Lionel ones], fast acting breakers between the transformers and the TIU and TPC’s and the TVS between the TIU/TPC’s and the track.
Have you tried using the TMCC direct lockon? The ones with the part number 73-4120-250 are not configured for direct connect to O tinplate track, you use wire leads to the track (or terminal bock if you use multiple feeds). They are rated for a max of 180 watts but do have a setting switch for 135 watts. They were meant for use with PH bricks but you can use the TPC adapter cables to feed them (Lionel part 6-14194).
What worries me is someone’s installing fast breakers in the mistaken hope of getting overvoltage protection when there is a simple, cheap, and effective alternative. There’s certainly no harm in using faster circuit breakers or fuses as well. The tradeoff as I see it is between arcing and nuisance tripping or fuse replacement. We can each go the route that is least annoying between those two.
Bob, I think you are right on with this subject. Why would you skimp on protection when expensive electronics are at stake. I have the fast acting breakers and now the TVS. All for less than $100 [not all spenrt at one time but worth it if I was starting from scratch].
Cooper Bussmann emailed me a PDF of the trip curve for the CBU-XX automotive breaker. It appears to be exactly the same as the trip curve for the CB174 series breakers used in the Scott’s Odds and Ends breaker box (link posted above). Unfortunately I do not have a way to post the PDF file of the CBU-XX trip curve for viewing.
Bussmann said that the UCB-XX blade style fuses are made by someone else, and purchased by them as a complete unit, so they do not have trip curves for those.
So here is the big question then. How can a modern CW-80, ZW or TMCC Lockon trip so fast? And hoe can I replicate that without replacing my postwar ZW’s? Can it be done? Iam tired of replacing fuses every 5 min when the kids are running the trains.
They use some sort of semiconductor pass element in series with the transformer, likely a triac, turned off by an amplifier looking at a series current-sense resistor, or rather not turned on at the next half-cycle. It can be done of course; but I don’t know who has done it. Perhaps you are one who would be happier with auto-resetting circuit breakers.