Fuse Placement tiu/transformer

use a fuse between the track and the TIU. I use a 10 amp fuse connected this way

I follow the manual and put mine between the Z and the TIU.

I use 10 amp fast blow fuses not 15 amp.

I've blown many fuses and not harmed the TIU.

I was wiring my layout the other day and looked it up in the Broskowitz book. He recommends between the transformer and TIU. 

I would think the fuse should be as close to the short circuit as possible. In the event of a short, the tiu should see the same magnityde and duration of short circuit current in either fuse position.

So what would be the reasoning to place it between the transformer and the tiu?

Between the Transformer and the TIU. A TVS diode accross the lode side of the TIU port is a good thing. But, from what I understand the new TIU units are much better at absorbing transients then the old, Barry would be the one to confirm this. 

As for me I fuse fifteen amps to the TIU ports and 8 amps fast blow after, with the TVS diodes. This is because I run short trains and I'm a little nuts when it comes to protection.

One should always break a short circuit immediately after the source of power, not the source of the short circuit.

The current draw is from the transformer to the track and the idea is to keep the current from passing through any components that follow the transformer in the circuit.

The fuse or circuit breaker should always be between the transformer and the TIU. Further, the fuse or breaker should be rated at a lower current carrying capacity than anything else in the circuit. Since most transformers max out at about 10 amps, the fuse or breaker should be rated to open the circuit between 10-15 amps, depending on how high typical operating needs peak on one's layout. 

Using a "standard" 3AG 10A fuse, it will take up to 1 second to open at a 20 amp load. By that time, your electronics are probably fried. I'd use 7.5A fuses instead unless you need the full  10 amps to run your train--- just my opinion--

OK - you've given me some sound advice - most of you agree that it should be placed between the transformer and TIU so here's my plan:

1. Keep the 15 amp breaker between the TIU and track.

2. Install another 15 amp breaker between the transformer and TIU.

Sound OK????

1. Keep the 15 amp breaker between the TIU and track.

Nope. That would be a complete waste of time and expense. It adds no protection for the TIU at all.

2. Install another 15 amp breaker between the transformer and TIU.

 

Sound OK????

Sounds good!

Quote corrected in original post, so this question was removed to avoid future confusion by me as well as others.

John,

Could you explain this

I don't understand what part of my post requires explanation. Please be more specific.

Since the TIU is only rated at 10A per channel, would it make sense to replace the 20A input fuses with 15A fuses or have external protection between the transformer and the TIU?

That's hard to say. I've never really understood why the TIU's fuses sit in the Common lines rather than the Hot lines. I have been told that they are 20 amp to protect against sustained short-circuits rather than an occasional voltage overdraw, which the TIU's electronics can handle.

As long as there are fast-acting circuit protection between the TIU and the transformer, I'd just leave the TIU's internal fuses alone. In the 10 years or so that I've been operating DCS, I've never had a TIU channel failure and have never had to replace an internal fuse, either.

Quote corrected in original post, so this question was removed to avoid future confusion by me as well as others.

Ugh - I reversed the answers. It's now fixed - thanks!

No problem, just wanted to make sure my understanding was correct.  I'll remove the quoted incorrect text to make sure there's no confusion for future readers of the thread.

I have a z4000. Would the transformer protection be quick enough or do I still need a fuse between the tiu and z4000?

Steve

Steve,

I have a z4000. Would the transformer protection be quick enough or do I still need a fuse between the tiu and z4000?

I run 3 Z4000's for track power into my TIUs and I do not have any additional fuse protection. 10 years and no issues.