[KISS]

Use slow at this point. If it becomes a nuscence blow, go to slow blow.

HCAV supply houses should have wired-in surge supressors. Here is one: Wire-in surge suppressors, Hard wired AC power line Interference filters, protectors, 120 V, 240 V

It might be worthwhile finding one with a good warrany. Good filters may make X-10 stuff work in your house,

You could also go to a "whole house" surge suppressor.

[KISS]

You could also place a ZNR or or transorb on the secondary after the fuse. If you want I can try to pick one out and size it. They are no more than a fe dollar each. Transorbs are excellent devives. Not sure if available in the voltage needed.

[sdk]

Use slow at this point. If it becomes a nuscence blow, go to slow blow.

OK, slow it is. And I'll check with the local HVAC supplier for one of those surge surpressors. The local power company here, Duke Energy, has been pushing those whole-house surge surpressors, maybe I'll have a look at those too. Thanks.

[KISS]

I meant to say go FAST blow unless there is nucence tripping. Then change to SLOW blow Sorry my haed is causing me troubles today.

[Missouri Bound]

WJ.. Kudo's to you for trying to maintain your equipment. May I suggest that you purchase a cheap VOM so you can do some simple testing of continuity and voltage? And I agree with HVAC1000... call Radio Shack or better yet, visit them and buy that inexpensive VOM.

Good luck

[sdk]

I meant to say go FAST blow unless there is nucence tripping. then change to SLOW blow Sorry my haed is causing me troubles today.

Just got back in town after about a week away. I switched off the system before I left and let the house heat up, it has not been too terribly hot here. The system was working but the root cause of the whole thing had not yet been "apprehended", so I figured better safe than sorry.

Yeah, I moved the fuseholder over to the 24 volt side of things and put in a 2.5 amp fast blow fuse just to be safe, 2.5 amps being 1.5 times the 40VA/24V thing. All seems well, the system ran most of the night cooling things back down, so it appears the gnawed wiring was the main issue. I think I will put the wiring inside one of those flexible wire looms for now, and set out some traps to catch the critters before they strike again.

I think the idea of putting in a zener or a Transorb would be a good one for the furnace designers to pick up on, but that would probably add 15¢ to the cost of a furnace, and they would sell fewer replacement transformers to poor sods like me, so I ain't holding my breath. I'll stick with a simple old fuse for now. As satisfying as it would be to see Alvin hanging from the wire by his incisors, I doubt 24 volts gives them much more than a little nip and probably doesn't even discourage them from coming back for seconds.

Thanks for the help.

[KISS]

Primary wires - doesn't matter which is L or N.

Secondary wired, don't use the "0" or black wire. Again, doesn't matter how it's hooked up.