The AM Forum

Since I am working on the PS in http://amfone.net/Amforum/index.php?topic=19034.0 (http://amfone.net/Amforum/index.php?topic=19034.0) I am reminded of a question I have.

What is the best (safest) order for the mains power cord, main power switch, and mains fuse?

A: cord -> switch -> fuse -> ...
B: cord -> fuse -> switch -> ...

Reasons why I am still uncertain:
A seems to be the most common
B seems to make the most safety sense, since a blown fuse will even remove power from the switch
A seems to make it easier to use multiple fuses in front of multiple primaries with different current needs
B seems to mimic the old fuse-in-plug idea and the fuse panel in your home infron of plugs and switches

David,

I prefer cord to fuse to switch (with the switch and fuse in the hot or load lead); to me it makes the most sense to have the fuse as close to the power entry as reasonable and switches can certainly fail.  I know that cord to switch to fuse is common.  For many of the pieces I repair/restore I use an inrush limiter after the fuse and before the switch.

If you want to use multiple fuses for different transformers those can be added in addition to the "mains" fuse.

Even with modern line rated bypass caps, I definitely don't want one of those on the hot side of the line prior to the fuse.

Rodger WQ9E

I don't think it matters, since the power cord, switch and fuse are all in series. 

No matter where the fuse is located, you should always unplug the equipment before attempting to work on it, so I say it's a non-issue.

A common practice is to connect the 120VAC cord lead directly to the END lug of the fuse holder. (not the center lug)  This will make it easier to prevent a shock when handling/changing a fuse.  Look closely at the fuse holder to understand what I mean.

I didn't pay attention to this until I got zapped a few times and figgered it out... duh. 

Don makes a good point about unplugging the unit first... ;D

T