Fuses on the panel, or not

On Wednesday, October 16, 2013 12:42:06 PM UTC-7, JohnDeRosa wrote:
A couple of comments about circuit protection some of which has been covered before in other threads;



- Pete Purdie's comment above about undersized wiring is on target. Bigger is better (within reason)! If you saw smoke you probably do not have Tefzel wiring. Get some!

- Fuses are great as they are cheap, fast acting and have ZERO voltage drop across its terminals. Cons are that they are more difficult to replace in flight and somewhat fragile (glass type).

Capitalized ZERO, like you really mean absolutely zero, nothing, zilch, nada? Ah in a word. No. A fuse will *not* have ZERO voltage drop. A fuse relies on resistance in the fuse element causing heating and mechanical failure of the element. A typical fuse for a few amp applciation might have a voltage drop of ~100mV to ~200mV drop at the fuse rated current, and that depending on the fuse type and ratings). If there was zero resistance the fuse would never work. Since there is resistance there will be a voltage drop. Now that voltage drop may be a lot less than a similar spec circuit breaker, especially for low trip current applications. And in both cases is not a simple linear relationship, vendors typically provide voltage drop as a part of the spec sheet of their fuses and breaker products and fuse specs will include both that drop at rated current and a cold resistance value.