Originally Posted by GordMay
Thanks for the correction (update), and the applicable, and definative quotation.
I'm so out of date, I'm getting dangerous!
No Worries Gord, it is not dangerous if you are erring on the safe side. I am not a mechanical engineer
but I have never had a problem with a bracket I designed which may have been a little stronger than what was needed. By the way, ABYC is a recommended standard, not the law. Law is the laws of physics and nobody can argue with that law and win (or live long).
Two principles that are relevant in this case :
1. "Ampacity" of a cable is determined by the resistance of the conductor and the temperature rating of the insulation
2. Purpose of a fuse at the source is to protect the downstream power cables
or blowing open during a short circuit. (ie: the fuse blows open instead of the conductor)
In order to minimize a voltage sag at the load, you may use a cable with an ampacity higher than what is needed and protect that wire at a current less than its nominal rating. (with proper design margins)
If you have installed a fuse or a CB at the current you need which is less than the ampacity of the power conductors, then it is perfectly OK to use a ground wire at the ampacity your fuse (or CB) is capable of protecting.
Why write all this instead of just say follow the ABYC recommendation?
I like to "blindly comply" only with the rules that I do not thoroughly understand. Actually ABYC chose the prudent path by recommending a bigger cable at first, and then revising their recommendation to a smaller (cheaper) cable only after analysis, recommendations and concurrence by many experts in the industry. ABYC is open to comments and recommendations from the industry to improve their standards, I am sure of it.
Cheers and all the best.