Re: cable amp ratings - answers to wrong questions

["David Roden (Akron OH USA)" <roden@ald.net>]

On 30 May 2002 at 19:05, Victor Tikhonov wrote:

> Not diminishing importance of NEC or criticizing them, but do you 
> honestly believe NEC cares about your personal well being when 
> they tell you to use certain wire gauge for x amps?

I do.  I think that the NFPA (National Fire Prevention Association), which 
promulgates the NEC, while not perfect, is one of the less compromised 
organizations.  They seem to mostly have their mission -- safety -- in the 
forefront.  They also seem fairly receptive to suggestions from real-world 
electrical professionals. 

IMHO, with a few exceptions (such as a few EV charging requirements, 
unfortunately), the code is mostly common sense.  Its recommendations for 
"ampacity" of various wire sizes are valid ones, and worth following when 
you are wiring your home or garage.  

> this kind of rating 
> in common electrician's books, without considering application
> specifics, is just nonsense.

I disagree.  The installer can't be sure how a wiring installation will be 
used 20 years hence.  You know how you'll use that receptacle for charging 
your EV, but what about the person who buys your house 20 years from now?  
NEC recommendations, while conservative, are designed to keep people safe in 
the most likely applications.  

There's also a practical issue: if you wire your charger receptacle using 
cable a size smaller than the code requires, and your installation causes a 
fire, your insurance agent may refuse to pay the claim because of the code 
violation.

BTW, I've never heard of Joe's "75 percent rule."  However, there is a code 
requirement that permanently connected equipment can't create a sustained 
load in excess of 80% of the circuit's rated capacity (16 amps on a 20 amp 
circuit).


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David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1970 GE Elec-trak E15 36vdc
1974 Avco New Idea rider 36vdc
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