Why the Limit Here?

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don_resqcapt19 said:
Probably because over that distance, there is not enough fault current to trip the breaker in its instantaneous range. But that is just a WAG.
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Most likely considering what I've read about in that UL doc...

So how did the CSA figure this out and not the NFPA?
 
Its interesting that the distance is from the supply side of the service and not from the branch circuit breaker. Must not be many large homes in Canada or they run really large branch circuits.

For many homes we wire its common to have feeders between the service and "sub" panels that would burn up most of that length.
 
I am not advocating this but it makes more sense than some of the "safety" requirements we have in the NEC.
 
There was a proposal a few cycles ago that would have required testing to prove the system could source enough fault current at the end of the line receptacle to open the OCPD in its instantaneous range, but it was rejected.
 
don_resqcapt19 said:
There was a proposal a few cycles ago that would have required testing to prove the system could source enough fault current at the end of the line receptacle to open the OCPD in its instantaneous range, but it was rejected.
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Perhaps enforcement? If this were passed what would be an easy way of verifying? Dummy load testing? Each point on a circuit would be different? Cant ohm it out, too impractical?
 
mbrooke said:
Chapter 9 Table 9
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That's how you do it on paper. That's not reality. You do a job, and the inspector show up and says,
"How long are each of those 89 circuits you ran?"
The EC says "Oh they all are within chapter 9 table 9 parameters"

How does the inspector prove it? Measure each conduit run? What's Practical? What happens when circuits are added that are partly concealed? Does the inspector guess? It becomes a nightmare for all. I agree with it and as Professionals we should be trusted to design and install safe circuits, but I don't see a practical enforcement method. Perhaps I am wrong.
 
I just bought a tester that determines available fault current at the point it is connected, don’t know how accurate it is, but I was surprised at how low the available fault current was at my house. Haven’t used it yet in a commercial setting.
 
hillbilly1 said:
I just bought a tester that determines available fault current at the point it is connected, don’t know how accurate it is, but I was surprised at how low the available fault current was at my house. Haven’t used it yet in a commercial setting.
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Loop impedance testing ?
That's interesting. Is it expensive?
 
hillbilly1 said:
I just bought a tester that determines available fault current at the point it is connected, don’t know how accurate it is, but I was surprised at how low the available fault current was at my house. Haven’t used it yet in a commercial setting.
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What values did you get? What was the lowest?
 
Can't the results of a voltage drop tester such as the Ideal SureTest be worked mathematically to give an available fault current at that point on the circuit? That device provides the following voltage drop testing.
% Voltage drop under load (12A, 15A, 20A load tests): 0.1% - 50.0%
 
don_resqcapt19 said:
Can't the results of a voltage drop tester such as the Ideal SureTest be worked mathematically to give an available fault current at that point on the circuit? That device provides the following voltage drop testing.
% Voltage drop under load (12A, 15A, 20A load tests): 0.1% - 50.0%
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In theory you could.
 
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