Should I upsize the wire on a 250ft run?

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RRJ said:
I could be wrong, but I will argue that a 200A wire will only be rated 200A at less than 160-200ft (ohms law). That’s just my opinion!


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Where do you draw the line then? How far can you run a 12AWG wire and still call it a 20A circuit? Do I really need to run 10AWG out to duplex recpt that is in a bedroom of a large house that is going to have a phone charger and a bedside lamp plugged into it?
 
ActionDave said:
Where do you draw the line then? How far can you run a 12AWG wire and still call it a 20A circuit? Do I really need to run 10AWG out to duplex recpt that is in a bedroom of a large house that is going to have a phone charger and a bedside lamp plugged into it?
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You draw the line with something concrete, mathematical, objective. Not money math, but electricity math. Feelings aren't objective, but voltage drop is.

We face scenarios all the time where somebody and the boys have always done it that way, but we should be a cut above the rest. If not, why not just call a handyman?
 
ActionDave said:
And the difference in fault clearing times for the two hundred fifty feet of wire under discussion in this thread on a 100A breaker and that same wire on an 80A is??
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PVC conduit, infinite source:

3 AWG- X= 0.047 R=0.25 per 1000 feet

8 AWG- X=0.052 R=0.78 per 1000 feet

X= 0.01175 R=0.0625

X=0.013 R=0.195


Total X=0.02475

Total R=0.2575


1612728069533.png


0.0006125625 + 0.06630625 = 0.0669188125

0.0669188125 square root= 0.2586867072348326 ohms


463 amps at 120 volts.





A 100 amp breaker it will take about 10 seconds on average to open, 15 tops.

An 80 amp breaker will take 5 seconds on average to open, 8 tops.

5 seconds is legal for table 41.1, and I'd argue up 10 seconds could work with our systems.

15 seconds is just getting dangerous and not recognized anywhere.
 
mbrooke said:
PVC conduit, infinite source:

3 AWG- X= 0.047 R=0.25 per 1000 feet

8 AWG- X=0.052 R=0.78 per 1000 feet

X= 0.01175 R=0.0625

X=0.013 R=0.195


Total X=0.02475

Total R=0.2575


View attachment 2555236


0.0006125625 + 0.06630625 = 0.0669188125

0.0669188125 square root= 0.2586867072348326 ohms


463 amps at 120 volts.





A 100 amp breaker it will take about 10 seconds on average to open, 15 tops.

An 80 amp breaker will take 5 seconds on average to open, 8 tops.

5 seconds is legal for table 41.1, and I'd argue up 10 seconds could work with our systems.

15 seconds is just getting dangerous and not recognized anywhere.
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You've done an excellent job making your case in an area I never really thought of. You're right. It's not just the functioning voltage and amperage, it's across the board
 
James L said:
You've done an excellent job making your case in an area I never really thought of. You're right. It's not just the functioning voltage and amperage, it's across the board
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Right. As an electrician you are tasked with assuring that you meet the requirements of the NEC, one of which is having an effective ground fault current path.

And while voltage drop is optional under the NEC, its a good idea to consider it when your name is on the job.
 
James L said:
You draw the line with something concrete, mathematical, objective. Not money math, but electricity math. Feelings aren't objective, but voltage drop is.

We face scenarios all the time where somebody and the boys have always done it that way, but we should be a cut above the rest. If not, why not just call a handyman?
Click to expand...
What's not objective about taking circuit loading into account when figuring voltage drop?
 
ActionDave said:
What's not objective about taking circuit loading into account when figuring voltage drop?
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It's not objective when you only want to consider one number (amps), while discounting or dismissing other numbers like footage.

If you intentionally refuse to include some paraneters because it leads to an inconvenient conclusion, it's intellectually dishonest.
 
James L said:
It's not objective when you only want to consider one number (amps), while discounting or dismissing other numbers like footage.

If you intentionally refuse to include some paraneters because it leads to an inconvenient conclusion, it's intellectually dishonest.
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I think it is you who refuses to include parameters that lead to a conclusion that you don't want to accept. Empirically it makes no sense to not consider circuit loading when figuring voltage drop and as a practical matter it makes no sense not to consider real world evidence of any malfunctions, or lack of, in time tested installations and methods.
 
ActionDave said:
I think it is you who refuses to include parameters that lead to a conclusion that you don't want to accept. Empirically it makes no sense to not consider circuit loading when figuring voltage drop and as a practical matter it makes no sense not to consider real world evidence of any malfunctions, or lack of, in time tested installations and methods.
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IIRC, UL considers full loading on all current carrying conductors , in all their testings .........~RJ~
 
75 posts and over a simple subject. :rolleyes:

The NEC doesn't care about voltage drop for this feeder, it's a design issue. If the installer wants to consider the voltage drop he can use the actual load or the size of the OCPD ahead of the feeder or some number in between. Any of those methods is code complaint.
 
infinity said:
75 posts and over a simple subject. :rolleyes:

The NEC doesn't care about voltage drop for this feeder, it's a design issue. If the installer wants to consider the voltage drop he can use the actual load or the size of the OCPD ahead of the feeder or some number in between. Any of those methods is code complaint.
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You been here long ? :) ? :) ?

IMHO the plausible values to use for the voltage drop calculations include the two you mention (actual load and OCPD rating), and also include 80% of the OCPD rating and transient starting current.

Plausible values for the amount of voltage drop are the NEC recommendation (total of 5% for circuit and feeder combined) when looking at long term operation, and 'what the load will tolerate' for transient current.

-Jon
 
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