Re: [Elecraft] [OT] NEC wire size requirements

[Eric Swartz - WA6HHQ, Elecraft]

Folks, let's wind down and close this thread. We are at 14 posts on an OT thread 
in a short time, well in excess of our list soft limit. As I noted earlier, 
please keep these OT threads short and sweet.


While we do not prohibit OT topics, please self moderate as the primary focus of 
this list is for Elecraft products and their use etc.  Excessive OT posts as we 
have seen lately, will overload the majority of our readers who are focuses on 
our products and their use etc.


73,
Eric
Moderator
/elecraft.com/


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Re: [Elecraft] [OT] NEC wire size requirements

[Jim Brown]

On Fri,8/12/2016 7:22 AM, Cortland Richmond wrote:
That's the famous power-factor- harmonics-in-the-neutral problem.  Got 
some attention, that did; electrical fire in a high-rise will do that. 


Yes. When I went through EE, power factor was the phase relationship 
between V and I. After harmonics were recognized as a BIG DEAL, the 
definition was expanded to include them.


73, Jim K9YC

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Re: [Elecraft] [OT] NEC wire size requirements

[Cortland Richmond]

On 8/11/2016 14:10, Walter Underwood wrote:

In the late 1980?s, we had some cubicle wiring fires at HP Labs caused by 
computer power supplies. They had to replace


That's the famous power-factor- harmonics-in-the-neutral problem.  Got 
some attention, that did;   electrical fire in a high-rise will do that.


Cortland Richmond

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Re: [Elecraft] [OT] NEC wire size requirements

[Robin Moseley]

So off topic - why start this here at all?
there are loads of general radio groups, facebook groups etc.. this is 
getting silly..


Robin G1MHU 


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Re: [Elecraft] [OT] NEC wire size requirements

[Jim Brown]

There are several issues with shared neutrals, one of which is that 
currents in single phase systems may not balance well. In the large 
sound systems I designed, I always specified a home run of all three 
conductors from each duplex that I distributed around a stage or worship 
area to the panel. I specified 20A outlets and #12 conductors. The 
intent was to allow portable gear at any of these locations to grab a 
lot of power.


The far greater issue with "shared neutrals" is related to 3-phase 
power, where, thanks to the harmonics present in distorted load 
currents, triplen harmonics (harmonics divisible by 3)  add in the 
neutral rather than cancel. This can result in neutral currents 
significantly larger than the current in one phase, even when loads are 
perfectly balanced. This is what overheated the wiring that started "The 
Towering Inferno," and it was the burning insulation that propagated the 
flames. That' why building codes were changed. :)


Few of us (none?) have 3-phase power in our homes, but most of us are 
fed from one phase of 3-phase systems in the alley or on the street. 
Those harmonics add in the "ground" for the same reasons that they add 
in the neutral, and because most of us are fed by "high-leg Delta" 
systems, we tend to see a lot of harmonic current on our grounds. THIS 
is why we hear "buzz" (triplen harmonics of 60 Hz) in our systems due to 
improper bonding rather than "hum" (pure 60 Hz).


There's an extensive discussion of this in several places on my website. 
The most detailed is in the "White Paper" for audio/video professionals, 
but it's also in the slide show for my talk on Power and Grounding for 
Hams.  k9yc.com/publish.htm


73, Jim K9YC

On Thu,8/11/2016 2:18 PM, Matt Zilmer wrote:
Was this a "shared neutral" type of problem?  I thought NEC ruled that 
out in post-1979 wiring plans. 



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Re: [Elecraft] [OT] NEC wire size requirements

[Clay Autery]

You are correct... it is new construction add-on to existing...

FYI, when using twisted-pair, each pair essentially functions as 4
parallel wires for cross-section...  So I had to upsize to 1" RWS FMC to
accomodate 2 x 6AWG twisted pairs and not violate the 40% fill limit.

Conduit is NOT required in my locale.  It is being used for shielding
only... although it is UL Listed and installed per code.

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MONTAC Enterprises
(318) 518-1389

On 8/11/2016 2:45 PM, Lewis Phelps wrote:
> Depends on the conduit size. Half inch conduit can only carry two #6 wires 
> per NEC, but 3/4” conduit is OK for four #6 wires.
>
> But we weren’t talking here about pulling wire out of an existing conduit, I 
> don’t think.. This was described as a new installation by a code-savvy op, 
> who no doubt is using properly sized conduit..
>
> Lew N6LEW
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Re: [Elecraft] [OT] NEC wire size requirements

[Clay Autery]

You make a lot of assumptions there:

1) It is not a 50 foot run carrying 120...  It's a 50 foot 4 wire run
carrying 240 volts to the sub-panel from the service plus the neutral
and the green wire. Then a 6-gang box containing 8 x 120 and 4 x 220
receptacles wired independently.
2) IF some day I NEED 60 Amps, I will be able to get it because I BUILT
for it...  No climbing back into the attic.  No buying all new wire.  No
pulling new wire.
3) I don't pay retail.
4) There are other considerations other than cost and electrical
there's RF radiation from and to the wire, etc.  Which is why the wire
is BOTH hand-twisted into pairs AND run in bonded flex-steel conduit.

IF I built for 20 amps now, and then later needed 20+ amps, I would have
to REBUILD...  my time is worth more than the cost differential.  I want
to TALK on the radio and build OTHER stuff... NOT do repeated upgrades
of my power infrastructure.

Bottom Line:  My stuff works and doesn't break.  I don't have to use my
time to do stuff twice.  And because I want to...  :-)

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(318) 518-1389

On 8/11/2016 2:03 PM, Lewis Phelps wrote:
> At retail rates (e.g. price per foot from lower.com) #6 wire is 89 cents per 
> foot, and #12 wire is 8.2 cents per foot;  assuming Clay’s 50 foot run and 3 
> wires for a 110 VAC circuit with ground, per NEC, the added cost for wire 
> would be $121.20.  
>
> Is it “good engineering practice?”  It seems to be to be OK from an 
> electrical standpoint, albeit unnecessary, and unnecessary from a cost 
> standpoint, albeit not harmful. 
>
>  I can certainly understand “over-specifying” wire size in a 12 volt circuit, 
> and using larger wire size than is required simply from considering ampacity, 
>  because the voltage drop is a much larger change proportionally, but I 
> really don’t see the benefit from the expense and added installation 
> difficulty of using larger-than-required wire for a 120VAC supply circuit.
>
> according to the online calculator at 
> http://www.southwire.com/support/voltage-drop-calculator.htm, which takes 
> into account both resistance and reactance of the wire:
>
> — for a 50 foot run of cable of #6 wire, at 20 amps and 120 volts AC single 
> phase,  the total voltage drop will be 0.884 volt, or 0.74%, for a net 
> voltage at the end of the circuit of 119.1 volts (rounding)
> — for the same run with #12 wire, the total voltage drop will be 3.472 volts, 
> or 2.90 percent, for a net voltage at the end of the circuit of 116.5 volts 
> (rounding). 
>
> The 3.47 volt drop would be intolerable in a 12 volt circuit providing power 
> directly to amateur radio equipment, but seems to me irrelevant if feeding a 
> competently-designed power supply that reduces the 120 volts AC  supply to 
> some lower voltage of DC supply. Any ham radio power supply that is specified 
> to operate on 120 VAC should be able to operate without difficulty from a 
> 116.5 volts supply.
>
> So, why go to the extra expense of #6 wire? While it seems to me to be to be 
> harmless to “over-spec” the wire size, it also seems expensive and not 
> necessary either per requirements of Section of 310-15 of the NEC or from a 
> “good operating practices” perspective. 
>
> Lew N6LEW
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Re: [Elecraft] [OT] NEC wire size requirements

[Walter Underwood]

I think it was shared neutral. The cubicle wiring design could well have been 
from before 1979.

On the other hand, one of the graphics boxes for the HP 300 series had two 
power supplies with two power cords, so we were pushing the cubicle wiring 
pretty hard.

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Aug 11, 2016, at 2:18 PM, Matt Zilmer  wrote:
> 
> Was this a "shared neutral" type of problem?  I thought NEC ruled that out in 
> post-1979 wiring plans.
> 
> 73,
> 
> matt W6NIA
> 
> 
> On 8/11/2016 2:10 PM, Walter Underwood wrote:
>> In the late 1980’s, we had some cubicle wiring fires at HP Labs caused by 
>> computer power supplies. They had to replace all  the wiring with bigger 
>> conductors and connectors for the neutral. The same thing happened with 
>> Project Athena at MIT.
>> 
>> wunder
>> K6WRU
>> Walter Underwood
>> wun...@wunderwood.org
>> http://observer.wunderwood.org/  (my blog)
>> 
>> 
>>> On Aug 11, 2016, at 1:09 PM, Jim Brown  wrote:
>>> 
>>> On Thu,8/11/2016 12:03 PM, Lewis Phelps wrote:
 So, why go to the extra expense of #6 wire?
>>> All the calculators assume sinusoidal current (i.e., a perfect 60 Hz sine 
>>> wave). That's not the real world -- only un-controlled heating elements 
>>> draw sine wave current. For at least the past 30+ years, electronic loads 
>>> dominate, and the what's connected to the power line is a 
>>> transformer-rectifier-capacitor power supply, and now usually as the input 
>>> to an SMPS. The line current drawn by such a supply takes the form of short 
>>> pulses at positive and negative peaks of the 60 Hz waveform, so both IR 
>>> drop and dissipation is much greater than predicted by simple sine wave 
>>> analysis. None of this is taken into account by NEC.
>>> 
>>> Thus, it IS good engineering practice to oversize AC conductors.
>>> 
>>> There's a tutorial discussion of this in
>>> 
>>> http://k9yc.com/GroundingAndAudio.pdf
>>> 
>>> 73, Jim K9YC
>>> 
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> 
> -- 
> Always store beer in a dark place.  - R. Heinlein
> 
> Matt Zilmer, W6NIA
> [Shiraz]
> 
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Re: [Elecraft] [OT] NEC wire size requirements

[Matt Zilmer]

Was this a "shared neutral" type of problem?  I thought NEC ruled that 
out in post-1979 wiring plans.


73,

matt W6NIA


On 8/11/2016 2:10 PM, Walter Underwood wrote:

In the late 1980’s, we had some cubicle wiring fires at HP Labs caused by 
computer power supplies. They had to replace all  the wiring with bigger 
conductors and connectors for the neutral. The same thing happened with Project 
Athena at MIT.

wunder
K6WRU
Walter Underwood
wun...@wunderwood.org
http://observer.wunderwood.org/  (my blog)



On Aug 11, 2016, at 1:09 PM, Jim Brown  wrote:

On Thu,8/11/2016 12:03 PM, Lewis Phelps wrote:

So, why go to the extra expense of #6 wire?

All the calculators assume sinusoidal current (i.e., a perfect 60 Hz sine 
wave). That's not the real world -- only un-controlled heating elements draw 
sine wave current. For at least the past 30+ years, electronic loads dominate, 
and the what's connected to the power line is a transformer-rectifier-capacitor 
power supply, and now usually as the input to an SMPS. The line current drawn 
by such a supply takes the form of short pulses at positive and negative peaks 
of the 60 Hz waveform, so both IR drop and dissipation is much greater than 
predicted by simple sine wave analysis. None of this is taken into account by 
NEC.

Thus, it IS good engineering practice to oversize AC conductors.

There's a tutorial discussion of this in

http://k9yc.com/GroundingAndAudio.pdf

73, Jim K9YC

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--
Always store beer in a dark place.  - R. Heinlein

Matt Zilmer, W6NIA
[Shiraz]

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Re: [Elecraft] [OT] NEC wire size requirements

[Walter Underwood]

In the late 1980’s, we had some cubicle wiring fires at HP Labs caused by 
computer power supplies. They had to replace all  the wiring with bigger 
conductors and connectors for the neutral. The same thing happened with Project 
Athena at MIT.

wunder
K6WRU
Walter Underwood
wun...@wunderwood.org
http://observer.wunderwood.org/  (my blog)


> On Aug 11, 2016, at 1:09 PM, Jim Brown  wrote:
> 
> On Thu,8/11/2016 12:03 PM, Lewis Phelps wrote:
>> So, why go to the extra expense of #6 wire?
> 
> All the calculators assume sinusoidal current (i.e., a perfect 60 Hz sine 
> wave). That's not the real world -- only un-controlled heating elements draw 
> sine wave current. For at least the past 30+ years, electronic loads 
> dominate, and the what's connected to the power line is a 
> transformer-rectifier-capacitor power supply, and now usually as the input to 
> an SMPS. The line current drawn by such a supply takes the form of short 
> pulses at positive and negative peaks of the 60 Hz waveform, so both IR drop 
> and dissipation is much greater than predicted by simple sine wave analysis. 
> None of this is taken into account by NEC.
> 
> Thus, it IS good engineering practice to oversize AC conductors.
> 
> There's a tutorial discussion of this in
> 
> http://k9yc.com/GroundingAndAudio.pdf
> 
> 73, Jim K9YC
> 
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Re: [Elecraft] [OT] NEC wire size requirements (was: Zip Wire Misrepresentation?)

[Mel Farrer via Elecraft]

Also, the number of wires by size in conduit should help the cost equation 
also.   3 ea #6 conductor requires 1" conduit, while 3 ea, #12 can be put in 
1/2" conduit.
Mel, K6KBE


  From: Lewis Phelps 
 To: Elecraft Reflector Reflector  
 Sent: Thursday, August 11, 2016 12:03 PM
 Subject: Re: [Elecraft] [OT] NEC wire size requirements (was: Zip Wire 
Misrepresentation?)
   
I’ve changed the subject line because this discussion has strayed from the 
original question.

At retail rates (e.g. price per foot from lower.com) #6 wire is 89 cents per 
foot, and #12 wire is 8.2 cents per foot;  assuming Clay’s 50 foot run and 3 
wires for a 110 VAC circuit with ground, per NEC, the added cost for wire would 
be $121.20.  

Is it “good engineering practice?”  It seems to be to be OK from an electrical 
standpoint, albeit unnecessary, and unnecessary from a cost standpoint, albeit 
not harmful. 

 I can certainly understand “over-specifying” wire size in a 12 volt circuit, 
and using larger wire size than is required simply from considering ampacity,  
because the voltage drop is a much larger change proportionally, but I really 
don’t see the benefit from the expense and added installation difficulty of 
using larger-than-required wire for a 120VAC supply circuit.

according to the online calculator at 
http://www.southwire.com/support/voltage-drop-calculator.htm, which takes into 
account both resistance and reactance of the wire:

— for a 50 foot run of cable of #6 wire, at 20 amps and 120 volts AC single 
phase,  the total voltage drop will be 0.884 volt, or 0.74%, for a net voltage 
at the end of the circuit of 119.1 volts (rounding)
— for the same run with #12 wire, the total voltage drop will be 3.472 volts, 
or 2.90 percent, for a net voltage at the end of the circuit of 116.5 volts 
(rounding). 

The 3.47 volt drop would be intolerable in a 12 volt circuit providing power 
directly to amateur radio equipment, but seems to me irrelevant if feeding a 
competently-designed power supply that reduces the 120 volts AC  supply to some 
lower voltage of DC supply. Any ham radio power supply that is specified to 
operate on 120 VAC should be able to operate without difficulty from a 116.5 
volts supply.

So, why go to the extra expense of #6 wire? While it seems to me to be to be 
harmless to “over-spec” the wire size, it also seems expensive and not 
necessary either per requirements of Section of 310-15 of the NEC or from a 
“good operating practices” perspective. 

Lew N6LEW



> On Aug 11, 2016, at 11:12 AM, Kevin - K4VD  wrote:
> 
> The added cost of a 3x over-build seems like it would be awfully high. Is
> this good engineering practice (seriously, I don't know)?
> 
> Kevin K4VD
> 
> On Thu, Aug 11, 2016 at 12:38 PM, Clay Autery  <mailto:caut...@montac.com>> wrote:
> 
>> How do you define "necessary".
>> 
>> Paraphrasing K9YC, Jim  "Big wire is your friend".
>> 
>> I agree...
>> 
>> I typically use wire at least 2 sizes larger than "required"  Often
>> the wire size is determined by how big of a wire I can FIT in the
>> application and how much money I can part with at the time.
>> 
>> For instance, on my current power project... I am running 6 AWG x 4 from
>> the service to the sub-panel @ 50 foot run for a 60 Amp separately
>> derived service where there'll never be more than about a 20 Amp total
>> demand...
>> 
>> From the sub-panel to the receptacles about 3-1/2 feet below, I am using
>> 10 AWG  only because that's the largest wire the receptacle
>> terminals are rated for.
>> 
>> From the receptacles to all equipment, minimum 10 AWG...
>> 
>> Bigger and shorter the wire, the better...
>> 
>> __
>> Clay Autery, KY5G
>> MONTAC Enterprises
>> (318) 518-1389
>> 
>> On 8/11/2016 10:43 AM, Ronnie Hull wrote:
>>> Is 10 gauge necessary?
>>> 
>>> Sent from my iPhone
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Re: [Elecraft] [OT] NEC wire size requirements

[Jim Brown]

On Thu,8/11/2016 12:03 PM, Lewis Phelps wrote:

So, why go to the extra expense of #6 wire?


All the calculators assume sinusoidal current (i.e., a perfect 60 Hz 
sine wave). That's not the real world -- only un-controlled heating 
elements draw sine wave current. For at least the past 30+ years, 
electronic loads dominate, and the what's connected to the power line is 
a transformer-rectifier-capacitor power supply, and now usually as the 
input to an SMPS. The line current drawn by such a supply takes the form 
of short pulses at positive and negative peaks of the 60 Hz waveform, so 
both IR drop and dissipation is much greater than predicted by simple 
sine wave analysis. None of this is taken into account by NEC.


Thus, it IS good engineering practice to oversize AC conductors.

There's a tutorial discussion of this in

http://k9yc.com/GroundingAndAudio.pdf

73, Jim K9YC

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Re: [Elecraft] [OT] NEC wire size requirements (was: Zip Wire Misrepresentation?)

[Guy Olinger K2AV]

It really depends on physical environment particulars, and what it is you
are sizing your DC currents for.

If you are talking about 4 feet, that's one thing. But if it's an RV and
you are wiring up a 13.8 V DC supply circuit run from house batteries,
which are where they are, to the only place in the RV you can stuff a ham
shack, and it's 46.5 feet via the only possible wiring routing, then
voltage drop is a big issue if you want to run a K3 plus whatever from
there. It's even more interesting if what you are planning for is TWO K3's
plus two laptops and whatever, and that's going to be two regular FD
operating positions in a lazy and air-conditioned comfortable RV with
facilities, and a cold fridge at the ready.

I'll run the #4 direct from the battery terminals, and fuse it at 50 amps.
That will allow the big T105 batteries to feed peak current to the shack,
without having to have up-size the charger-converter (which needs to be
sized to the batteries' bulk charge rate, not the load). Let the
charger-converter and all that house DC wiring just worry about keeping the
battery charged, just like we had gone to a site without park power, and
had to do the battery plus generator afternoons thing. Gen comes on and
charger-converter runs bulk charge current for a long period. They're made
to do that.

Also it allows us to run the air-conditioning and the house on the
generator and use the T105's for class 2B on FD. Just use the regular house
battery disconnect and the big batteries are all the transceivers ever see.

In this kind of consideration, spending the absolute least amount of money
possible is not the prime consideration, and a stiff supply voltage at the
far end would justify spending money for copper.

73, Guy.

On Thu, Aug 11, 2016 at 3:03 PM, Lewis Phelps  wrote:

> I’ve changed the subject line because this discussion has strayed from the
> original question.
>
> At retail rates (e.g. price per foot from lower.com) #6 wire is 89 cents
> per foot, and #12 wire is 8.2 cents per foot;  assuming Clay’s 50 foot run
> and 3 wires for a 110 VAC circuit with ground, per NEC, the added cost for
> wire would be $121.20.
>
> Is it “good engineering practice?”  It seems to be to be OK from an
> electrical standpoint, albeit unnecessary, and unnecessary from a cost
> standpoint, albeit not harmful.
>
>  I can certainly understand “over-specifying” wire size in a 12 volt
> circuit, and using larger wire size than is required simply from
> considering ampacity,  because the voltage drop is a much larger change
> proportionally, but I really don’t see the benefit from the expense and
> added installation difficulty of using larger-than-required wire for a
> 120VAC supply circuit.
>
> according to the online calculator at http://www.southwire.com/
> support/voltage-drop-calculator.htm, which takes into account both
> resistance and reactance of the wire:
>
> — for a 50 foot run of cable of #6 wire, at 20 amps and 120 volts AC
> single phase,  the total voltage drop will be 0.884 volt, or 0.74%, for a
> net voltage at the end of the circuit of 119.1 volts (rounding)
> — for the same run with #12 wire, the total voltage drop will be 3.472
> volts, or 2.90 percent, for a net voltage at the end of the circuit of
> 116.5 volts (rounding).
>
> The 3.47 volt drop would be intolerable in a 12 volt circuit providing
> power directly to amateur radio equipment, but seems to me irrelevant if
> feeding a competently-designed power supply that reduces the 120 volts AC
> supply to some lower voltage of DC supply. Any ham radio power supply that
> is specified to operate on 120 VAC should be able to operate without
> difficulty from a 116.5 volts supply.
>
> So, why go to the extra expense of #6 wire? While it seems to me to be to
> be harmless to “over-spec” the wire size, it also seems expensive and not
> necessary either per requirements of Section of 310-15 of the NEC or from a
> “good operating practices” perspective.
>
> Lew N6LEW
>
>
>
> > On Aug 11, 2016, at 11:12 AM, Kevin - K4VD  wrote:
> >
> > The added cost of a 3x over-build seems like it would be awfully high. Is
> > this good engineering practice (seriously, I don't know)?
> >
> > Kevin K4VD
> >
> > On Thu, Aug 11, 2016 at 12:38 PM, Clay Autery  > wrote:
> >
> >> How do you define "necessary".
> >>
> >> Paraphrasing K9YC, Jim  "Big wire is your friend".
> >>
> >> I agree...
> >>
> >> I typically use wire at least 2 sizes larger than "required"  Often
> >> the wire size is determined by how big of a wire I can FIT in the
> >> application and how much money I can part with at the time.
> >>
> >> For instance, on my current power project... I am running 6 AWG x 4 from
> >> the service to the sub-panel @ 50 foot run for a 60 Amp separately
> >> derived service where there'll never be more than about a 20 Amp total
> >> demand...
> >>
> >> From the sub-panel to the receptacles about 3-1/2 feet below, I am using
> >> 10 AWG  only

Re: [Elecraft] [OT] NEC wire size requirements

[Lewis Phelps]

Depends on the conduit size. Half inch conduit can only carry two #6 wires per 
NEC, but 3/4” conduit is OK for four #6 wires.

But we weren’t talking here about pulling wire out of an existing conduit, I 
don’t think.. This was described as a new installation by a code-savvy op, who 
no doubt is using properly sized conduit..

Lew N6LEW

> On Aug 11, 2016, at 12:39 PM, Lynn W. Taylor, WB6UUT 
>  wrote:
> 
> On 8/11/2016 12:03 PM, Lewis Phelps wrote:
>> So, why go to the extra expense of #6 wire? While it seems to me to be to be 
>> harmless to “over-spec” the wire size, it also seems expensive and not 
>> necessary either per requirements of Section of 310-15 of the NEC or from a 
>> “good operating practices” perspective. 
> IIRC, there is discussion in the NEC about the total cross section of wires 
> in conduit.  Pulling #10 from existing conduit and replacing it with #6 could 
> in fact be a code violation?
> 
> -- Lynn

Lew Phelps N6LEW
Pasadena, CA DM04wd
Elecraft K3-10 / KXV144 / XV432
Yaesu FT-7800 
l...@n6lew.us
www.n6lew.us

Generalized Law of Entropy: Sooner or later, everything that has been put 
together will fall apart.





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Re: [Elecraft] [OT] NEC wire size requirements (was: Zip Wire Misrepresentation?)

[Lewis Phelps]

Sorry, auto spell correct got in the way. That should have read “lowes.com”

lew

> On Aug 11, 2016, at 12:03 PM, Lewis Phelps  wrote:
> 
> I’ve changed the subject line because this discussion has strayed from the 
> original question.
> 
> At retail rates (e.g. price per foot from lower.com ) #6 
> wire is 89 cents per foot, and #12 wire is 8.2 cents per foot;  assuming 
> Clay’s 50 foot run and 3 wires for a 110 VAC circuit with ground, per NEC, 
> the added cost for wire would be $121.20.  
> 
> Is it “good engineering practice?”  It seems to be to be OK from an 
> electrical standpoint, albeit unnecessary, and unnecessary from a cost 
> standpoint, albeit not harmful. 
> 
>  I can certainly understand “over-specifying” wire size in a 12 volt circuit, 
> and using larger wire size than is required simply from considering ampacity, 
>  because the voltage drop is a much larger change proportionally, but I 
> really don’t see the benefit from the expense and added installation 
> difficulty of using larger-than-required wire for a 120VAC supply circuit.
> 
> according to the online calculator at 
> http://www.southwire.com/support/voltage-drop-calculator.htm 
> , which takes 
> into account both resistance and reactance of the wire:
> 
> — for a 50 foot run of cable of #6 wire, at 20 amps and 120 volts AC single 
> phase,  the total voltage drop will be 0.884 volt, or 0.74%, for a net 
> voltage at the end of the circuit of 119.1 volts (rounding)
> — for the same run with #12 wire, the total voltage drop will be 3.472 volts, 
> or 2.90 percent, for a net voltage at the end of the circuit of 116.5 volts 
> (rounding). 
> 
> The 3.47 volt drop would be intolerable in a 12 volt circuit providing power 
> directly to amateur radio equipment, but seems to me irrelevant if feeding a 
> competently-designed power supply that reduces the 120 volts AC  supply to 
> some lower voltage of DC supply. Any ham radio power supply that is specified 
> to operate on 120 VAC should be able to operate without difficulty from a 
> 116.5 volts supply.
> 
> So, why go to the extra expense of #6 wire? While it seems to me to be to be 
> harmless to “over-spec” the wire size, it also seems expensive and not 
> necessary either per requirements of Section of 310-15 of the NEC or from a 
> “good operating practices” perspective. 
> 
> Lew N6LEW
> 
> 
> 
>> On Aug 11, 2016, at 11:12 AM, Kevin - K4VD > > wrote:
>> 
>> The added cost of a 3x over-build seems like it would be awfully high. Is
>> this good engineering practice (seriously, I don't know)?
>> 
>> Kevin K4VD
>> 
>> On Thu, Aug 11, 2016 at 12:38 PM, Clay Autery > > wrote:
>> 
>>> How do you define "necessary".
>>> 
>>> Paraphrasing K9YC, Jim  "Big wire is your friend".
>>> 
>>> I agree...
>>> 
>>> I typically use wire at least 2 sizes larger than "required"  Often
>>> the wire size is determined by how big of a wire I can FIT in the
>>> application and how much money I can part with at the time.
>>> 
>>> For instance, on my current power project... I am running 6 AWG x 4 from
>>> the service to the sub-panel @ 50 foot run for a 60 Amp separately
>>> derived service where there'll never be more than about a 20 Amp total
>>> demand...
>>> 
>>> From the sub-panel to the receptacles about 3-1/2 feet below, I am using
>>> 10 AWG  only because that's the largest wire the receptacle
>>> terminals are rated for.
>>> 
>>> From the receptacles to all equipment, minimum 10 AWG...
>>> 
>>> Bigger and shorter the wire, the better...
>>> 
>>> __
>>> Clay Autery, KY5G
>>> MONTAC Enterprises
>>> (318) 518-1389
>>> 
>>> On 8/11/2016 10:43 AM, Ronnie Hull wrote:
 Is 10 gauge necessary?
 
 Sent from my iPhone
>>> __
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft 
>>> 
>>> Help: http://mailman.qth.net/mmfaq.htm 
>>> Post: mailto:Elecraft@mailman.qth.net 
>>> 
>>> This list hosted by: http://www.qsl.net 
>>> Please help support this email list: http://www.qsl.net/donate.html 
>>> 
>>> Message delivered to ke...@k4vd.net 
>>> 
>> __
>> Elecraft mailing list
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>> 
>> Help: http://mailman.qth.net/mmfaq.htm 
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>> 
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>> Please help support this email list: http://www.qsl.net/donate.html 
>> 

Re: [Elecraft] [OT] NEC wire size requirements (was: Zip Wire Misrepresentation?)

[Lewis Phelps]

I’ve changed the subject line because this discussion has strayed from the 
original question.

At retail rates (e.g. price per foot from lower.com) #6 wire is 89 cents per 
foot, and #12 wire is 8.2 cents per foot;  assuming Clay’s 50 foot run and 3 
wires for a 110 VAC circuit with ground, per NEC, the added cost for wire would 
be $121.20.  

Is it “good engineering practice?”  It seems to be to be OK from an electrical 
standpoint, albeit unnecessary, and unnecessary from a cost standpoint, albeit 
not harmful. 

 I can certainly understand “over-specifying” wire size in a 12 volt circuit, 
and using larger wire size than is required simply from considering ampacity,  
because the voltage drop is a much larger change proportionally, but I really 
don’t see the benefit from the expense and added installation difficulty of 
using larger-than-required wire for a 120VAC supply circuit.

according to the online calculator at 
http://www.southwire.com/support/voltage-drop-calculator.htm, which takes into 
account both resistance and reactance of the wire:

— for a 50 foot run of cable of #6 wire, at 20 amps and 120 volts AC single 
phase,  the total voltage drop will be 0.884 volt, or 0.74%, for a net voltage 
at the end of the circuit of 119.1 volts (rounding)
— for the same run with #12 wire, the total voltage drop will be 3.472 volts, 
or 2.90 percent, for a net voltage at the end of the circuit of 116.5 volts 
(rounding). 

The 3.47 volt drop would be intolerable in a 12 volt circuit providing power 
directly to amateur radio equipment, but seems to me irrelevant if feeding a 
competently-designed power supply that reduces the 120 volts AC  supply to some 
lower voltage of DC supply. Any ham radio power supply that is specified to 
operate on 120 VAC should be able to operate without difficulty from a 116.5 
volts supply.

So, why go to the extra expense of #6 wire? While it seems to me to be to be 
harmless to “over-spec” the wire size, it also seems expensive and not 
necessary either per requirements of Section of 310-15 of the NEC or from a 
“good operating practices” perspective. 

Lew N6LEW



> On Aug 11, 2016, at 11:12 AM, Kevin - K4VD  wrote:
> 
> The added cost of a 3x over-build seems like it would be awfully high. Is
> this good engineering practice (seriously, I don't know)?
> 
> Kevin K4VD
> 
> On Thu, Aug 11, 2016 at 12:38 PM, Clay Autery  > wrote:
> 
>> How do you define "necessary".
>> 
>> Paraphrasing K9YC, Jim  "Big wire is your friend".
>> 
>> I agree...
>> 
>> I typically use wire at least 2 sizes larger than "required"  Often
>> the wire size is determined by how big of a wire I can FIT in the
>> application and how much money I can part with at the time.
>> 
>> For instance, on my current power project... I am running 6 AWG x 4 from
>> the service to the sub-panel @ 50 foot run for a 60 Amp separately
>> derived service where there'll never be more than about a 20 Amp total
>> demand...
>> 
>> From the sub-panel to the receptacles about 3-1/2 feet below, I am using
>> 10 AWG  only because that's the largest wire the receptacle
>> terminals are rated for.
>> 
>> From the receptacles to all equipment, minimum 10 AWG...
>> 
>> Bigger and shorter the wire, the better...
>> 
>> __
>> Clay Autery, KY5G
>> MONTAC Enterprises
>> (318) 518-1389
>> 
>> On 8/11/2016 10:43 AM, Ronnie Hull wrote:
>>> Is 10 gauge necessary?
>>> 
>>> Sent from my iPhone
>> __
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft@mailman.qth.net
>> 
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to ke...@k4vd.net 
>> 
> __
> Elecraft mailing list
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> 
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> Please help support this email list: http://www.qsl.net/donate.html 
> 
> Message delivered to l...@n6lew.us 
Lew Phelps N6LEW
Pasadena, CA DM04wd
Elecraft K3-10 / KXV144 / XV432
Yaesu FT-7800 
l...@n6lew.us
www.n6lew.us

Generalized Law of Entropy: Sooner or later, everything that has been put 
together will fall apart.





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