# 100 foot rule



## 480sparky (Sep 20, 2007)

RICK BOYD said:


> .........is there a length rule


No. Your only limit is the length of your rope/fish tape/rodder.

The is no length specified in any derating rules other than the nipple rule of Chapter 9, Note 4.


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## RICK BOYD (Mar 10, 2008)

480sparky said:


> No. Your only limit is the length of your rope/fish tape/rodder.
> 
> The is no length specified in any derating rules other than the nipple rule of Chapter 9, Note 4.


I am installing a 200 amp panel 98' from the meter so I am concerned about whether 3/0 copper is big enough or should I use 4/0 ? 
who knows what they may add in the future


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## raider1 (Jan 22, 2007)

RICK BOYD said:


> I am installing a 200 amp panel 98' from the meter so I am concerned about whether 3/0 copper is big enough or should I use 4/0 ?
> who knows what they may add in the future


Do a voltage drop calculation for the panel. There is no NEC requirement to upsize wires for voltage drop but there is a FPN to 215.2(A) that recommends that you size your feeders to prevent a volatge drop exceeding 3% at farthest load and 5% on both the feeder and branch circuit to the farthest load.

Chris


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## Dennis Alwon (May 9, 2009)

RICK BOYD said:


> I am installing a 200 amp panel 98' from the meter so I am concerned about whether 3/0 copper is big enough or should I use 4/0 ?
> who knows what they may add in the future


What is the calculated load? Once you have that use this online VD calculator


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## 480sparky (Sep 20, 2007)

raider1 said:


> Do a voltage drop calculation for the panel. There is no NEC requirement to upsize wires for voltage drop but there is a FPN to 215.2(A) that recommends that you size your feeders to prevent a volatge drop exceeding 3% at farthest load and 5% on both the feeder and branch circuit to the farthest load.
> 
> Chris


FYI (not you, Chris... I'm sure you know this!), FPNs are not enforcable.



> *90.5 Mandatory Rules, Permissive Rules, and Explanatory Material.*
> *(C) Explanatory Material.* Explanatory material, such as references to other standards, references to related sections of this Code, or information related to a Code rule, is included in this Code in the form of fine print notes (FPNs). Fine print notes are informational only and are not enforceable as requirements of this Code.


(Red highlight is mine)


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## B4T (Feb 10, 2009)

Dennis Alwon said:


> What is the calculated load? Once you have that use this online VD calculator


I just tried 100' @ 15 amp and got #8


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## raider1 (Jan 22, 2007)

480sparky said:


> FYI (not you, Chris... I'm sure you know this!), FPNs are not enforcable.


Thats why I said there is no NEC requirement to upsize for voltage drop.

Chris


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## Celtic (Nov 19, 2007)

RICK BOYD said:


> who knows what they may add in the future


Who cares?
You could spend many days wondering what the answer is...and just when you are satisfied with the debate in your mind ~ the client does something different 

Give 90.1(B) a little eyeballing...then give the FPN some attention also.


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## manchestersparky (Mar 25, 2007)

480-

Thats were a lot of electricians get in trouble, they don't realize that Fine Print Notes are not enforceable. They look in the code book and assume that if it's written in there it is "code".
That and the fact they listen to all those " know it alls" and just take it as gospel with out ever looking it up or questioning it.

There are days that I think Code classes should be mandatory every couple years


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## kbsparky (Sep 20, 2007)

manchestersparky said:


> ....There are days that I think Code classes should be mandatory every couple years


You are in the wrong section of Maryland, then.

Continuing education classes are now mandatory in: Caroline, Cecil, Dorchester, Prince George's, Queen Anne's, and Wicomico counties. :blink: There may be others coming on board as well.


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## B4T (Feb 10, 2009)

Black4Truck said:


> I just tried 100' @ 15 amp and got #8


I'm still waiting for someone to explain how come these numbers are so wacked :blink:


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## kbsparky (Sep 20, 2007)

That ain't whacked. You only need a #8 to prevent excessive voltage drop with a 15 Amp load on a 100 foot run.
:whistling2:


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## wildleg (Apr 12, 2009)

the 100' rule was a rule of thumb some guys used to upsize wire for vd (not a code rule)


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## RePhase277 (Feb 5, 2008)

Black4Truck said:


> I'm still waiting for someone to explain how come these numbers are so wacked :blink:


They're not whacked. To maintain a 3% drop at 120 V over 100' at 15 A would require a wire size between #10 and #8, so #8 it is.

The calc is CM = (2kID)/VD, where k is the resistivity of copper @ 75C of 12.9, I is the current, and D is the one way length of the circuit in feet, VD is the voltage drop.

This will give the wire size in circular mils.


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## Dennis Alwon (May 9, 2009)

I believe I heard that NJ has put the FPN on the VD rule into effect in their amendments. Celtic????


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## Dennis Alwon (May 9, 2009)

Black4Truck said:


> I just tried 100' @ 15 amp and got #8


Others answered that for you but you do realize that if the circuit calls for a #14 wire and you upsize to a #10 then your EGC must also be #10 even if the breaker is 15 amp. 250.122(B)

Also the vd calculator does get strange with numbers in certain circumstances.


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## Dennis Alwon (May 9, 2009)

Here is an example. If the voltage is 240 , single phase copper conductors and the distance is 100' and the amperage on the cir. is 200 amps then the VD calculator states you need a #1 .

The problem is the communicative nature of multiplication. Thus if you had the same example as above but the distance was 200' and he amperage was 100 amps then a #1 is called for. That makes more sense then the other way around.


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## drsparky (Nov 13, 2008)

How about this line of reasoning. You still must follow the manufacture listing, therefore an under voltage is a violation in that respect. 
The FPN are good guides on how to achieve the proper voltage to operate the equipment without violating its listing.


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## Celtic (Nov 19, 2007)

Dennis Alwon said:


> I believe I heard that NJ has put the FPN on the VD rule into effect in their amendments. Celtic????



NJ has accepted all the FPNs as "law".





Black4Truck said:


> I'm still waiting for someone to explain how come these numbers are so wacked :blink:


They are not "wacked"....imagine a parking lot w/poles....the ckt might be at 277V @ 20A but what size wire? Usually some where is the #4 and larger arena.


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## kbsparky (Sep 20, 2007)

On the 277/480 systems, voltage drop is not as much a problem as it is on 208 Volt systems.

I've seen more upsizing on lower volt systems.


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## Magnettica (Jan 23, 2007)

Using 480 volts for parking lot light lighting solves a lot of voltage drop issues.


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## manchestersparky (Mar 25, 2007)

kbsparky said:


> You are in the wrong section of Maryland, then.
> 
> Continuing education classes are now mandatory in: Caroline, Cecil, Dorchester, Prince George's, Queen Anne's, and Wicomico counties. :blink: There may be others coming on board as well.


I am on board for state wide, required licensing for ALL electrical workers and CEU's

I am serious when I say I think a CODE class should be mandatory as a required CEU. I mean a real code class that takes more then 6 hours. A true code class takes at least 3 days (or 24 hours) Most code classes are geared toward one aspect or another commercial or residential.
One of the organizations that I belong to is going through the code book from the rear to the front. We chose this approach as most code classes never reach the back of the book.


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## JohnJ0906 (Jan 22, 2007)

manchestersparky said:


> I am on board for state wide, required licensing for ALL electrical workers and CEU's


 I agree.



> One of the organizations that I belong to is going through the code book from the rear to the front. We chose this approach as most code classes never reach the back of the book.


 I like that approach.


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## wildleg (Apr 12, 2009)

I'm beginning to think that the code book is just too complicated for most working guys to understand. I've been wondering lately that maybe parts of it could be rewritten in the form similar to that of a triage decision tree (flow chart) like the paramedics use, for portions that require, say, wire sizing, fuse sizing, load calcs, etc. The guys that are interested in keeping up with the code can find the answers, but there's a lot of guys that just want the answer, and the book is just too damn confusing to them.


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## Bob Badger (Apr 19, 2009)

wildleg said:


> but there's a lot of guys that just want the answer, and the book is just too damn confusing to them.


Then they should go flip burgers or sell sunglasses at the mall.


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## sparky970 (Mar 19, 2008)

Black4Truck said:


> I just tried 100' @ 15 amp and got #8


Have you ever seen #8 on a receptacle? 100' is not that far.


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## Bob Badger (Apr 19, 2009)

sparky970 said:


> Have you ever seen #8 on a receptacle? 100' is not that far.


That does not change the reality of the calculations.

For what it's worth I have done jobs where 4 AWG copper was used to supply 20 amp duplex receptacles ......... of course the distances where more than 100'


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## MDShunk (Jan 7, 2007)

sparky970 said:


> Have you ever seen #8 on a receptacle? 100' is not that far.


No, silly. You'd do it the same way you feed, say, a 20 amp circuit for parking lot lights with #4. Put some #12 on the breaker for a few inches and bug on your #4 to the #12.


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## brian john (Mar 11, 2007)

Previously posted.

From a inspection report I did for a large school; system that had VD issues. The contractor went bankrupt and the county was trying to figure out why they had a low voltage issue.. 

Panels were as far as 350 feet from some classes. The county swore this was not an issue at the other school's with the exact same design but this one. All schools identical.










There is more to this table on my work PC.


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## 480sparky (Sep 20, 2007)

brian john said:


> Previously posted.
> 
> From a inspection report I did for a large school; system that had VD issues. The contractor went bankrupt and the county was trying to figure out why they had a low voltage issue..
> 
> ...


I don't get it. Lower voltage drop with larger amperages? Higher drops with larger wires?


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## RePhase277 (Feb 5, 2008)

brian john said:


> Panels were as far as 350 feet from some classes. The county swore this was not an issue at the other school's with the exact same design but this one. All schools identical.



Of course not. It's only an issue when you put a load on the circuit!


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## MDShunk (Jan 7, 2007)

480sparky said:


> I don't get it. Lower voltage drop with larger amperages? Higher drops with larger wires?


That chart is the distance you can go with a certain size wire and a certain load to maintain the percentage drop noted for each column.


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## micromind (Aug 11, 2007)

The table lists maximum distances for the load, wire size, and voltage drop.

Rob

Rats! Marc beat me by 2 minutes!


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## 480sparky (Sep 20, 2007)

MDShunk said:


> That chart is the distance you can go with a certain size wire and a certain load to maintain the percentage drop noted for each column.


OK... the light bulb just came on!


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## RICK BOYD (Mar 10, 2008)

Dennis Alwon said:


> What is the calculated load? Once you have that use this online VD calculator


thanks for the VD calculator lead. I punched in 240 volts and 200 amps at 98 feet and it told me #1 but 310-16 says 3/0 so I still am thinking going 4/0 just in case besides, I make more money selling big wire than smaller wire.
Rick

ps I've never said thanks for the vd to any one before!


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## heel600 (Oct 31, 2007)

Celtic said:


> NJ has accepted all the FPNs as "law".
> 
> 
> 
> ...


 
Where did you hear that NJ adopted the FPN? Not according to Suzzane Borek.

But NJ did adopt the ASHREA (I think) energy codes, and that's where the voltage drop rules come from.


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## Lighting Retro (Aug 1, 2009)

> ps I've never said thanks for the vd to any one before!


:laughing:


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## Celtic (Nov 19, 2007)

heel600 said:


> Where did you hear that NJ adopted the FPN? Not according to Suzzane Borek.


Here:

The '05:


> 2. The National Electrical Code 2002 *2005*may be known and cited as "the electrical subcode."
> 
> i. Codes and standards referenced in the Fine Print Notes (FPNs) of the electrical subcode (NEC 2002 *2005*) shall be considered adopted by reference to the extent prescribed by each related section. These codes and standards also are printed in DCA Bulletin #03-1 *#05-2*, which contains a list of adopted codes and standards that are applicable to the enforcement of the electrical subcode.


http://www.nema.org/stds/fieldreps/codealerts/20051107nj.cfm



The '08


> COMMUNITY AFFAIRS
> Division Of Codes And Standards
> Uniform Construction Code
> Electrical Subcode
> ...


http://www.state.nj.us/dca/codes/ruleadoptions/nec_adopt.pdf


...maybe I overstated a wee bit :whistling2:


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## McClary’s Electrical (Feb 21, 2009)

sparky970 said:


> Have you ever seen #8 on a receptacle? 100' is not that far.


He figured #8 for a 15 amp LOAD,,,,,,,,NOT breaker size,,,,,,,you cannot load a 15 amp breaker past 12 amps,,,,,,#8 for 15 amp LOAD at 100' is correct if you stay within 3%


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## macmikeman (Jan 23, 2007)

mcclary's electrical said:


> He figured #8 for a 15 amp LOAD,,,,,,,,NOT breaker size,,,,,,,you cannot load a 15 amp breaker past 12 amps,,,,,,


You can. 210.20 (A) Exception And also 210.23


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## 480sparky (Sep 20, 2007)

mcclary's electrical said:


> ,,,,,,,you cannot load a 15 amp breaker past 12 amps,,,,,,


According to who?


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## McClary’s Electrical (Feb 21, 2009)

Sorry, I should have clarified myself better. When he replied to me, "Have you ever seen a #8 on a receptacle" I meant that IF this was a 15 amp LOAD plugged into a receptacle on a 15 amp circuit, you could not load the breaker past 12 amps thru that receptacle per 210.21 B (2)


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## Inspector Grump (Jun 4, 2008)

:thumbup:I'm happy to see someone reads the UCC code in NJ


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## longbeach1125 (Sep 7, 2009)

i was taught for every 100 feet, you go up 1 wire size. I dont know about feeders off hand but if i were to put in a 20 amp circuit 130 feet away i would run #10.


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