ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
Potseal 11
Recent Posts
600 KW 120/208 3 Phase Y protection
by Yooperup. 07/24/17 12:20 PM
1913 American Electrician's Handbook
by gfretwell. 07/20/17 01:08 PM
Green House wiring
by ghost307. 07/20/17 09:10 AM
Permit Snafus...AHJs and Contractors Jump in
by HotLine1. 07/18/17 08:06 PM
New in the Gallery:
SE cable question
Popular Topics(Views)
239,330 Are you busy
174,797 Re: Forum
167,171 Need opinion
Who's Online Now
0 registered members (), 80 guests, and 14 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
Page 1 of 2 1 2
#187853 - 07/11/09 06:29 PM Will voltage drop calcs be required in NEC?  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,099
Estero,Fl,usa
There is an article in the IAEI magazine this month advocating that the 3% and 5% in the FPN be made code.
It is no surprise the author is from the copper lobby but he does make a compelling argument that it might be part of an energy code. He even has a poll saying 94% of respondents think it should be in the NEC but that poll may have been taken around the doughnut box at copper.org.

If you actually put pencil to paper you will find that 310.16 and perhaps even 240.4(D) may not be very useful.
We could be using yet larger wire.
We might actually end up changing the typical topology of most wiring systems with more sub-panels and more use of multiwire circuits ... when the 2 pole AFCIs hit the market.

Thoughts?


Greg Fretwell

2017 / 2014 NEC & Related Books and Study Guides

#187855 - 07/11/09 09:05 PM Re: Will voltage drop calcs be required in NEC? [Re: gfretwell]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Instituting such a rule is pure silliness - and ignores the most important factor: what is the supplied voltage?

For example, NEMA standards require motors to operate within 10% of the nameplate voltage. Let us, for the sake of this discussion, assume a motor is marked "220v"

If that motor is installed on a nominal 208v system, it can operate as low as 198v. The 5% rule would give you 197v. You're outside the motor specs.

If that motor is installed on a nominal 240v system, you're OK - as long as the supplied voltage does not exceed 242v. Since the utility might very well be providing 250v, you're in trouble unless you make sure you have at least 4% drop.

Moreover, about half of that 5% is assigned to the PoCo side of the circuit - the one part you have no control over.

Why are PoCo voltages a concern? Because areas still under development tend to have really high voltages, while older installations have voltages drop as loads increase. That's what transformers do at full capacity: lose voltage.

Therefore, the really important issue is the actual voltage delivered to the motor, and not some percentage of voltage drop.

If you want to check your overall circuit, then test it for impedence. A higher impedence -reflected in voltage drop under load - might suggest a bad connection somewhere. Still, keep in mind the critical voltage range of the appliance.

After all, a motor marked "230" will be fine at 208 - but out of spec at 207!


#187856 - 07/11/09 09:17 PM Re: Will voltage drop calcs be required in NEC? [Re: gfretwell]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,853
Brick, NJ USA
There are times VD calcs are necessary, however there are many times when they are not.

Comm/Ind here in NJ requires plans, one-lines, etc prepared by a Lic Architect/PE/EE. Instances where this could become an issue are noticed sometimes during plan review, and only 'suggestions' can be mentioned. Changing the FPN to 'code' eliminates 'suggestion' to 'comply'.

As to EC's and electricians being affected by this, in the McMansions it may become an issue. I include VD calcs in one of the classes I teach at Vo-Tech, and it is usually well received.


John

#187857 - 07/11/09 10:04 PM Re: Will voltage drop calcs be required in NEC? [Re: renosteinke]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,099
Estero,Fl,usa
The point the article is trying to make is excessive voltage drop represents wasted energy.


Greg Fretwell

#187877 - 07/13/09 10:37 AM Re: Will voltage drop calcs be required in NEC? [Re: gfretwell]  
ghost307  Offline
Member
Joined: May 2005
Posts: 906
Chicago Illinois USA
It's mandatory in Chicago; you'd be amazed now many 225A panels need to be fed with 500kcmil to meet the voltage drop limits.

It gets to be interesting when you're trying to save money by using smaller wire and the building owner finds out that he isn't permitted to use the NEC wire sizes, but that he COULD reduce the wire size if his building was 2 miles further West.


Ghost307

#187878 - 07/13/09 11:46 AM Re: Will voltage drop calcs be required in NEC? [Re: ghost307]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Ahh ... the article is using 'voltage drop' as an excuse to introduce 'green thinking' and 'global warming' into the NEC. (And, yes, the article brings up 'global warming').

Humbug! Stop these fanatic missionaries ay the gates! Their message has NO place in a document dedicated to the concept of the ''minimum for the the practical safe use of electricity.' The NEC is all about 'safety,' saving the planet is outside the scope of the NEC.

Voltage drop is both a design issue, and a quality issue.
We have little control or influence over the 2% on the utility side of the equation.

As for 'our' 3%, the calculations may be nice .... but are largely irrelevant.

Irrelevant, first, because they cannot evaluate connections - which is likely to be a greater source of loss than simple wire length.

Second, because the voltage drop depends upon the actual current draw. While it can easily become an issue when you're drawing 15 amps on a 15 amp circuit (or even more if you're trying to start a motor under load), it's meaningless if all that branch circuit is powering is the TV set.

There's the rub: most of our work involves the very circuits that are NOT sized according to the loads to be used - the household 'convenience' circuits.

As to this 'green' nonsense: For convenience circuits, you have a choice: more receptacles on a circuit, or more circuits. Either way, you're going to 'lose," as you either use much more material, or risk greater voltage drop in the calculations.

The 'save the world' crowd will then adopt the same approach they do with regard to parking spaces: fewer receptacles will be their goal. This is in direct conflict with the NEC.

Beware of wolves in sheep's clothing.


#187890 - 07/13/09 06:05 PM Re: Will voltage drop calcs be required in NEC? [Re: renosteinke]  
ChicoC10  Offline
Member
Joined: May 2007
Posts: 169
CA
Stop them at the gates? Ha!! They are already in your bedchambers!!!

About 220 miles to your west, Reno, the thinking is likely to be on the "save energy whatever the cost" side. And a great number of misguided people want to adopt CA's standards as those of the entire US.

Include the word green in it somewhere and its as good as sold.

I have always interpreted the VD notes to mean 2% on the feeders from the service entrance and a total of 5% to the furthest branch point and have designed accordingly. Not for green-ness but for the best power transmission and least chance of my wishing I had run larger conductors.

As far as it becoming code, anyone want to bet against it?


#187903 - 07/13/09 10:28 PM Re: Will voltage drop calcs be required in NEC? [Re: ChicoC10]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,099
Estero,Fl,usa
I have been told this is already the law in Florida, via the energy code but I didn't include any V/D calculations in my plans when I added onto my house, nor were they part of the process, so I am not sure how it is getting enforced.


Greg Fretwell

#188259 - 07/27/09 07:09 PM Re: Will voltage drop calcs be required in NEC? [Re: gfretwell]  
KJay  Offline
Member
Joined: Nov 2007
Posts: 763
MA, USA
Originally Posted by gfretwell
It is no surprise the author is from the copper lobby but he does make a compelling argument that it might be part of an energy code.


Great... It seems like the NEC is apparently just a rump swab for every lobbyist with an agenda or a hip pocket to fill. Nema's little cash cow as well as the more Holy than tho’ do gooders guide to salvation for the plebeian unwashed masses.

Wait... did that come off as too cynical? grin


#188313 - 07/30/09 03:25 AM Re: Will voltage drop calcs be required in NEC? [Re: KJay]  
macmikeman  Offline
Member
Joined: Jul 2002
Posts: 717
Honolulu, Hawaii
It will make the home inspectors happy, cause if it is adopted then their cute little VD testers ( Ideal Shure Test ) will suddenly become real.......


Page 1 of 2 1 2

Member Spotlight
JoeKP
JoeKP
Berkley, MA
Posts: 144
Joined: March 2008
Show All Member Profiles 
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.021s Queries: 16 (0.003s) Memory: 0.8236 MB (Peak: 1.0055 MB) Zlib enabled. Server Time: 2017-07-25 18:51:08 UTC