ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
Video: Inventor of the GFCI self-testing shocks
by Bill Addiss. 01/17/18 11:11 PM
FPE in Germany
by HotLine1. 01/17/18 07:07 PM
VDE 0100 to introduce AFCIs
by LongRunner. 01/17/18 10:32 AM
Fujifilm Recalls Power Adapter Wall Plugs
by Admin. 01/16/18 07:04 PM
Air Compressor feeder conductor sizing
by Potseal. 01/15/18 09:08 PM
New in the Gallery:
Housebilding DIY wiring
SE cable question
Who's Online Now
1 registered members (Potseal), 9 guests, and 12 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Service size dispute #211584
10/29/13 06:12 PM
10/29/13 06:12 PM
V
Vindic8ed  Offline OP
New Member
Joined: Oct 2013
Posts: 1
UT
We are working on this mansion with a 600 amp panel and our boss wants to pull 250 kcmil aluminum wire (we don't even think his load "calculations" are correct for the house, probably only need 400 amp service). We have a guest house and a detached garage we are pulling to from the house. We measured the garage piping and it will be 450 feet and a 200 amp panel. The two journeymen on the job aren't getting the same numbers in their calculations for the of size wire we need, but we all agree that the boss is wrong because with the voltage drop that aluminum wire isn't going to cut it. What equations should we be using to calculate this? And what size wire should we actually be using?

Last edited by Conner; 10/29/13 06:16 PM.
Tools for Electricians:
Re: Service size dispute [Re: Vindic8ed] #211585
10/29/13 07:59 PM
10/29/13 07:59 PM
HotLine1  Online Content

Member
Joined: Apr 2002
Posts: 6,917
Brick, NJ USA
This is a commonly used voltage drop calculation formula:


(2xK) x A x L
_________________
CMils

SINGLE PHASE (1) FORMULA

The "K" for Al is 21.2
The "A" is your load in amps (200)
The "L" is the length of the run, in feet, one way
The "CMils" is the conductor size (250,000)



John
Re: Service size dispute [Re: Vindic8ed] #211586
10/29/13 08:15 PM
10/29/13 08:15 PM
HotLine1  Online Content

Member
Joined: Apr 2002
Posts: 6,917
Brick, NJ USA
You should get an answer of 15.26 Vd, which is excessive for a feeder.

Understand that the "200 amp" load is a major factor. Do you know what the calculated load is for this panel??



John
Re: Service size dispute [Re: Vindic8ed] #211621
11/01/13 09:48 PM
11/01/13 09:48 PM
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
Elaborating on John's Post (AKA "HotLine1"):

Quote

Understand that the "200 amp" load is a major factor. Do you know what the calculated load is for this panel??


Using my Custom Made Volt-Loss Spreadsheet, the following values were obtained across several scenarios:

FEEDER SCENARIO #1: 250 MCM ALUMINUM FEEDERS
Feeder Length: 450 Feet,
Duct Material: Non-Metallic,
System: 120/240V 1 Phase 3 Wire,
E L-L at point of Delivery: 240V,
Loads: =/> 0.884PF; connected L-L...
"L-L" = Line-to-Line
"(AVG)" = Averaged
"(WCS)" = Worst-Case Scenario

1A.: 30 Amp Load:
Volt Loss Percentile: 0.893% (AVG), 0.954% (WCS)
Averaged Working Voltage: 237.86 VAC

1B.: 50 Amp Load:
Volt Loss Percentile: 1.489% (AVG), 1.590% (WCS)
Averaged Working Voltage: 236.43 VAC

1C.: 80 Amp Load:
Volt Loss Percentile: 2.382% (AVG), 2.544% (WCS)
Averaged Working Voltage: 234.28 VAC

1D.: 125 Amp Load:
Volt Loss Percentile: 3.722% (AVG), 3.975% (WCS)
Averaged Working Voltage: 231.07 VAC

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

FEEDER SCENARIO #2: 250 MCM COPPER FEEDERS
Feeder Length: 450 Feet,
Duct Material: Non-Metallic,
System: 120/240V 1 Phase 3 Wire,
E L-L at point of Delivery: 240V,
Loads: =/> 0.884PF; connected L-L...
"L-L" = Line-to-Line
"(AVG)" = Averaged
"(WCS)" = Worst-Case Scenario

2A.: 30 Amp Load:
Volt Loss Percentile: 0.707% (AVG), 0.8325% (WCS)
Averaged Working Voltage: 238.30 VAC

2B.: 50 Amp Load:
Volt Loss Percentile: 1.178% (AVG), 1.3875% (WCS)
Averaged Working Voltage: 237.17 VAC

2C.: 80 Amp Load:
Volt Loss Percentile: 1.884% (AVG), 2.220% (WCS)
Averaged Working Voltage: 235.48 VAC

2D.: 125 Amp Load:
Volt Loss Percentile: 2.949% (AVG), 3.46875% (WCS)
Averaged Working Voltage: 232.94 VAC

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

The above figures plot High Power Factor Loads connected across the Secondary (Output) of a Single Phase Transformer, with a Center-Tapped & Grounded Secondary Winding - either Physical Tap, or Tap between X2-X3 Terminals.

Balanced L-N Loads may be figured as L-L
(i.e.: Two separate 50A L-N Loads connected A-N and B-N)
For a completely L-N Load, double the Volt-Loss Percentiles listed above.
Example: Feeder = CU, 30 Amp L-N Load:
Volt Loss Percentile: 1.413% (AVG), 1.665% (WCS)
Averaged Working Voltage: 118.30 VAC

Volt Loss results are from Two (2) Calculation Types:
a. Conductor Resistance-Only
and
b. Conductor Impedance (Resistance & Reactance).

Averaged Volt Loss Calculations are the mean of the Two, while Worst-Case Scenario is the higher of the Two.

Lastly;
If the System is "120/208V 1 Phase 3 Wire Open Wye", derived from a 208Y/120V 3 Phase 4 Wire Transformer's Output, values will be much different than the results from a 120/240V 1PH. 3 Wire Transformer.

--Scott (EE)


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
Trumpy
Trumpy
SI,New Zealand
Posts: 8,231
Joined: July 2002
Show All Member Profiles 
Top Posters(30 Days)
Admin 20
sparky 18
Potseal 13
Popular Topics(Views)
243,543 Are you busy
180,346 Re: Forum
170,832 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.014s Queries: 15 (0.004s) Memory: 0.9634 MB (Peak: 1.0930 MB) Zlib enabled. Server Time: 2018-01-19 03:24:20 UTC