VD question

[Tulsa Electrician]

I was sent an email from a fellow Tulsa electrician asking me to do a Voltage drop on a feeder. I was like sure what you got.
This is the info he gave me.
System Voltage 208/120 three pahse four wire
Three phase four wire feeder from MDP to New 400 amp main lug panel for kitchen equipment 421 feet.
Circuit amps 205.85 Max unbalanced neutral load 115 amps
Breaker in MDP 250 amp
Feeder is ran in a ceiling of conditioned space (open bar joist) 18" down from ceiling. No ambient correction

He and I both come up with a single 350 mcm copper
The engineer said two set of 350 MCM. He told me he ask the engineer to check and came back with the same number.
From engineer: (2) set 350 mcm cu with a VD of 2.8%

I inputted a 2% just in case and still did not come up with 2-350's I even ran the 5% over all based on largest load.

I did tell him an engineer designed it and should follow his recommendation. This is more for me to learn.

Any advise as to where I may have went wrong?

VD	VOLTS	3-p	Exact K	D	I	CM	AWG	VD %
3.55	120	2	12.845	421	115	350000	350	2.96%
5.51	208	1.732	12.845	421	205.85	350000	350	2.65%

				CM=( pahse x Ka x distnce x I)/VP permited
	cm				CU			3%​
				3 phase	app K	Feet	Amps	VD p
(N)	346,974​	350	350	2​	12.9​	421​	115​	3.6​
(P)	310,303​	350	350	1.732​	12.9​	421​	205.85​	6.24​

Phase Conductors
	AMP	AWG		CM	RATIO
OCD	250
CM	Selected	250		250,000
CM	Requireds	350		350,000
EGC Rtaio					1.40000
EGC	OLD	4		41,740
	NEW	2	66360	58,436

			(t)
	cycle	HZ	seconds
	0.5	60	0.008333333
	CM	/ 42.5	I²
#2	66360	1570.651	2,466,944
	I²	(t)	(CWR)
	2,466,944	5	12,334,721
I²T @1/2 cycle		38,473	AMPS

Jam Ratio
EMT	(D)	AWG	(d)	Ratio
2 1/2​	2.731	350	0.817	3.34

 

[Tulsa Electrician]

Here is the largest load from panel.

VD	VOLTS	3-p	Exact K	D	I	CM	AWG	VD %
2.08	208	1.732	12.85592	60	65	41740	4	1.00%

 

[Dsg319]

I just plugged your numbers in on the south wire app and came up with 2 sets 250kcmils.

 

[Tulsa Electrician]

I see it's based @ 60c and 90%pf
I should have used 90% since it's comm kitchen loads.
I will change my number from 30c to 90c and use 90%pf
Thanks

 

[Tulsa Electrician]

Table

 

[Dsg319]

I see it's based @ 60c and 90%pf
I should have used 90% since it's comm kitchen loads.
I will change my number from 30c to 90c and use 90%pf
Thanks

Tbh I never even paid much mind to the temp and PF numbers, I seen them but that was about it.

I typically don’t use apps but just the over simplified calculation on paper.

 

[hillbilly1]

Dsg319, you are set on single phase, here’s three phase.

 

[Dsg319]

Dsg319, you are set on single phase, here’s three phase.

Good catch.

 

[Tulsa Electrician]

Can some one use that app set to 1 set instead of 2 sets

 

[Tulsa Electrician]

Thanks

 

[ramsy]

I see it's based @ 60c and 90%pf
I should have used 90% since it's comm kitchen loads.
I will change my number from 30c to 90c and use 90%pf
Thanks

421 feet is a long way for 120 volt loads. Might consider a transformer for future expansion near the kitchen.

205A Neutral VD = 2.67% with 4/0cu x 2 parallel, using home made AC formula spreadsheet.

Verified & validated engineering systems may be more accurate, since me poor man's NEC Table 9 impedances are only good at pf=0.85

 

[ramsy]

Can some one use that app set to 1 set instead of 2 sets

Poor man's calc shows VD = 5.7% for 1-set of 4/0

 

[hillbilly1]

Here ya go!

 

[Tulsa Electrician]

What does your poorman calc say using 1set of 350
Feel free to 85%pf

 

[Tulsa Electrician]

Wow 600
Wonder how that breaks down

 

[Tulsa Electrician]

Thanks

 

[hillbilly1]

Wow 600
Wonder how that breaks down

 

[ramsy]

What does your poorman calc say using 1set of 350
Feel free to 85%pf

Poor man's calc shows VD = 4% for 1-set of 350

 

[hillbilly1]

App is available for free.

 

[hillbilly1]

Oops! I screwed up too Dsg319! I was thinking op was going underground, but he is going overhead, so it will probably be in EMT.