voltage drop for feeders

[lowryder88h]

does the nec require the calculation for voltage drop at a commercial building??? art. 215.2 (A) (1) (3) FPN#2 reference for dwelling unit or mobile home, no reference to commercial applications. I know that FPN's are not enforceable. Scenario, 400A 460V 3Ph 4W needed to power sub panel 750 ft away.

 

[petersonra]

does the nec require the calculation for voltage drop at a commercial building??? art. 215.2 (A) (1) (3) FPN#2 reference for dwelling unit or mobile home, no reference to commercial applications. I know that FPN's are enforceable. Scenario, 400A 460V 3Ph 4W needed to power sub panel 750 ft away.

Don't you want to know this information? It is easy to come by and might well save you an expensive hassle down the road.

 

[lowryder88h]

voltage drop

voltage drop

my fingers work faster than my mind. I know that FPN's are not enfroceable

 

[radiopet]

While probably not enforceable......it is a good thing to know because equipment can be problematic if not working at the correct voltage level.

I know that when we do commerical jobs that would require something of this size the plans have already been done on that by an electrical eng. who has done the math for us.

But we still need to know how to do it.....you can even do it with the online calcs as well..check out www.electrician2.com and you will see a online voltage drop calculator you can play with.

 

[kingpb]

does the nec require the calculation for voltage drop at a commercial building??? art. 215.2 (A) (1) (3) FPN#2 reference for dwelling unit or mobile home, no reference to commercial applications. I know that FPN's are not enforceable. Scenario, 400A 460V 3Ph 4W needed to power sub panel 750 ft away.

My rule thumb is, anything over 200 ft gets a check, and certainly a feeder of 750ft would be checked. It's a lot cheaper to do then a lawsuit would be later.

 

[bphgravity]

The Florida Building Code requires a maximum voltage drop of 2% on feeders and 3% on branch circuits at design load. See section 13-413 of the 2004 FBC. I check for the calculations on plan review. So make sure you check your state's Energy Efficiency Code and requirements.

 

[lowryder88h]

voltage drop

voltage drop

The reason I asked is that I due electrical estimating for contractors on the side. The scenario mentioned above is one that I did all the calcs and was blown out of the water, 2-4" cond w/ 4-600mcm, 1-#3, the winning contractor is doing it w/ 1-4"cond. I was thinking about calling the AHJ, or just lick my wounds and move on.

thanx for you comments

 

[tom baker]

I allow 5% on a service and 3% on branch circuits. After a while you get a feel for when you will be in trouble

 

[iwire]

I did all the calcs and was blown out of the water, 2-4" cond w/ 4-600mcm, 1-#3, the winning contractor is doing it w/ 1-4"cond.

If I am not mistaken one set of 600 CU would result in less than 3% drop if the circuit was loaded to 400 amps.

It is usually a safe bet that the real load will never be 100% of the OCP.

 

[ramsy]

was blown out of the water, w/ 4-600mcm..

With those motor feeds power factor and conduit reactance will kill you on voltage drop. You need something more than just a web-page, DC voltage-drop calculator for estimating these kind of jobs.

Assuming a 0.85 PF, The one I play with, shows your 400A project with #300al x2 in parrallel performing better than a #600cu x1, but 3 al. sets in non-reactive PVC would be needed in Florida to come in under 3%.

 

[iwire]

Roger the program I use take into account the conduit,

Instead of just tossing out things you have looked up on the web why not do the calcs and show us?

 

[kingpb]

does the nec require the calculation for voltage drop at a commercial building??? art. 215.2 (A) (1) (3) FPN#2 reference for dwelling unit or mobile home, no reference to commercial applications. I know that FPN's are not enforceable. Scenario, 400A 460V 3Ph 4W needed to power sub panel 750 ft away.

Assuming 480V, 400A, 750ft, pf= 0.85, above ground installation of magnetic conduit, and limiting VD = 2%

(1 set) 1/C 600 KCMIL = 5.3% VD
(2 set) 1/C 600 KCMIL = 2.6% VD
(3 set) 1/C 500 KCMIL = 1.8% VD

if installation is underground duct, using PVC, then;

(2 set) 1/C 500 KCMIL = 2.4% VD
(3 set) 1/C 350 KCMIL = 2.0% VD

Good engineering practice dictates limiting feeders to 2% (sub-panel). This is substantiated by bphgravity. If it were my design, depending on the installation method, it would require 3 sets either way.

 

[iwire]

That is good news as that is what I got with my freebie program....and no that does not mean I think I am now an engineer.

1 set 600 Copper in PVC conduit 750 feet long operating at 480 3 phase with a 400 amp load.

2.4% drop

if I switch to steel conduit it does increase to 2.7%

At least now I have reason to believe the program.

 

[ramsy]

Roger the program I use take into account the conduit..

I referred to radiopet's VD-calulator at www.electrician2.com, since these web-site calculators ignore pwr.factors & reactance with their DC formulas. The web-site calculators linked from this forum in the past often showed me different results for the same problem.

I found variation in the AC formulas as well; the ones that consider Pf and XL. However, the only AC-voltage drop implement I found that justified itself with the NEC handbook and published engineering examples is the one I'm using now.

iwire, your VD calcultor may have provision for conduit, but if "Set"=1, your results closely follow those web-site DC calculators, as shown below:

See the different results for 400A, 750ft, 480V 3-PH, using 1-set #600cu

1) electrician2.com   DC calc = 2.3%
2) iwire  using PVC           = 2.4%
3) kingpb using pf=0.85 & EMT = 5.4%
4) ramsy  using pf=0.85 & EMT = 5.01%
5) ramsy  using pf=1.0  & PVC = 2.49%

AC & DC formula results can be similar when Pf = 1, with non-metalic raceways.

Instead of just tossing out things you have looked up on the web why not do the calcs and show us?

To see results match the published engineering & NEC-handbook examples, open the application's example section. It seems to me, the people who engineered this application did a lot of work, and explain it much better than I could.