250MCM for 21.7 amps? Voltage drop calc must be wrong?

[ptonsparky]

Quit thinking gate motors only. Add a bit for the lighting that will be there. LEDs won't add much, but what about the Seasonal lighting that is beginning to show up in ever larger configurations?

 

[Mgraw]

I did some work around a house where the front gate was about 3500 feet from the house. The rear gate was about 1200 feet from the house. The POCO and EC decided to put meters at each location. Everybody was happy.

 

[mivey]

I don't know why the supposedly "smart engineer" didn't think of that!

What did you ask for? If you asked for a particular voltage then...

I had a similar question last year and the electrician was shocked (no pun intended) at the wire size. I suggested a higher voltage but got a "well we really can't put a transformer in because the most convenient junction box is located in a bad spot ... blah, blah, blah". OK then, the math is what it is. The result?: Well maybe we don't need that receptacle after all!

 

[Bri22]

What did you ask for? If you asked for a particular voltage then...

I had a similar question last year and the electrician was shocked (no pun intended) at the wire size. I suggested a higher voltage but got a "well we really can't put a transformer in because the most convenient junction box is located in a bad spot ... blah, blah, blah". OK then, the math is what it is. The result?: Well maybe we don't need that receptacle after all!

The customer and GC told him (The engineer) what they needed. Power for two gate arms: 120 volts, 7.6 amps each and power for the coms which is a license pale reader, card access, and video/intercom. When I saw he came up with a 58 amp load I questioned it. Then saw the parallel 250MCM wire and I was really shocked. I would of thought he would of suggested using transformers as many of you did instead of trying to pull that huge wire run. Not to mention the wire would cost over $10,000.

 

[Bri22]

I was referring to texie's idea of using 250.30(A)(1) Exception 2 to permit the feeder to be two wires only, with no EGC or bonding jumper. See also 250.30(A)(2) Exception. That idea applies when one of the two circuit conductors is grounded, regardless of the voltage.

As to 480V vs 600V, I have no information about the cost and availability of transformers, so I'll leave that to others.

Cheers, Wayne

Thanks Wayne!

 

[kwired]

Sounds like a good place to at least consider a solar panel, storage battery and inverter - or even go with a DC powered gate operator.

 

[Bri22]

You would not have 15A @ 600V; your 21.7A load @ 120V (2604va) would be a 4.34A load @ 600V. Going to 600V would let you use #12cu @ 3.3% VD. #12 isn't a lot cheaper than #10, so if the xfmrs are appreciably more expensive than the 120/480, better to stick to the 480 (or 240 as others mentioned).

I've never pulled wire that distance, but I'd imagine pulling in #10 is easier than #4, and easier/cheaper to splice at the junction boxes. Also, you can go with smaller conduit with the higher voltage/smaller conductors.

Thanks for the correction on my calculation.

This will save the customer a lot of money and me a lot of work! There actually two sets of gates, one is 1317' away and and the other 967' at the opposite end of the property. Just doing a rough estimate, the wire cost alone would of been around $20,000 for what the engineer was proposing.

 

[jim dungar]

I would of thought he would of suggested using transformers as many of you did instead of trying to pull that huge wire run.

Did you discuss the installation and alternatives with him, as you have been doing on this forum?

 

[badbanano]

A VFD with a smaller gear reduction motor would also suffice. Automation Direct builds all types of solutions to your problems.

Sent from my XT1254 using Tapatalk

 

[Ingenieur]

600:120 and 480:120 ~ same $ for a given capacity
Grainger is a good reference but your supplier can probably do better

ps: please quit bustin' on Engineers, not all are knuckleheads :lol:

Now buy one lunch Feb 21-27 as penance lol
http://www.discovere.org/our-programs/engineers-week
65th anniversary

 

[Bri22]

Did you discuss the installation and alternatives with him, as you have been doing on this forum?

Actually I did. I sent him an email this morning and he called me back today and said he thought it was a great idea. He was going to recalculate his numbers and get back to me.

 

[Bri22]

A VFD with a smaller gear reduction motor would also suffice. Automation Direct builds all types of solutions to your problems.

Sent from my XT1254 using Tapatalk

Thanks for the suggestion. Yea, automation direct is great. I have ordered from them several times and their customer device is very helpful as well.

 

[Bri22]

600:120 and 480:120 ~ same $ for a given capacity
Grainger is a good reference but your supplier can probably do better

ps: please quit bustin' on Engineers, not all are knuckleheads :lol:

Now buy one lunch Feb 21-27 as penance lol
http://www.discovere.org/our-programs/engineers-week
65th anniversary

Thanks Ingenieur. Yea, Granger is a good reference but their prices always seem to be at least double of my supply house Graybar.

I didn't mean to bust on engineers in general, just the one I'm working with. There are great, bad and somewhere in-between in all professions. If I can find a option that is going to save my customer some money (quite a bit in this case) and it's safe, code compliant, effective, efficient and fits their needs, I'm going to suggest that as my first option. I hate spending extra a money for no good reason and wouldn't want to charge a unsuspecting customer more either. This particular customer (and many others that I have) don't even ask for a price. They just trust I will be fair, tell me what they want I want and I do it.

 

[Bri22]

Sounds like a good place to at least consider a solar panel, storage battery and inverter - or even go with a DC powered gate operator.

That was actually my first thought (solar panel) but I was concerned about reliability. If there happened to be a few cloudy days and if the gates couldn't open I would be held accountable so I abandoned the idea. I know solar and batteries are getting better but am not up on it. I'll have to research it more so I am informed in the future.

Thanks for the reply BTW

 

[Ingenieur]

Thanks Ingenieur. Yea, Granger is a good reference but their prices always seem to be at least double of my supply house Graybar.

I didn't mean to bust on engineers in general, just the one I'm working with. There are great, bad and somewhere in-between in all professions. If I can find a option that is going to save my customer some money (quite a bit in this case) and it's safe, code compliant, effective, efficient and fits their needs, I'm going to suggest that as my first option. I hate spending extra a money for no good reason and wouldn't want to charge a unsuspecting customer more either. This particular customer (and many others that I have) don't even ask for a price. They just trust I will be fair, tell me what they want I want and I do it.

I know you meant no harm, I was just messing with you
peace

that guy needed cuffed 250 kcmil for 20 A!!!

 

[electrofelon]

I like the 600 volt idea with the exception mentioned so you dont need the EGC - just two wires. Here is an example of some transformers, not sure how good the price is.
http://www.transformeronline.com/product/600v-120240v-single-phase-transformers/

Use aluminum wire. For the 120 V option, say 20 amps = 350 URD aluminum (2 X 350 USE/RHH plus 1 X two size reduced neutral/ground) is $3 per foot, keeps you around 4% drop. With 600 volts, you would just need 2X #6 aluminum which is about .20 per conductor per foot, plus smaller pipe as a bonus. So save $3500 on wire, a little more on smaller pipe, but have to pay a grand for the two transformers. Still seems worth it.

 

[Cloud]

Ran the numbers myself. Sorry dont know how to rotate the image.

 

[electrofelon]

I am a little confused by your entries. I dont see how three phase is applicable to the OP. Also how many amps or VA are you using in those figures (I was using 2400 VA). Why schedule 80? And finally, are those pipe fill figures assuming 2 conductors or 3?

 

[Cloud]

I am a little confused by your entries. I dont see how three phase is applicable to the OP. Also how many amps or VA are you using in those figures (I was using 2400 VA). Why schedule 80? And finally, are those pipe fill figures assuming 2 conductors or 3?

the 3 phase was from the suggestions on the previous post(post #10), i dont think 480V 1ph is readily available. i just let him see what can fit his installation. 21.7 A loading as he stated in his very first post. Conduit calculation is calculated with 40% fill code, 2 for single phase 3 for 3 phase. schedule 80, just assumption for high impact. i have missed the location of installation.

if 1PH

480 V 1PH 90° CU @125%
1 AWG
83,690 CM
50mm²
9.2V VD
PVC SCH 80 1.25 in


finally, I'm just helping him to see the overview of the calculations with his given values. it is up to the OP on what he can use, and was not suggesting nor requiring him to use what's posted.

 

[kwired]

i dont think 480V 1ph is readily available.

Sure it is, even if you already have three phase 480 volt system - take any 2 conductors besides a neutral to a load and you essentially only have 480 single phase available to that load.

Most of the discussion on 480 volts has been about stepping up with a single phase transformer.