ELECTRIC GATE LOAD CALCULATIONS

Houston714

Member
Location
Nashville Tn
Hi all! Just looked at an electric gate gate job. My first one! Based on what they have this is what I came up with. Will some of you much smarter guys please confirm theses calculations?

126/242 volts at panel
Gate 324 feet away. I figured 330 feet.
Need 7 amps at gate and call box: (2 amp 120 volt Trickle Charger for gate) and (5 amps 240 volt for Call Box). I just figured 10 total.

I'm running UF 6/3 with ground.

Voltage Drop = I x R

“I” is equal to 10 amperes

“R” is equal to 0.324 ohms (Chapter 9, Table 8 for a 6 AWG wire: (.491/1,000 feet) x 660 feet

Voltage Drop = 10 amperes x 0.324 ohms

Voltage Drop = 3.24 volts, (3.24 volts/126 volts = 2.57% volts drop)
Voltage Drop = 3.24 volts, (3.24 volts/242 volts = 1.33% volts drop)

Operating Voltage = 126 volts – 3.24 volts = 122.76
Operating Voltage = 242 volts - 3.24 volts = 238.76


Your help is appreciated!
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
I would not worry about a 3 volt drop however your numbers seem odd. Usually if you have 126V your phases you would get 252 across phases. I assume this is single phase service????

You can probably use #8 if you wanted to but having a little more capacity won't hurt. I assume you are adding a small panel.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
It looks like OP is using metered voltage not rated voltage. When doing voltage drop calculations do you want to use metered or listed voltages? (IE 120/240). Metered voltages will continuously vary coming from the utility.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
It looks like OP is using metered voltage not rated voltage. When doing voltage drop calculations do you want to use metered or listed voltages? (IE 120/240). Metered voltages will continuously vary coming from the utility.

It really won't make that much difference but it can. Most of the calculators use listed voltages
 

Houston714

Member
Location
Nashville Tn
LOL I may have made an error on the 242! Even at 240 I came our OK. I used Mikes Calculator as well.
No panel. The gate guy wants the 240 call box hard wired and the 1 GFI for the trickle charger. I'm using an 8x8x4 PVC box. The GFI will sit to one side of the box and hard wire the call box in the 8x8x4.
 

Jerramundi

Senior Member
Location
Chicago
Occupation
Licensed Residential Electrician
Anything less than 3% VD on a branch circuit and you're good by NEC standards, but this isn't a code requirement, merely a "recommendation."

The only time VD could be a code violation is if the resulting operating voltage is outside of manufacturer's specifications. Some manufacturers give you a range of acceptable operating voltage. Some just say straight up nominal 120V/240V, in which case the conventional wisdom is anything within a %10 VD is usually okay... or so I've read.

Obviously the closer you are to the recommended value, the longer the equipment will last and the better it will operate.
 

Houston714

Member
Location
Nashville Tn
10%??????????? I would not think you could power much at 10%VD... Just my thoughts. That's 108 V on a 120 v circuit.
That'd be something to see... I've never done that one. I feel like there would be a call back from the customer coming at some point down the road LOL
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
10%??????????? I would not think you could power much at 10%VD... Just my thoughts. That's 108 V on a 120 v circuit.
That'd be something to see... I've never done that one. I feel like there would be a call back from the customer coming at some point down the road LOL
I don’t see a problem with it either in most cases.
small motors nameplate is around 115. Some old ones are 110
 

Houston714

Member
Location
Nashville Tn
Its all good pal! I've read about the history of voltages and how it has changed over the decades and it still blows my mind about stuff.

Thanks again for all the knowledge and input about my situation!
 

Jerramundi

Senior Member
Location
Chicago
Occupation
Licensed Residential Electrician
10%??????????? I would not think you could power much at 10%VD... Just my thoughts. That's 108 V on a 120 v circuit.
That'd be something to see... I've never done that one. I feel like there would be a call back from the customer coming at some point down the road LOL
Me personally, I shoot for the -3% recommended max value. I look at the code as a required minimum, not a maximum.. and going a little above and beyond as a good thing as long as it's balanced w/ cost effectiveness.

But I have read that +/-10% is a general rule of thumb... and it seems @Hv&Lv 's post backs that up. I'm curious to see what the source is on that and read into it a little bit more.

I've also read that over voltage can be more dangerous than under voltage, which @HvLv 's post also seems to back up with the -13% / +6% Utilization column.
 
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