The concern is voltage drop. The longer the distance, the greater the drop. If one of your machines draws a lot of current it could have more issues with voltage drop than small power tools. When equipment experiences voltage drop it could malfunction or burn out. In the case of microprocessor controlled equipment, the machine may start to act funny.
Max cable length between padmounted transformer and structures
I am designing my own house and site plan, and intend to possibly be my own general contractor for my build. I own 63 acres of land that I have been working on for 10 years now, logging 10 acres, digging two ponds, and a bunch of other stuff. It is now time for me to finalize the site plan, and contact the utility companies.
The site plan so far has the house and a barn/shop about 700ft from the road, with possible future pole barn structures even further back.
I have contacted the power company, and so far the site planner has provided me with the specifications for installing a single phase padmounted transformer: https://www9.nationalgridus.com/niag..._esb754a-1.pdf
I fully understand what is required of me in terms of the high voltage trench and the transformer pad excavation. What I need better definition on is the low voltage cable from the transformer to the structures, in particular what kind of cable, and the max length.
I know that this particular power company requires home owners to sign waivers if their service line from a pole mounted transformer is longer than 300ft, the waiver is to absolve the power company from any customer claims of "degraded" service etc.
Here is an image of two possible transformer locations on my site plan: http://i.imgur.com/QRWbAcP.jpg
Option 1 would cost me about $6400 for installation of the transformer and meter. Option 2 would cost me about $9300.
My question is basically, do I NEED to keep the structures within a certain distance from the transformer? I have been told the "closer the better", and "try" not to exceed 300ft.
Is the extra cost of more high voltage cable worth keeping the structures closer to the transformer? Not being an electrical engineer, I don't know exactly what the consequences are if I'm "too far" away from the transformer for "good power".
I will have a fair amount of equipment in these structures, welders, plasma cutters, overhead cranes, basic farm equipment etc.
I should add that, the power company has ruled out the use of the west power pole, as it has a capacitor bank on it. So my only option is the east power pole.
The site plan so far has the house and a barn/shop about 700ft from the road, with possible future pole barn structures even further back.
I have contacted the power company, and so far the site planner has provided me with the specifications for installing a single phase padmounted transformer: https://www9.nationalgridus.com/niag..._esb754a-1.pdf
I fully understand what is required of me in terms of the high voltage trench and the transformer pad excavation. What I need better definition on is the low voltage cable from the transformer to the structures, in particular what kind of cable, and the max length.
I know that this particular power company requires home owners to sign waivers if their service line from a pole mounted transformer is longer than 300ft, the waiver is to absolve the power company from any customer claims of "degraded" service etc.
Here is an image of two possible transformer locations on my site plan: http://i.imgur.com/QRWbAcP.jpg
Option 1 would cost me about $6400 for installation of the transformer and meter. Option 2 would cost me about $9300.
My question is basically, do I NEED to keep the structures within a certain distance from the transformer? I have been told the "closer the better", and "try" not to exceed 300ft.
Is the extra cost of more high voltage cable worth keeping the structures closer to the transformer? Not being an electrical engineer, I don't know exactly what the consequences are if I'm "too far" away from the transformer for "good power".
I will have a fair amount of equipment in these structures, welders, plasma cutters, overhead cranes, basic farm equipment etc.
I should add that, the power company has ruled out the use of the west power pole, as it has a capacitor bank on it. So my only option is the east power pole.
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Yes, thank you, I do understand that par of it. What I need to know is, how close do the structures need to be to the transformer? 50ft, 100ft, 150ft etc?The concern is voltage drop. The longer the distance, the greater the drop. If one of your machines draws a lot of current it could have more issues with voltage drop than small power tools. When equipment experiences voltage drop it could malfunction or burn out. In the case of microprocessor controlled equipment, the machine may start to act funny.
I know the "closer the better", but that doesn't help me plan my site layout atm, I need finer detail than that.
The high voltage cable is extremely expensive, $17.00/ft installation cost, so I need to optimize cost.
You married?
Light flicker from high inrush loads seem to drive women crazy.
My opinion upsize all conductors eat the cost now.
Of course this all depends on what you heat and cool with, cook with, appliances, tools...........
Light flicker from high inrush loads seem to drive women crazy.
My opinion upsize all conductors eat the cost now.
Of course this all depends on what you heat and cool with, cook with, appliances, tools...........
You can to some degree minimize losses on long runs by using larger cables.The concern is voltage drop. The longer the distance, the greater the drop.
This is common practice here in Australia.
Lets say you want to push 300A thru a long cable,
instead of using 300A cable use 600A cable.
initial cost of cable will be higher,
but you get the extra distance.
Ok guys, thanks for the responses so far.
So, it's all about voltage drop, nothing else?
I have read that for service entrance cables, you want to keep the voltage drop 2% or less, as inside a given structure there could be an additional 3% voltage drop from the wiring in the walls, so at the appliance outlet the max total voltage drop is 5%.
Does this sound correct?
So, it's all about voltage drop, nothing else?
I have read that for service entrance cables, you want to keep the voltage drop 2% or less, as inside a given structure there could be an additional 3% voltage drop from the wiring in the walls, so at the appliance outlet the max total voltage drop is 5%.
Does this sound correct?
Correct,,, enough for the topic.
As long as your branch circuits are sized correctly voltage drop will not be an issue.
If you do not plan to upsize your feeders, place the transformer as close to the load as possible.
Don't plan to feed under structures or across your septic field. Keep in mind that a straight line on paper rarely ends up as a straight line in the ditch. Your cost per foot is something to be eaten and forgotten. Kinda like the price of milk. You gotta but it anyway so don't worry about the cost.
Depending on your area and utility company, summer time loads on their system can cause a voltage drop on their side of the house before your transformer. Don't cut yourself short on feeder sizing.
As long as your branch circuits are sized correctly voltage drop will not be an issue.
If you do not plan to upsize your feeders, place the transformer as close to the load as possible.
Don't plan to feed under structures or across your septic field. Keep in mind that a straight line on paper rarely ends up as a straight line in the ditch. Your cost per foot is something to be eaten and forgotten. Kinda like the price of milk. You gotta but it anyway so don't worry about the cost.
Depending on your area and utility company, summer time loads on their system can cause a voltage drop on their side of the house before your transformer. Don't cut yourself short on feeder sizing.
Yeah those dimensions I put on my drawing was just to get an idea, I know the cable path will increase as I weave around stuff.Correct,,, enough for the topic.
As long as your branch circuits are sized correctly voltage drop will not be an issue.
If you do not plan to upsize your feeders, place the transformer as close to the load as possible.
Don't plan to feed under structures or across your septic field. Keep in mind that a straight line on paper rarely ends up as a straight line in the ditch. Your cost per foot is something to be eaten and forgotten. Kinda like the price of milk. You gotta but it anyway so don't worry about the cost.
Depending on your area and utility company, summer time loads on their system can cause a voltage drop on their side of the house before your transformer. Don't cut yourself short on feeder sizing.
I have been doing some voltage drop calculations and am wondering, if I have 200 amp service, do I use a 200 amp load when calculating the voltage drop?
I assume a residence with 200 amp service probably never approaches 200 amp load...
Why is primary cable so much more than secondary? In my experience the cable is not that much of a difference in cost, and the installation is pretty much the same. It should not be a huge cost difference to have the pad closer to the structure.
Our POCO likes to see 250' or less of secondary (120/240V) before upsizing the cable. Persoanlly I'd put the pad as close to the house as possible and practical. 100-150' would be nice.
Who is doing this part of the install, the POCO or your electrician? Around here this is all on the electrician to do. You give a National Grid link, are you in NYS?
Our POCO likes to see 250' or less of secondary (120/240V) before upsizing the cable. Persoanlly I'd put the pad as close to the house as possible and practical. 100-150' would be nice.
Who is doing this part of the install, the POCO or your electrician? Around here this is all on the electrician to do. You give a National Grid link, are you in NYS?
In my experience ASSUMING you do not have electric heat the max load one time on a residential service 30-90 amps. I had a 400 amp service 5000+ square foot house all gas I think 75 was my max not considering inrush. Summer was the highest draw when the AC were on.Yeah those dimensions I put on my drawing was just to get an idea, I know the cable path will increase as I weave around stuff.
I have been doing some voltage drop calculations and am wondering, if I have 200 amp service, do I use a 200 amp load when calculating the voltage drop?
I assume a residence with 200 amp service probably never approaches 200 amp load...
Load calculations are never a good indicator of actual max load.
There is as noted light flicker, bite the bullet now.
The cost of the primary cable from the pole to the transformer is tariff based costing. Meaning, the cost is much higher than the actual cable material. National Grid (I'm in NY) embeds all kinds of costs into the "per foot" cost of installing the cable. At the moment, this cost is $17/ft. So 200 extra feet for me = $3400...Why is primary cable so much more than secondary? In my experience the cable is not that much of a difference in cost, and the installation is pretty much the same. It should not be a huge cost difference to have the pad closer to the structure.
Our POCO likes to see 250' or less of secondary (120/240V) before upsizing the cable. Persoanlly I'd put the pad as close to the house as possible and practical. 100-150' would be nice.
Who is doing this part of the install, the POCO or your electrician? Around here this is all on the electrician to do. You give a National Grid link, are you in NYS?
I ran a similar analysis when I was considering purchasing a property where the house would have been 800 feet from the road. My supplier would have been Eversource. After some analysis, it turned out that the cost to run high voltage cable from the street to a transformer was similar to the cost to run the much larger cable from the transformer to the house, so it was advantageous to place the transformer as close to the house as possible.
The primary cable is much smaller than the secondary cable, since the voltage is much higher. Where I was looking, the primary voltage was 4180, and the secondary would have been 240, so about 17 times the amperage on the secondary, hence the need for much larger cable. Voltage drop is also an issue, but if you are less than 150 feet from transformer to building, likely not to require upsizing cable, but this needs to be determined by your electrician.
Where I was, the POCO would not allow the homeowner to do anything between the power pole and the transformer, that all had to be done by a licensed electrician and a designated civil contractor to dig the ditch. Not sure if an electrician was required between the transformer and the house, but I was not planning to do any of that work either. Sort of stuck with the price the POCO charges, there was only one game in town.
The primary cable is much smaller than the secondary cable, since the voltage is much higher. Where I was looking, the primary voltage was 4180, and the secondary would have been 240, so about 17 times the amperage on the secondary, hence the need for much larger cable. Voltage drop is also an issue, but if you are less than 150 feet from transformer to building, likely not to require upsizing cable, but this needs to be determined by your electrician.
Where I was, the POCO would not allow the homeowner to do anything between the power pole and the transformer, that all had to be done by a licensed electrician and a designated civil contractor to dig the ditch. Not sure if an electrician was required between the transformer and the house, but I was not planning to do any of that work either. Sort of stuck with the price the POCO charges, there was only one game in town.
National Grid does not dig the trench nor the transformer pad excavation, I have to either do it myself (which I will), or contract someone out to dig the trench and pad excavation.
All National Grid does is show up, inspect the trench, then throw the cable in. Then they place the transformer pad and transformer. Then I backfill the trench and transformer pad.
I have to provide somewhere to place the meter. National Grid will hook me up to the meter, then they're done. All the secondary stuff is up to me hiring an electrician.
The National Grid planner told me the primary voltage needs to be 7620, but right now at the road the voltage is only 4800, so they have to install a voltage converter (or somesuch) at the pole before they run the primary cable.
In any event, it looks like it's going to cost me about $12,000 to get the transformer installed.
All National Grid does is show up, inspect the trench, then throw the cable in. Then they place the transformer pad and transformer. Then I backfill the trench and transformer pad.
I have to provide somewhere to place the meter. National Grid will hook me up to the meter, then they're done. All the secondary stuff is up to me hiring an electrician.
The National Grid planner told me the primary voltage needs to be 7620, but right now at the road the voltage is only 4800, so they have to install a voltage converter (or somesuch) at the pole before they run the primary cable.
In any event, it looks like it's going to cost me about $12,000 to get the transformer installed.
why would the primary voltage be a problem? i know sometimes that they put regulators on the line to increase voltage, but i can't see where there is a problem. what is there main line voltage? is this a branch line off of the main? could it go overhead?just a couple of thoughts. around here we tell the co-op what we need & they supply it.:smile::smile:
I don't know that is it, all I know is that the NG person I am talking to said the voltage at the road is not high enough, I just don't know enough about it.why would the primary voltage be a problem?
He told me 4800Vwhat is there main line voltage?
I do not want it overhead due to all the trees I have, plus UG power just looks nicer than crappy leaning poles.could it go overhead?
National Grid does not dig the trench nor the transformer pad excavation, I have to either do it myself (which I will), or contract someone out to dig the trench and pad excavation.
All National Grid does is show up, inspect the trench, then throw the cable in. Then they place the transformer pad and transformer. Then I backfill the trench and transformer pad.
I have to provide somewhere to place the meter. National Grid will hook me up to the meter, then they're done. All the secondary stuff is up to me hiring an electrician.
The National Grid planner told me the primary voltage needs to be 7620, but right now at the road the voltage is only 4800, so they have to install a voltage converter (or somesuch) at the pole before they run the primary cable.
In any event, it looks like it's going to cost me about $12,000 to get the transformer installed.
4,800 is the existing voltage that most POCOs used and 7,620 (13,200 volts between phases) is what new lines are being converted to in an effort to increase capacity. As a result the new power lines at 7,620 volts are stepped down to 4,800 volts via transformer for the old existing infrastructure. Most likely your pad mount will have a dual voltage primary (adjustable taps), so when they upgrade from 4,800 to 7,620 they will just change the taps and bypass the step down transformer. Either that they will use a 7,620 volt pad mount and back feed a step down transformer to boost the existing 4,800 volt on the old overhead line to 7,620 volts when going underground to your pad mount. Once the line is upgraded to 7,620, the conversion transformer will by bypassed.
But the real concern is the secondary. Whether the primary voltage is 2,400 volts or 20,000 volts makes little difference as voltage drop at those levels is measured in miles.
My advice is to get the pad mount as close to your home as possible since that will reduce the size of cable needed to offset voltage drop. If curious, there is a calculator in the middle of this link that can be used to determine the amount of voltage drop for a given current in relation to the cable size:
http://www.electrician2.com/calculators/vd_calculatoradv.htm
This sounds familiar, I think the engineer I was talking to mentioned this.Either that they will use a 7,620 volt pad mount and back feed a step down transformer to boost the existing 4,800 volt on the old overhead line to 7,620 volts when going underground to your pad mount.
Yes, thank you, I have been playing with voltage drop calculators for a few days nowIf curious, there is a calculator in the middle of this link that can be used to determine the amount of voltage drop for a given current in relation to the cable size
It really seems like I need to try to have all structures within 100 ft or less of the transformer to avoid having to go with conductors larger than 4/0 alum.
This sounds familiar, I think the engineer I was talking to mentioned this.
Yes, thank you, I have been playing with voltage drop calculators for a few days now
It really seems like I need to try to have all structures within 100 ft or less of the transformer to avoid having to go with conductors larger than 4/0 alum.
Highly recommend being within 100 feet. Voltage drop at 240 volts is measured in feet, not miles so having the unit as close as possible will certainly save on wire. But in any case don't be afraid to up-size a bit if think you need it, now is the time and there is no going back.
My question is.....if you put the transformer closer to the house, can you bury the feed to it?
If it was me, I'd rather trench everything and not have overhead power lines. If they will let your bury the HV, then put the transformer closer to the house.
A few extra bucks to not have to look at telephone poles would be worth it.
And if you are trenching....I'd do it along the driveway....and have a few breakouts along the way....for street/driveway lamps.
If it was me, I'd rather trench everything and not have overhead power lines. If they will let your bury the HV, then put the transformer closer to the house.
A few extra bucks to not have to look at telephone poles would be worth it.
And if you are trenching....I'd do it along the driveway....and have a few breakouts along the way....for street/driveway lamps.
If the primary voltage out on the street is too low then your pad transformer (or pole transformer) generally has multiple taps to choose from at installation time so the secondary voltage comes out right (close to 120/240 volts).
Except that the primary voltage may vary from "normal" to "low" depending on how much power everyone in the neighborhood is drawing altogether. So selecting a tap on the transformer could give the right secondary voltage during peak usage but during off hours the secondary voltage would be too high.
The power company could use voltage regulators so the primary voltage out on the street does not change too much.
You don't have control over the preceding; you just have to take what the power company gives you.
Except that the primary voltage may vary from "normal" to "low" depending on how much power everyone in the neighborhood is drawing altogether. So selecting a tap on the transformer could give the right secondary voltage during peak usage but during off hours the secondary voltage would be too high.
The power company could use voltage regulators so the primary voltage out on the street does not change too much.
You don't have control over the preceding; you just have to take what the power company gives you.
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