1000+ft from the road... Long run to the grid or Generator?

rpvietzke · January 2015

Hi folks -

Some holiday weekend fodder...

I have an off grid weekend cabin in Vermont, under construction, current with 672 Ah of 24v bank with 1500w of solar charge (Schneider MPPT60 and CSW4024). In the grey days of December (there are many), there are weeks where there isn't a enough sun to charge the batteries, let alone power basics like the furnace and circulator pump. To date, what we've done is let the place "freeze" and we just heat it up when we arrive for the weekend and run a portable generator for a day to bring things back to life. However, as the place gets more finished, its time to do something more permanent.

I've always thought I'd buy a reasonable standby generator (ecogen 6kw?), get a big propane tank (can't drive up there in the winter, have to hike in, so one fill needs to do heat, stove and generator for the winter) and continue completely off grid. However, there is street power about 1000 feet away, and it recently occurred to me that if I'm okay with a little voltage drop, I could probably put a meter on a shed down by the road, run 20-30 amps up the hill at 118v and still have 100-105v and enough juice to keep the batteries charged and have backup for the furnace... (I am not interested in running a full 100/200 amp service through the not cleared woods as it would cost a fortune to trench, conduit, *cable*, etc and I'm not interested in a pole line or transformer up in the woods either. Burying conduit or wire in my "driveway" would add at least another 500-700 feet.)

If I look at a classic voltage calculator, I could do 20 Amps at 1000 feet. That is assuming I start with 120/240 V, use direct burial 6/3, I could deliver 104/208 volts at the top of the hill with two 20 amp legs... probably plenty to supplement the solar and keep the batteries toped off or to run the place on a cloudy day without a generator (and I'd presumably have charged batteries anyway.) Figure $2500 for the U/F wire and $1000 for a meter and basics at the bottom of the hill and I'm probably at the same cost as a permanently installed generator?

Curious what folks who have experienced life with a generator would say? I'm guessing the generator option may cost more in the long run as propane prices and maintenance weigh in. There is the possibility of squirrel damage unless I really trench the wire deep too...

Rob

BB. · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Do some pencil designs and see what works out best for you...

Grid power is probably going to be cheaper--But check the utility rate plans. A new wrinkle from some utilities is a high minimum connection fee (as a shot against GT solar, cabins, and energy efficient homes). Instead of $5 per month and $0.15 per kWH, you may find $40-$96 per month charge and $0.06 per kWH.

We had one person here that found it was cheaper to go full off grid with a small genset than to pay the minimum charges for his weekend/seasonal cabin.

For a battery bank, you are looking at 10% to 20% rate of charge typically from a genset. For your 672 AH @ 48 volt battery bank, a genset in the range of:

672 AH * 29 volts charging * 1/0.80 charger eff * 1/0.80 genset derating * 0.10 rate of charge = 3,045 VA genset
672 AH * 29 volts charging * 1/0.80 charger eff * 1/0.80 genset derating * 0.20 rate of charge = 6,079 VA genset

I tend to recommend a minimum size genset as they tend to be more efficient when charging a genset (generators are more efficient at 50% or greater of rated output--Running at less than 50% rated power usually pulls ~50% of fuel flow--As the battery progresses through Absorb, the power needed falls). A 6 kW genset may use ~0.5 to 1.0 gallon per hour of propane (or even a bit more). A Honda eu2000i will run 4-9+ hours on a gallon of gasoline.

Now, many people will have two gensets... A smaller one to charge the battery bank efficiently, and a larger genset for backup and running large loads (shop, tools, etc.).

Check to see if your inverter has "generator support" (basically when the genset is running, the inverter-charger will either use excess power to charge the battery bank, and if there is an increase in load that exceeds the generator's AC output, the inverter will help the generator with extra power from the batteries). This allows you to run a small genset and still run your home normally (well pump, furnace, microwave with 2-3 kWatt genset).

A propane genset can be more difficult to start in very cold weather... Gasoline can be a better cold weather option if you cannot preheat.

Generac has a bit of an iffy reputation. You might want to look at other brands/models. Besides the Honda eu family, there is the em4000sx (make sure "sx" model with electronic engine control module--no manual choke needed).

Even a Champion ~7 kWatt model looks interesting--Costco has been selling a duel fuel (gasoline/propane) unit for ~$800 (might have to call around--Costco's in my area are hit and miss on this unit now).

http://www.amazon.com/Champion-Power-Equipment-71531-Compliant/dp/B00LLZ4VUI
http://www.championpowerequipment.com/news/new-item/

-Bill

jonr · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

I have two voltage correction devices. One is a box with a stepped transformer that automatically switches between taps to get the right voltage. The second is a ferro-resonant transformer. Additionally, many devices don't care about somewhat low voltage.

rpvietzke · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

jonr wrote: »

I have two voltage correction devices. One is a box with a stepped transformer that automatically switches between taps to get the right voltage. The second is a ferro-resonant transformer. Additionally, many devices don't care about somewhat low voltage.

John, That's interesting. So you just step-up the low voltage after a long run? How does that effect available current? I would assume it drives down current carrying ability?

Rob

jonr · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

True, there is no free lunch.

oil pan 4 · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Get grid power.
A really fuel efficient 4 pole, 3 phase very expensive diesel generator will cost in fuel alone about 5 times more per KWH than what grid power costs.
You could also use a varrac to step your line to line volts down to 120 and adjust it as needed. I would cut the amps in half on your 1000 foot extension cord and make the 120 voltage at the point of use more consistent for most of your 120 volt stuff.

waynefromnscanada · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

rpvietzke wrote: »

John, That's interesting. So you just step-up the low voltage after a long run? How does that effect available current? I would assume it drives down current carrying ability?

Actually I've seen these used with long distance submersible water pumps. The degree of voltage boost needed of course depends on load, wire gauge and length. In the cases I've seen, the small transformer boosted the voltage at the source, just added perhaps 15 volts to what was already available, thus sending out perhaps 245 VAC, and with the pump load it was back down to roughly 230 VAC at the pump. The transformer did not handle all the power going to the motor, just the extra 15 or so volts it then added in series to the existing 230 VAC, so it didn't have to be large at all. And since the boost xformer was at the source instead of at the load, there was no extra current through the long wires to the pump.
There would of course be problems in the case of the original poster, as the voltage drop on his long run would almost completely depend on the load. Would work well with a constant load, but start changing loads up or down and the voltage will be all over the place.
A better solution might be to send 400 or so volts up the wire and have a transformer at the house drop it back down.

jonr · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

I agree that you could go to 480 volts on just two wires (vs 3) by putting transformers on both ends. I have no idea about any code issues.

rpvietzke · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

jonr wrote: »

I agree that you could go to 480 volts on just two wires (vs 3) by putting transformers on both ends. I have no idea about any code issues.

So, I think we used to have a "variac" on the workbench back in the 70's to troubleshoot voltage-related issues on tube TV's. I just looked them up on E-Bay and they look -exactly- the same 40 years later. Sort of amusing.

The town we're in has no code compliance regime, so we could probably get away with anything on my side of the meter. Running at 480v up the hill would be fine, i think so long as I buried the cable deep enough that it didn't become a hazard.

I think I can set the "input breaker" on my CSW4024 to something like 5 or 10 amps max draw so that it would be a constant load when "on". I do want to prioritize solar charging and avoid using this except when its really cloudy... Maybe I could setup a low voltage relay to allow this feed of AC in to come on only after I hit a certain voltage threshold that indicated batteries were low and close to LVD?

Rob

BB. · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

I tried looking up the questions/issues of installing a setup and step down transformer pair--And I could not find much about it. And I do not know enough to recommend how/best way to do it.

I would call around a couple of transformer mfg. support lines. You should be able to take any 240:~600 VAC max transformer. Wire as step up on one end and step down on the other... However, one place I ran across said that the transformer for the step up should be 3 kVA minimum rated if using "generic" transformers (not sure why).

You will find a lot on Buck/Boost transformers--But those are only used for fractional step up/down uses -- Approximately 25% maximum autowound (not isolated output). Not what I would suggest for your needs.

-Bill

oil pan 4 · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Good idea on the high voltage.
If you can run L to L 480 single phase (240 L to N) then more power to you.
I have seen eaton 2 to 1 single phase step down transformers that would do what you want but the only ones I have seen are 10kw minimum in size and I bet they are really expensive.

techntrek · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

I would worry about the variable load issue mentioned above. Activate the utility connection after several days of no sun and you'll have a heavy battery charging load plus your house loads. Limit the amps through the charger and you lose the advantage of having that connection - you might as well use a Honda 2000 inverter-genset for low gas consumption but still get a full 1600 watts.

jonr · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

An easy way to get some automatic load shedding is to buy some "refrigerator brownout protectors". They open the circuit when voltage falls too low (or high) and then switch back on several minutes later.

I've also found these devices to be an effective front-end add-on to traditional surge protectors - because most surge protectors can't survive extended (ie, many msec) high voltage that a utility sometimes supplies.

rpvietzke · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

techntrek wrote: »

I would worry about the variable load issue mentioned above. Activate the utility connection after several days of no sun and you'll have a heavy battery charging load plus your house loads. Limit the amps through the charger and you lose the advantage of having that connection - you might as well use a Honda 2000 inverter-genset for low gas consumption but still get a full 1600 watts.

Thanks for these thoughts. I was sort of assuming I could set this up to keep the batteries up, so there would never be a really big charge load from the utility. 10 days out of 14 there is almost zero load (a couple of security cameras, a DSL modem and the heater/circulator), so most of the time topping off the batteries shouldn't take much work. The sun is fine except the worst days of the year. Maybe I'm thinking about this wrong, but even on say the Monday after we are there for a weekend, if there was a big recharge needed, my thought was it wouldn't take much grid power to charge up the batteries. Say 3600 watts (2 x 15 amps @ 120v each from the grid) into the charger is a 150 amps charging capability at 24v dc, more than my inverter (CSW4024) could do at one time.

Ultimately, this is a weekend place, which is part of why I am trying to keep the cost down... In the summer, solar is plenty of power. In winter, I really just need the safety net of knowing the heat will keep the battery room around 40-45 degrees and that the pipes won't freeze. December was tough and we had about 3 weeks where there simply wasn't enough sun to charge batteries enough to keep the propane circulator and direct vent water heater fan running for the heat. Also, when I did get there on the weekend, the batteries had been sitting at 22.5 for 2 weeks. So, the whole purpose here is not to power "house loads", but to keep the batteries charged for when I am there and to keep the safety of the heat working a bit.

Rob

waynefromnscanada · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

rpvietzke wrote: »

when I did get there on the weekend, the batteries had been sitting at 22.5 for 2 weeks. Rob

OUCH !!!! NOT, NOT good for the life of your batteries! I hope sincerely that they're not ruined!

Ethan Brush · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

I have done long wire runs often so I am very familiar with this issue. Here is what I recommend:

1. Use aluminum wire not UF cable
2. do not use step up then step down down transformers. Aluminum wire is cheap - cheaper than transformers
3. Get or rent a mini trencher. I have an edger that will cut a 1 -3" wide trench (depending on the rotor) about 7 inches deep. It is basically like a push mower but with a blade spinning on a horizontal axis

I have a 1400 foot run to my wind turbine and solar array and it is 5 #6 aluminum conductors in 1" PVC. U can direct bury type USE conductors but that really freaks me out - seen them fail too often. Maybe if you have more friendly soil than here.....

One option would be to put a "meter/main" by the road and call it an rv hookup if need be. Send 240 V on two #6 aluminum (or three if you want to do it correctly and have an EGC to bond the other end) in 3/4 pvc conduit, or #6 URD which is three strand direct bury. #6 is super cheap, probably .17 cents a foot for a spool length (per single conductor). Get a 3 KVA 240 primary 120/240 secondary transformer for the other end. That would give you 20 amps of 120 with 5% voltage drop. Thats probably the best option, or you could run #2 URD and skip the transformer on the far end. That would give you 4.4% voltage drop assuming a completely unbalanced 10 amp 120V load. Not sure off the top of my head price on the #2 URD, but besides being more than the #6, remember its bigger conduit (if you use conduit) and wider trench, but you do save the transformer cost....

vtmaps · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Another consideration is future troubleshooting. It might be smart to divide the 1000 ft run into several legs, and bring the cable up to a junction box every few hundred feet. If the cable ever fails, you will be very happy to be able to determine easily which leg the fault is in.

--vtMaps

oil pan 4 · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

If its in the ground and not in conduit the whole way then it has to be UF or something listed to be in contact with dirt and moisture. Such as direct buried pump cable (expensive).
Aluminum has horrible performance in wet conditions too.

Ethan Brush · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

oil pan 4 wrote: »

If its in the ground and not in conduit the whole way then it has to be UF or something listed to be in contact with dirt and moisture. Such as direct buried pump cable (expensive).
Aluminum has horrible performance in wet conditions too.

The URD I was referring to is a jargon word which stands for "underground residential distribution" is technically not an NEC approved conductor type, however all URD I have ever seen is rated type USE-2 and RHH. I have heard of URD used by utilities that doesnt have these ratings but have never seen it myself. Single conductor aluminum is typically available in XHHW-2 or USE-2, the latter is what you would use for direct bury. IF it was in pipe I would have no preference and go with whatever is cheaper. I see no issue at all with aluminum in wet locations. Tell the utilities it has horrible performance in wet locations, tell them soon as they have a lot of work to do upgrading the nations electrical grid conductors from aluminum to something else

oil pan 4 · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

There is a big difference between bare over head lines and what is in the ground.
I have my linemans hand book I am well aware of how widely aluminum is used and more specifically where it is used.

Ethan Brush · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

oil pan 4 wrote: »

There is a big difference between bare over head lines and what is in the ground.
I have my linemans hand book I am well aware of how widely aluminum is used and more specifically where it is used.

Ill give you that. However I still dont think that is a valid statement. I have seen maybe 8 direct bury aluminum failures in my 17 year electrical career, but direct bury copper is very rare and hardly ever used so its not a fair comparison. I think that when the insulation is compromised, the conductor WILL fail in a few years regardless of what it is made out of. Around here aluminum is used practically everywhere for underground feeders and services of any significant length, often to meter and disconnect pedestals outside, and I dont recall a single failure of aluminum conductors in conduit or at lugs of equipment, except for a few where it was clear the lug was just never tightened. I would recommend anti-ox compound on any outdoor connections.

oil pan 4 · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Yes if its in conduit it wont fail.

Since the longest run of under ground wire I have seen was a roll of pump cable that was 850 feet long and at most hardware stores you are limited to their 500 foot rolls, then splices will have to be made to get to 1000ft. If the wire is aluminum, just laid out straight and spliced under ground they just don't see to last a long time. The wires expand and contract with the seasons and if the splices are not put in something like an under ground or above ground vault they will likely fail.
If some one runs an under ground line the way farmers around here do it then it will be very prone to fail every several years, sad thing is the farmers around here all use copper.
If the wire is laid so it remotely resembles whats in the linemans hand book it will likely last a very long time and wont matter if its copper or aluminum.
The anti oxide paste should be used on all aluminum connections, at least that is what I was always told to do.

Ethan Brush · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

oil pan 4 wrote: »

Yes if its in conduit it wont fail.

Since the longest run of under ground wire I have seen was a roll of pump cable that was 850 feet long and at most hardware stores you are limited to their 500 foot rolls, then splices will have to be made to get to 1000ft. If the wire is aluminum, just laid out straight and spliced under ground they just don't see to last a long time. The wires expand and contract with the seasons and if the splices are not put in something like an under ground or above ground vault they will likely fail.
If some one runs an under ground line the way farmers around here do it then it will be very prone to fail every several years, sad thing is the farmers around here all use copper.
If the wire is laid so it remotely resembles whats in the linemans hand book it will likely last a very long time and wont matter if its copper or aluminum.
The anti oxide paste should be used on all aluminum connections, at least that is what I was always told to do.

Oh yeah, forgot about submersible pump cable out to wells when I said that direct bury copper is hardly ever used

Regarding anit-ox, I was also originally taught to always use it and used it religiously for years. I have changed my stance on it a bit the last few years and now usually only use it damp or outside locations. The reason is that A) its not required by code

wire manufacturers seem to be neutral on its use C) the aluminum termination problem was due to the old aluminum alloy which had more creep and lug materials that didnt play well with aluminum. Modern tin plated lugs and alloys have taken care of the problem. That said, its use doesnt hurt anything.

rpvietzke · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Ethan Brush wrote: »

I have done long wire runs often so I am very familiar with this issue. Here is what I recommend:

1. Use aluminum wire not UF cable
2. do not use step up then step down down transformers. Aluminum wire is cheap - cheaper than transformers
3. Get or rent a mini trencher. I have an edger that will cut a 1 -3" wide trench (depending on the rotor) about 7 inches deep. It is basically like a push mower but with a blade spinning on a horizontal axis

Thanks, this is really great advice. I have a couple of months before the snow melts, so lots of time to get ready for this. I am curious... Have you ever done multiple #6 runs in parallel (Say 2 #6's for the two legs and one #6 for the EGC) or would you always go to the larger wire size.

Also, completely agree about running conduit. The ground won't be easy to put a 36" deep trench perfectly lined with sand, but a 12" ditch-witch style trench might be doable. I kind of like popping up a few times along the run to have junction boxes above ground and hopefully dry, but that adds some 90 degree bends in to the pulls too...

Rob

Ethan Brush · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

rpvietzke wrote: »

Thanks, this is really great advice. I have a couple of months before the snow melts, so lots of time to get ready for this. I am curious... Have you ever done multiple #6 runs in parallel (Say 2 #6's for the two legs and one #6 for the EGC) or would you always go to the larger wire size.

Also, completely agree about running conduit. The ground won't be easy to put a 36" deep trench perfectly lined with sand, but a 12" ditch-witch style trench might be doable. I kind of like popping up a few times along the run to have junction boxes above ground and hopefully dry, but that adds some 90 degree bends in to the pulls too...

Rob

Probably just go with a larger size than paralleling smaller size. Also note that if you are going by the NEC, you are not permitted to parallel conductors smaller than 1/0. Actually I will be paralleling two 6's at my house because I already bought the wire, then expanded the array so now I need more metal. Depending on the length, you may want to just sleeve the pipe over the wire rather than try and pull it through later. I have done 600 foot wire pulls with bigger pipe, but its hard to suck or blow through a line in the smaller pipe and can just be a hassle and not worth it. My well is 600 feet, and I just glued up 30 or 40 foot pieces and sleeved it over, really didnt take that long...

BB. · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Check your code--But isn't 18 inches deep trench minimum required by NEC?

-Bill

Ethan Brush · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

BB. wrote: »

Check your code--But isn't 18 inches deep trench minimum required by NEC?

-Bill

Yeah generally, but can be less in some situations but that would require Rigid steel conduit and/or concrete cover. I was assuming this could be cheated a bit

Dont know details of the OP's situation, but if he gets a "RV hookup" at the road, he can add the feeder later....

vtmaps · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Ethan Brush wrote: »

Probably just go with a larger size than paralleling smaller size. Also note that if you are going by the NEC, you are not permitted to parallel conductors smaller than 1/0. Actually I will be paralleling two 6's at my house because I already bought the wire, then expanded the array so now I need more metal.

I believe that if each conductor terminates on a different device (such as a fuse or circuit breaker), then the two conductors are not technically in parallel. My belief is not based on any advanced understanding of NEC, but is based on comments by 'inetdog' in another thread.

Regardless of code, this should only be done if the reason for the 'parallel' conductors is to reduce voltage drop. If the reason for multiple conductors is to increase ampacity, then the use of multiple fuses/CB will lead to a cascading failure of the fuses/CB.

--vtMaps

rpvietzke · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Home Depot (first hit on the web) shows a southwire 1,000 ft. 2-2-2 Aluminum URD Ramapo Service Entry Electrical Cable for $864 bucks. That is indeed pretty cheap compared to alternatives. An appropriate sized non-metallic conduit shouldn't be too expensive either.

I do think I would have to "cheat" between the RV hookup panel down by the road and the top of the Hill. It wouldn't be hard to go 12-18 inches with a trencher, drop a conduit in, and backfill with existing material. But, going to 42", putting 6 inches of sand down, laying conduit, putting in more sand, and then filling with "clean fill" back to grade would cost a bazillion dollars through the woods... (IE, I'd have to clear trees the whole way to get the materials and probably larger machinery in.)

The 3 x#2 seems cheap enough to make something work. No problem breakering it at both ends too.

Rob

westbranch · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

I don't know anything about the terrain so this may not be viable... A friend a lineman got such a horrendous quote for installing an overhead service to his place, 2 poles from existing power line, that he rented a bobcat (skid steer0 with a hoe attachment and dug his own trench... maybe it would work for you?

icarus · January 2015

Re: 1000+ft from the road... Long run to the grid or Generator?

Consid getting a price from a wholesale electrical house. They ought to be able to beat the HomeDepot price pretty easily. You might also contact the utility. Perhaps they can supply you with the wire. Personaly, I would go with direct burial and not bother eight he conduit. If I needed a pipe simply to fish through, I would consider light weight PVC instead. I suppose it depends to a great deal on your code/inspection authority. 18' really ought to be pleanty deep if you don't have any reason to molest the trench, ie,plowing or landscaping etc.

Tony

1000+ft from the road... Long run to the grid or Generator?

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