200 amp 700 feet

[PVfarmer]

i was right!! wow.

i was right!! wow.

Ok, thanks! I was starting to panic.
About the lights flickering/motor startup...how complex an issue is that, and how is 3% involved?

There is no right or wrong answer here, it comes down to how little voltage drop the customer is willing to pay for / how much voltage drop they can tolerate.

Some folks will live with lights dimming when the AC compressor starts other folks will not.

Now a 200 amp service might never see a constant load over 60 amps but it could see high currents during motor start ups.

from the same link as my previous comment-
The NEC recommends that the maximum combined voltage drop for both the feeder and branch circuit shouldn't exceed 5%, and the maximum on the feeder or branch circuit shouldn't exceed 3% (Fig. 1). This recommendation is a performance issue, not a safety issue.

So...I realize a 5.1% VD isn't always going to immediately cause all the lights to flicker like crazy, but two things-
1- If you are shooting for 5% on the feeder, does that mean you want to shoot for 0% on the branches?
2- And in a case when there is a transformer involved. From that link again:
What is the maximum length of 6 AWG THHN you can use to wire a 480V, 3-phase, 37.5kVA transformer to a panelboard so voltage drop doesn't exceed 3%?
A: 376 feet.

So 6 AWG is out for a 500 foot run. (copper here)
But am I over-simplifying here- you *could* use 4 AWG for 500 feet/480V/3ph, that would be over 3% but under 5% VD.
However, with 24kVA/100 amps of constant loads (a good 80% of that being motors)... this is where I'm confused- would it be 2, 1, or 1/0 AWG to stop flickering?

I get (1 AWG * 3%) / (1.732 * 12.9 * 100 amps) = 539 feet?
(83680cm * 14.4V) / (1.732 *12.9 *100) = 539.

If I should start a new thread, let me know.

 

[kwired]

You can size a conductor to achieve a specific voltage drop at a specific load level.

You can still have a sag in voltage because of a motor starting, this sag can even be partly because of too high impedance in the source itself.

In a dwelling the most offensive load for such voltage sags is usually HVAC compressors. You can size your supply for low voltage drop at say 100 amps of load, but that compressor may draw over 100 amps for a few cycles when first energized, plus any existing running loads are already there. Many of us do notice some flicker when such loads start, but they become more obvious with long service/feeders. I have always found for so called occupied structures the closer you can get the source the better, especially when dealing with a source that is 100 or more feet away.

 

[PVfarmer]

YYou can size your supply for low voltage drop at say 100 amps of load, but that compressor may draw over 100 amps for a few cycles when first energized, plus any existing running loads are already there. Many of us do notice some flicker when such loads start, but they become more obvious with long service/feeders. I have always found for so called occupied structures the closer you can get the source the better, especially when dealing with a source that is 100 or more feet away.

Thanks. In one particular case, the source (grid) sort of could be moved closer to the loads, but then the PV (other source) would have to be run 500+ feet instead of 100.
So in the pic, if the MV xfmr/meter were moved to the barn (where the "old" meter is), there could be 20 feet from source to load, but the PV output would have to run 600 feet @ 480V to get to the meter, instead of 100' to the "new" meter.
So while there's no way to avoid the 500 feet, fortunately it is @ 480V either way (on the customer side).

How about this- when the load is mostly 1-2hp (or less) motors, and they aren't all turned on at the same time (say 1 second between switch flips...)
so 100 amps total when everything is on...
does the 1 second between motors avoid the over 100A bolded part of your comment?

The total load is 100A @ 240V, so 24kVA.
Some motors run on 208V and some are 240V (which is whole other story...)
I was actually thinking a 37.5kVA xfmr, 480 to 208/120 3ph and an 80amp main breaker in the 208/120V 3ph panel (80A = 28.82kVA), so if 1AWG is good for 539 feet @ 100A, it is plenty for 80A @ 500 feet.
Or...is 1 AWG too much?
The 208/120 xfmr is at the barn/where the "M old" is marked.

 

[PVfarmer]

I was actually thinking a 37.5kVA xfmr, 480 to 208/120 3ph...

No!
I was not thinking that. The 37.5kVA is a 480 delta to 240/120 center tapped xfmr.
I meant a 45kVA, 480V delta to 208Y/120V xfmr for the ~24kVA of loads, pretty sure I stated the rest correctly.

 

[kwired]

Line losses on the line to the PV aren't as much direct cost loss as line losses from the utility, but at same time is losses that you could have put into the grid or lessened the grid load being used at that time.

 

[petersonra]

Maybe the Poco would be willing to give you a higher voltage service like 600 volts single phase. Then you would only need one Transformer.

 

[Cow]

It's 700' guys, not a half mile. Who wants to pay for all the extra equipment/potential maintenance as well as the idle losses from the transformer when all it takes is some bigger wire and conduit?

We've done 2500' runs to irrigation pivots, and no, we don't use transformers.

 

[petersonra]

How much extra maintenance do you think a Transformer takes? As for the losses in the Transformer we're not talking Lots of money. On the other hand if you're against a Transformer or two then run some big wires.

 

[kwired]

It's 700' guys, not a half mile. Who wants to pay for all the extra equipment/potential maintenance as well as the idle losses from the transformer when all it takes is some bigger wire and conduit?

We've done 2500' runs to irrigation pivots, and no, we don't use transformers.

Center pivot irrigation machines only draw 10-15 amps max and at 480 volts three phase. So conductors don't need to be all that large to begin with even after adjusting size for voltage drop. On top of that you may not even notice any problems if they only were running at say 445-450 volts, biggest issue is that the control voltage doesn't drop too far that the motor contactor coils can't pull in, avoid that and you may never notice voltage drop.

Not quite the same to have a similar length run of 120/240 single phase and supply 50 amps plus at times and not notice some issues with lighting and consumer electronics or appliances.

 

[Cow]

Center pivot irrigation machines only draw 10-15 amps max and at 480 volts three phase. So conductors don't need to be all that large to begin with even after adjusting size for voltage drop. On top of that you may not even notice any problems if they only were running at say 445-450 volts, biggest issue is that the control voltage doesn't drop too far that the motor contactor coils can't pull in, avoid that and you may never notice voltage drop.

Not quite the same to have a similar length run of 120/240 single phase and supply 50 amps plus at times and not notice some issues with lighting and consumer electronics or appliances.

I agree, I just think 700' isn't far enough to justify getting into weird scenarios such as step up and down transformers or setting a 600v single phase service and a stepdown transformer at the house. If they can afford a home 700' from the utilities, I would wager they'll understand that they are going to spend more on electrical and it may take bigger wire and conduit to get it done.

 

[kwired]

I agree, I just think 700' isn't far enough to justify getting into weird scenarios such as step up and down transformers or setting a 600v single phase service and a stepdown transformer at the house. If they can afford a home 700' from the utilities, I would wager they'll understand that they are going to spend more on electrical and it may take bigger wire and conduit to get it done.

Parallel 4/0 aluminum conductors are relatively inexpensive for only 700 feet compared to having a transformer on each end. If you can have a transformer on just one end, might be worth a little more consideration, still may need to get to that 1000 feet or so distance before it starts to be worth the investment. Then you need to know if POCO will charge more for other then 120/240 supply as well. 240/480 transformers (by POCO) are not uncommon here, but most of them are on irrigation services or other limited loads and most are only 10 - 15 kVA max. They have all sorts of 120/240 transformers in stock the bulk of them is 50 kVA or less though.

 

[petersonra]

You can probably blame most of this on the developer. Most places the developer has to pay to run the utilities into the development and build the streets and sidewalks and sewers etc. The POCO probably would not accept the idea of building the infrastructure as they go along like he can do with the streets and such. So the developer forces that cost onto the HO so the developer's upfront costs are reduced.

 

[Ingenieur]

You can probably blame most of this on the developer. Most places the developer has to pay to run the utilities into the development and build the streets and sidewalks and sewers etc. The POCO probably would not accept the idea of building the infrastructure as they go along like he can do with the streets and such. So the developer forces that cost onto the HO so the developer's upfront costs are reduced.

many government subdivision requirements mandate that electric infrastructure is put in as a condition of approval
doesn't say who pays, utility or developer

most of the time it is ug mv with pad mounted transformers
most I have seen the developer will put in the pads/stub ups, and ug cable in trench connecting the pads (all per util spec)
then the utility will mount the xfmr as build out progresses (sometimes the HO will pay for the xfmr, around here overhead is free, pad is extra)
HO pays for his ug service

 

[Skokian]

Vector Impedance Voltage Drop Calculations.

Vector Impedance Voltage Drop Calculations.

Note that for larger sizes of conductors, the reactance of the wire becomes important factor. At 400 MCM the reactance can exceed the resistance of the wire. Hence, the complex impedance should be used when calculating voltage drop.

Use the values of Table 9 in Chapter 9 of the NEC for the values.

Note that resistance also varies depending on the type of conduit used (steel, aluminum, oe non-metalic).

 

[tom baker]

In WA yes as we can have up to six feeders to a dwelling unit per state code
Under the NEC no, each building can only have one feeder, with exceptions.
With a transformer there is a cost to pay for the losses in the transformer.

 

[Nuber]

2 options that I didn't see discussed -

1. Install 4/0 AL for the feeder. Install oversized branch circuit wiring to HVAC, sump, well, or any other large motors to minimize the light flicker. Install individual UPS systems on sensitive circuits like flat screen tv's and personal computers. I would suspect this is a lot less money than oversizing the conductors, but would mitigate a lot of the negative effects.
2. Install 4/0 AL for the feeder. Install a boost transformer system to account for some of the voltage drop. There are some drawbacks here, but I think this would be cheaper than a parallel or oversize feeder install.

 

[ActionDave]

2 options that I didn't see discussed -


Install 4/0 AL for the feeder. Install oversized branch circuit wiring to HVAC, sump, well, or any other large motors to minimize the light flicker. Install individual UPS systems on sensitive circuits like flat screen tv's and personal computers. I would suspect this is a lot less money than oversizing the conductors, but would mitigate a lot of the negative effects.

A bigger factor in light dimming is the stiffness of the supply from the POCO, we have no controll over that so let's pretend we have total controll of voltage drop on the feeders. If that is the case over sizing the branch circuit conductors to the HVAC would would allow more current on inrush and would flicker the lights more. I think the ups on electronics is a good idea, very cheap insurance. I have a couple and I don't have much of a stereo or TV or computer.

Install 4/0 AL for the feeder. Install a boost transformer system to account for some of the voltage drop. There are some drawbacks here, but I think this would be cheaper than a parallel or oversize feeder install.

Since voltage drop is tied to the load you end up with over voltage during light loaded events if you boost your voltage for your full load, plus you still have the cost of all the associated gear to set a transformer. A size or two bigger wire is cheaper.

 

[iwire]

Install oversized branch circuit wiring to HVAC, sump, well, or any other large motors to minimize the light flicker.

Installing oversize conductors to only the loads that cause flicker without increasing the service conductors will only make the problem worse.

Install individual UPS systems on sensitive circuits like flat screen tv's and personal computers.

Unless you are talking about some commercial grade UPS the typical cheap home style 'Standby UPS' does nothing at all to protect equipment from undervoltage until the voltage drops below the threshold and switches to battery.

They are not voltage regulators or filters, some may have basic surge protection that you could get in a plug strip.

More info here http://www.apc.com/us/en/faqs/FA157448/

Install a boost transformer system to account for some of the voltage drop.

That will not work well either as the voltage will still vary per the load at the time.

 

[Sahib]

Not just flickering of lights, starter type fluorescent lamps will not light up if voltage drop is allowed to be excessive.

 

[Nuber]

I am curious if we could expand on a couple of concepts -

1. "Installing oversize conductors to only the loads that cause flicker without increasing the service conductors will only make the problem worse." How so?
2. "... over sizing the branch circuit conductors to the HVAC would would allow more current on inrush and would flicker the lights more." The total impedance of the load is fixed while the voltage at the load is effectively higher, I don't see how load current goes up here relative to the smaller conductor.

"Since voltage drop is tied to the load you end up with over voltage during light loaded events if you boost your voltage for your full load, plus you still have the cost of all the associated gear to set a transformer. A size or two bigger wire is cheaper."

No perfect solution here and I didn't run the expense numbers, the boost concept is just a theoretical solution. You would certainly want to size the "boost" to only compensate for the voltage drop, not overcompensate. If you upsize the wire one or two sizes you still have voltage drop, just at a lower level. If you boost the voltage at the house, you might be able to restore full system voltage at the house (depending on a lot of variables, of course). I would clarify that a potential boost system be designed for no-load voltage at the house. It is quite correct to state that an overvoltage situation would be created if you design the system based on full load current.