what size conductor?

[Alain Dappen]

what size conductor do i need to feed a 100 amp residential panel if my
source is 700 feet away?

 

[iwire]

I bet at least a 4/0 copper assuming 100 amps of load and 240 volt.

What you really need is a couple of transformers, boost it to about 550 send it the 700' and then reduce it back to 120/240.

Along with reducing the wire sized needed you can also leave the neutral out and create a new one at the far end.

 

[bob]

4/0 100 amps 240 volts 4.4% VD
250 kcm 100 amps 240 volts 3.7% VD
#2 50 amps 480 volts 2.8% VD
#4 50 amps 480 volts 4.5% VD. You adjust taps for VD.


Edit: add 4/0 cu.

 

[ptonsparky]

Don't know what leaving the neutral out would do. You still need an EG and sizing proportianately (sp) for VD won't reduce the size all that much. Plus the homeowner gets to pay for two transformers, the inefficiency of both, the additonal fusing and maintenance. Bigger wire is better I think.

 

[QES]

why not 4.16kv :smile:

I think 4/0 will be cheaper and a better choice.

 

[stickboy1375]

I bet at least a 4/0 copper assuming 100 amps of load and 240 volt.

What you really need is a couple of transformers, boost it to about 550 send it the 700' and then reduce it back to 120/240.

Along with reducing the wire sized needed you can also leave the neutral out and create a new one at the far end.

I would opt for another service if possible...

 

[iwire]

Don't know what leaving the neutral out would do.

700' less copper.

Instead of four conductors 700' long it would be three conductors 700' long.

Plus the homeowner gets to pay for two transformers, the inefficiency of both, the additional fusing and maintenance.

I am guessing you have not recently priced 2,100' of 250-300 Kcmil copper.

Not much maintenance to dry transformers.

Assuming 100 amps at 240 that is 24 KW

24 KW at 550 volts is 43 amps, a substantial reduction in conductor size needed.

Looking at Bobs figures above it appears a 4 AWG would do it at 550.

Sticks idea of another service is a good one, I assume that is not an option or why would they be asking this question.

 

[ptonsparky]

Acme transformer says their dry type units are 6% impedance. Two units would be 12%. Your customer pays for this. Using the 25kva load continuous for simplicity:
KW*cost*hours*days= yearly cost
25*.10 (use local cost)*24*365= $21,900

Now add 12% because of transformer losses on the load side of the meter. I read that the typical life span is 30 years for an electrical installation. 30 years*$2628=$78840 just for the two transformers.

Use bigger wire, parallel AL or have POCO supply you with 600v drop and use one transformer at buildings.

I am not required to have a disconnect directly below the POCO meter 700' away, are you? This means I only need to bring 3 wires to the building site. May be different in your area.

 

[wasasparky]

Using the 25kva load continuous for simplicity:

I don't think a 104A continous load is typical for a residence...

Plus, you only wan't to compute the additional load due to the actual transformer losses which will be a small percent of the load, of which will average much below 25kva...

 

[iwire]

Tom, it's just a mater of design.

Does the customer want to pay a lot now, or spend more spread out over time?

As illogical as it sounds most customers choose to go cheap now and pay more in the long term.

If you can get them to pony up for the larger wire then good for you. :smile:

 

[iwire]

I don't think a 104A continuous load is typical for a residence...

When figuring voltage drop I would not consider continuous or not.

But I agree the 100 amp size is not the real load, it is all we have to go on yet.

 

[wasasparky]

When figuring voltage drop I would not consider continuous or not.

But I agree the 100 amp size is not the real load, it is all we have to go on yet.

My point was, you have to buy the power no matter what.
The EXTRA cost for using transformation is "only" maybe $1,000/yr vs $22,000/yr. (bigger wire probably makes more sense for the long haul...)

Transformer load losses vary around maybe 1% at no load to 5% at full load (I threw those out as gross approximations, they will vary on transformer type and size...there are also energy efficient transformers...)

 

[bob]

Acme transformer says their dry type units are 6% impedance. Two units would be 12%. Your customer pays for this. Using the 25kva load continuous for simplicity:
KW*cost*hours*days= yearly cost
25*.10 (use local cost)*24*365= $21,900

Now add 12% because of transformer losses on the load side of the meter. I read that the typical life span is 30 years for an electrical installation. 30 years*$2628=$78840 just for the two transformers.

6% impedance does not represent transformer lossses.

 

[haskindm]

what size conductor do i need to feed a 100 amp residential panel if my
source is 700 feet away?

Alain,
Calculate the actual load on the service. You will probably find that it is MUCH less than the 100-amp rating of the panel. Calculate the voltage drop based on this amperage and then determine which wire to use. An explanation of why a residential panel would be 700' from the power source, may help generate additional ideas. For example if this panel is only for occasional use, it may be cheaper to install a generator. It is certainly not "normal" to need to run residential power 700'.

 

[Alain Dappen]

Thank you gentelman. We calculated 4/0 as well. Unfortunatly the costumer
(Gov't) requires 2% VD max, and our 2" conduit is already in the ground.
Pulling 3-4/0 in a two inch is max and a bear. We wonder if compacted cable
or some sort of deisel cable would be allowed.

 

[Bob NH]

How about getting the POCO to run a primary line to a transformer on a pole or pad nearer the user? The cost to run the line might be less than the cost of the other solutions and the losses.

It should not be much more expensive to run a primary line underground than it will be to run 4/0 copper.

 

[ptonsparky]

Thank you gentelman. We calculated 4/0 as well. Unfortunatly the costumer
(Gov't) requires 2% VD max, and our 2" conduit is already in the ground.
Pulling 3-4/0 in a two inch is max and a bear. We wonder if compacted cable
or some sort of deisel cable would be allowed.

When is the hernia repair scheduled for?

 

[Bob NH]

Thank you gentelman. We calculated 4/0 as well. Unfortunatly the costumer (Gov't) requires 2% VD max, and our 2" conduit is already in the ground.
Pulling 3-4/0 in a two inch is max and a bear. We wonder if compacted cable
or some sort of deisel cable would be allowed.

Cost is no object to the Government. They are spending Other People's Money (OPM).

They also have different color money for different purposes. Green money is considered real money for costs that are the responsibility of the current project manager. Any other color, such as for future operating expenses that are the responsibility of someone else, is like Monopoly Money and is not a consideration in the decision.

 

[Trocken]

Bob how are you doing your Voltage drop?
I am using IEEE Standard 141 which gives me 3.3% at 250 wire size.
I got the calculator from www.arkansoft.com its called LectriCalc
which has over 150 calculators.

 

[wirenut1980]

Thank you gentelman. We calculated 4/0 as well. Unfortunatly the costumer
(Gov't) requires 2% VD max, and our 2" conduit is already in the ground.
Pulling 3-4/0 in a two inch is max and a bear. We wonder if compacted cable
or some sort of deisel cable would be allowed.

If the conduit is buried deep enough in the ground, IMO extending medium voltage underground is your best bet. Or, forget the conduits and extend overhead primary if that is possible. These days I will bet that is less expensive than running oversize copper, or paying for 2 transformers. If this is on a government base, then POCO probably is not in the picture at this point (even better!), they usually stop at the substation, stepping down transmission to distribution.