Parallell 430' Aluminum Cables for 400amp Single Phase Service

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steve66 said:
Have you tried 4 sets of smaller wire? It may be harder to terminate - you may even need a terminal box at each end to get the wire back to something that will land on the breaker.

But with really large wire (750KCM) the current tends to flow on the outside of the cable, and not in the middle. That means you have a lot of extra copper that isn't helping much.

For example, I think 4 sets of 3/0 is less copper, but only about 70% of the voltage drop.
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Thanks for the insight...

I thought the individual strands that make up the larger size wires had the current travelling on the outside, rather than the current travelling along the outer strands of the one insulated phase wire?
 
I'd be asking what POCO would charge to put in underground primary and put transformer closer to load, this also makes less cost down the road when customer wants to add additional facilities and needs more power.
 
powerplay said:
Thanks for the insight...

I thought the individual strands that make up the larger size wires had the current travelling on the outside, rather than the current travelling along the outer strands of the one insulated phase wire?
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you are correct. skin effect is on the individual strands.
not on the outer layer of strands only.

if you load is primarily lighting ballasts, and you need
120 volt for incidental loads, pull a straight 240 volt circuit
to a 240 volt panel, run the lights on 240 volts, and put
a small 240/120 volt transformer feeding a six circuit panel
to provide your incidental 120 volt loads.

how many amps do your ballasts draw on 240, and how many
are there, and then do the voltage drop calcs, and hold your
voltage drop to 5%.
 
OK. here ya go.

OK. here ya go.

a straight 240 volt circuit, going 430' with
320 amps, give you these numbers, without
transformers.

500 MCM AL gives 4.86% voltage drop.

two 500' spools of direct burial aluminum in 500 MCM
is about $2,100.
 
After 2/0 you cannot simply use the DC resistance 'K'. The skin effect takes part. These are conductors in free air. Chapter 9 table 9 can be useful for a quick check. 0.85 Zs given in PVC.

240*0.03 = 7.2V max drop

7.2 = 2*430'*320A*Z

This yields 0.026 ohms per 1000 linear feet. So parallel AL 600s.

As mentioned by others, 80% of the breaker is not the way to approach VD. You should instead consider actual expected load.

If your 400A service comes from NEC requirements, 50% is likely peak load.

This makes parallel sets off 300 AL more reasonable. Is this a big building? Do you actually expect 2% VD for branch circuits? If you allow 5% on the feeder at 50% load you could do this with one 350 AL.

Don't forget to proportionally upsize your ground.
 
kwired said:
I'd be asking what POCO would charge to put in underground primary and put transformer closer to load, this also makes less cost down the road when customer wants to add additional facilities and needs more power.
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I'm in Canada, but the option to get Primiary Line Overhead is the last expensive option, but there a lot of trees to clear to make that happen. Underground here takes co-ordination with City Excavators etc and triples the cost.
 
We decided to go with step up transformer to 600volts, run parallel 3 conductor 250Kcmil the 440' to an 600 volt disconnect, then step it down with an 600volt to 120/240 Transformer feeding an 4' Splitter with an couple of 200amp Panels.

Thanks for all the feedback!
 
I just can't see how it's cheaper either right now or in the long run for the customer to have all that extra electrical equipment and 24-7 transformer losses on a run that is only 440' long.

We pulled an 800 footer a couple weeks ago, it's really not that big of a deal with the right size conduit and pulling equipment.
 
Cow said:
I just can't see how it's cheaper either right now or in the long run for the customer to have all that extra electrical equipment and 24-7 transformer losses on a run that is only 440' long.

We pulled an 800 footer a couple weeks ago, it's really not that big of a deal with the right size conduit and pulling equipment.
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Yes, me Tacoma could do that easily.:p
 
ptonsparky said:
For me, 20 HP single phase grain bin fans add up in a hurry. The utility may not provide a full 400, but at certain times of the year they may all need to be On. They are hard starting devils and voltage drop will come into play.
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One would think, or I would, that multiple numbers of 20HP/15kW motors would merit a three phase supply. In fact, I can't recall coming across a motor of that rating that wasn't three phase.
I was brought up on a farm in Scotland with lots of hills and sheep and other beasts. Not quite like your mid-west praries. We had grain, wheat, oats, barley but not on a grand scale.
And my engineering background is industrial.
 
Besoeker said:
One would think, or I would, that multiple numbers of 20HP/15kW motors would merit a three phase supply. In fact, I can't recall coming across a motor of that rating that wasn't three phase.
I was brought up on a farm in Scotland with lots of hills and sheep and other beasts. Not quite like your mid-west praries. We had grain, wheat, oats, barley but not on a grand scale.
And my engineering background is industrial.
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Remote areas may not have three phase distribution nearby. Once you reach a demand level determined by POCO they may still require you to go with three phase, which will mean some cost for them to upgrade their distribution to get it to you.

Single phase general purpose motors are rare to see over 10 HP. But in recent years I have seen many 15 and 16 HP motors that are basically a general purpose motor. For many years there has been special purpose aeration motors that are common on grain storage aeration fans. They take a motor design that is about the same thing as a 10 HP general purpose motor, but rate it for 12-15 HP as long as it is installed in the airstream of the fan it drives.

You might end up with multiple lower HP fans instead of one larger HP fan because there is limitations on how large of a motor is available. POCO's may also have a limit on how larger of a motor they will allow across the line starting for.

In recent years the storage capacity of such bins has been increasing, which is also requiring higher capacity for aeration.

30 years ago when I was first starting in this trade, we seldom connected an aeration fan on a grain storage bin that was over 10 HP, on a farm - commercial elevators maybe. I have a storage bin coming up this season that will have a single 50 HP fan on it. The existing bin next to it has two 25 hp fans and was constructed last season, and several same sized structures by same customer at different sites were the same in recent years. They decided to try just a single 50 HP on this one to see how it works out.
 
electrofelon said:
Here in the states, many rural areas do not have three phase. IS it different overt there?
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Thanks guys. I appreciate the feedback I'm being given here.
Is it different here? Well, where I grew up we had just single phase. No particularly heavy machinery. There It's a lot of years ago and it has since turned into a stud farm (Clydesdales) so I don't know what supply they have now.
I suppose a significant difference is geographical. It's quite a small island so nowhere is particlarly far from utilities.

Our local distribution transformer is 11kV/400V DYn11 1500kVA. It feeds our street and maybe another.
 
powerplay said:
We decided to go with step up transformer to 600volts, run parallel 3 conductor 250Kcmil the 440' to an 600 volt disconnect, then step it down with an 600volt to 120/240 Transformer feeding an 4' Splitter with an couple of 200amp Panels.

Thanks for all the feedback!
Click to expand...

Sounds like a good plan. I'm curious, what size (kva) transformer did you decide to go with and are you using a step up transformer that is a designed step up transformer or just hooking on up in reverse?

Also, if you wanted to save a couple of dollars, could you do away with that 600-volt disconnect at the step down transformer?

Edit: it may not be a good idea, I was more asking from a code compliant view.
 
Besoeker said:
Thanks guys. I appreciate the feedback I'm being given here.
Is it different here? Well, where I grew up we had just single phase. No particularly heavy machinery. There It's a lot of years ago and it has since turned into a stud farm (Clydesdales) so I don't know what supply they have now.
I suppose a significant difference is geographical. It's quite a small island so nowhere is particlarly far from utilities.

Our local distribution transformer is 11kV/400V DYn11 1500kVA. It feeds our street and maybe another.
Click to expand...

Could I get some help understanding this?

Edit, are you saying it's 11kv primary with a 400v secondary?

Can't guess on the DYn11
 
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