Hi all experts,

I have a project in Costa Rica, just getting ready for the arrival of electricity. My house is 450' from the public road where the transformer is. Because we have a gate at the entrance to the property, the service meter needs to be at the location it is.

Our electrical engineer down there has specified a conduit run with 3/0 THHN (two cables) and 2/0 THHN for the ground. Our panel is 200amps at the house, tied in to a 30KW generator.

I'm looking for a second opinion on the service plans. Any other options? It has to be run underground.

Any advice would be much appreciated!

#3/0 wire, not sure if your using copper or aluminum, my guess is copper, is nominal size for 200 amp feeder, and does not appear to be sized for voltage drop considerations.

But I am only a lowly electrician, no engineer.

450 feet is a very long distance to deliver 120/240 volts, and attempt to keep voltage drop to a recommended maximum of 5%.

Not only do you need to consider this feeder, but also need to consider the longest branch circuit and any other feeders that may be in the home. My guess is that this would not be a small home.

Vd can be 3% max for a feeder and 2 % for a branch circuit, or vice versa. Which ever works best. Vd does not need to be either of these, can be whatever you like, or can live with.

One piece of the puzzle is what is the maximum load in amps, KW or KVA. One of these values is needed to perform voltage drop calculations, along with knowing the conductor material. And really need to know what the nominal utility voltage is, and the reliability of that voltage remaining somewhat constant. If brownouts are frequent, then all bets are off.

Can the engineer show his calculations?


I personally would attempt to deliver high voltage that distance, even if I need to have a small transformer at the gate, if that area needed 120/240 volt power for gate power, lighting, etc.

In lieu of that, if 120/240 volt 200 amp absolutely needed to go the 450 foot, the conductors could be up in the range of #250 MCM copper, depending on various values.

And of course, this is not my money. But, if someone decides to have a feeder than long, and wants a reliable system, not my worry.

Since you have hired an engineer, he is, or should be, entirely responsible for the performance of the installation.

Be sure to have the proper clauses in the contract that if his design does not perform properly, that he pays to do any necessary upgrades, and any costs incurred due to subsequent damage to appliances, etc.

Watch out for any "hold harmless" clauses in his contract to you. Something like that could leave you in the dark, no pun intended, and having to pay for any improvements yourself.

May be wise to have your attorney review the contract between you and the engineer.

I used a few on line calculators, and assumed that the neutral current would be 100 amps, to arrive at the 250 MCM Cu.

The lower this value is, the smaller the wire can be. The last one listed uses 3% Vd automatically.


Voltage Drop Calculator

Voltage Drop Calculator

Voltage Drop Calculator JavaScript

You could, to save money and insure good performance, is to use aluminum wire, possibly.

Now that I think about it, being an island surrounded by sea water, AL may not be the best choice, due to the corrosive action of sea salt on aluminum. We have an expert here from the Florida Keys, and due to the proximity to the ocean, aluminum is not allowed there.

Try the calculators I provided, plugging in the various values, to see the various answers.

By the way, you mentioned two hots and a ground, here in the USA we use two hots and a grounded conductor, (AKA Neutral), for 120/240 volts. May be what you meant, but ground and grounded are two different animals, to us anyway, and just wanted to be clear on that.

Thanks TKRussell.