ELECTRICAN GURUS:

[machmeter62]

I have a question for you gentlemen? Our home has a 400 AMP service panel. This spring, I want to run an electrical line for a future small care-takers home... (two bdrm), that will be about 250-300 feet from our existing home. The line will come from the main house service panel.

Can I go with a direct burial wire, or is that a local code decision, and what type of wire and size in aluminum or copper? The prices have seemed to have fallen with copper....would that be the best, and somewhat economical route; or go with a larger aluminum line to carry a 100 AMP service panel there?

If I go with copper wire and conduit, what size conduit would be suitable? Will an aluminum wire size conduit have to be larger too, because of its ampacity? The property is located in Northern Calif.

Thanx in advance for your help and suggestions.
LEE

 

[biggerten]

Check local codes, but here is a link to codes in my area, service requirements start on page 5.

http://www.ci.lakeville.mn.us/departments/departmentspdf/ElectricalPermits.pdf

 

[quicksandfarmer]

I'm not an electrician but I play one on my farm.

First off, codes are all local, your best bet is to talk to the local inspector.

That said, there are two things you have to worry about. One is the ability of the wire to carry current without overheating. The other factor is losses due to resistance in the wire. Thinner wires can carry less current, and they have more resistance for the same length, than thicker wires.

At that length, resistance is going to determine your wire gauge rather than current carrying capacity. A 1/0 wire will carry 100 Amps, but it will have a drop of 8%, so your voltage will be 111 volt instead of 120.

Is that OK? This is where it gets local. The national codes are non-commital as to what is an acceptable voltage drop. You also have to think about what you're going to be doing with that electricity -- lights work fine at lower voltages, motors less well. It might be a good idea to measure what your current voltage is at the panel -- if you currently have a big drop, you probably want to be more conservative.

 

[cmuncy]

When I built my house and shop, I had the utility company run primary underground to a transformer smack dab between my shop and the house. Now, the runs from the transformer to either the shop or the house are under 150 feet. This minimised voltage drop as well as conenction costs.

 

[Highflier]

Exactly as mentioned above. Your 400 amp panels distance from the last transformer + the additional run to the new panel will dictate the need for another transformer (or not). Call the local power provider, the co. that owns and maintains the actual lines and have them come out and do an audit per your needs. In our area when we are doing projects requiring upping power needs, the utility will regularly provide transformers, bigger gauge drops, etc. The only catch is the labor is a hit and miss deal, sometime free, sometimes not.

 

[Erik_in_Hoyt]

check your local code.
that said, we put ours in 2" gray (Carlon) PVC, which is considered overkill in our area, but also makes future repair/work easier because i won't have to dig a new trench.
our electric company installed a meter with 3 sets of lugs for running primary service as well - so I have the option of slaving my shop (when I get it built) off the house panel or running it's own service from the pole - which in my case will be the shorter distance.

 

[LBrown59]

I'm not an electrician but I play one on my farm.

First off, codes are all local, your best bet is to talk to the local inspector.

.

There are no codes here.
Just the way i like it.

 

[Erik_in_Hoyt]

even in a "no-code" county (state?) you still have to meet federal minimum standards.
on the other hand, not having to have an inspection every time you turn around makes the construction process quicker.

 

[podagrower]

Here's my two cents, and feel free to ignore it

I do not like direct bury wire. If there is ever a problem with one wire (damaged insulation), it can not be fixed with direct burial, you will have to replace. If it is in conduit, and one wire is damaged, you can pull it out and replace it.
That being said, 11/4" conduit would work for copper wire at minimum size. 11/2" would work for aluminum. Neither would be much fun at this distance, so I would suggest 2", which would leave room for future upgrade, and make pulling a little easier.
Wire size: there is a table in the NEC for residential feeders which says. #4 copper or #2 aluminum is enough for a 100 amp service. If you take voltage drop into account (no more than 5% recommended to the furthest point of the system) then wire needs to be upsized to the area of #1 or #2 copper or 1/0 or 2/0 aluminum.
For feeder conductors, I have no preference of copper or aluminum, other than copper is more fun to scrap
One final note, if possible, make sure you get THHN (THWN, THHN-2, THWN-2) type insulation. It is a thinner coating of insulation, and this type of insulation slides easier in conduit than XHHW (XHHW-2).
Good luck, post photos.

 

[SPYDERLK]

I'm not an electrician but I play one on my farm.

First off, codes are all local, your best bet is to talk to the local inspector.

That said, there are two things you have to worry about. One is the ability of the wire to carry current without overheating. The other factor is losses due to resistance in the wire. Thinner wires can carry less current, and they have more resistance for the same length, than thicker wires.

[[[At that length, resistance is going to determine your wire gauge rather than current carrying capacity. A 1/0 wire will carry 100 Amps, but it will have a drop of 8%, so your voltage will be 111 volt instead of 120.]]]

Using the equation p=ie (Power = current x voltage) You will see that at 100A you are conducting 12kW on a 120V line. You are losing 900Watts of this (100x [120-111] in the wire. I assume you will be running both legs and taking 240V to the addition. If you divide the load equally on each leg at the addition, with 12KW you will be conducting just 50 A on each leg and you will lose only 4.5V instead of 9v on the round trip. Now P=IE = 50 X 4.5=225W lost. Still that Wattage is wasted heating the earth. If you are anticipating high loads at the addition use the biggest wire you can justify. Otherwise the electricity you pay for to heat the earth on the way there will eat back at your initial savings.
larry

 

[Onthesauk]

One other issue. If you go from current panel to barn everything goes through current meter. If you run a new line from the transformer you need another meter and at least out here, means another monthly meter charge and minimum usage charge. Looking at those charges over time, you can afford to step up the size of wire from the current box.

 

[Erik_in_Hoyt]

sorry - I must not have made my situation clear.
my meter has a main breaker under it (between it and my house panel) and under that breaker are 3 sets of connections for running 3 separate main feeders, so I can run power to main panels in 3 different buildings from the pole off that one meter.

also - I used 2" PVC to run the 2/0 aluminum thhn insulated cable that my electric company both recommended and sold to me "at cost" (which was significantly less expensive than buying the same cable from Lowe's) and they threw in an extra 25' for waste at both ends free of charge.

 

[rambler]

You will end up with a large aluminum feed wire. 100 amps at that distance = big fat wire - They don't like 5% voltage drop, and some feel 3% on feed wires - local code might dictate this, as mentioned National will dictate size not to overheat, only suggests voltage drop issues. Less voltage drop means happier electric motors, less light flicker, etc.

Direct burial, unless local codes prohibit it. I believe you will end up with 4-conductor, tho there is some provisions for doing 3-conductor but I don't think that works for house to house.

Had my farm rewired, some runs were 400+ feet, wired for 200 amps. The aluminum was as thick as my thumb..... Copper wasn't even considered.

--->Paul

 

[cmuncy]

One other issue. If you go from current panel to barn everything goes through current meter. If you run a new line from the transformer you need another meter and at least out here, means another monthly meter charge and minimum usage charge. Looking at those charges over time, you can afford to step up the size of wire from the current box.

Fortunately for me, running another meter panel on my shop will only run me $9.00 a month base before usage. For me, a great investment.

The only bad side is my wife can see how much electricity I'm using out there.......

 

[cowsrus]

Aluminum wire v copper for the same amp carrying ability is larger and harder to work with. If your going to pull the wire through conduit, you better get 2" at least. Also if your doing it yourself, pull the wire as you go instead of trying to pull it all at once. You can get some wire lube to help.

 

[machmeter62]

Today, I priced a 500' roll of 1/0 copper at Home Depot. $1172....= $2.34/ft. Yikes!! They claimed the price has gone down recently??!

 

[3RRL]

Today, I priced a 500' roll of 1/0 copper at Home Depot. $1172....= $2.34/ft. Yikes!! They claimed the price has gone down recently??!

Well, it's just like gas or diesel.
Now we're all happy when it goes "down" to $3.50 a gallon. Shees.

 

[MossRoad]

There are no codes here.
Just the way i like it.

I'll bet your home owner's insurance company will disagree with you come time to replace your home after a fire due to electical problems that were caused by faulty wiring done by you.

Better check on that.

 

[MACDABS]

We do 100amp subfeed runs all the time at work. If you check with your local electrical supply house,not a box store they can supply you with everything you need . A 300ft run with the right size triplex or cable in conduit is not that unusual. If you anticipate a large draw at once you could consider a step up /step down transformer from square D. We have run 100 amp services 1800 ft with such a setup.

Macdabs

 

[machmeter62]

I'll bet your home owner's insurance company will disagree with you come time to replace your home after a fire due to electical problems that were caused by faulty wiring done by you.

Better check on that.

Thanx for your thoughts; the wires will be circuit protected (CB's)on both ends to avoid any "melt downs!"