I am trying to find out the wire sizes needed for a 250' underground feeder from the main panel, to a sub panel in the garage. I would like a 220, 50 or 60 amp service. What type wire would be the least expensive/
Thanks, cliff
At that distance, for the neutral and the two hot conductors, minimum of 6AWG copper for 50A or 4AWG copper for 60A, and for the ground, minimum of 8AWG copper at either 50A or 60A.
Grounding requirements are different in subpanels. You must make sure that:
- the subpanel has two separate bars for ground and neutral
- the two bars are NOT connected to each other (they ARE in the main)
- the neutral bar is insulated from the panel chassis
- the ground bar is NOT insulated from the panel chassis
You may also need a separate ground rod at the garage; check with your local building inspector.
You'll need to make a few phone calls to find that out.
There will be a trade-off: more investment in copper will result in reduced resistive loss in line over time.
J
There are two issues here for wire size:
1) Minimum code required size for the current, regardless of length. That would be 8AWG for copper and 6AWG for Aluminum, for either 50 or 60A. 2) Acceptable voltage drop at maximum current for that length: My old 1990 NEC does not specify, but only recommends a voltage drop percentage of 3% for the feeder or 5% including the branch circuit. This would be based on the actual load, not the subpanel rating. Also, if you will always have a balanced load, you can compute it based on percentage of 240 V, and you may be able to get away with a lesser wire for the neutral, if you may have a way unbalanced load, you would have to compute it based on a percentage of 120 V. Here is a bit of data:AWG ohms/500' V drop @ 50A % of 240V
6 Cu .25 12.5 5.2 4 Cu .154 7.7 3.2 2 Cu .1 5.0 2.1 6 Al .404 20.2 8.4 4 Al .254 12.7 5.3 2 Al .16 8.0 3.3 1 Al .13 6.3 2.6%You may find Aluminum to be cheaper for those wire sizes even though you need a larger size for Al.
If you need to ask these questions, you probably should be talking to you local building inspector because there are many other code issues to do this right.
I ran underground wiring to the garage I built 150 feet from the panel. I wanted only 30 amp service and used # 4 copper. Has been very satisfactory for ten+ years. Bob-tx
Possible typo: #8 Cu won't do it for a 60 Amp feeder.
...
Oops -- thanks for catching that. I was looking at the table on the wrong side of the page. For underground UF, #8 Cu will only do 40 A.
#6 Cu 55 A #4 Cu 70 A
#4 Al 55 A #3 Al 65 A
At 250 feet, I'd set a second meter and a seperate service, assuming there is a line near enough. Or are you fed out at the road, and this is the back forty, and you'd have to pay for another pole? Yes, the upfront costs would be higher, but if you use much juice out there, it'll be more reliable, and would certainly scare the eventual purchaser of the place less.
aem sends...
Not a good idea in some areas depending on the electrical utility. A separate service at an outbuilding may be considered "commercial" even though it's a residential garage. This means you might be paying commercial rates plus a meter-reading/billing fee each month. In my case, this meant about $12 a month whether I used any power or not. Much better to keep it on the residential meter. YMMV
What? You can't put a mother-in-law trailer behind the barn any more?
(Yeah, you're right- but it does vary by area. A rural co-op company would probably understand, but an electric company with a pretty building downtown might not. Probably best to call their customer service line and ask hypothetical questions.)
aem sends...
Are you up on NEC?????
First, your amp ratings do not account for voltage drop at 250'.
Secondly, if you are suggesting that he use UF for a service entrance, read NEC 340.12 (it shall not be used as a service entrance cable)
Are you?????
A feeder to a garage is not a service entrance as defined in the NEC.
Where's this stated in the NEC2005?
In the "definitions" section at the beginning:
Service: The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.
If the garage is being fed from the main panel, then by definition that feed is not a "service".
Chris
Article 100, Definitions
"Service. The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served."
"Feeder. All circuit conductors between the service equipment ... and the final branch circuit overcurrent device."
What the OP has is a feeder, not a service.
Two examples...
#1 HV lines to transformer, trans to house meter, meter to panel, panel to garage.
#2 HV lines to transformer, trans to meter on pedestal, meter to distribution panel on ped, d-panel to house - d-panel to garage.
Using the two examples, please list the feeders and service conductors for each.
Which is the situation the OP has.
So, for clarification, Ex #2 as posted earlier...
#2 HV lines to transformer, trans to meter on pedestal, meter to distribution panel on ped, d-panel to house - d-panel to garage.
Can you run UF from the d-panel to a house/garage?
Not relevant.
It's a question, so yes, it *is* relevant.
So, for clarification, Ex #2 as posted earlier...
#2 HV lines to transformer, trans to meter on pedestal, meter to distribution panel on ped, d-panel to house - d-panel to garage.
Can you run UF from the d-panel to a house/garage?
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