How are you guys figuring voltage drop for underground services? Are you using demand load or 200A or what? As you need amps to properly calculate VD and the max amps are variable and undertermiable in a dwelling.
I am prepairing a proposal for a 600 Ft UG service with copper conductors.
Bob, You're numbers are right on track and you are correct about the NEC,but my point was (in my area at least) that the POCO has to approve of the size cable and length of run OR they won't hook it up.They will do a site survey and tell you what pole they want you to come from and which side a the house they want you to locate the meter socket on.(At least in my neck of the woods)
Re: UG service VD#90949 12/18/0405:56 PM12/18/0405:56 PM
In this particular area it is my responsibility and if it dont work its my problem. A couple towns and a county over the utility accually supplies and installs and maintains the conductors. 310.15 states flat out a 2/0 is ok but I might go 4/0 just to cover my ass. I dont ever recall hearing about anyone having a VD prob on an UG service?
Re: UG service VD#90951 12/19/0412:34 AM12/19/0412:34 AM
Well, no, 310.15 doesn't just flat out state that 2/0 is OK. 310.15 states that 2/0 is recognized as safe from the point of view of being unlikely to overheat to the point creating a fire hazard. It says nothing about whether 2/0 is adequate in regards to having an acceptably low voltage drop over a distance of 600 feet.
Re: UG service VD#90952 12/19/0407:30 AM12/19/0407:30 AM
Something else to consider for Voltage Drop calculations:
How 'steady' will the voltage drop be. If the lights run a little bit dimmer when every thing in the house is on, than that probably is acceptable.
But if every light in the house gets substantially dimmer for a moment whenever the well pump cycles or the heat pump turns on, than that might not be acceptable to the homeowner. Even worse if the voltage dip is enough to cause electronics to reset!
I would strongly suggest finding the load with the largest inrush or startup current, and checking the voltage drop when that load starts up. If you run the bare minimum 2/0 wire for a 200A service, you might easily get >10% momentary voltage drop if there is a large motor load on the property.
Another thing to consider: given the length of the underground run, would the POCO place a padmount transformer near the home, with most of the underground run at distribution voltage?
Re: UG service VD#90953 12/19/0410:36 AM12/19/0410:36 AM
Yes the utility would do the trans. thing if the customer wants to pay for it.
I had another thought on the subject. What about te utility overhead line supplying the service. They just run a # 4 solid aluminum that could go for a thousand feet to the transformer with seven other houses attached to it. I know its in free air, but the rules of VD should still apply. The reason I say that is the customer may op to let the utility set a couple poles to reduce his cost, Whats the diference if I go the extra 400 feet with a 2/0 copper or let the utility run a #4 aluminum?
Re: UG service VD#90954 12/19/0410:53 AM12/19/0410:53 AM