Service Lateral Question

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Rivkid

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Amesbury, MA
I've been reviewing all of the posts/threads and haven't found an answer to my particular question.

The situation is this: I'm installing a service lateral for a single family dwelling which currently has an overhead, upgrading from 100A to 200A. On this property the owner has an additional outbuilding (apartment/office all of 1500 sq. feet) which also has a separate overhead to a 100A meter socket and 60A main panel for that building. Keep in mind this property is a deeded single family dwelling.

He wants to eliminate the overheads altogether, install a dual meter socket e/w disconnects at the main house and pipe an underground feeder from the meter/disc. to a new 100A panel at the outbuilding. The 200A feeder for the main house will enter as usual.

Do the factors listed in table 310.15 b.6 apply here? Will a 4/0 Al SE cable suffice for the lateral or am I looking at a 350 Al?

...Hopefully this makes sense.
 
What will be the connected load for the two new installations? Right now you have a separate 100 and 60 amp services. When you're done you will have a new 200 amp lateral to feed both buildings. Is this adequate? You mentioned a new 200 amp service for the house. Are there any new additional loads that require the full 200 amps at the house?
 
090923-0632 EST

If I understand your question correctly, then the only common impedance between the two services is the transformer impedance.

This means that any load change in one building only affects the other building voltage by the impedance of the transformer.

When you run a single line from the transformer to building A and then continue to building B there is the added impedance of the line from the transformer to building A that affects both buildings from load changes in either building.

Suppose the transformer impedance is such that a 200 A load produces a 16 V drop at the transformer, then the transformer impedance is 0.08 ohms. Now add another 0.05 impedance between the transformer and building A. Assuming both impedances can be considered to be resistive, then the impedance becomes 0.13 ohms.

Start a 1.5 HP motor that draws 80 A on start up and a voltage change of 10 V is seen at both buildings. With the present up this motor in building B would only change the voltage at building A by 80*0.08 = 6.4 V.

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Let me get this straight, and try to help you.:)

You have a single utility service feeding a dual meter base.
The meter base contains (2) main disconnects....one (200A) for the house, and one (100A) for the out-building.
The main bonding is located inside this meter base(s)/disconnect.

From there, you want to run a underground feeder to the house, and a underground feeder to the out-building.
Both originating at the meter base (Main), and independant of each other.

Is this correct?

If so, are you asking if you can apply table 310.15(B)(6) to the feeders for each individual building?

If so, then yes, in my opinion, you can use table 310.15(B)(6) to size each individual feeder.

steve
 
I agree with hillbilly, but add, if you (and not POCO) are installing the lateral to the meter, IMHO then 310.15(B)(6) would NOT apply to that lateral as 310.15(B)(6) only apples to individual units.
 
I'm just back from vacation. Thank you all for your posts, they've been helpful. I should have clarified earlier, the out building is, in fact, a dwelling unit, though is in all parts detached from the dwelling where the new service will enter into the property.

Since my initial post the owner has instructed me to upgrade the panel to the detached "dwelling" to 200A. This is overkill, since the unit (a small 4 room house) will never see this demand. Still he insists...and pays. The main dwelling is, in part, an historical early 1700's home less than 1000 sq'. The detached dwelling is not so historical, but is equally as small (<600 sq').

So to recap: Hillbilly, you hit it--here's the amendment to your post:

-Single utility service feeding a dual 200A meter base.
-The meter base contains (2) main disconnects....one (200A) for the Main house, and one (200A) for the detached "dwelling".
-The main bonding IS located inside this meter base(s)/disconnect.

There are no A/C loads or other significant motor loads (other than standard dryer, exhaust fans, etc.)

The trench inspection (for the detached unit) is in the morning--I'll let you know what the WI says. Still, I'd appreciate your input.

...by the way, POCO, IMHO ?
 
Thanks, LarryFine; I might have known!

The inspection went w/o a hitch:

2 @ 2" PVC raceways, e/w 2/0 CU feeders & 4/0 Al lateral from the meter.

Thanks all for your input. I'm liking this forum!
 
Rivkid,

There could be a reason that these buildings have seperate drops, POCO is not usually

keen on more than one meter on a building. Has the POCO given you the o.k. on this ?
 
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