Subpanel phasedown from 200 amp to 100 amp

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  #1  
Old 04-02-06, 02:10 PM
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Question Subpanel phasedown from 200 amp to 100 amp

Here is my question. service from my transformer to the meter box then to a subpanel is 200 amp with 442 wireing. Now I need to service an eventual total of three units. two small log homes and one main house.. Can I phase down at the subpanel to 100 amp for each ? What size wire?? 221?? Each unit would have its own breaker panel. Can this be done? THE LENGTH of the run from the subpanel breaker box would be 200 ft to one log home,contiueing another 130ft to the other log home.. THE RUN TO THE MAIN HOUSE WOULD BE about 75 ft. All info would be appreciated..
 
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Old 04-02-06, 02:59 PM
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> service from my transformer to the meter box then to a
> subpanel is 200 amp with 4/0-4/0-2/0 wiring.
> I need to service an eventual total of three units.
> two small log homes and one main house.
> Can I phase down at the subpanel to 100 amp for each?

There is no "phase down". You simply use a smaller circuit breaker.


> What size wire?? 221??

There's no such thing as 221. Gauge numbers are exponentially related, not linear.
You don't use multiplication of division to determine the size.


> Each unit would have its own breaker panel. Can this be done?

If the poco tariff permits it for your type of service (commercial, not residential).


> THE LENGTH of the run from the subpanel
> breaker box would be 200 ft to one log home,
> continuing another 130ft to the other log home..

Wow. You'll need some heavy cable if you really want 100A actual.

If you have A/C, electric hot water, electric heat, that kind of stuff, you'll want the 200A cable (4/0-4/0-2/0-2).

I suggest 200A XLPE mobile home cable for all runs except the last 130' can be 100A (2-2-4-6), and only a 60A main breaker in each cabin (100A breakers where they subdivide and in the house).

Trenches should be at least 28" deep. Conduit is advisable.
 
  #3  
Old 04-02-06, 05:43 PM
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Thankyou for your timly responce,Very informative, the cabins are small 400+ sq ft and 800 sq ft so the 60 or 70 amp breaker for each seems good since each will have only three in wall electric self contained heaters No A/C needed here in Washington and a small elec.water heater & stove in each cabin. I May as well do an individual run from the subpanel to each and a run for the main house(100) amp..trying to avoid any more 4-0,4-0,2-0 wire..just using the 2-2-4..How does this sound? Code here is 24 in deep in conduit
 
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Old 04-02-06, 06:38 PM
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> I might as well do an individual run from the subpanel to each
> and a run for the main house(100) amp.

I'm not clear on the topology here.
I was under the impression that running to one cabin and then to the next was going to save you 200' of cable.

> trying to avoid any more 4-0,4-0,2-0 wire.

On a run of 330', it would be a good idea of you need a lot of power.


> just using the 2-2-4..How does this sound?

Based on the power requirements you anticipate, 50A at each cabin is fine.
Put a 100A breaker at the head of the line.
Then run the 2-2-4-6 to the first cabin, then to the second cabin (assuming that this saves a lot of distance).


> Code here is 24" deep in conduit
Sounds good. You need to provide a steel conduit sleeve or bury it a lot deeper where you cross a driveway or road.
A muddy road makes poor cover.
 
  #5  
Old 04-02-06, 08:08 PM
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We are getting close ! OK Picture this on a sketch pad. draw a circle with the 200 A subpanel in the middle which is feed by 200A meter at the 6 O' clock (OC)from 442---- at the 10 OC is cabin#1 800 sq approx 150 ft and at the 1 OC cabin #2 400 sq. approx 150 ft. also...At the 3-4 OC is the main house approx 75 ft desirering the 100 a service main breaker. Let say 50-70 A OK for cabins,I buy that for sure... " 100 A Breaker at head of line" not sure what you mean? So Can I use 2246 to both cabins in series or should I parrellel from the subpanel to each ? and 2246 to the house also? No roads just drive way conduit is sch 40 PVC 2 " for 442 and I guess 1,5" for 224 ...Grey elect conduit type.Things getting a little clearer ?? I do appreciate the education on the heavy duty stuff this is my first time but done at few inside homes with breaker, recp, outlets, etc. My page is still open so keep me on my toes.. Kal
 
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Old 04-03-06, 06:28 PM
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star topology

> At the 3-4 OC is the main house approx 75 ft desiring the 100A service main breaker.

Basically, you have a star topology.
You could run to the house then daisy-chain to cabin #2. But you would have to use heavier cable to assure the 150A.

> Let say 50-70 A OK for cabins, I buy that for sure...
> 100 A Breaker at head of line" not sure what you mean?

I was trying to got two cabins on one 100A line because I thought they were successively farther from the service.
But you won't be sharing any lines.



> So can I use 2-2-4-6 to both cabins in series or should I parallel from the subpanel to each?

The word is daisy-chain.


> No roads just driveway

Plastic conduit can break. In fact, in can become brittle under some conditions.


> conduit is sch 40 PVC 2" for 4/0-4/0-2/0, and
> I guess 1.5" for 2-2-4-6 ...Grey elect conduit type.

2" makes pulling easy. You might be surprised how hard it is to pull this cable through 1.5"
If you can afford it, use 2" for the 150' run.

At the service disconnect install three 100A DP breakers.

You will be using 2-2-4-6 or larger everywhere.

At each cabin use a small main lugs subpanel (like an 8/16) with a 50 or 60A breaker as the main.
(It has to be locked in as it will backfeed the panel.)

The reason for the main breaker in the subpanel is that if there is an collective overload, this improves the odds that you won't have to walk 150' to reset the breaker.
In fact, you might want to keep the panel at the meter locked.

At the house put in a full 100A main breaker panel.
 
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Old 04-03-06, 09:55 PM
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Thanks Bolide, Since house is a few years down the road WILL DAISY CHAIN cabin #1 & 2. with 2-2-4 from subpanel and a direct 100 A to stub out at house location. Will ponder your other advisors also..Keeo up the good advise. Kalr
 
  #8  
Old 05-02-06, 12:38 PM
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Dont know if you can still do this but they used to have a thing called a "farm or rural installation". The meter is mounted at a central location with a special meter that uses current transformers mounted at the top of the pole and the meter is on the power pole at eye level then each location is treated as if it were fed directly from the lines. Ive seen the with buried cables too. I would check with the PC to see if you can do something like this.
 
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