320 AMP Overhead service

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Having trouble locating 3” RMC. I did a fill calculation and I can parallel 4/0 in a 2 1/2. I got 36 percent fill. Did I calculate this right?
4-4/0 and 2-2/0= 3.99
 
luke_ said:
Having trouble locating 3” RMC. I did a fill calculation and I can parallel 4/0 in a 2 1/2. I got 36 percent fill. Did I calculate this right?
4-4/0 and 2-2/0= 3.99
Click to expand...
FYI you can use EMT outside for service conductors, just not inside, unless you are in Seattle where it is neither. From the WAC:

043 Wiring methods for 1000 volts, nominal or less.
(7) The installation of service conductors not exceeding 1000 volts, nominal, within a building or structure is limited to the following methods: Galvanized or aluminum rigid metal conduit; galvanized intermediate metal conduit; wireways; busways; auxiliary gutters; minimum schedule 40 rigid polyvinyl chloride conduit; cablebus; or mineral-insulated, metal-sheathed cable (type MI).
(8) Electrical metallic tubing must not be installed as the wiring method for service entrance conductors inside a building. Existing electrical metallic tubing, installed prior to October 1984, which is properly grounded and used for service entrance conductors may be permitted to remain if the conduit is installed in a nonaccessible location and is the proper size for the installed conductors.
 
suemarkp said:
I don't believe you need to have 250 Al in the feeders to the house. As long as the calculated load is 180A or less, you can use the round up rule to have them land on (or source from) a 200A breaker. It is a long run, so perhaps you are accounting for voltage drop. But even if your calculated load is 180A, in reality that would rarely happen.
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Yeah generally, I wouldnt go from 4/0 to 250 until I got near 200 feet.
 
Around here a rural 320 amp services gets a 25 kVA transformer, unless you submit a load sheet to the POCO and ask for a bigger transformer. And in some areas your forced to do anything over 200A underground.
 
I would like to do schedule 40 PVC. I have a bunch of 3” and I don’t need a crane to lift it up. I agree the only thing I see in the WAC about RMC is when the mast is coming through the roof. This will be the one and only 320 service I do overhead what a PITA. I wish I could go underground but unfortunately, I only have an easement to go overhead.
 
luke_ said:
I wish I could go underground but unfortunately, I only have an easement to go overhead.
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Wont hurt to ask, the reason given here is too much wildfire danger. If your willing to go thru the expense of doing it I bet your neighbor would acquiesce.
 
luke_ said:
I would like to do schedule 40 PVC. I have a bunch of 3” and I don’t need a crane to lift it up. I agree the only thing I see in the WAC about RMC is when the mast is coming through the roof. This will be the one and only 320 service I do overhead what a PITA. I wish I could go underground but unfortunately, I only have an easement to go overhead.
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If the PVC is not what's supporting the service conductors, meaning there is a pole, you're okay with it.
 
Remember that you can use an additional demand factor for single-phase residential services 100 amp through 400 amp. 2/0 CU. or 4/0 AL. would be sufficient sizes for your service conductors per T.310.12 (2020 NEC). If still under the 2017 NEC it states 83% of the service rating which still works out the same. They finally changed it back the way it used to be. As far as 3/0 AL. for your grounded conductor, I don't know the total amount of line to neutral loads but it could probably be sized smaller, a load calc. would be necessary. Your original post stated using 2 grounds rods. If that's the case, a #6 cu. GEC would be fine. You stated later about using a UFER ground, so a #4 cu. GEC would be required. You can use an EMT riser since your point of attachment will be from the pole and not the riser. All of these are contingent upon your local codes which may or may not supersede these.
 
Rick 0920 said:
Your service rating is not the 320 rating of the meter socket enclosure. Your service rating is the combined sizes of your main breakers. I see this as you have a 400 amp service. ( 2- 200 amp disconnects) 500 mcm AL. @ 75°C has an ampacity of 350 amps. T. 240.6 (A) shows that 350 amps is a standard breaker size. You would have to use 600 mcm AL. for 400 amps. I would use 500 mcm cu. which has an ampacity of 380 amps @ 75°C. Art. 240.4 (B) would allow the next higher overcurrent device. I agree with Buck on the GEC. If 2 rods are used for the electrodes and the GEC doesn't extend to other electrodes that require a larger conductor, a #6 is sufficient. Art. 250.66 (A)
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Lets dig a little deeper into code though. Since he has multiple service disconnecting means 230.90(A) exception 3 specifically allows one to supply the common supply conductors to 2-6 service disconnecting means with conductors sized to the calculated load and not to the sum of the overcurrent devices. One could in theory have less than 200 amp conductor here as long as the load calculation is less than ampacity of the conductor selected. Or you if reading between the lines one might think you can't go any less than a 200 amp conductor here. But if your load calculation were say 275 amps then NEC will allow a conductor with at least 275 ampacity here.
 
luke_ said:
Having trouble locating 3” RMC. I did a fill calculation and I can parallel 4/0 in a 2 1/2. I got 36 percent fill. Did I calculate this right?
4-4/0 and 2-2/0= 3.99
Click to expand...
Keep in mind parallel conductors in same conduit puts you over 3 current carrying conductors and you will be required to apply ampacity adjustments to those conductors.
 
Rick 0920 said:
Remember that you can use an additional demand factor for single-phase residential services 100 amp through 400 amp. 2/0 CU. or 4/0 AL. would be sufficient sizes for your service conductors per T.310.12 (2020 NEC). If still under the 2017 NEC it states 83% of the service rating which still works out the same. They finally changed it back the way it used to be. As far as 3/0 AL. for your grounded conductor, I don't know the total amount of line to neutral loads but it could probably be sized smaller, a load calc. would be necessary. Your original post stated using 2 grounds rods. If that's the case, a #6 cu. GEC would be fine. You stated later about using a UFER ground, so a #4 cu. GEC would be required. You can use an EMT riser since your point of attachment will be from the pole and not the riser. All of these are contingent upon your local codes which may or may not supersede these.
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OP has two feeders supplying the dwelling though. That is not generally allowed but since he has a transfer switch ahead of one of them it should be permitted by 225.30(A)(4).

But each feeder is no longer carrying the entire dwelling load so those reduced conductor provisions can not be utilized. However as long as the load on each feeder is under 180 then 4/0 aluminum is still acceptable on a 200 amp OCPD, but copper feeders would need to be 3/0.
 
kwired said:
OP has two feeders supplying the dwelling though. That is not generally allowed but since he has a transfer switch ahead of one of them it should be permitted by 225.30(A)(4).

But each feeder is no longer carrying the entire dwelling load so those reduced conductor provisions can not be utilized. However as long as the load on each feeder is under 180 then 4/0 aluminum is still acceptable on a 200 amp OCPD, but copper feeders would need to be 3/0.
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we are regulated by 2020 NEC here but yes 225.30A would also permit the use of two feeders.

N 225.30(B) Common Supply Equipment. Where feeder conductors originate in the same panelboard, switchboard, or other distribution equipment, and each feeder terminates in a single disconnecting means, not more than six feeders shall be permitted. Where more than one feeder is installed in accordance with this section, all feeder disconnects supplying the building or structure shall be grouped in the same location, and the requirements of 225.33 shall not apply. Each disconnect shall be marked to indicate the load served.
 
luke_ said:
we are regulated by 2020 NEC here but yes 225.30A would also permit the use of two feeders.

N 225.30(B) Common Supply Equipment. Where feeder conductors originate in the same panelboard, switchboard, or other distribution equipment, and each feeder terminates in a single disconnecting means, not more than six feeders shall be permitted. Where more than one feeder is installed in accordance with this section, all feeder disconnects supplying the building or structure shall be grouped in the same location, and the requirements of 225.33 shall not apply. Each disconnect shall be marked to indicate the load served.
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Wasn't aware of that change. So far about the only one I actually like in 2020 NEC.(y) We aren't on 2020 yet, might be later this year though.
 
Well I figured I’d give you an update now that the project is complete and passed inspection. Ended up going with 600 MCM with a 500mcm neutral at the mast. The neutral is larger than needed but it was what I access to at the time . I had a good discussion with PSE about paralleling 4/0. It was recommended that I do not go this route. They said “Yes you can go this route but they’ve had issues with the taps at the weather head causing issues with parallel lines”. Long story short, I only wanted to deal with this one time so that was out. The ATS that I got ended up having a 200 amp disconnect so that saved me some equipment and time. Went with a number 6 ground to two rods protected by half inch conduit. Used 4/0-2/0 to feed the two 200 amp disconnects. FYI The inspector did say that he believes I could’ve went with 500 MCM with a 350mcm neutral. I did not drive too far into this conversation with him so I’m not sure how that would have turned out. I think looking at the NEC that would have not met the requirements But I’m not putting any more research into it.

On a different note I had a discussion with the inspector on exterior disconnects. We looked up the code together and Washington’s WAC. The disconnects at the pole will count as my exterior disconnects as long as the panels inside the house can be accessed within 15 feet of the entrance. I believe this is allowed because of the Washington code. The inspector and me talked about it for 15 minutes then he called two other inspectors and this is what we came up with. It was an interesting conversation so I thought I’d pass it on.

All that’s left is to run the wire from the pole to the house. Going with 4/0-2/0 with a 4awg AL ground For the two runs to service the house. I search the NEC and did not find anything about separation requirements on the two feeds to the house. Anyone have any input here? I plan on putting them in the same 36” deep ditch and separating them by about 12 inches, surrounded in sand.

766EA34D-0A41-481A-9CBE-6937FEB6E182.jpeg
 
luke_ said:
Well I figured I’d give you an update now that the project is complete and passed inspection. Ended up going with 600 MCM with a 500mcm neutral at the mast. The neutral is larger than needed but it was what I access to at the time . I had a good discussion with PSE about paralleling 4/0. It was recommended that I do not go this route. They said “Yes you can go this route but they’ve had issues with the taps at the weather head causing issues with parallel lines”. Long story short, I only wanted to deal with this one time so that was out. The ATS that I got ended up having a 200 amp disconnect so that saved me some equipment and time. Went with a number 6 ground to two rods protected by half inch conduit. Used 4/0-2/0 to feed the two 200 amp disconnects. FYI The inspector did say that he believes I could’ve went with 500 MCM with a 350mcm neutral. I did not drive too far into this conversation with him so I’m not sure how that would have turned out. I think looking at the NEC that would have not met the requirements But I’m not putting any more research into it.

On a different note I had a discussion with the inspector on exterior disconnects. We looked up the code together and Washington’s WAC. The disconnects at the pole will count as my exterior disconnects as long as the panels inside the house can be accessed within 15 feet of the entrance. I believe this is allowed because of the Washington code. The inspector and me talked about it for 15 minutes then he called two other inspectors and this is what we came up with. It was an interesting conversation so I thought I’d pass it on.

All that’s left is to run the wire from the pole to the house. Going with 4/0-2/0 with a 4awg AL ground For the two runs to service the house. I search the NEC and did not find anything about separation requirements on the two feeds to the house. Anyone have any input here? I plan on putting them in the same 36” deep ditch and separating them by about 12 inches, surrounded in sand.

View attachment 2560140
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sounds like they need to maybe re-evaluate how they terminate and/or weather proof those connections
 
electrofelon said:
Yeah that's the most ridiculous thing I've heard in a few months. In the commercial world having multiple sets at the weatherhead is probably the rule not the exception.
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Even if you have a service lateral they sometimes run up a pole and are terminated with out in the open connections, basically about the same thing.
 
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