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Trying to figure out the service requirements on rewiring my…

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Trying to figure out the...
Trying to figure out the service requirements on rewiring my duplex. I have submitted some other questions, so you will probably see the record.
I have a 400 amp twin meter base. Do you know what size wire would come in from the masthead?. One electrician said two-500MCM and one-350 MCM. He also said it could be two 4/0 aluminum and one 2/0. Next if this were in PVC conduit what would be the size requirement? I looked at a similar installation in the neighborhood and I think the PVC size was 3 inches. If I went with rigid metal conduit this is 2.5 inches, but that is expensive! The electrician said I could opt for two service masts ( the meterbase will accept two) with 2 inch conduit, which is a lot cheaper but I don't know if the aluminum wire could be run in these.The other questions is: From the tables that Portland General Electric has, I can install the waetherhead just below a fascia board that has 14' 4 " clearance. Their manual states that the point of attachment must be 12 feet, the drip loop at least 10 feet 6 inches, and clearance above a driveway 16 ft. I can meet all of these using a single length of conduit, preferably the PVC, or else the 2.5 inch rigid metal conduit. But the previous PGE meter locator said I would have to go through the roof, even though this is adding 3 feet. It's a lot more expensive, requiring an added length of rigid conduit, and roof flashing. Plus the metal conduit puts a lot more weight on the meterbase, even though it would be well attached with adequate backing.My preference is to use PVC conduit, going up to the 14' 4' height at the top of the weather head. And this is exactly what I have seen on a nearby house with the same meterbase (Siemens Unipak). Then I need to know what service wire they will allow. The MCM or KCMIL is a lot more expensive. I am not sure, though, if a 2.5 inch PVC is big enough for the 4/0 aluminum cable, either. Then I had seen some discussion of whether 500 MCM was even big enough for a 400 amp service. So I'm in the dark, basically, and PGE is taking forever to get out here.
Submitted: 8 months ago.Category: Electrical
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Answered in 21 minutes by:
10/3/2017
Electrician: Kevin, Licensed Electrical Contractor replied 8 months ago
Kevin
Kevin, Licensed Electrical Contractor
Category: Electrical
Satisfied Customers: 4,359
Experience: 31 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) A 400 amp service requires either 400 kcm copper or 600 kcm aluminum conductors. The neutral conductor may be reduced by one conductor size, but a load calculation is required. If the overhead utility service conductors will be rated @ 400 amps, then either 400 kcm copper or 600 kcm aluminum will be required if the main service disconnect breaker is 400 amps.

See table shown in the link below:

2) Your local electrical codes will determine of PVC or Rigid metal conduit is required for the mast riser. The local electrical inspector always has the final say so on the mast type material.

3) If reducing the neutral conductor, minimum PVC conduit diameter will be 2 1/2 inch Sch. 80. If using all 3 service conductors as 400 kcm copper, minimum PVC conduit diameter will still be 2 1/2" diameter, Sch. 80.

4) If reducing the neutral conductor, minimum PVC conduit diameter will be 3 inches, Sch. 80. If using all 3 service conductors as 600 kcm aluminum, minimum PVC conduit still be 3 inches diameter, Sch. 80

5) If using Rigid metal conduit and reducing the neutral with copper conductors, minimal RMC diameter will be 2 1/2" diameter rigid metal conduit. If using all 3 service conductor as 400 kcm copper, RMC diameter will still be 3 inches in diameter. If using aluminum conductors, same RMC diameter as using copper.

6) RMC conduit is always recommended over PVC conduit for rigidity and stability purposes. Penetrating the riser mast thru the roof is very common. The local electrical inspector will need to be contacted to confirm what your local electrical codes are. Keep in mind that local electrical codes can always take precedence above the National Electrical Code.

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Electrician: Kevin, Licensed Electrical Contractor replied 8 months ago

1) Correction due to a typo........ 2 1/2" diameter RMC conduit will be required whether using copper or aluminum conductors.

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Electrician: Kevin, Licensed Electrical Contractor replied 8 months ago

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks.................Kevin:)

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Customer reply replied 8 months ago
There are two tenant main breakers, each at 200 amps. So apparently 400 KCmil Cu is allowed. I'm checking prices on this from local suppliers. Looks like the wire could run 650--800 bucks depending upon their clearances requirement.
1. Is XHHW wire typically allowed? This is a lot cheaper. The THHN in those sizes is around $9-10 per foot. The XHHW is more like $2.50 per foot.
2. Is triplex wire used between the POCO wires and the meterbase? Sorry if this is a dumb question, because I assume the wire coming from the masthead would be individual conductors.
3. The other question is---according to the electrician---they also allow 4/0 aluminum, which is really cheap. But it does not have high ampacity according to the table, so I don't know how this would be workable.When I wired my garage and had a service installed I don't remember it being this complicated, but it was just a single panel, not two as in this case. And I did have to go through the roof, and also guy the mast to the roof. It will be a lot simpler if I don't have to go through the roof with this new service, and I do seem to meet all of their clearance requirements. I think the PVC would be just as secure since it also has to have brackets and has to be secured at the top, also, and in those big sizes is a lot less weight on the meterbase. I canscrew any fastener into about three layers of planks that they used on this 130 year old house. Luckily, that is all there and do not have to put in backing.
Electrician: Kevin, Licensed Electrical Contractor replied 8 months ago

Thanks for the replies.

1) Triplex cable is only used as the overhead conductors. Once the overhead conductors splice onto the service entrance conductors going into the weather head/riser mast, the 3 service entrance wires are 3 separate wires with each being insulated. Yes, 400 kcm Cu is allowed for the riser conductors.

2) 4/0 Aluminum is used and is code compliant where it will extend from the 400 amp meter socket going to each 200 amp panel. The 400 amp meter socket will contain 2 sets of lugs where the 4/0 AL conductors will terminate and feed to the 200 amp panels. You just need to confirm that the meter socket lugs are rated for aluminum. Most likely, the meter lugs are dual rated for Cu and Al.

4/0 aluminum is rated for 200 amps. Therefore can only be used as the feeder conductors extending from the meter socket to each 200 amp panel.

3) Type THHN is not rated for wet conditions. Type THWN is wet condition rated. The "W" stands for wet rated. However, many THHN conductors are now dual rated as type THHN and THWN.

4) XHHW is also a common conductor type. However, local electrical codes will take precedence as to the insulation type required. You will need to run this past the local electrical code official.

5) If using RMC, the weight on the meter socket will not be an issue since the riser conduit will need to be securely fastened to exterior wall.

6) Guying of a PVC riser mast is somewhat common, depending upon the height requirements. RMC riser mast guying is seldom required since it is stronger than PVC conduit. Once again, local codes will always take precedence as to the material type used for a riser. RMC conduit will always pass code when used as a riser mast. If desiring PVC for the riser mast, that is determined by local electrical codes and height requirements.

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Customer reply replied 8 months ago
Got to do something important. I will rate you when I get back.
Electrician: Kevin, Licensed Electrical Contractor replied 8 months ago

No problem, take your time.

Thanks...........Kevin:)

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Customer reply replied 8 months ago
Kevin, I'm contacting city of Portland to see if they have requirements that are any different. Hopefully they will get back today. Our city is busting at the seams with growth, so the inspectors are very busy. I will credit you when I get it wrapped up. Thanks!
Electrician: Kevin, Licensed Electrical Contractor replied 8 months ago

Very good.

Thanks............Kevin

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