320 AMP Overhead service

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luke_

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Commercial Electrical Maintenance
Hello, i’m doing a 320 amp overhead service for my personal home. I do mostly commercial so I do not have a great handle on residential services. I have done a 320 service before but they’ve all been underground. My situation is the following: I’m coming over head to a customer owed pole with a 320 meter can mounted on the pole. From the 320 meter can I will be going to two 200 amp disconnects. From one of the disconnects I will go straight to the house. The other disconnect will go to a 200 amp ATS and then from the ATS to the house. The ATS I have does not have a service disconnect so I need to have a disconnect in front of it. I will be using 4/0 2/0 aluminum with a ground to go from the 200 amp disconnects to the house. Neither panel will have a load rating greater than 180 Amps. The biggest question I have is the size of the conductors that go up the mast. Looking at the NEC service conductor size I believe 500mcm Aluminum would be adequate. some things may seem odd but with my materials but I’ve had to improvise a little Because of product shortages. I also have a question on the ground I will be running a ground from one disconnect through the two ground rods and back up to the other disconnect. Will number 4 copper be acceptable for this Since I’m going to each disconnect? or do I need to size it to the 500mcm? Which would be 1/0.

thanks for the help.
 
To the ground rod, #6 CU will satisfy the requirements. Although in some cases larger is desirable. 250.66(A)
Building steel and metal water piping is different 250.66
 
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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)
 
Washington has Code provisions beyond the NEC so hopefully one of the members with knowledge of those Codes will reply.
In terms of NEC, the 2 feeders would be questionable under the 17 Code per 225.30.
The conductors in your riser should be sized to carry the calculated load since you have more than 1 service disconnect or 600 AL for a 400 amp residential service.
As noted above, #6 is the largest GEC required for ground rods although #4 is often used due to physical protection requirements.
 
Thank you for the input. #6 for the GEC was the easy part to agree on.

I agree I believe per 225.30 The wire gauge going up the mast would have to supply the calculated load because of the two disconnects. The combined calculated load is calculated at 170 Amps. Panel one will be at 120 AMPs panel two with the generator backup is at 50amps. We are going with the 320 amp panel because we are already splitting the service because of the generator and our calculated load leaves us no room for growth with a 200 service. We will never exceed 350 AMPS. correct me if I’m wrong but I am also under the belief that the feeders from the disconnects to the house are based on load size as well? If I have to match the feeder to the 200 and breaker I would need 250MCM.
 
ptonsparky said:
Have you actually done a load calculation?
Are you supplying the overhead to your pole or is the POCO?
If POCO, that 500 is going to look oversized compared to the #1 triplex they bring to it.
Click to expand...

I agree, this whole process has been quite interesting. According to the POCO who is PSE, The meter mast and feeder lines 18 inches out the weatherhead are the owners responsibility. It needs to be done per the NEC. most of the other services I’ve done have been with other POCO and their handbook has been very useful. PSE he does not have a 320 overhead service in their handbook. I know that they are not going to be running 500 triplex overhead. It will likely be much smaller. When I emailed the inspector on this, they told me to ask the PSE, PSE told me to ask the inspector. Now you understand why I’m here. I could not imagine using 600 for 320 service. I’m trying to future proof and even at that I question 500. My last 320 was an underground with PSE and they ran 350 to meter. I just need the proper information so when the inspector starts asking questions I have answers. Again thanks for your guys help.
 
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Sorry I did not explain my first response very well. I believe I’m compliant with 225.30. The feeder disconnects supplying the building will be grouped in the same location. This being the two 200 amp disconnects at the house. Both disconnects originate from the same distribution equipment, the meter. Is your thought process that this may not be originating from the same distribution equipment because I am splitting it at the meter?

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.
 
the utility wires are not your concern.

if the utility connection point is 18 inches from the weatherhead, then that is where whatever the calculated load comes into play. In any case whatever wire size you use has to be protected by the downstream OCPD. If you want to put in a 400 Amp CB there, than you have to put in an appropriate wire size for that.
 
(Questioning the 2 feeders was based on '17 NEC. Yor quoted text is from the '20. I mentioned it as I do not know which Code is applicable in your area).
The 83% rule (old 310.15(B)(7) allows a 600 kcmil AL (340 amp) conductor on a 400 amp service. Since you are supplying more than 1 main, you can size it to your calculated load. Anything less than a 600 might required documentation.
 
augie47 said:
(Questioning the 2 feeders was based on '17 NEC. Yor quoted text is from the '20. I mentioned it as I do not know which Code is applicable in your area).
The 83% rule (old 310.15(B)(7) allows a 600 kcmil AL (340 amp) conductor on a 400 amp service. Since you are supplying more than 1 main, you can size it to your calculated load. Anything less than a 600 might required documentation.
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Makes sense, no suppliers in my area carry 600 Kcmil Alum. I would need to change over to 400 copper Or go with a 200 amp disconnect and a 150 amp disconnect to be at 350 amps so I can use 500.
 
Your mast conductors can be sized to the load. Honestly 99% of the time I would probably use two sets of 4/0 AL for a 400 amp resi service as I never really do load calcs for these and no one asks. Conductors to the individual panels are sized "normally" to the breaker serving them plus next size up.
 
electrofelon said:
Your mast conductors can be sized to the load. Honestly 99% of the time I would probably use two sets of 4/0 AL for a 400 amp resi service as I never really do load calcs for these and no one asks. Conductors to the individual panels are sized "normally" to the breaker serving them plus next size up.
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Two sets of 4/0 up the mast?
 
I did a 400A overhead service on my last house here in WA. I debated whether to run two parallel sets of wires up the mast or just go with individual large ones. PSE was no help as to what they preferred, so I ran 400/400/350 KCMIL copper up the mast. Looks pretty stupid with 1/0 aluminum coming from the street pole hitting those giant conductors. The street pole also seemed to bend after they put a 50 KVA transformer on the pole (and I had to pay to upsize that, as 25 KVA is the standard service).

Since I ran 400 KCMIL up the mast, I had to run a 1/0 copper to the water pipe for bonding it.

Finally, make sure you look at the WAC modifications to the NEC. You can't use EMT for your mast, must use Rigid (note the WAC rule says masts through roofs, so not sure this applies to a separate pole. But Note 5 implies intermediate masts must also follow the same rules).

WAC 296-46B-230:

app.leg.wa.gov app.leg.wa.gov

Chapter 296-46B WAC:

app.leg.wa.gov app.leg.wa.gov
 
suemarkp said:
I did a 400A overhead service on my last house here in WA. I debated whether to run two parallel sets of wires up the mast or just go with individual large ones. PSE was no help as to what they preferred, so I ran 400/400/350 KCMIL copper up the mast. Looks pretty stupid with 1/0 aluminum coming from the street pole hitting those giant conductors. The street pole also seemed to bend after they put a 50 KVA transformer on the pole (and I had to pay to upsize that, as 25 KVA is the standard service).

Since I ran 400 KCMIL up the mast, I had to run a 1/0 copper to the water pipe for bonding it.

Finally, make sure you look at the WAC modifications to the NEC. You can't use EMT for your mast, must use Rigid (note the WAC rule says masts through roofs, so not sure this applies to a separate pole. But Note 5 implies intermediate masts must also follow the same rules).

WAC 296-46B-230:

app.leg.wa.gov app.leg.wa.gov

Chapter 296-46B WAC:

app.leg.wa.gov app.leg.wa.gov
Click to expand...
Good catch on the EMT I don’t know why I put that probably just because I’m used to using it I intend on using RMC. I like the idea of paralleling.
 
suemarkp said:
I did a 400A overhead service on my last house here in WA. I debated whether to run two parallel sets of wires up the mast or just go with individual large ones. PSE was no help as to what they preferred, so I ran 400/400/350 KCMIL copper up the mast. Looks pretty stupid with 1/0 aluminum coming from the street pole hitting those giant conductors. The street pole also seemed to bend after they put a 50 KVA transformer on the pole (and I had to pay to upsize that, as 25 KVA is the standard service).

Since I ran 400 KCMIL up the mast, I had to run a 1/0 copper to the water pipe for bonding it.

Finally, make sure you look at the WAC modifications to the NEC. You can't use EMT for your mast, must use Rigid (note the WAC rule says masts through roofs, so not sure this applies to a separate pole. But Note 5 implies intermediate masts must also follow the same rules).

WAC 296-46B-230:

app.leg.wa.gov app.leg.wa.gov

Chapter 296-46B WAC:

app.leg.wa.gov app.leg.wa.gov
Click to expand...
I will be using a Concrete-Encased Grounding Electrode (Ufer Ground) at the building, 4 AWG copper
 
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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