# 400-amp service



## electricista

BIGRED said:


> I am replacing a residential 200-amp service to a 400-amp service with a 320-amp meter socket. What size conductors should I use co and or al? Can I undersize the neutral conductor like service cable? What size ground to cold water?


Can we assume you have 2- 200 amp disconnects or panels next to the meter? If that is the case 3/0 copper is required with a #2 to the water pipe. Of course there could be variation of that. Let us know.


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## BIGRED

There is one new existing 200-amp panel inside that I am going to re-feed. I am going to add a 200-amp, 2 circuit panel next to it for a sub panel in another location in the basement.


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## electricista

Since T. 310.15(B)(6) does not apply here you must use T. 310.16 for your conductors. As I said before 3/0 copper if you are using conduit with 75 or 90 C wire. If you are using SE cable you will be limited to the 60C col. in which case it would be 4/0 copper if you loads don't exceed 195 amps in either panel. 
The GEC would be #2 in this case.


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## BIGRED

I am going to run 2 200-amp cables from the meter to inside. I wanted to know the size conductors from the taps to the meter socket.


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## electricista

BIGRED said:


> I am going to run 2 200-amp cables from the meter to inside. I wanted to know the size conductors from the taps to the meter socket.



I got you now-- you are talking about the riser wires. Correct?

I believe the riser only needs to be as large as the calculated load but I would use T. 310.15 and use 400 KCM copper or 600 MCM alum. 

You could parallel the riser with 4/0 copper or 300KCM alum.-- (assumed one riser with derating and 90 C wire.

Hope this helps-- someone correct me if I am off base here.


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## Speedy Petey

electricista said:


> Since T. 310.15(B)(6) does not apply here you must use T. 310.16 for your conductors.


How do you figure? This is a residential service.
Do you know something we don't?


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## Speedy Petey

electricista said:


> I believe the riser only needs to be as large as the calculated load but I would use T. 310.15 and use 400 KCM copper or 600 MCM alum.
> 
> You could parallel the riser with 4/0 copper or 300KCM alum.-- (assumed one riser with derating and 90 C wire.


Not just the riser. The whole service entrance.


For 320/400 you can use parallel 4/0AL (2/0CU) or 500AL (350CU).


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## electricista

Speedy Petey said:


> Not just the riser. The whole service entrance.
> 
> 
> For 320/400 you can use parallel 4/0AL (2/0CU) or 500AL (350CU).


How are you applying 2/0 copper in this scenario? 2/0 copper is good for a 200 amp service but t. 310.15(B)(6) cannot be used for two 200 amp panels. The se conductors must carry the entire load of the service for T. 310.15(B)(6) to be used.


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## Speedy Petey

electricista said:


> How are you applying 2/0 copper in this scenario? 2/0 copper is good for a 200 amp service but t. 310.15(B)(6) cannot be used for two 200 amp panels. The se conductors must carry the entire load of the service for T. 310.15(B)(6) to be used.


I completely don't understand this logic. 

You are saying 2/0cu is good for one 200A service, but it is not good for two 200A panels in parallel??? I am very curious as to how you come to this interpretation. 

A 320/400A service, using 500mcm AL (or 350mcm CU) on the line side of the meter, and TWO sets of 4/0, 4/0, 2/0 AL (or the CU equiv) on the load side run to two 200A panels, is a VERY typical installation.

What am I missing here?


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## electricista

Speedy Petey said:


> I completely don't understand this logic.
> 
> You are saying 2/0cu is good for one 200A service, but it is not good for two 200A panels in parallel??? I am very curious as to how you come to this interpretation.
> 
> A 320/400A service, using 500mcm AL (or 350mcm CU) on the line side of the meter, and TWO sets of 4/0, 4/0, 2/0 AL (or the CU equiv) on the load side run to two 200A panels, is a VERY typical installation.
> 
> What am I missing here?


It use to be very typical here also. Where in T. 310.15(B)(6) des it allow you to use 2 sets of 2/0 for a 400 amp service. The table shows 400 amps 400KCM. Nowhere does the table allow for your install because this table is base on the diversity of the load for residential units. When you split the loads then the diversity is skewed. 

There is a reason why the calculation for a service is different for a residence. I understand why you don't get this because it is a bit odd but, for one, I did not come with with it. It is clear to me and many others that this would be non compliant.

Other then *assuming* that because 2/0 is good for 200 amps then two 200 amp panels must be good for 400 amps, can you support your reason for 2- 200 amps being compliant. 



NEC 2008 Art. 310.15(B)(6) said:


> *120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders.* For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in *Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unit *and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.


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## Speedy Petey

Your argument that only the lateral or riser is allowed to use this table holds no water. Clearly as shown below the "main power feeder" is included, which is what feeds the service panel. 

*NEC 2008 Art. 310.15(B)(6)* _ *120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders.* For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unitand are installed in raceway or cable with or without an equipment grounding conductor. *For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit.* The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.


_


> Other then *assuming* that because 2/0 is good for 200 amps then two 200 amp panels must be good for 400 amps, can you support your reason for 2- 200 amps being compliant.


I NEVER said I though it was good for "400 amps". I said it was good for two separate 200A amp panels in parallel.
To answer your question, no I can't. I also can't find any specific wording disallowing it either.




Now I see in 2008 there is a supposed change supporting your claim, but I do not see where it is written. All I can see is the handbook commentary. 
I am new to the 2008 NEC changes, and do not even use the NEC for residential.
Here is the handbook commentary, but can you point to the exact text they are referring to?

_Section 310.15(B)(6) permits the main feeder to a dwelling unit to be sized according to the conductor sizes in Table 310.15(B)(6). For the 2008 Code, the panel clarified that this permission to use this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load.
Provided a single set of 3-wire, single-phase, service-entrance conductors in raceway or cable supplies a one-family, two-family, or multifamily dwelling, the reduced conductor size permitted by 310.15(B)(6) is applicable to the service-entrance conductors, service-lateral conductors, or feeder conductors that supply the main power feeder to a dwelling unit. The feeder conductors to a dwelling unit are not required to be larger than its service-entrance conductors.
Exhibits 310.8 and 310.9 illustrate the application of 310.15(B)(6). In Exhibit 310.8, the reduced conductor size permitted is applicable only to the service-entrance conductors run to each apartment from the meters. In Exhibit 310.9, the reduced conductor size permitted is also applicable to the feeder conductors run to each apartment from the service disconnecting means, because these feeders carry the entire load to each apartment._


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## electricista

Speedy Petey said:


> Your argument that only the lateral or riser is allowed to use this table holds no water. Clearly as shown below the "main power feeder" is included, which is what feeds the service panel.



I am sorry that you thought I said this but I did not. I said the riser was allowed to be sized to the calculated load of the service but I have heard that and would need to double check that. 

You are correct that the main power feeder is included and that's is why I said 2/0 cannot be used in this situation.

Yes the change in the 2008 is really a clarification of what was meant in the past, IMO. 



> I NEVER said I though it was good for "400 amps". I said it was good for two separate 200A amp panels in parallel.
> To answer your question, no I can't. I also can't find any specific wording disallowing it either.


The op is installing a 400 amp service using 2- 200 amp panels. T. 310.15(B)(6) is not allowed-- that is a 400 amp service. By the way I don't believe 2- 200 amp panels are considered a parallel install. To be parallel they must begin and terminate together.

In either case I must disagree that 2/0 is allowed for the 200 amp panels when used to have a 400 amp service. Around here we consider 2- 200 amp panels a 400 amp service.


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## Speedy Petey

I guess it is a locational difference. 

I agree that two panels is not technically a parallel run. I use that term more as a descriptive term. The two panels are basically in parallel. They start and end in the same locations. 

Also, this is not considered a true "400A" service here. We can use the calculated load which is why 350cu or 500al is accepted as they are rated for 350A in 310.15(B)(6). 
Taking this into consideration, each half of the service (each 200A panel) could then be considered 160A continuous, so then even 310.16 agrees that 2/0cu is fine being that it rated for 175A.


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## NY Inspector

*400 amp parallel service*

I see this a lot. A 400 amp meter pan with 2, 4/0 service cables feeding 2 200 amp panels. This does not constitute a 400 amp service in parallel. Parallel conductors must be terminated _in the same manner at both ends!_
you would have to bring both service cables into a trough, bug them and then feed each 200 amp panel from the NOW paralled service conductors. 
So, If an inspector was having a bad day he could knock this down as a violation of the parallel conductor rule. Andrew


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## NJWVUGrad

*Black/Yellow/Blue Phasing*

Came across a 277/480V service today in Northern Central NJ, PSEG territory that was phase taped Black/Yellow/Blue for 277/480V.

New combination for me, should I just assume incompetence?


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## Dennis Alwon

NY Inspector said:


> I see this a lot. A 400 amp meter pan with 2, 4/0 service cables feeding 2 200 amp panels. This does not constitute a 400 amp service in parallel. Parallel conductors must be terminated _in the same manner at both ends!_
> you would have to bring both service cables into a trough, bug them and then feed each 200 amp panel from the NOW paralled service conductors.
> So, If an inspector was having a bad day he could knock this down as a violation of the parallel conductor rule. Andrew


I agree with the parallel definition however 4/0 conductors are allowed to feed 2- 200 amp panels. The 320 amp meters have double lugs so there is no need for a trough.


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## Clintmiljavac

Here in Missouri we build a "400" amp service as the load side of meter base is 2/0 copper to each 200 amp panel


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## frenchelectrican

Speedy Petey said:


> I guess it is a locational difference.
> 
> I agree that two panels is not technically a parallel run. I use that term more as a descriptive term. The two panels are basically in parallel. They start and end in the same locations.
> 
> Also, this is not considered a true "400A" service here. We can use the calculated load which is why 350cu or 500al is accepted as they are rated for 350A in 310.15(B)(6).
> Taking this into consideration, each half of the service (each 200A panel) could then be considered 160A continuous, so then even 310.16 agrees that 2/0cu is fine being that it rated for 175A.


I can see it pretty clear when you use the 2/0 CU THHN's that I have no issue for long time when we do the twinner 200's panels for 320 service but once we hit a true 400 amp the bet is out of the window due our state of Wisconsin codes did change a little ( they did tweak it more to commercal side :blink: )

I know one city in Wisconsin really did nail my rear end due their city code change and they fail to inform few EC's whom they don't go in that city often but I did show the art #'s and they seems back off a little but they inform me next time I did show up in that city better prepared for larger conductor sizeing.

But in France we have a bit of leeway for 360 amp service we do simair to your set up in stateside.

Merci,
Marc


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## BBQ

Pete, any service conductor that does not carry the entire load of the home must use 310.16.

So picture this

*Utility > weatherhead > riser > 400 meter socket > two 200 amp panels.*

In my above example only the riser could be sized per 310.15(B)(6).

The two runs from the meter to the panels are required by the NEC to be sized per 310.16 becuse those runs do not carry the entire load of the home. I understand you may have local rules but what I am saying is what the NEC requires and actually has for many years.

(By the way, I am using old section numbers, they numbers have changed in the 2011)


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## Dennis Alwon

BBQ said:


> Pete, any service conductor that does not carry the entire load of the home must use 310.16.
> 
> So picture this
> 
> *Utility > weatherhead > riser > 400 meter socket > two 200 amp panels.*
> 
> In my above example only the riser could be sized per 310.15(B)(6).
> 
> The two runs from the meter to the panels are required by the NEC to be sized per 310.16 becuse those runs do not carry the entire load of the home. I understand you may have local rules but what I am saying is what the NEC requires and actually has for many years.
> 
> (By the way, I am using old section numbers, they numbers have changed in the 2011)



Remember this thread and Petes response was back in 2009


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## BBQ

Dennis Alwon said:


> Remember this thread and Petes response was back in 2009


:laughing: DOH!:blush:


Well that was the code then as well.

It actually has been the _intent_ forever.


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## Dennis Alwon

BBQ said:


> :laughing: DOH!:blush:
> 
> 
> Well that was the code then as well.
> 
> It actually has been the _intent_ forever.


 I agree and I remember arguing with Pete about it. BTW- electricista is my old screen name in this thread.


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## chicken steve

T310.15(B)(7) applies to dwelling services _and_ feeders

~CS~


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## BBQ

chicken steve said:


> T310.15(B)(7) applies to dwelling services _and_ feeders
> 
> ~CS~


Yes that is correct, but only service conductors or feeders that carry 100% of a dwelling units loads.


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## backstay

BBQ said:


> Yes that is correct, but only service conductors or feeders that carry 100% of a dwelling units loads.


This comes up with sub feeds to garages al the time. Some want to feed a 100 amp panel with 2-2-4 AL from that table, but you can't. Panel is not carrying 100 % of the dwellings load. The table works for feeders when the feeder supplies a sup panel in a duplex for one half.


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## NY Inspector

*400 amp service*

Just reading through some of these responses and I an quite amazed at some of them.

First off the NEC is not a referance book, it is the law. So please remember that. We are talking about service entrance conductors. The 400 amp meter pan has tandem lugs, agreed. Once you attach more than one set of conductors on those lugs you are now in parallel. Those conductors MUST be connected in parallel in a trough and then the 2 200 amp panels are tapped off those conductors. Period. Those of you who are coming off those lugs with 2 200 service cables Directly into 2 separate 200 panels are in violation of article 310.4 A. You are leaving yourselves open to lawsuit if there is a fire. Parallel conductors MUST be terminated at both ends. There is no way around it. If the inspectors aren't picking this up, find a better inspector. As stated by someone else the service conductors must carry the compete load, not individual 200 amp panels. You also cheating your customer who is paying for a 400 amp service. Another lawsuit. Wise up.


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## Dennis Alwon

NY Inspector said:


> Just reading through some of these responses and I an quite amazed at some of them.
> 
> First off the NEC is not a referance book, it is the law. So please remember that. We are talking about service entrance conductors. The 400 amp meter pan has tandem lugs, agreed. Once you attach more than one set of conductors on those lugs you are now in parallel.


This is not true. You defined parallel earlier and two wires under one lug, in and of itself, is not a parallel install



> Those conductors MUST be connected in parallel in a trough and then the 2 200 amp panels are tapped off those conductors.


Please show me a code article that supports this.



> Those of you who are coming off those lugs with 2 200 service cables Directly into 2 separate 200 panels are in violation of article 310.4 A.


 You are incorrect as it is not a parallel installation.



> You are leaving yourselves open to lawsuit if there is a fire. Parallel conductors MUST be terminated at both ends. There is no way around it. If the inspectors aren't picking this up, find a better inspector. As stated by someone else the service conductors must carry the compete load, not individual 200 amp panels. You also cheating your customer who is paying for a 400 amp service. Another lawsuit. Wise up.


Every comment you made is inaccurate and yet you tell us to wise up. What is the difference if a trough is installed and from there 2 separate runs are made to the panel. You are way off base here. 310.4 is about parallel conductors and these are not parallel. These are basically a tap in the meter using the two lugs.


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## Dennis Alwon

NY Inspector said:


> As stated by someone else the service conductors must carry the compete load, not individual 200 amp panels. You also cheating your customer who is paying for a 400 amp service. Another lawsuit. Wise up.


I think you misinterpreted what was said. The use of art. 310.15(B)(6) requires the use of the total connected load. Using 4/0 alum. will work fine to each panel if the calculated load is 180 or less on the panels & 75C rating is used, otherwise you can use 2- 250kcm or 2- 3/0 copper to each 200 amp panel.

This setup is standard throughout the country.

Apparently I was not clear with this post. Basically look at post #4- that was what I was trying to say. With 2- 200 amp panels they must be fed using T.310.16 not 310.15(B)(6)


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## Dennis Alwon

Clintmiljavac said:


> Here in Missouri we build a "400" amp service as the load side of meter base is 2/0 copper to each 200 amp panel


This is not compliant


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## NY Inspector

Dennis Alwon said:


> This is not true. You defined parallel earlier and two wires under one lug, in and of itself, is not a parallel install
> 
> 
> Please show me a code article that supports this.
> 
> You are incorrect as it is not a parallel installation.
> 
> 
> 
> Every comment you made is inaccurate and yet you tell us to wise up. What is the difference if a trough is installed and from there 2 separate runs are made to the panel. You are way off base here. 310.4 is about parallel conductors and these are not parallel. These are basically a tap in the meter using the two lugs.


Ok so what you are saying is that the twin lugs in the meter pan are not in parallel? so if a contractor decided to use two sets of 4/0 instead of one set 500, would he not need a trough to terminate the conductors of each phase, and then make the tap to each of the 200 amp panels? 
To me, the lugs in the meter pan are in parallel to allow the above scenario, and if they start out paralled, they need to be terminated in parallel? explain to me why it is considered a tap, and why the lugs in the meter pan are not in parallel? the better contractors I see all do new houses in this manner, although some do it with two separate 4/0 service cables as you stated. 
if this were a 600 amp meter are you saying also that three sets of 4/0 cables to 3, 200 amp panels is correct ? ty for your explanation


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## chicken steve

NY Inspector said:


> Just reading through some of these responses and I an quite amazed at some of them.
> 
> First off the NEC is not a referance book, it is the law. So please remember that. .


 
yup, and they pump out laws like they're on a mission from God, but there's never a cop when one is needed .....

~CS~


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## Dennis Alwon

Lugs are not what the NEC calls parallel. Parallel conductors are electrically joined at both ends. The NEC allows us to run conductors in parallel but they are only in parallel if they are electrically joined at both ends. A double lug is just a means of joining the conductors at one end. Each conductor has the ampacity of 200 amps whether they are joined at both ends or not. I am allowed to have six disconnects to disconnect a building at one service. If I could get a 1200 amp meter base with 6 lugs I could have 200 amp conductor wire going to 6 different panels- of course there is no such animal but yes that would be compliant. If I ran two parallel conductors to a trough then tied the conductors from each panel to it how is that different then just coming off the lugs. 

There is nothing in the code that says if we join two wires together they must stay together- their entire length. You stated that if they start out parallel they must stay parallel. That simply is not in the NEC.

I hope this helps.


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## Service Call

Very good discussion.


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## Pete m.

NY Inspector said:


> If the inspectors aren't picking this up, find a better inspector.


Just thought I would share an experience that I had when I first started as an inspector. My background, prior to the inspection side of things, was strictly commercial and industrial. When I was hired as an inspector the jurisdiction I covered included 10k+ square foot homes. I did my best to educate myself on the nuances of the NEC when it came to residential. I ignorantly fell into the trap of seeing an installation done a certain way and assuming that it was required by code without looking into it for myself.

For example: I got used to seeing contractors installing a light in the attic at the attic access. Here is where I assumed this was a code requirement. There was a contractor that was from Cincinnati that came into my jurisdiction to wire some tract homes and on the first one I inspected they didn't have that light that I was used to seeing. So, I rejected the rough inspection and the contractor installed the light without question. Same for the next house. 

Then one day after finishing all my inspections I'm in the office and got a call from the contractor. He simply asked me to whom should he send the bill for installing the light in the attic per my request. It took that to make me open the NEC and realize that the light wasn't necessarily a code requirement.

The reason I wrote all of that is to simply provide some advice (although unsolicited) to a fellow inspector.

Don't assume that seeing something done time and again, even by different contractors, makes it "code". There are electricians out there that will eat your lunch for you if you try to enforce requirements that don't exist.

Pete


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## kaboler

you weren't required to cite code references?


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## Pete m.

kaboler said:


> you weren't required to cite code references?


No, not at that time. I wish it was a requirement... Would've saved me from myself and the embarrassment.

Pete

Actually I'm glad that the contractor handled the situation like he did. It was an excellent way to provide me with an education that I obviously needed


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## Joseph C.

BBQ said:


> Pete, any service conductor that does not carry the entire load of the home must use 310.16.
> 
> So picture this
> 
> *Utility > weatherhead > riser > 400 meter socket > two 200 amp panels.*
> 
> In my above example only the riser could be sized per 310.15(B)(6).
> 
> The two runs from the meter to the panels are required by the NEC to be sized per 310.16 becuse those runs do not carry the entire load of the home. I understand you may have local rules but what I am saying is what the NEC requires and actually has for many years.
> 
> (By the way, I am using old section numbers, they numbers have changed in the 2011)


Your part about the feeders from the meter to the panels, each not carrying the entire load of the home is gold. This really helped me see big picture, thanks. . I just needed to know what is the minimum size paralleled copper service conductors I could use from the weather head to the meter for a 320amp single phase 120/240 residential service. These service conductors do serve the entire dwelling IE both 200amp panels so then I believe I can install parallel 2/0 cu. and a 1/0cu for the neutral due to not allowed to parallel a #1awg cu. I am using the 2020 NEC In my jurisdiction. Great discussion on this topic.


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## Dennis Alwon

You have open a 9 year old thread... BBQ is not even here anymore....

It would be good if you filled out your profile so we know who you are. Are you an electrician or a homeowner?


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## Southeast Power

Dennis Alwon said:


> You have open a 9 year old thread... BBQ is not even here anymore....
> 
> It would be good if you filled out your profile so we know who you are. Are you an electrician or a homeowner?


He said it helped him see the big picture. Not everyone ponders at the same pace.


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## Bird dog

Southeast Power said:


> He said it helped him see the big picture. Not everyone ponders at the same pace.


He could also be a Craigslist bottom feeder.


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## westwuz1

400 Amp meter would take 600’s from meter to weather head, at what point is it assumed 350 would be ok What am I missing here?


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