# 400 amp three phase service entrance



## Old Spark

I prefer copper to feed panels (I've see to many problems with Aluminum.) It does cost more. But with copper I'd run parallel runs of 3/0 THHN for both grounded and ungrounded wires. If I were to run aluminum, I'd run parallel runs of 250 XHHW in 2.5" conduit. This will allow someone to fully load the panel. 750 XHHW Al. is good for 385 amps. I don't know what the nu wire is. Is that something you use in Canada? P.S. its much easier to work with the smaller wire is why we run parallel runs.


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## NolaTigaBait

You can't make sure that someone will add more later. Thats what a load calc is, it's the minimum , it doesn't provide for future expansion.


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## Dennis Alwon

First you need to do a load calculation but if you are protecting the service with 400 amps then it would be wise to use a wire that has a 400 amp rating. Table 310.16 in the NEC will help determine this info.

Do you have a code book? Lets just assume we are not running parallel conductors. This means that each phase conductor must be able to carry 400 amps. I lets also assume we are running wires that are rated 75C. 

Look at the tables. Now tell me what size copper or what size aluminum wire we will need. There are lots of things involved in deciding what size we need and we sometimes can use wires that are actually smaller than the size of the service.

For instance, if we have a 300 amp service and the calculated load is under 285 amps, then we can go to the table and see that we can actually use 300kcm copper. Why? Because article 240.4(B) allows us.


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## jojoschauss

This building is going to be a rental building. It is going to have 3 units/stores (3 panels + house panel). At this point it is hard to determind the load since the building will later be customized to the tentants wishes. The 4in pvc for the service entrance goes underground to the pole, then up the pole and is connected up there. This conduit was already in place.
So it sounds like parallel is the way to go then ((8) 250 kcmil, but in our case having 6 current carring and 2 neutrals in one coduit there would be a derating factor there as well.
How do you determind the wire size needed when they are run in parallel.


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## Old Spark

If you want to be able to fully load the 400 amp panel, then you will use two sets that can carry 200 amps. But you are correct in considering derating since you have more than 3 current carrying conductors in the conduit. With a 4" conduit you have plenty of room for either copper or alum. even with derating.
P.S. Did you guy already bid this job? What wire size was bid. Hate to up the wire size over what the boss bid without a change order.


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## jojoschauss

This is a time and matterial job so no bidding was required. So as long as the non linar load doesnt make up more then 50% of the total load the 2 neutrals wouldn't count as current carring conducters. Hence the derating factor would be .80 .So if we would go with david's suggestion of parallel runs of 250 XHHW aluminum.
They are rated for 205A @ 75degress
410 x .8 + 328A ussable amperage.
Yes No

thanks for all the help


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## Old Spark

That's the way I read it too. Just be sure to do a good phase tape job and then double check with a continuity tester before you power up. I had a crew who phase taped every thing, but somehow did not do it right. They did'nt test either, they were so sure they did it right. Insisted someone must have been messing with them. I don't think so.


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## Dennis Alwon

jojoschauss said:


> This is a time and matterial job so no bidding was required. So as long as the non linar load doesnt make up more then 50% of the total load the 2 neutrals wouldn't count as current carring conducters. Hence the derating factor would be .80 .So if we would go with david's suggestion of parallel runs of 250 XHHW aluminum.
> They are rated for 205A @ 75degress
> 410 x .8 + 328A ussable amperage.
> Yes No
> 
> thanks for all the help


Yeah, you will need parallel 300KCM alum. in this case


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## wire stuff

My boss just had us pull parallel 4/0 aluminum for our 400 amp service. We were red tagged by the inspector who made us remove our 400 amp fuses and put in 300 amp. My boss still swears up and down that he is right and is taking things up with the city.Can any one see how this size could be used any code loop holes to make this ok?


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## Brynn217

*the Service...*

ok... this is all something you learn when you Get your Masters, I am a Master in the State of Maryland...

the Service Calculation is used to size the Service needed for the building... In this case, the Calculation that someone did came with with a 400Amp Service or less, the Calculation tells you to use the next higher size Main Breaker available.

You then size the Service Entrance Cables to the Breaker. This is where the problem Occurs... All terminals on all Breakers are rated to be used at 60c or 75c at most... (60 is for Romex) When you size the wire, you cannot use the 90c Column off Table 310.16 (actually this table moved in the 2011 but mine is at work, looking at a 2008 codebook now) (read the label on the side of the Breaker, it tells you what it is rated for...)

4/0 Wire is only listed for 180 amps, on the 75c column and running two of them would allow for a max service of 360amps... Next lowest breaker is 300amps which is what the inspector indicated....

A Breaker is there to protect the wire and Transformer only... The Trip timing of most breakers will only protect the equipment and not a person. GFCI's where introduced to help protect people, the same with ARC Fault. 

Most Services do provide for future additions. The Demand Factors decrease with more equipment you have, why? because you are never going to use everything at the same time... Also, large scale changes require permits to be pulled and one of the things that is checked is if the new additions will exceed the existing service.. Then that just creates more income for US, because it requires the customer to upgrade the service for his proposed addition....

James


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## McClary’s Electrical

wire stuff said:


> My boss just had us pull parallel 4/0 aluminum for our 400 amp service. We were red tagged by the inspector who made us remove our 400 amp fuses and put in 300 amp. My boss still swears up and down that he is right and is taking things up with the city.Can any one see how this size could be used any code loop holes to make this ok?


 
If the calculated load on your bosses panel was not over 180 amps then you could use 4/0 al on a 200 amp breaker


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## Brynn217

*Btw*

In case you are wondering what the 90c column is for, that is for Sizing wire in the pipe and boxes when you need to derate the size of the wire... The Pipe Sizes are based on the number of wires in the pipe. The Breaker size is based on the size of the load in a branch circuit. Then you size the wire at 125% of the Branch Circuit Breaker, derated for The Type of Wire, # of conductors & Length of the conduit and temperature... the derating fomula uses the tempature rating of the wire you are using....

For example, you use


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## McClary’s Electrical

Brynn217 said:


> Then you size the wire at 125% of the Branch Circuit Breaker,


 
:blink:


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## Flyboynxs

jojoschauss said:


> This building is going to be a rental building. It is going to have 3 units/stores (3 panels + house panel). At this point it is hard to determind the load since the building will later be customized to the tentants wishes. The 4in pvc for the service entrance goes underground to the pole, then up the pole and is connected up there. This conduit was already in place.
> So it sounds like parallel is the way to go then ((8) 250 kcmil, but in our case having 6 current carring and 2 neutrals in one coduit there would be a derating factor there as well.
> How do you determind the wire size needed when they are run in parallel.


You will need to run parallels in separate conduits NEC, neutral is not counted. it only carries the unbalanced loads.


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## hornetd

wire stuff said:


> My boss just had us pull parallel 4/0 aluminum for our 400 amp service. We were red tagged by the inspector who made us remove our 400 amp fuses and put in 300 amp. My boss still swears up and down that he is right and is taking things up with the city. Can any one see how this size could be used any code loop holes to make this ok?


*PLEASE TAKE NOTE! I DO NOT HAVE CURRENT COPY OF THE 2017 EDITION OF THE National Electric Code (NEC). PLEASE HELP BY CHECKING MY SUGGESTION AGAINST THE MORE RECENT ADDITION OF THE CODE USED IN WIRE STUFF'S AREA.*

2 sets of 4/0 wire is not acceptable for 400 ampere service. 4/0 is only allowed for 200 amperes when it carries "the entire load associated with a one-family dwelling,"... Neither of the 2/0 conductor sets to the separate 200 ampere Service Disconnecting Means does that. Each only carries what would nominally be 1/2 of the 400 Amperes. Without the use of the 83% multiplier for the calculated load you are stuck with the 180 ampere ampacity for the 4/0 size. If 350 ampere fuses are available for that disconnect then you could use them but there may be another possibility. 

*WARNING: I'M ABOUT TO SHOOT FROM THE HIP OR, TO BE MORE ACCURATE, TO RELY ON MY MEMORY. I HAVE NOT FULLY INVESTIGATED WHAT I'M ABOUT TO WRITE FOR COMPLIANCE WITH THE RULES ON PARALLEL CONDUCTORS! IT IS YOUR RESPONSIBILITY TO CHECK THE SUGGESTED INSTALLATIONS COMPLIANCE WITH THOSE RULES. 
*
If it is practical to convert those 2 sets of 4/0 to parallel sets; meaning the same length for all of them and they terminate to 3 multi terminal lugs at the load end; then it would be a single set of conductors carrying "the entire load associated with a one-family dwelling," Warning: If you do not "Ring Out;" which is a particular way that the continuity of conductors is verified; the 2 separate sets of conductors to assure that the same energized conductors and the neutral conductors of each set land on the same terminals you will end up closing your service disconnecting means on a dead fault. If by chance, the withstand rating of the disconnect is not high enough to handle the fault current which the utility's transformer can deliver at the existing number of wire feet from the transformer's terminals you could get seriously hurt and maybe even killed by an arc blast! If it were me doing the conversion I would lift the terminal lugs from the grounded enclosure and Meg them with an actual megohmmeter to be certain no conductors got crossed up or have become faulted in the process of converting them into parallel sets. *If this suggested installation does meet the requirements for parallel conductors* then the combined ampacity of those conductors at, 360 amperes, would be greater than the 83% of the entire load which calculates to 332 amperes. You could then reinstall the 400 ampere fuses.

What it would take to convert the conductors to parallel sets, in the installation you have described, I do not have access to the necessary references to say. If you provide photographs of the service equipment as it is now we might be able to be of more help. Much depends on if the present installation can be economically changed so that all conductors are the same length and would still be long enough to terminate in 3 multi barreled lugs. From the common lugs you could run short lengths of 3/0 Copper or 250 MCM Aluminum, which ever is more practical, to the 2, 200 Ampere, Over Current Protective Devices; Molded Case Circuit Breakers in this instance; that will be the grouped Service Disconnecting Means.

Excerpted from the *2014 edition* of the National Electric Code (NEC) pursuant to the Fair Use Doctrine of copyright law.
310.15 Ampacities for Conductors Rated 0–2000 Volts.
(A) General.
(7) 120/240-Volt, Single-Phase Dwelling Services and Feeders. For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, service and feeder conductors supplied by a single-phase, 120/240-volt system shall be permitted be sized in accordance with 310.15(B)(7)(1) through (4).
(1) For a service rated 100 through 400 A, the service conductors supplying the entire load associated with a one-family dwelling, or the service conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the service rating. 

Tom Horne


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