400 amp service

Status
Not open for further replies.
My new home has a 400 amp service consisting of two - 200 amp panels. I have 2/O wires from the meter base to both panel lugs. The electric company came and pulled in 350 wire to the meter base. Will 350 handle my application? Thanks
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
The utility always pulls in smaller conductors then the NEC requires but they have their own rules. In general they pretty well know what a customer will use so they install what will work. If it doesn't then it is their problem.
 

kwired

Electron manager
Location
NE Nebraska
I agree POCO can install whatever they want.

I think the 2/0 conductors feeding each panel is not allowed.

310.15(B)(6) allows 2/0 (copper) to be used for 200 amps.

310.15(B)(6) however can only be used for conductors that carry the entire load of a dwelling. Since there is two feeds to the house neither one of them is carrying the entire load.
 

augie47

Moderator
Staff member
Location
Tennessee
I agree POCO can install whatever they want.

I think the 2/0 conductors feeding each panel is not allowed.

310.15(B)(6) allows 2/0 (copper) to be used for 200 amps.

310.15(B)(6) however can only be used for conductors that carry the entire load of a dwelling. Since there is two feeds to the house neither one of them is carrying the entire load.
This is a very common way of doing a 2 panel 400. It actually provides 2 2/0 copper cables in parallel to carry the load. Too small? I think not.
I find this describes a common discrepancy in this area. I feel kwired is 100% correct in that neither of those conductors carry the "full load" of the dwelling and are not parallel conductors and 2/0 should not be allowed but, locally, as Stew notes, it is accepted 99% of the time.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I agree POCO can install whatever they want.

I think the 2/0 conductors feeding each panel is not allowed.


310.15(B)(6) allows 2/0 (copper) to be used for 200 amps.

310.15(B)(6) however can only be used for conductors that carry the entire load of a dwelling. Since there is two feeds to the house neither one of them is carrying the entire load.
I agree, and this is a new home so I'm guessing that it was inspected. :roll:
 
yes here its 99.99999 % gotta stay away from kwire if hes the inspector! lol
Ditto here. IMHO and of those of local inspectors the rule does not make sense. You will hear people on this forum regurgitate the phrase diversity of loads but the truth is there are situations where it just does not make any sense.
So if the inspectors allow it I say save your money and do it.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
I believe that what you have is actually a 320 amp service, unless it is a K base(bolt in meter). Normally the bases are S base (socket base), and these are rated for 320 amps continious duty. The 350 aluminum wire the POCO used is rated at 320 amps. Actually the power company can feed that installation with #2 aluminum if the engineers believe that the #2 will carry the load. I work for a POCO and generally size 320 amp services with 4/0 aluminum if the service is short enough so as to have very little voltage drop. We actually try to account for, to a point, inrush currents causing dimming lights when AC units kick on and off.
One must remember that the service size is based on calculations done by the electrician. If the electrician does all his (or her) calculations, and comes up with 205 amps, guess what?, they must go to a 320 amp base.
If the service is unusually long, (over 250 feet) then the only reason the POCO installed the 350 was to account for voltage drop, or it was lazy engineering, and a waste of money. Must be a cooperative...
 

kwired

Electron manager
Location
NE Nebraska
Ditto here. IMHO and of those of local inspectors the rule does not make sense. You will hear people on this forum regurgitate the phrase diversity of loads but the truth is there are situations where it just does not make any sense.
So if the inspectors allow it I say save your money and do it.
How much do you save between 2/0 and 3/0 if you end up having to replace it? Especially if the meter is within 10 feet or so of the panels. Do it right the first time. The more of the entire service there is on a single feed the more of the possible diversity that does exist will be on that feed. Make two feeds and put mostly HVAC on one and general purpose circuits on the other and the diversity of the HVAC may not be much diversity at all. That is why the entire load of the dwelling must be supplied by the conductors to use this table.

I believe that what you have is actually a 320 amp service, unless it is a K base(bolt in meter). Normally the bases are S base (socket base), and these are rated for 320 amps continious duty. The 350 aluminum wire the POCO used is rated at 320 amps. Actually the power company can feed that installation with #2 aluminum if the engineers believe that the #2 will carry the load. I work for a POCO and generally size 320 amp services with 4/0 aluminum if the service is short enough so as to have very little voltage drop. We actually try to account for, to a point, inrush currents causing dimming lights when AC units kick on and off.
One must remember that the service size is based on calculations done by the electrician. If the electrician does all his (or her) calculations, and comes up with 205 amps, guess what?, they must go to a 320 amp base.
If the service is unusually long, (over 250 feet) then the only reason the POCO installed the 350 was to account for voltage drop, or it was lazy engineering, and a waste of money. Must be a cooperative...
Since when was service size determined by what type of meter is used?

If you have a 320 socket supplying a 100 amp main do you have a 100 amp service or a 320 amp service?

If you have a 320 socket supplying two 200 amp mains will the 320 meter say "OK that is enough" if current being drawn surpasses 320, or will current be allowed to continue to rise if the demand is there until one or both of the breakers trip?
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Since when was service size determined by what type of meter is used?

If you have a 320 socket supplying a 100 amp main do you have a 100 amp service or a 320 amp service?

If you have a 320 socket supplying two 200 amp mains will the 320 meter say "OK that is enough" if current being drawn surpasses 320, or will current be allowed to continue to rise if the demand is there until one or both of the breakers trip?
Ease up brother, we seem to be going back and forth between posts. What I posted was that he had a 320 amp service. The actual UL listed meterbase mounted to the wall, that will accept a socket meter is rated at 320 amps continuous duty, unless it is a K base, or bolted meter, which is rated at 400 amps. http://milbankmfg.com/products/ResMeterSockets/index.asp A 320 amp meter base used for a 400 amp service is being asked to supply energy at 125% of it's listed continious duty rating. If a meter base is rated at 150 amps, can it be used for 187.5 amps continious duty? That is 125% of it's listed continuous rating, just like the 320 amp meter base being asked to supply a 400 amp service.
Although the nomenclature is used interchangibly, a meterbase that is rated at 320 amps is simply not a 400 amp service in my opinion. Now for the fun part, can a 150 amp main be used behind a 100 amp meter base?can a 200 amp main be used behind a 150 amp meter base? Can 2-200 amp mains be used behind a 320 amp meter base?;)
 
How much do you save between 2/0 and 3/0 if you end up having to replace it? Especially if the meter is within 10 feet or so of the panels. Do it right the first time. The more of the entire service there is on a single feed the more of the possible diversity that does exist will be on that feed. Make two feeds and put mostly HVAC on one and general purpose circuits on the other and the diversity of the HVAC may not be much diversity at all. That is why the entire load of the dwelling must be supplied by the conductors to use this table.
I'm not going to argue with you. We know there are also times when you can use the table for the entire load but if with less load you can't and would require a bigger wire for less load. Such as HVAC CBs prior to the panel.

In any case I agree with you about what the code says. I'm just stating that the code is not completely reasonable and should be revised. And also to say that some AHJs allow the use of the table other than when the code allows.
 

kwired

Electron manager
Location
NE Nebraska
Ease up brother, we seem to be going back and forth between posts. What I posted was that he had a 320 amp service. The actual UL listed meterbase mounted to the wall, that will accept a socket meter is rated at 320 amps continuous duty, unless it is a K base, or bolted meter, which is rated at 400 amps. http://milbankmfg.com/products/ResMeterSockets/index.asp A 320 amp meter base used for a 400 amp service is being asked to supply energy at 125% of it's listed continious duty rating. If a meter base is rated at 150 amps, can it be used for 187.5 amps continious duty? That is 125% of it's listed continuous rating, just like the 320 amp meter base being asked to supply a 400 amp service.
Although the nomenclature is used interchangibly, a meterbase that is rated at 320 amps is simply not a 400 amp service in my opinion. Now for the fun part, can a 150 amp main be used behind a 100 amp meter base?can a 200 amp main be used behind a 150 amp meter base? Can 2-200 amp mains be used behind a 320 amp meter base?;)

All I am saying is the 320 in no way limits current allowed to flow. If you have more than 320 amps continuous calculated load then the 320 should not be used. The service size is still whatever the overcurrent devices will allow to flow.

If service size is 320 then shouldn't we only have to use 320 amp conductors instead of 400 amp conductors?

How about a service consisting of three 200 amp main breakers in one panel fed by only 500 KCmil conductors where calculated load is less than 400 amps, metered with CT's?

What is rating of that service? You have 600 amps worth of overcurrent protection and 400 amps worth of conductor. Maybe it averages out to 500:D

Thing is NEC does not mention 'size of service'. It has a section on conductor size, and a section on overcurrent protection size. Sometimes the final result of each section do not have to match each other. Any other device such as a meter just has to be able to carry the calculated load.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
What is the continuous amp rating of a service with two 200A disconnects? It is most likely 200 * .8 = 160 times 2 panels = 320 amps.

This whole 320/400 amp meter thing is weird. Since all the service disconnects need to have continuous loads multiplied by 125%, they should just call it a 400A meter. Only fly in the ointment would be disconnects with 100% rated breakers.

Can you use a 200A meter on a 225A 80% rated main disconnect? Is that 200A meter rating continuous or peak?
 

iwire

Moderator
Staff member
Location
Massachusetts
All I am saying is the 320 in no way limits current allowed to flow. If you have more than 320 amps continuous calculated load then the 320 should not be used.
I am not following you.

If you have more than 320 amps continuous calculated load you cannot use a standard 400 amp breaker or panel either.

The 320 meter socket is a perfect match with a standard 400 amp panel or a pair of standard 200 amp panels. If you are overloading the 320 you are also overloading the breaker(s) unless they happen to be 100% rated breakers.
 
Status
Not open for further replies.
Top