Service Upgrade

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I have a friend who has built a 30x50 pole barn detached from his residence. He currently has a 200 amp service to the home and would like to add a 150 amp or 200 amp service to the detached pole barn. He wants a common riser to be installed so the service entrance conductors terminate in a dual meter base. The meter base needs to be able to disconnect the 150 amp or 200 amp panel in the new pole barn. Question: Why do I see the meter bases on line rated for 320 amps? What is significant about 320 amps? Is it because any higher amperage would require cts? I have seen the dual meter bases rated for 320 amps, yet the come with (2) 200 breakers inside the meter base. What am I missing? Is a 320 amp dual meter base rated for (2) 200 amp services?

Thanks,
Eddie
 

Ponchik

Senior Member
Location
CA
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Electronologist
My guess is 320Amps is 80% of 400Amps and the meter base is rated for 320 continuos amps.

You can probably change the 2nd OCPD for 150Amp.
 

GoldDigger

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Location
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The 320A value is a continuous rating. By NEC guidelines equipment rated at 400A can handle 80% of that (320A) on a continuous current basis.
The 320A meter and base are what POCO uses for a 400A service and it works just fine.
You are correct that higher current meters will use CTs.
 

Ponchik

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Location
CA
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Electronologist
If local AHJ allow you may use table 310.15.b.7 and use 400 MCM copper
 

GoldDigger

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The meter is usually on the POCO side of the service point so the NEC does not apply. As long as POCO is OK with the installation and it is sized under their guidelines and safety code (usually NESC), it will be safe.
As for the conductor size it again depends on which side of the service point it is on. If it is governed by NEC the conductors would have to be sized for the calculated load and not the service size. And under some restrictions (which may or may not apply to both buildings) the conductors can be rated at only 83% of that number.
 

GoldDigger

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Not around here, for overhead services anyway. The service point is typically at the weatherhead of the service riser.
Good point. It may still be under the control of POCO, in terms of telling the owner what types of meter base are acceptable. The conductors from the weatherhead to the meter would still be sized per NEC.
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
The meter is usually on the POCO side of the service point so the NEC does not apply. As long as POCO is OK with the installation and it is sized under their guidelines and safety code (usually NESC), it will be safe.
As for the conductor size it again depends on which side of the service point it is on. If it is governed by NEC the conductors would have to be sized for the calculated load and not the service size. And under some restrictions (which may or may not apply to both buildings) the conductors can be rated at only 83% of that number.

Calculated load: So if the calculated load is 100 Amps and the panel is rated at 400 amps (with two 200amp disconnects) with the service conductors are based on 100Amps?

Not the service size: you mean the rating of main disconnect/s or the rating of the service equipment?

Thanks
 
Thanks to everyone for the educated responses. I do have one last question: If I do not know the calculated load , is it safe to assume that if a dual meter rated at 320 amps is installed, the amount of available current used cannot exceed the 80% rating based on 400 amps?
 

iwire

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Staff member
Location
Massachusetts
Thanks to everyone for the educated responses. I do have one last question: If I do not know the calculated load , is it safe to assume that if a dual meter rated at 320 amps is installed, the amount of available current used cannot exceed the 80% rating based on 400 amps?

No.

How was the service size chosen if you do not know the calculated load?
 

Dexie123

Senior Member
If you have a dual meter rated at 320amps how can you have 2 breakers that are rated higher than 320amps total (2 400 amp breakers) especially if the calculated load is rated higher than 320?
 

Tony S

Senior Member
I have a friend who has built a 30x50 pole barn detached from his residence. He currently has a 200 amp service to the home and would like to add a 150 amp or 200 amp service to the detached pole barn. He wants a common riser to be installed so the service entrance conductors terminate in a dual meter base. The meter base needs to be able to disconnect the 150 amp or 200 amp panel in the new pole barn. Question: Why do I see the meter bases on line rated for 320 amps? What is significant about 320 amps? Is it because any higher amperage would require cts? I have seen the dual meter bases rated for 320 amps, yet the come with (2) 200 breakers inside the meter base. What am I missing? Is a 320 amp dual meter base rated for (2) 200 amp services?

Thanks,
Eddie

Standard european breaker sizes changed around the mid 80’s. I noticed this when installing a new 1MVA board. The original board had 150, 200, 250, 300, 400, 600A breakers.
The new board had 160, 200, 250, 320, 400, 630A.

The change was brought about by the EU (don’t ask me why).

I would guess the manufacturers are assimilating the US in to the collective.

BTW, there was absolutely no difference what so ever in construction, just a new label.
 

iwire

Moderator
Staff member
Location
Massachusetts
Standard european breaker sizes changed around the mid 80’s. I noticed this when installing a new 1MVA board. The original board had 150, 200, 250, 300, 400, 600A breakers.
The new board had 160, 200, 250, 320, 400, 630A.

The change was brought about by the EU (don’t ask me why).

I would guess the manufacturers are assimilating the US in to the collective.

BTW, there was absolutely no difference what so ever in construction, just a new label.

Here are the US standard OCPD sizes

240.6 Standard Ampere Ratings.
(A) Fuses and Fixed-Trip Circuit Breakers.
The standard
ampere ratings for fuses and inverse time circuit
breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50,
60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300,
350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000,
2500, 3000, 4000, 5000, and 6000 amperes.
Additional
standard ampere ratings for fuses shall be 1, 3, 6, 10, and
601. The use of fuses and inverse time circuit breakers with
nonstandard ampere ratings shall be permitted.
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
........ If it is governed by NEC the conductors would have to be sized for the calculated load and not the service size. And under some restrictions (which may or may not apply to both buildings) the conductors can be rated at only 83% of that number.

No.

How was the service size chosen if you do not know the calculated load?


Let's assume the calculated load is 100Amps but the service is being installed 400Amp for possible future expansion. Per NEC the size of the service conductors are sized per 100Amps or 400Amps? I would guess 400A.
 

Tony S

Senior Member
Re: #14

Re: #14

They may be the published standards and they are identical to when I started in the trade in the UK.

The manufacturers supplying worldwide will decide on their own standards.

You order a 300A widget, you will get a 320A widget because that is what the manufacturer makes for the rest of the world.

You are being assimilated in to the Borg collective!
 

iwire

Moderator
Staff member
Location
Massachusetts
Let's assume the calculated load is 100Amps but the service is being installed 400Amp for possible future expansion. Per NEC the size of the service conductors are sized per 100Amps or 400Amps? I would guess 400A.

In the situation you describe if there is only one service disconnect it would have to be sized at no more than 100 amps. See 230.90(A)

On the other hand if there was more than one service disconnect, lets say two 200 amp main breaker panels from the 320 socket.

If you did the load calculations and they showed a calculated load of under 100 amps you could those 100 amp conductors to supply both of those 200 amp main breakers.

See 230.90(A) Exception 3.
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The NEC does not prevent you from installing larger service conductors in anticipation of future loads, it just does not require you to.
And you can put a 100A main in a 200A panel connected to a 200A service and use 100A conductors per the NEC.
Some POCOs might object.
 
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