Sizing a single disconnect for a 320A meter socket

Location
Seattle
Occupation
Electrician
My customer has a 320A power meter on a residential home in Texas. He use to have a Iline distribution with 5 breakers to various panels. We are remodeling and have to change the service. I want to keep the meter socket but have to add a single outdoor disconnect.
If I add a single Fuse or CB disconnect, wouldn't it have to be 320A or less to protect the meter socket.
Fuses and CB standard sizes are 300, then 350. So do I size down to 300A.

Do I then rate my conductors from the meter to the disconnect at .83 x 320A = 265A for 300MCM copper at 75*
Then the feeder from my 300A fuse to the panel indoor is sized the same as the entire feeder is for a single family dwelling.
Thanks
 
Location
Seattle
Occupation
Electrician
There is no requirement to protect the meter socket at it's rating with an OCPD. Besides it's rated 400 amp anyway.
Why would it not require protection. And why do you think its rated for 400A. I have seen 400A meter sockets and 320A meter sockets. My assumption would be a 400A socket has more wire bending space for larger wires. Maybe the enclosure is not designed for 400A wire????
 
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Location
Seattle
Occupation
Electrician
FYI you can have multiple disconnects so two 200s if that helps.
I have another project and was thinking about this. I have some Holt study guides and in one there is a single pipe that leaves the meter socket and enters a disconnect, passes through it to another disconnect. This book is older. Is this still acceptable. I was thinking of taking 2 set of 2/0 in one pipe, enter the first disconnect and drop one set in the 200A CB disconnect. The second set would pass through the first disconnect to the second CB disconnect and terminate. I was wondering if I am allowed to use the first CB disconnect can as a raceway.
 
Location
Seattle
Occupation
Electrician
Tom, You are saying Yes to the 2 disconnects correct.

Per my first question, is Electrofelon correct. My customer has a year long load analysis from the utility. His max usage is 170A. He has 5 AC. He is adding a 100A car charger. He wants maximum current capacity and wants a 400A Fused or CB disconnect going to a new Iline panel that accepts 400A feed through lugs. Its a generator sizing thing. I did not want to run into issues with the meter socket being 320A.
 
Why would it not require protection.
Because there is no NEC requirement.

And why do you think its rated for 400A. I have seen 400A meter sockets and 320A meter sockets. My assumption would be a 400A socket has more wire bending space for larger wires. Maybe the enclosure is not designed for 400A wire????
A class 320 socket is rated 320A continuous, 400A non continuous. Note your 400A OCPD is only rated 320 continuous also.
 
Location
Seattle
Occupation
Electrician
Ok,
I can accept that.
I am then going to say .83 x 400 = 332 so its 400 MCM copper or parallel 2/0 from the meter through the Fuse/CB to the distribution Iline panel.
 
Location
Seattle
Occupation
Electrician
Wait a second. 310.15(C)(1) says each current carrying conductor of a paralleled set of conductors shall be counted as a current carrying conductor.
That means I would have to derate to 80% with 6 in the pipe.
With copper
A 3/0 at 200A x .8 = 160 x 2 =320A.
320 is less than the 332A allowed by .83% rule for a single family dwelling.
Do I actually have to go to a 4/0 if I want to parallel with a 400A disconnect when feeding a singe family dwelling.
My other option is to use 3 x 400MCM
 

kwired

Electron manager
Location
NE Nebraska
Wait a second. 310.15(C)(1) says each current carrying conductor of a paralleled set of conductors shall be counted as a current carrying conductor.
That means I would have to derate to 80% with 6 in the pipe.

With copper
A 3/0 at 200A x .8 = 160 x 2 =320A.
320 is less than the 332A allowed by .83% rule for a single family dwelling.
Do I actually have to go to a 4/0 if I want to parallel with a 400A disconnect when feeding a singe family dwelling.
My other option is to use 3 x 400MCM
read on further in the subsections. If you have short nipple (no more than 24") you don't need to adjust ampacity.

The 83% rule would allow less than 3/0 conductors but you do need to apply ampacity adjustments if they apply. For a 400 amp single OCPD that means final conductor ampacity must be at least 332 amps.

For two to six disconnects you only need conductor sized per calculated loads, but still need conductors to any individual OCPD to be no less than what corresponds to that OCPD.
 
Location
Seattle
Occupation
Electrician
read on further in the subsections. If you have short nipple (no more than 24") you don't need to adjust ampacity.

The 83% rule would allow less than 3/0 conductors but you do need to apply ampacity adjustments if they apply. For a 400 amp single OCPD that means final conductor ampacity must be at least 332 amps.

For two to six disconnects you only need conductor sized per calculated loads, but still need conductors to any individual OCPD to be no less than what corresponds to that OCPD.
I have many feet on the side of the building in Houston so a nipple does not apply.

I was looking at XHHW-2 and wondering why I could not use the 95* column. And the deration for ambient temperature seems to say you don't need to apply it it XHHW-2. But I'm slightly unsure on that. It seems to specifically call out pipe and wire on a roof. Not the side of a building.

I told my customer he should ask the inspector and I cited all the code I feel applies. I said he can ask to use the 3/0 and see what they say. He does have a 2 year utility analysis of his usage that is a snapshot every 15 minutes. His largest draw is around 40 Amps. That seems low to me with 5 AC. But maybe its accurate if you figure they are 240 volt and maybe draw 10A per leg and only 4 might run at a time. And 3 are newer.
 

kwired

Electron manager
Location
NE Nebraska
I have many feet on the side of the building in Houston so a nipple does not apply.

I was looking at XHHW-2 and wondering why I could not use the 95* column. And the deration for ambient temperature seems to say you don't need to apply it it XHHW-2. But I'm slightly unsure on that. It seems to specifically call out pipe and wire on a roof. Not the side of a building.

I told my customer he should ask the inspector and I cited all the code I feel applies. I said he can ask to use the 3/0 and see what they say. He does have a 2 year utility analysis of his usage that is a snapshot every 15 minutes. His largest draw is around 40 Amps. That seems low to me with 5 AC. But maybe its accurate if you figure they are 240 volt and maybe draw 10A per leg and only 4 might run at a time. And 3 are newer.
XHHW-2 still subject to temperature adjustment, but does not need to apply the rooftop adder, which is a pretty significant adder when it does apply. Adjustment for number of conductors in raceway applies whether temp adjustment applies or not.
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Why would it not require protection. And why do you think its rated for 400A. I have seen 400A meter sockets and 320A meter sockets. My assumption would be a 400A socket has more wire bending space for larger wires. Maybe the enclosure is not designed for 400A wire????
You may have seen "self-contained" single phase FM2S (Socket base) CL320A rated meters and FM2A (A Base) CL400A meters, but the 400A would be an A-base bottom connected (hardwired) meter, not a socket base. They are old school. The 320A (80% of 400) is what nowadays replaces the 400A. It's still rated for a 400A service, but is limited to 80% continuous load. Any metering over 400A requires CT's.
 
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Location
Seattle
Occupation
Electrician
XHHW-2 still subject to temperature adjustment, but does not need to apply the rooftop adder, which is a pretty significant adder when it does apply. Adjustment for number of conductors in raceway applies whether temp adjustment applies or not.
Ok, I reread 310.15(B)(2) exception and it says "This"adjustment.
 
Location
Seattle
Occupation
Electrician
You may have seen "self-contained" single phase FM2S (Socket base) CL320A rated meters and FM2A (A Base) CL400A meters, but the 400A would be an A-base bottom connected (hardwired) meter, not a socket base. They are old school. The 320A (80% of 400) is what nowadays replaces the 400A. It's still rated for a 400A service, but is limited to 80% continuous load. Any metering over 400A requires CT's.
Good to know. My other project will use the 320A and have a single pipe with parallel wires going to 2 separate disconnects on the side of the house. Oregon, so the temp could actually make the wires smaller.;)
 
Location
Seattle
Occupation
Electrician
Does anyone see why this would not be an acceptable installation? Hopefully the pdf will open. Let me know if it can not be viewed.

The meter, gutter and fused disconnects would be on the outside of the house.
The panels are indoor. The loadcenter would be a main circuit breaker but the NQ panel would be a MLO.
 

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Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Does anyone see why this would not be an acceptable installation? Hopefully the pdf will open. Let me know if it can not be viewed.

The meter, gutter and fused disconnects would be on the outside of the house.
The panels are indoor. The loadcenter would be a main circuit breaker but the NQ panel would be a MLO.

There shouldn't be a problem with that install. I wouldn't use fuses if that is what you really meant. I would use a 200 amp main disconnect panel. They make them just large enough for the one main disconnect.
 
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