400A Meter (320 continuous) with 2 outdoor service panels (w/ main disconnects)

[Eliasc94]

Doing my first custom house as an electrical supervisor and trying to do it right. Lots of old heads in my company that don’t really know the code. I want this done right.

We’ve got the 320/400A meter can already and service panels 200a SQ D QO.

I know the POCO can run whatever wire they choose. We are going to provide a 3” pipe and perhaps they could parallel or more likely run 500kcmil aluminum.

From the load side of each leg on the meter can I can come out with a 600kcmil ungrounded conductor into a gutter and Polaris tap it with 2x 250kcmil that will go to each service disconnect.

In my opinion and understanding of the code, not to mention everything I’ve read between this forum and others, I don’t believe the 83% rule will apply to the tapped conductors but only the conductor that comes directly from the meter can as it will see 100% of the load.

Other option would be to use double lugs on the load side of the meter can and use 4x 250kcmil that sends a pair to each service panel.

Does this sound right? Is my understanding correct? My boss seems to think we will parallel 2.5” pipes with 4/0 to the line side of the meter, 4/0x4 load side of meter to Polaris taps 4/0x4 sending a pair to each service panel. I think this would be violating code.

I’m in Houston Texas and I think the actual calculated load is around 280 amps. This may or may not include all the specs we were just given.

Thanks in advance and I apologize for my jumbled thoughts in advance.

 

[LarryFine]

Welcome to the forum.

I would skip the gutter and taps, and come directly out of the meter with twin load lugs.

 

[Eliasc94]

Sounds good to me. Have a service panel on either side of the meter can with each being fed with 250 kcmil is my plan.

Now I’m kinda hung up on how it would best be to establish grounding electrode system to both panels.

 

[Dsg319]

Run a single GEC to your rods and tap off of the main GEC with an irreversible crimp to the other panel would be the least wire amount probably. Or run one long one that leaves one panel than to the rods and back off the second rod to the other panel like a big U.

 

[Elect117]

Does this sound right? Is my understanding correct? My boss seems to think we will parallel 2.5” pipes with 4/0 to the line side of the meter, 4/0x4 load side of meter to Polaris taps 4/0x4 sending a pair to each service panel. I think this would be violating code.

I'm guessing everything is in aluminum.

The parallel 2.5" pipe might be a utility choice? If not, then just do a fill calc.

Your boss will have 360A of conductor for a 400A service (okay), and 180A of conductor for each service panel protected at 200A (okay). That is fine as long as the load is less than 360A combined and less than 180A individually.

You are allowed to round up. You size the conductor to the load, and the protection from that. You can also size the conductor based on 310.12 for single family single phase dwellings. That partially agrees with your boss. I think your boss's thought was that only needing one wire size would make it cheaper to build.

You are also correct in sizing the conductor a little larger than the OCPD and load. The NEC is a minimum.

 

[Eliasc94]

I'm guessing everything is in aluminum.

The parallel 2.5" pipe might be a utility choice? If not, then just do a fill calc.

Your boss will have 360A of conductor for a 400A service (okay), and 180A of conductor for each service panel protected at 200A (okay). That is fine as long as the load is less than 360A combined and less than 180A individually.

You are allowed to round up. You size the conductor to the load, and the protection from that. You can also size the conductor based on 310.12 for single family single phase dwellings. That partially agrees with your boss. I think your boss's thought was that only needing one wire size would make it cheaper to build.

You are also correct in sizing the conductor a little larger than the OCPD and load. The NEC is a minimum.

Yes we mostly just use aluminum.

I am under the impression that 310.12 would not apply because the service entrance conductors are split to two services. So either set of service entrance conductors isn’t seeing 100% of the load. Then the 83% rule doesn’t apply. That is my understanding.

Also, how can you have a 180A conductor going to a 200a panel? Wouldn’t that leave the conductor unprotected at its ampacity? Only reason that 4/0 is normally fine to be used is that the 83% rule is in play afaik.

 

[Eliasc94]

Run a single GEC to your rods and tap off of the main GEC with an irreversible crimp to the other panel would be the least wire amount probably. Or run one long one that leaves one panel than to the rods and back off the second rod to the other panel like a big U.

I was thinking of making a giant U like you said. What about gas pipe bond? Take it to one panel or to both? And should I still run a #4 to the ufer like we normally do? And would this also need to be taken to both panels?

 

[Dsg319]

Yes we mostly just use aluminum.

I am under the impression that 310.12 would not apply because the service entrance conductors are split to two services. So either set of service entrance conductors isn’t seeing 100% of the load. Then the 83% rule doesn’t apply. That is my understanding.

Also, how can you have a 180A conductor going to a 200a panel? Wouldn’t that leave the conductor unprotected at its ampacity? Only reason that 4/0 is normally fine to be used is that the 83% rule is in play afaik.

4/0 aluminum 180amp can be protected with 200 amp OCPD due to the next size up rule which I don’t know exactly where it is but someone will.

 

[roger]

240.4

 

[Dsg319]

I was thinking of making a giant U like you said. What about gas pipe bond? Take it to one panel or to both? And should I still run a #4 to the ufer like we normally do? And would this also need to be taken to both panels?

Gas pipe bond I am unsure. But yes if the Ufer is there you have to use it, incorporate it into your GEC somehow instead of having to run extra wires.

 

[roger]

I was thinking of making a giant U like you said. What about gas pipe bond? Take it to one panel or to both? And should I still run a #4 to the ufer like we normally do? And would this also need to be taken to both panels?

Just land the GEC in the meter. making a "U" is just creating a parallel neutral current loop

 

[Elect117]

230.42 says you have to have a minimum ampacity to feed the load.

230.90(A) Exception 2 - Allows you to use 240.4 (round up rule when less than 800A).

And I would assume 310.12 applies since these conductors are going to supply the whole load to a single family dwelling.

Even if you ignore 310.12, your boss's install is still compliant.

 

[zbang]

if the Ufer

Be careful about whether or not there should be one, and then whether or not there is one. After the concrete is poured is rather too late to figure this out.

 

[Eliasc94]

Just land the GEC in the meter. making a "U" is just creating a parallel neutral current loop

Grounding Electrode Conductor: The grounding electrode conductor shall be continuous without splices from the neutral bus in the service equipment to the grounding electrode. The grounding electrode conductor, minimum size #8, or its enclosure shall be securely fastened to the surface on which it is carried. A #4, or larger, conductor may be exposed but shall be protected if exposed to severe physical damage. A #6 grounding conductor that is free from exposure to physical damage shall be permitted to be run along the surface of the building construction without metal covering or protection where it is rigidly stapled to the construction; otherwise, it shall be in conduit, electrical metallic tubing, or cable armor. Grounding conductors smaller than #6 shall be in conduit, electrical metallic tubing, or cable armor. The National Electrical Code requires grounding to a "Grounding Electrode." A driven ground rod is preferred by CenterPoint Energy.

Bonding (Jumper) Conductor: A bonding conductor (jumper) shall not be installed on the meter socket neutral lug. The meter socket neutral lug bonds the meter socket to the grounded system conductor.

From my POCO. Would landing the GEC in meter can still be allowable?

 

[roger]

You have one GEC and that stops at the first GE, after that you can use individual jumpers, IOWs they can be broken. And your POCO should allow landing the GEC in the meter unless they're clueless like some are.

 

[roger]

As your POCO says the Main Bonding Jumper(s) will be in the panels or disconnects, not in the meter

 

[jap]

I take it the (2) Service disconnects still meet the rule for amount of movements since they are in (2) separate enclosures?

JAP>

 

[Eliasc94]

As your POCO says the Main Bonding Jumper(s) will be in the panels or disconnects, not in the meter

So take GEC to the meter can and then the services are bonded together through the metal parts? Or…

 

[roger]

So take GEC to the meter can and then the services are bonded together through the metal parts? Or…

No, when you install the MBJ's they are bonded through the neutral conductors. After the MBJ's are in place the EGCs take over. Even though metallic raceways may actually bond everything it is more of the neutrals job, think about if you were using PVC.

 

[LarryFine]

And your POCO should allow landing the GEC in the meter unless they're clueless like some are.

Mine is clueless, but the localities agree, because the tag makes it inaccessible.