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In my 2014-built United States mainland home, I have two side-by-side 200A panels. They both have a 200A main breaker. One really neat thing this let me do is have two lighting circuits in the basement, so that I can work on a panel with the main off and have great lighting to see what I'm doing. There are of course, no loads that pull from both panels.

Both panels receive power from the same meter can on the other side of the wall,which I believe is rated 320A. The meter can does not have a breaker. The meter can is designed with one input and two outputs for each conductor. I believe the meter can is a Milbank U4702-X-5T9-K3-K2-IL  U4702-X-5T9-K3-K2-IL

In both panels, the ground and neutral are bonded together as they should be in a main panel.

Obviously both of the neutrals come out and tie to the same lug under the meter. And both of the ground wires coming out of the tandem main panels are tied to the same building steel and grounding rods.

My question is this: Why isn't Neutral-to-Earth bonding done in the meter can in a "class 320" service? (before it splits off to two separate panels)

Is it just that the interior of the meter can isn't as inspect-able as the interior of the panels?

The two main panels are in some way sub-panels of the meter can right? I read all the time neutral and ground should only be bonded in one place. I understand why if I hang a sub panel off a main it should be isolated there. But why would the same logic not affect my tandem main panels?

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  • Who's your electric utility? Also, what is this thing you're saying is your service disconnect? – ThreePhaseEel May 11 '20 at 4:07
  • Evergy, Formerly KCPL is the utility. The meter can has a large, red-rubber-covered manual lever on the side that is used to disconnect the output of the meter can. I've never operated it actually. It can be padlocked in the on or off position, and is currently locked on. I presume its purpose is that it is most suitable to break connection under load. It resembles the handles I've seen on other equipment that have a spring loaded contact system designed to minimize arcing during make and break. – Billy C. May 11 '20 at 5:08
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    Is that lever inside the meter can (I have no idea why you're in there?!) or on the outside of the meter can? – ThreePhaseEel May 11 '20 at 12:19
  • The meter can lever I'm referring to is on the outside of the meter can. There is also a lever inside to bypass the meter during meter replacement. I didn't mention the second one but i know it's there because i watched the utility install a whole house surge protector once on the meter – Billy C. May 12 '20 at 14:17
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    I was mistaken. There is no external lever on the meter can. @ThreePhaseEel I did ya one better than that. I found the make, model, and spec sheet. – Billy C. May 17 '20 at 0:43
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In my neck of the woods (Pacific NW) we call that a "class 320" service: A single meter feeding 2 main panels. Because both panels are considered main panels, neutral and ground need to be bonded together. In the meter panel, in most cases, the neutral is already bonded to the can just by how the lugs are attached. I recently installed a class 320 service on my son's house that did have a "service bypass" that would enable the power company to swap a meter without interrupting service, but I don't think that is what you have. A pic would help.

2020 code is requiring the ability to cut off power to a structure externally. That may have been required locally for some reason back in 2014...local codes vary. class 320 meter base with service bypass

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  • OK. This is getting a bit trickier here. I just don't know if because you have a "service disconnect" switch that your main panels would need to be treated as sub-panels. Maybe one of the "big 3" here could comment. Regarding a true 400 amp service: That generally requires CT metering where only a small amount of current used actually goes through the meter. – George Anderson May 12 '20 at 14:36
  • @GeorgeAnderson -- yeah, a 400A continuous rated service will be either CT or K-base (not a normal meter socket, either way, in other words) – ThreePhaseEel May 12 '20 at 14:56
  • My mistake. There is no externally accessible service disconnect. Class 320 rings a bell. I remember thinking how odd that it wasn't 400 if I had 2x200A panels. I agree they're main panels in the sense of over-current protection, but how are they not functionally two sub-panels as far as grounding goes? Would not the same logic requiring sub-panels and appliances to not bond neutral and ground together apply to my mains because they're both split off the same meter can. Then again all the houses on my transformer aren't bonded together.... But they're separate structures.... – Billy C. May 17 '20 at 0:50
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The lever on the inside is a bypass

The lever on the inside of your meter can that you saw when the power company was working is what's known as a bypass lever that lets the power company take the meter out of circuit for service or replacement without interrupting the flow of power, which would be problematic for both you (power outage) and the utility worker (arc flash hazards). Most utilities require some form of safety bypass, either a lever bypass for utilities that use ringless metering such as KCP&L/Evergy or a test block bypass for utilities that use ring style metering such as PG&E, on class 320 services due to the higher energy levels involved.

As to your configuration of panels...

What you have is a two-panel service based on the "rule of six", with each 200A panel carrying its own service disconnecting means. As a result, you have two neutral-ground bonds (main bonding jumpers), one per service disconnect enclosure, as per NEC 250.24(B):

(B) Main Bonding Jumper. For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor within the enclosure for each service disconnect in accordance with 250.28.

Exception No. 1: Where more than one service disconnecting means is located in an assembly listed for use as service equipment, an unspliced main bonding jumper shall bond the grounded conductor(s) to the assembly enclosure.

Note that the only case where a neutral-ground bond is ever found in a meter can is when you are using a combination meter/main-breaker, meter/loadcenter, or multi-meter/main assembly, as the service disconnects are in the same box as the meter in that case, separated by barriers. (Note further that the neutral-ground bonds in these devices are permanent and nonremovable, unlike the bonding jumper on a loadcenter, which can be installed/removed as-needed depending whether there's a service disconnect in that box or not.)

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