Multiple Panels on One Feeder
This isn’t specifically a green building question, but I know there are people here who likely have experience with these parts of the NEC.
(Diagram attached for reference)
My current electric service (that I installed ~3 years ago, before my project scope-crept and I decided to go all electric) has a 200A combination meter-disconnect on the outside of the garage, feeding a 3/0 copper-in-2″ EMT feeder. The feeder passes through a 100A main breaker panel in the garage, where I used Siemens ECRLK250 tap blocks to tap the feeder and supply the main breaker in the panel — this follows the NEC tap rules for the smaller tap conductors supplying the 100A main breaker. The main feeder conductors continue out the bottom of the garage panel and on to the main panel in the basement, a 200A rated, 40-space main lug panel. This has all been approved and AFAIK follows all relevant NEC rules.
Now, as my project has exploded, and water heating, cooking, and HVAC are all moving to electric, I realized the 40-space panel doesn’t have enough spaces, and I should have put the panel on the other side of the basement staircase to have easier access to the kitchen and laundry circuits. I’m planning to add a second panel on the other side of the basement and reroute the original feeder to it, while leaving the existing panel which primarily serves general lighting and receptacle loads (kitchen, laundry, and HVAC have not been wired yet). My first thought was to just feed the current panel as a subpanel off the new panel, but then I remembered the tap rules and thought I could actually just add a big junction box to the feeder conduit and split the feeder into two for the new and existing panels.
I’d just continue using 3/0 copper for both sides of the split, and both panels would be 200A rated, so this doesn’t actually fall under the tap rules (which define a tap as a smaller-than-normally-allowed conductor). I *think* this should all be fine, and I haven’t found anything in the NEC that limits the number of breakers or panels that can be served by a single feeder, but it’s also not something I’ve done before. Any objections to this plan from those who’ve read the NEC more thoroughly than I have?
(As an aside, the keen-eyed might notice that the existing condition actually slightly violates NEC — the 200-A main lug panel isn’t sufficiently rated given the 200A breaker on the feeder plus the 20A solar PV connected to the garage panel. The garage panel is fine because the PV breaker is at the bottom of the bus with the appropriate stickers saying not to move it, and the 3/0 feeder itself is adequate, and the inspector didn’t call me on it when I installed the solar panels….. Regardless, as a separate project, I’m looking into replacing my meter main with a Siemens MC0816B1200RTH, which would give me a 200A rated bus structure where I could replace the main with a 150A breaker, allowing expansion up to 50A PV without overloading anything, and providing additional breaker slots so I could tie said PV and maybe an EV charger and a feeder to another building into the exterior panel. Unfortunately, that panel doesn’t have bypass capability, and my utility requires bypass horns, so I’m asking them if they can waive that particular requirement.)
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Bump -- I fear my question got lost in the shuffle of yesterday's updates that made everyone reset their passwords!
You should be fine doing this. The “feeder” in this case is just a big “circuit”, and you can tap off the panels as long as the overcurrent protection provided ahead of that feeder isn’t too big for the panels you’re using (which isn’t a problem with 200A main lug panels on a 200A feeder). Note that ALL those panels should have four wire feeds (hot/hot/neutral/ground), since the ground-neutral bond should be at the main disconnect in your combo meter/disconnect panel. I’m also assuming there is a 200A fuse or circuit breaker in there acting as the “disconnect” so that you also have over current protection for the feeder and downstream panels. BE SURE you don’t have a bonding screw in the neutral busbars of any of this three panels. You can have ONLY ONE ground-neutral bond, and it’s supposed to be at the main disconnect.
200A circuits need a 4 gauge ground (with copper wire) per NEC rules. You can tap other panels off of that no problem. Note that I would use only compression splices and connectors to tap that ground, which would mean H or C taps in the junction boxes. If you have a pool, the inspector might require that due to some special rules with pool grounding. I would do it that way just as a matter of good practice though.
Btw, those Siemens tap blocks you’re using, if they are what I think they are (I didn’t look up the part number to be sure) are known as “clear taps” in the trade. There are several manufacturers.
Bill
Thanks, glad to get your confirmation, I figured you'd be the most knowledgeable in this!
Heard on the separate ground & neutral feeds -- I've got this covered, ground & neutral are only bonded at the meter/disconnect & run separately from there on, and I removed the bonding screws in the panels. In the garage panel, I did the ground connection with a split bolt connector, which seemed a bit dubious but a friend told me that counts as a "permanent" connection for code purposes. I'd like to crimp these, but as much as I like buying tools, it'd be hard to justify buying the crimp tool to make a couple connections!
I'd personally get nervous about two main breaker panels in the house. Very easy down the road for things to get funky. Someone does a reno and the hot from one panel accidently gets connected to the hot from the other panel.
My gut reaction says that this configuration (with two independent main panels) shouldn't be allowed but I don't know if it's against code. One section of the code you may want to consider is the length/routing of the main cable before the second (new) panel. Obviously there is always some length of cable inside a house before the main breaker (except in jurisdictions where they put the breaker panel outside of the house), but I believe you are supposed to minimize that. If someone puts a nail through a wall, you don't want them to hit a feeder cable that is not protected. Your proposal may run awry of that section of the code.
Now.... because your meter box has a 200 amp breaker (am I reading that right?,) maybe its a moot point in this case. However - the principle should still be similar - you want all of the cables running in walls inside of your house to be protected by a breaker inside of that house. You don't want to rely on an upstream breaker that may be out of your sight/control while you are working in the house.
Any chance you can install a disconnect upstream of the first panel and inside the basement so that you have a single disconnect that you can use to de-energize the entire house? In that case, each panel would then effectively become a subpanel.
Re-reading this - I think I misunderstood - sounds like your garage/house are the same building. I still like having access to a disconnect that can kill everything. Relying on four switches to be confident you have de-energized the house (solar, garage, two house panels,) is not something I would design in if I could avoid it.
The combination meter/disconnect boxes are typically a main breaker, so they shut off everything downstream. This is much better (safer) than an in-house main breaker, since there is no non-protected cabling in the house. With the usual "meter outside, panel inside" setup, the cable between the meter and the main breaker in the panel has no overcurrent protection you can access, and usually the only overcurrent protection at all is the primary side fuse on the utility transformer which will deliver quite a bit of power for quite a while before it blows if there is a problem.
Regarding breakers that are out of sight, you can "tag out" these breakers when you want to make sure they stay off. This is very common in the commercial world, where breakers may be hundreds of feet away from whatever you're working on.
What you are NOT allowed to do is to have more than 6 "main" disconnects for a structure. That means you can't have more than 6 main breakers fed off of the meter directly. You can have as many downstream panels as you want though, as long as there are 6 or less main breakers feeding them. With the OP's setup, there is ONE main breaker, which is ideal.
BTW, I always recommend having a main "main" disconnect. I don't like multiple "mains" as they complicate things, especially if you need to work on any of the main breakers themselves. I have right now two commercial projects at work where we are adding main "main" disconnects (one 800A and the other 1,200A, both 480v services), and in both projects we're having to have the utility shut the power to the building off so that we can do the work we need to do.
Bill
Yeah this makes sense. I read things way too quickly this morning.
That said, I do wonder if Jonny_h may be pushing the limits on a single 200 amp service. Will there be EV charging in the garage? Is it a tankless water heater? Hot tub? Any big tools in the garage? How big is the house? 200 amps starts to look small when it is the only source for everything.
Yep, Bill got the general picture right -- there's a single main breaker built into the meter enclosure, which is mounted to the outside wall of the attached garage. The interior feeder & panels are all protected by that. I just went ahead and ordered a second panel for the basement as I was proposing in this question, and it's a main breaker panel only because that's what was available (supply chain ugh...) but could have been main lug.
You make a good point on 200A starting to look small.... No tankless water heater, no hot tub, house is ~2200 square feet, yes EV charging intended in the future, and biggest tool might be occasional use of a small welder. When I ran through the NEC sizing calculations for just my kitchen and laundry, it came to nearly 150A, which got me to start worrying a bit -- but on the other hand, 200A is 48kW and when I lived in the house and had energy monitoring, the highest load I ever saw was less than 10kW -- sure, going to electric instead of gas heat adds to that, but the mini-splits I'm looking at max out at 2-3kW draw, and even straight resistance electric water heaters are like 4-5kW. It's the kind of thing where I feel like if I actually added up everything, it might point me to a larger service being necessary, but it also feels like it's be a quite unrealistic scenario to ever actually max out a 200A service -- and if I did max it out, it'd be costing me 10 cents a minute, so maybe I would want it to trip ;)
Anyway, anything over 200A would be a special request for my utility, and a bunch of costly restructuring of my stuff, so I'm going to be happy with the 200A I've got. I'm more in the "consume less" crowd than the "outdoor hot tub in december" crowd anyway! Just don't charge an EV, weld, cook dinner for 20 people, and do laundry all at the same time maybe :P
200A is enough for almost every normal house, even with an EV charger. The next standard step up is a "400A" service, which is actually 320A, and typically involves two seperate 200A feeds off of the meter feeding two seperate panels. Depending on how the OP places his junction box, there would be some future upgrade flexibility here.
I doubt you'd need more than 200A. When I size generators, I find that a 12-15kw generator (about 50-60A), is typically enough to run everything in a home normally without issue. You'd potentially go over that if you had an electric resistance water heater and possibly an EV charger, but you'd have to be almost FOUR TIMES that amount before a 200A service is going to start having problems. For most homes, paying for a 400A service doesn't really gain you anything.
Bill
Most fire department will require the solar disconnect within a few feet of the power meter so they can be certain all the power is off before they enter the building.
Walta
Yup -- My oneline was pared down a bit, and didn't show that there is a separate solar disconnect switch on the outside of the garage right next to the meter. I've got Enphase microinverters, so the disconnect switch also counts as the rapid shutdown for the array, and is plastered with the assortment of stickers saying that.