Correct way to tap a 2/0 sub panel neutral conductor?

Question

This is not a question about neutrals and grounds bonding.

I have a 200A sub panel which is fed from a 200A utility disconnect. In this 200A sub is really just the tie in for a 20A solar system. It then has a 200A breaker than feeds a 200A interior “main” (which I’m assuming is really a sub because it doesn’t have a main breaker) that has all my home loads.

I am adding an EV charging 125A sub panel in the garage and plan to feed it off of this 200A sub. The 125A breaker will land on the bus bars and connects to 2/0 AL SER.

For the neutral 2/0 is a lot to land on the bar directly. I am wondering how to do this appropriately. Do I buy a lug kit for 2/0 and land it on the neutral bar? If so does the lug need to be close to the feed lug or does it not matter? Should I be using a multi tap instead so that the neutrals have a beefy piece of metal to connect and not just a neutral bar? Thanks

Answer 1

TLDR: your panel manufacturer will offer a neutral lug kit that attaches to 2 slots on the neutral bar. 2/0 is a lot to attach to a 125A breaker and I advise revisiting the size choice.

Wow, you don't need anything like that much power.

I am adding an EV charging 125A sub panel in the garage

Wow, you don't need all that for EV charging. We see people spend crazy amounts of money putting in huge charging rigs, overloading their house - when it's just not necessary.

People get confused by the travel unit that comes with the EV. That's for "opportunity charging" on the road. This here (at 26:14) is the textbook, correct use of it. Notice how Grey has been traveling all day, and the battery is empty, and must be full by morning, because y'know, travel. That's why a travel unit needs 50A and a home unit doesn't need anywhere near that.

If you want to use the travel unit for home charging, you can just get a dongle plug for whichever amp circuit makes sense at home.

And then people think if they get two EVs, they'll need two of them. No, that actually works even better.

Power Sharing allows two EV wall units to share a single power feed. Say you have two EVs. You never know which one will need a big charge, so you install Power Sharing wall units sharing as little as 30A (giving 200 miles in a 10-13 hour overnight charge, that starts when the FIRST car plugs in). The 30A is split until the lightly used car is full, then the hungry car gets all of it. This happens automatically. The Tesla Wall Connectors just do this right out of the box, and they make a "every other brand of car" version of that, so you can even mix and match.

Go for it if you got it, but you probably don't.

The electric service to your house has limits. 125A is a huge impact no matter how you count it. What your house can support is determined by a NEC Article 220 Load Calculation. That generally pops out a number like 155A on a 200A service, and then you know you can have up to a 45A circuit for EV charging (300 miles in 10-13 hours). Again, bonkers for a single car, but would make sense Power Sharing 2-3 cars.

The feeder size

I hope that a more realistic view of EV charging will have tempered your EV power demands because now it simplifies a bunch of your problems - not least, how to get the wires onto a 90-125A breaker, their support of 2/0 is hit and miss.

• If 90A feeder will suffice, #2 aluminum won't be a problem, and it's a commodity.
• For 100A, #1 aluminum.
• For 120A, #1/0 aluminum - you can only plan loads of 120A, but you can "round up" to the next available breaker size of 125A.
• I can't recommend 2/0 because some 125A breakers are not approved for it. Absolutely do not break off wire strands.
• I'm not listing copper because aluminum is proven reliable at these power levels, copper is obscenely costly and I'd rather you spend that coin intelligently, and 2/0 copper would be 175A wire anyway - gross overkill.

The 125A panel

Many smaller panels have a bus rating of 125A. You probably know this, but that's an absolute maximum redline - like the 112 MPH speed rating on your car tires. You don't have to drive 112 MPH, and you don't have to feed 125A to that panel. Any amount less is fine! In fact, spaces are cheap, getting more is always a good idea. So a 200A-rated panel may be a better choice, even if you're only feeding it 50 or 90 amps.

Answer 2

I have a 200A sub panel which is fed from a 200A utility disconnect. In this 200A sub is really just the tie in for a 20A solar system. It then has a 200A breaker than feeds a 200A interior "main" (which I'm assuming is really a sub because it doesn’t have a main breaker) that has all my home loads.

Actually, that "main" is really a subpanel, not because it doesn't have a main breaker (a main panel must have a main breaker, but a subpanel can too) but because it is after that first disconnect. The main is defined by where the neutral/ground bond is. That is likely at the utility disconnect, though it is possible (depending on what you really have) that it is at that 200A "sub" that has the tie-in for solar. Note that you can can almost certainly put other things, such as a feed to a garage subpanel, in that first 200A subpanel.

I am adding an EV charging 125A sub panel in the garage and plan to feed it off of this 200A sub.

WHY???

An EV charging subpanel in the garage makes sense. And using a big panel, rated for 125A (or even for 200A) is fine. And it can be a main-breaker panel rather than a no-main-breaker panel, as having a main breaker can be a convenience for maintenance and doesn't cost much more if you shop smart.

But why 125A? There are garages that use 100A or more, typically when they are really more "workshop" than "garage". But you stated "EV charging", so presumably this is one or two EVSE circuits plus a 15A 120V lighting circuit and maybe an additional 20A 120V circuit, or even two of them, for tools, etc. The key is that those EVSE circuits typically need to be only 20A or 30A in order to charge a typical EV overnight based on typical usage. You could even put in somewhat larger circuits, but if installed properly with EVSEs that communicate to share power, the total load can be kept relatively low.

The confusion about this often comes from "50A RV park charging connector" + might as well have 2 of them in a 2 car garage. But that connector (which you wouldn't use anyway in your own garage - hardwired EVSE is much better than plug-in) is for a specific use case which makes sense for travel (RV park available but no Tesla Superchargers or equivalent available) and not for use at home.

The 125A breaker will land on the bus bars and connects to 2/0 AL SER.

Yes, that makes sense if you actually need 125A (100A continuous). But you almost certainly don't. You'd probably do just fine with 60A or 70A and 2 AWG AL wire.

For the neutral 2/0 is a lot to land on the bar directly. I am wondering how to do this appropriately. Do I buy a lug kit for 2/0 and land it on the neutral bar? If so does the lug need to be close to the feed lug or does it not matter? Should I be using a multi tap instead so that the neutrals have a beefy piece of metal to connect and not just a neutral bar?

The details of all that will depend on your specific panel. Each manufacturer has particular specifications of what size wire can go into each part of the panel. But it is totally irrelevant if you put in a smaller feed.

If you really, really need 100A continuous to the garage then I would worry about whether the 200A utility feed (and various 200A components along the way) has enough spare capacity for 100A to the garage. You should do a load calculation in any case, but especially if you plan on more than 30A for charging.