How to wire a second sub-panel from outdoor main disconnect

Question

I need to install a 240v 50amp breaker for an EV charger. There’s no space on my main panel in the basement. I’m hoping to install a new subpanel outside near my main disconnect next to the meter.

1. Can I modify the lugs here to double them to go to another sub-panel next to this meter enclosure? If so, which lugs might fit this QOM2200MM disconnect? (Or, alternately, replace this disconnect with one with double lugs if not? Though these 200amp disconnects are pricey.)

(Or am I on the wrong track and better to run the wires from the existing subpanel to a new (intercepting) subpanel, and then wire that panel to this main disconnect? In this case do I need another (200amp?) breaker in the intercepting subpanel to attach the current subpanel in the house to?)

2. I understand the new subpanel has to be rated for (more than?) the 200 amps of the disconnect even if the loads are lower. Can someone suggest an appropriate subpanel with 4-8 spaces on it? (Maybe I’d install a second 240v/50amp breaker some day.) Most high-amp sub-panels seem to be for large number of spaces.

3. If I can do double lugs on the existing disconnect, do I need to upgrade the ground / neutral bar currently full in this picture, or can I use two of the lugs on the bar below the second meter? (Current just has a ground wire going to the phone/cable enclosure on it.)

This is in Northern California. Wire size advice for your suggested solution would also be nice if easy—- assume I’d never need more than 2 50-amp breakers / 40 amp loads added to this new subpanel.

Answer 1

You should be able to employ the "tap rule" as defined in the NEC. Downstream of the main breaker, the wire would be cut, or removed from the main breaker and a short length of 4/0 AL used to connect the disconnected wire to a listed tap connector appropriately sized for the wire. Then the tap would run to the sub panel. There are lots of rules regarding this setup, but it's doable. Some of the rules are listed below, I don't take credit bc it's copied and pasted from my research. BTW, I have done this exact same thing and actually had to school the inspector by quoting chapter and verse from the NEC regard tap rules, he passed it! The other thing you might consider, if practical, to free up some breaker space in your main panel to make room for the sub-panel feed is to move a few circuits to the new sub. But I think your best bet is install the new sub using a tap. All of it MUST be installed in a raceway (conduit).
Based on a comment, I want to add that the sub needs a main breaker appropriately sized for the wires feeding the sub-panel. It's in the NEC, but just wanted to add this here.

Below are a portion of the rules from the NEC:

10-ft feeder tap rule [240.21(B)(1)] — You don't have to install an OCPD at the tap point of a feeder tap if its length doesn't exceed 10 ft and if it meets the following requirements (Fig. 1 above):

The ampacity of the tap conductor is not less than the computed load in accordance with Art. 220, and not less than the rating of the device supplied by the tap conductors or the OCPD at the termination of the tap conductors.

The tap conductors aren't extended beyond the equipment they supply.

The tap conductors are installed in a raceway if they leave the enclosure.

The tap conductors have an ampacity of no less than 10% of the ampacity of the OCPD from which the conductors are tapped.

Answer 2

The tap suggestion in the other answer is legitimate. But I think that a better solution is:

• Install a subpanel near the main panel. Assuming you are happy with the existing panel type, get a subpanel of the same brand/type so you can move breakers instead of having to buy any new breakers.
• Move a few circuits from the main panel to the subpanel
• Add a large feed from the main panel to the subpanel - minimum 60A but assuming feed breakers are available and affordable, 100A would be great.

By doing this:

• Your subpanel is inside, away from the elements.
• You can add more circuits inside easily. While the EVSE will be outside, most new circuits you will add in the future will be inside.
• You don't mess with the big feeder, and you don't need to shut power to the rest of the house.

For the EVSE, I highly recommend hardwiring it. 50A can be done on a plug/receptacle but there are some disadvantages to doing that, particularly new requirements (may or may not be in place in your area, yet) for GFCI on plug-connected large 240V equipment.

Harper will tell you don't bother with 50A, 20A - 30A is enough. That's your choice, depending on your specific needs. (But Harper is usually right.)

Answer 3

A few gotchas with EV charging

First, in multi-unit housing (i.e. everything but a single-family home owner-occupied) all work must be done by a licensed electrician. You can peek, design and even lay conduit (and stick pull-strings in it) so long as the licensed guy will be doing the sparky things and can physically inspect your work. My strongest recommendation is EMT or IMC/RMC metal conduit, because no professional will ever snub properly laid EMT, IMC or RMC. And it's super easy to adjust/fix/alter since it's bolted not glued.

Second, "I need 50A" is a myth based on a string of misconceptions. EV charge rate is configurable to any value, and 20A is sufficient for almost everyone (i.e. most people will never need more, and the few who do will need it very rarely - and DC fast charging or simply using a 60A level 2 unit at work or mall will easily close the gap).

Third, tying back to the second, a NEC Article 220 Load Calculation must be done on the electric service to determine what size is possible and limit EV charging to what is safe. That will then dictate you which charge rate to program (via DIP switches or swapping dongle plugs on the travel EVSE).

On multi-unit services, the power company must ALSO be consulted to determine the sum total of EV charging that can be accommodated by the site's power drop. And here's happy news: You can use "Share2" Power Sharing to split a power allocation among multiple EVs, even on different services/meters. If the power company says "only 30A TOTAL on the site", you don't need to give each 15A. You can give each a 30A wall unit and they'll get 30A if the other guy isn't charging. The magic of 1980s microcontroller tech!

On your setup, though

Yes, you can use the Tap Rules. You can get vampire taps for cables, or pigtail both into a set of Polaris connectors. Since this is the main breaker, neutral and ground are tied here any you might be able to use smaller ports on the neutral-ground bar, or move grounds to an accessory bar.