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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.

QOM2200MM disconnect

  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?)

  1. 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.

  2. 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.)

picture of meter enclosure with two ground bars

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.

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  • you don't have to have 200A wiring if its short enough, under 30 feet you can use 70A wiring to a box with a 70A or smaller main breaker. or better: (100A to a 100A box etc)
    – Jasen
    Commented Nov 21, 2022 at 10:13
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    missing screw top right.
    – Jasen
    Commented Nov 21, 2022 at 10:18
  • Do you really need 50A feed to the charger? EVSE can work fine on lower amp circuits, all that means is that your car charges slower. And you would be doing an overnight charge anyway, no need to overspec that to that amount. Commented Nov 21, 2022 at 10:32
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    Please search this site for "50amp EV charger". It's highly unlikely you actually need one, there's a user named "Harper" who has explained why not multiple times, please save him the effort of typing up a whole new response. Now, if you simply need an additional panel for additional circuits because your current panel is full, that's a different question (also answered here multiple times), that you could ask.
    – FreeMan
    Commented Nov 21, 2022 at 14:04
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    Just for what it's worth: I recently upgraded from 100A to 200A service, and as part of that the electrician both moved the master breaker to outside (per current practice) and, at my request, replaced the inside panel with a larger one (the old one was both running out of space and becoming hard to get the right breakers for). At the same time we ran 100A cable for a secondary box at the other end of the house to power workshop, new air conditioning/heating, and to make future work at that end of things simpler; this is powered via a linked pair of 100A breakers in the new primary box.
    – keshlam
    Commented Nov 21, 2022 at 15:58

3 Answers 3

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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.

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    I'd like to understand why there are two meters and four wires exiting the box. I wonder if that would complicate this approach.
    – jay613
    Commented Nov 21, 2022 at 14:20
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    Isn't it the case that the tap conductors have to have a suitable OCPD somewhere? IE, if it's a 50A sub with suitable wires feeding it from a tap but only protected by the 200A main, the sub should have a 50A main breaker ? This answer seems to leave that out, suggesting that if less than 10 feet the 200A breaker can be used with wires rated for 50A.
    – jay613
    Commented Nov 21, 2022 at 14:25
  • @jay613 yes, the sub must have a main breaker to at least protect the sub's feed of an ampacity equaling the ampacity of the feed. Thanks for the feedback. I'll add it to my answer to make it more clear. Commented Nov 21, 2022 at 14:29
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    @jay613 Actually, if I interpret the rules correctly, you could run 12 ga (200 amps times 10% = 20 amps) as a tap conductor. No way I'd do that. I thought the tap conductor needed to be at least 20% of the main conductor, but apparently I was mistaken. Again, thanks for your comment, it helped me improve my answer. Commented Nov 21, 2022 at 14:37
  • I think the 10% rule allows, for example, a regular 15A outlet to be installed near the meter main using a tap with #12 wire if a suitable 15A or 20A breaker or fused outlet is used. I think this is useful if the meter main is far from the building where the main panel is and there's no other provision there for outlets or lights. I've never done this or even seen it, I'm just assimilating things I've read here over the years. Probably outdated and unnecessary now that battery tools are so much more reliable.
    – jay613
    Commented Nov 21, 2022 at 14:49
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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.)

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  • Thanks for participating, but I do need to point out that I also suggested freeing up space in the main panel for the subpanel breaker and moving those circuits to the sub IF PRACTICAL...not always the case. I also maintain that a quality rain tight outdoor sub is perfectly OK. And YES, working with 4/0 AL is a total PITA, but it might be the best approach. At the end of the day, I don't really care: I can''t see it from my house! ( LOL, just having a bit of fun!) Commented Nov 21, 2022 at 17:06
  • One of my neighbors has a heavy-up "almost done" for over a year (probably several years, but I only first saw it about a year ago) - new cable sticking out of empty new meter pan up to old meter - looks horrible, but nothings burned down... Commented Nov 21, 2022 at 17:12
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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.

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