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I am planning to use/replace the top right 60 amps (that has been setup for the welder in my garage that I never used) for the new EV charger. What I know so far:

  1. The EV max output is 48 amps (continuous) load for the Circuit breaker 60 amps.
  2. Direct wire (no receptacles)
  3. Plan to use 6/2 MC Cable, Aluminum Armored, stranded copper Conductor

My questions:

  1. How do I know the max load of my breaker box?
  2. Should I need to stop the AC from running while charging the Tesla? Assuming it would take couple of hours or less, so we can reduce the load on the breaker?
  3. It looks like it is Rule of Six panel (no main switch). I will turn off the top 6 240v breakers and make sure the panel has no power before replacing/feeding new wire to the top right 60amps breaker for the EV charger.
  4. Anything else I am missing here?

My goal is that I am trying to avoid replacing it with the new breaker but make sure it is still safe with my setup I am planning to do.

1976 Cutler-Hammer breaker box

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nobody
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T Tran
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    Double-check the stab limits. Some of the older CH Rule of Six panels had specific stab limits, and it looks like the welder circuit isn't original. A welder has a low duty cycle so ignoring the stab limit isn't as big of a deal as it is with a continuous load like EV charging. – KMJ Dec 28 '23 at 07:53
  • Yeah, can you post photos of the labeling on the inside of your panel's door please? – ThreePhaseEel Dec 28 '23 at 12:39
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    If you’re worried about overloading your panel/service, remember that EVSE can be told during setup that it’s on any size circuit from 15A-60A. Unless you empty the battery every day, 20A or 30A is probably plenty. I don’t think you actually need to change the breaker as long as you use 60A+ wire, but if you do a BR230 is less than $20. – nobody Dec 28 '23 at 12:57
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    If it was "set up for a welder in your garage" why do you need new wiring? And why are you defaulting to copper for that wiring? Just hook the charger to the welder wiring in the garage... And realize that a rule of 6 panel is always hot on the rule of 6 bus bars. – Ecnerwal Dec 28 '23 at 15:04
  • @ThreePhaseEel I just added more photos of the inside of my panel. I think my panel can handle at least 100 Amps. Thanks – T Tran Dec 30 '23 at 03:16
  • @Ecnerwal As I mentioned below, I need to run longer wiring for the new charger. That is why I want to disable the current welder wiring. As you mentioned, it is still hot on the rule of 6 bars, how easy/safe to remove the 60-amp breaker and replace it with the new one? If it is not safe, I can re-use the current 60-amp breaker so I do not need to take it out. Thanks – T Tran Dec 30 '23 at 03:20
  • @TTran is there not a label on the inside of your panel's hinged door then? – ThreePhaseEel Dec 30 '23 at 04:50
  • @ThreePhaseEel all it shows on the panel's hinged door is "Cutler-Hammer Safety Breaker - CH control - Mark of the Finest Electrical Protection" :-) – T Tran Dec 31 '23 at 00:14
  • @TTran -- there should be a label on the inside left or inside right of the cabinet then – ThreePhaseEel Dec 31 '23 at 01:25

2 Answers2

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A few key steps:

What is your utility service size? 100A? 200A?

If it is 100A then FULL STOP. You MUST do a Load Calculation before proceeding. You may well find that your load, even without the EVSE, is at or near the limit. If that's the case then it is time for a heavy-up.

The good news is that, unlike my situation a couple years ago, you already have a very good panel. So you replace the feed from meter to panel with a 200A feed (and utility will decide what else needs to be done), possibly put in a meter-main with disconnect (depends on local rules) and replace this old panel with a new CH 42 space panel. Transfer all your existing circuits - the old breakers are all compatible.

Load Calculation and Load Shedding

Assuming you have 200A service, or after upgrading to 200A, then you look at your Load Calculation. If it has 60A of headroom, great, you're all set. If it has at least 20A of headroom, configure your EVSE to use whatever you've got and you're all set.

If it has less than 20A of headroom (or possibly even a bit more and you want better performance) then you look at automatic load shedding. Basically a bunch of EVSE and other companies (depending on whether it is "EVSE monitors and lowers usage to what is available" vs. "entire system is monitored and different loads, including EVSE, turned on/off based on a priority schedule") now provide ways to monitor your electricity usage and adjust the EVSE charge rate based on available power. Middle of the night, HVAC and not much else running - you get 60A (48A actual). Busy evening - electric cooktop, oven, washer and dryer, dishwasher, etc. all running at the same time, EVSE drops to 20A. And so on. The possibilities are endless. Not inexpensive to do, but once you hit 200A the next level up (320A/400A) gets far more involved and so this type of system can make a lot of sense.

manassehkatz-Moving 2 Codidact
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  • +1. replace this old panel with a new CH 42 space panel or add a new panel if there's space for it, maybe in the garage. Nobody ever lamented having extra spaces for a new circuit. I am, however, surprised you didn't address the waste of money spending on copper vs aluminum, or even question the need to replace wiring at all since the wire in the wall should already be capable of carrying a full 60A. – FreeMan Dec 28 '23 at 16:28
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    As far as whether the existing wiring is capable, no idea what it is. And if it is even a few feet short then it won't work anyway (because splices cost a lot at large sizes). But I saw "aluminum" in the cable description and didn't notice that was the armor and not the conductors! As far as a new panel elsewhere (e.g., garage), the issue here is not "panel full" (because swap welder for EVSE) but "service may be full and no main disconnect". – manassehkatz-Moving 2 Codidact Dec 28 '23 at 16:32
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    Thanks guys. The reason I want to replace the wiring because I want to setup the new location for the EV charger where it is more convenient to use every day. It would be 30 feet away from the location of the welder which is just less than one foot away from the breaker box. – T Tran Dec 28 '23 at 17:16
  • @FreeMan Many EVSE can't connect to aluminum. If it is a long distance then splice with Polaris or an ac disconnect is worth it. Otherwise copper the whole run. – manassehkatz-Moving 2 Codidact Dec 28 '23 at 19:24
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    @manassehkatz-Moving2Codidact Thank you for your advise. It made total sense to me. I will give it a try the setup first and monitor it to see how it goes. If there is a need to replace it, I will consider it as the next homework to do. Thanks again. – T Tran Dec 30 '23 at 03:26
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Not without an EVEMS, no.

This panel is the obsolete and dangerous old "Split-bus / Rule of Six" panel. The top 6 breakers are the main breaker, all six of them! They all must be turned off to de-energize the panel. All six should be marked "Main breakers". The bottom left, currently marked "Main" should be marked "Lighting main". It powers the "Lighting Area", or all the breakers in the section below it intended for small loads.

The original purpose of split-bus / Rule of Six is that breakers larger than 60A used to be prohibitively expensive. In their rush to electrify large appliances, the compromise was this Rule of Six design, where the sum of breakers can significantly exceed the service size. The promise was that there would always be a NEC Article 220 Load Calculation on the loads in the panel, and that Load Calculation would assure that overload is unlikely.

Of course the problem is people coming along and adding things without re-running the Load Calculation, and these additional loads overloading the panel.

So the right answer is to do a NEC Article 220 Load Calculation, such as this worksheet from Sacramento which accurately reflects NEC 220.82.

It would really help to adjust expectations, though. Here, Technology Connections has extremely good advice: you don't need anything near 60A to charge at home; that's only needed for travel.

So if you can downsize your charging circuit to something to live with, grats! You're running your EV circuit with cheap 12/2 or 10/2 Romex instead of costly #6 MC.

If you refuse to do this, then we must resort to the thing mentioned at the top - EVEMS. Since you want a 60A breaker it sounds like you're already on board with a hard-wired charge station; so now we just need to add the current sensor module and you're all set. Examples are the Wallbox Pulsar Plus with power meter (a hardwired cable data connection) , or the Emporia Load Management bundle (WiFi to the cloud for a data connection: no cloud, no charge!), or Tesla's fairly obscure offering using a Criteo power monitor (hardwired). Canadians have an Elmac unit, and Europeans have the impressive Myenergi Zappi (proprietary wireless; no WiFi needed).

Harper - Reinstate Monica
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