An electrician installed a Tesla wall charger with a 60A breaker. I've added a NEMA 14-50 receptacle to the circuit behind a toggle switch (either the wall charger is powered or the plug, not both). The question is: do I need a 50A breaker between the switch and the 14-50?

This thread seems to emphatically say "YES: You must use a 50A breaker", the logic being that

The outlet is rated for 50a. If something goes wrong in the WC and pulls > 50a the outlet is not safe. The breaker wouldn’t trip until 60a [with the implication that the plug could melt before the breaker tripped].

Essentially, this falls into a philosophy of "the breaker protects the wires and the receptacle."

However, as has been pointed out many times on DIY (e.g., here), it's standard practice to install multiple NEMA 5-15 outlets on a 20A breaker, with roughly the reasoning that "devcies with a 5-15 plug are designed not to pull more than 15A; anything else is a short which will quickly exceed 20A and will therefore trip the breaker". This philosophy is that the breaker protects the wires only, and the end device itself protects the receptacle [the device is designed to pull <15A, so a single device cannot be in the 15-20A gray area that could potentially melt the outlet without tripping the breaker].

Which philosophy is correct? Is there something more subtle going on here where 5-15s are a special case, or is it fine (according to NEC) to use a 14-50 on a 60A circuit?

(Throughout, I'm assuming wires are of an appropriate size: this question is about the receptacles.)

  • 1
    What kind of toggle switch are you using? A 2-pole 50A switch is usually not a simple thing. Commented Jul 13, 2020 at 16:10
  • well written for a first post here!
    – FreeMan
    Commented Jul 13, 2020 at 16:11
  • @manassehkatz-Moving2Codidact amazon.com/Baomain-Universal-Changeover-SZW26-63-D303-3/dp/… I was surprised to see how few options there were: why is this such a hard thing?
    – crockeea
    Commented Jul 13, 2020 at 16:13
  • 3
    Lack of mass market need for it. ...and shopping at Amazon, not an electrical supply house. Without looking at the link I'm guessing Chinese product - North American (or European in Europe) product would be easy to find via industrial supply or electrical supply, but not at your local hardware store unless it's unusual - though having one at all is becoming unusual...
    – Ecnerwal
    Commented Jul 13, 2020 at 16:20
  • 2
    Because Amazon is a lousy place to buy electrical gear, for a litany of reasons. 1) being absolutely flooded with cheap Chinese junk, which they pay extra to SEO-boost in search results, crowding out any listings for proper electrical gear. And 2) Proper gear sellers dislike mail-order because most gear is low-value but rather heavy. Mail-order is not a good business model. A proper DPDT center off 60A switch costs a fortune. Commented Jul 13, 2020 at 18:23

1 Answer 1


No philosophy: Code is data-driven

Code is the result of analysis of systematically collected data about actual electrical accidents as they happened in the field. It’s the nature of science that you must take the field data as it comes, and not try to force it to conform to some notion of what it should be.

In the case of 15/20A, the data has shown that there’s no problem there. Keep in mind, UL was a partner in developing that use-case in the first place, by requiring as a condition of UL listing that everything from receptacles to appliances all play nice on a 20A breaker, unless they are on a dedicated circuit. In that case UL needs the breaker to conform to the device ampacity.

In particular, UL requires that every 15A receptacle be rated for 20A internally. And obviously 15A appliances must show they fail safe on a 20A breaker.

Conversely, data has shown that when “the big stuff” (40-60A) is mis-fused, trouble follows. The closest thing I can see to a “philosophy” is “little things have little trouble; big things have big trouble.”

Another aspect often overlooked is how NEC 110.2 (must use approved devices, i.e. UL) and 110.3(B) (must install the device according to its instructions) intersect with UL’s listing standards. UL approves the instructions as part of the product’s listing, hence 110.3(B), and those instructions are the scope of the design review and testing. When you misuse a device off-label, you’re in uncharted territory. No one can vouch for the safety of that device.

By the way, the cheap Chinese switch you linked violates NEC 110.2 right out of the box, since it does not meet the basic standard of “Approved” — it lacks a UL listing, or any competent NRTL competitor like ETL or CSA. It is illegal for stores to sell such a thing at retail; Amazon exploits loopholes in our consumer protection laws to sell it. Send it back as defective; the lack of a UL mark, a thing required on anything sold in the US, makes it defective.

Amazon denies responsibility because they say they’re only a “platform” connecting independent sellers to buyers, and the sellers also use Amazon’s billing, warehousing and shipping system. This is hollow, as far as I’m concerned.

Our best advice is to never buy AC mains equipment on Amazon. It’s either unlisted junk, or wildly overpriced because of the realities of how Prime shipping is paid for, and the fact that most electrical gear is both low value and quite heavy. Just work with your local electrical supply or home store, many do curbside pickup.

It isn’t constructive to “overthink” Code like this. What possible endgame is there to that, except deciding to ignore Code because the reasons are stupid? That’s a mistake because its premise is wrong: the premise is that the Codebook is full of rules both smart and stupid, and that it’s worth figuring out which is which, and that a novice is capable of this distinction. Every aspect of that premise is wrong.

I can tell you that everytime I’ve looked deeply into the reasons for a particular rule, I’ve seen several of them, and they interlock with other aspects of Code to provide multi-layered protection. A Code deviation will have unexpected side-effects.

The right way is easy and cheap

The easiest/cheapest way to implement that is actually a subpanel - $20 panel, two $9 breakers (50A and 60A) and you’re Code legal and done.

You’re not actually required at that point to interlock both loads, but if you really feel the need, you can choose your brands carefully to find one that has a $25 generator interlock in a box size you like. If I was min-maxing for price, I’d look at Eaton, as Square D “QO” is pricey and Siemens’ cheap interlock requires a 12+ space panel (which might be a virtue of its own actually, because you can put other loads there, heck you could power a whole wood shop, presuming the Tesla is out of the garage when you’re making sawdust).

My advice is send that switch back, and slap a subpanel there with or without interlock, and with or without extra space for other loads (not to be used concurrently with the charger, of course).

  • 2
    @crockeea -- the thing is that 15A and 20A receptacles are really the same on the inside, something that's not true for the higher amperage receptacles Commented Jul 13, 2020 at 17:03
  • 2
    I don't know why none of the big-3 here have chimed in about the PURPOSE of the different configurations of outlets. They are all configured differently to insure that whatever device is plugged into the outlet gets the correct voltage and amperage connection, assuming overcurrent protection is provided at the breaker supplying the outlet. The device plugged in may or may not provide it's own over-current protection, most large tools do. I wouldn't supply my 3 hp table saw at any more than a 20 amp 240v circuit. The motor has internal thermal protection, but a 20a brkr doubles that safety. Commented Jul 13, 2020 at 17:27
  • 2
    @Harper-ReinstateMonica This is pretty hostile, especially to a new user. I'm not challenging the code, I'm trying to understand 1) what the code says, and 2) why. I have two seemingly conflicting answers, neither of which is the definitive code, so I'm asking for clarification. I'm not proposing ignoring code, and I certainly don't claim to be smarter on this topic that those who wrote it.
    – crockeea
    Commented Jul 13, 2020 at 17:45
  • 5
    This is a frame challenge. You asked a very specific question. But the background raises bigger questions - why are you switching, why are you using a non-listed switch, etc. - to which @Harper is responding to the implied question of "I have a big charger. I want to have other electrical stuff. How can I make it all safely coexist?" And he answered that question. Commented Jul 13, 2020 at 18:03
  • 4
    @crockeea you know, on further thinking, I realize you are right. I’ve dealt with so many of these I see the glass as half empty. But here you are asking about what Code is, and taking an interest, and that puts you far above most. I’m sorry for being snippy. Commented Jul 13, 2020 at 18:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.