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I just got the results of a home inspection where they claim there is mismatched breakers and wires in my electrical panel. Specifically, the range (40A breaker) and heat pump (50A). He claims the wires are 30A.

Assuming this is true, is this a code violation (Nebraska)? Or a safety issue?

-edit- adding more info here for future readers so they don't have to read all the comments.

The heat pump had been replaced within the last 2 years. I called the company who installed it and they claim the heat pump installed only pulls 27A max but they would send an electrician out to swap the breaker that they missed. When the electrician came, he discovered that the 2nd over-sized breaker was not for the range (range was on a 50A wire with 50A breaker) but instead it was on an unused circuit that lead to the newly installed furnace (capped inside the furnace housing, just there for "future expansion"). Both breakers ended up getting swapped for free.

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    "Is this a code violation or a safety issue?" - Both. Why do you think they made it a code violation? - Because it's a safety issue! – AndyT Nov 23 '16 at 11:43
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    First rule of breakers and fuses: everything behind it must be able to handle the specified current. Either upgrade the wiring or downsize the breakers. – Mast Nov 23 '16 at 11:53
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    Note that even a "30 A" wire is not always "30 A". Wires may be down rated if they are bundled or in an area of elevated temperature, such as an un-insulated attic. – mickeyf Nov 23 '16 at 13:17
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    @AndyT I presume it's the difference between "you must properly color code your wires" or so that the next person to work on your wiring doesn't have to waste time figuring out WTF is going on or "you must space wall outlets no more than 2X feet apart" because power cords are only X feet long and you shouldn't use 'permanent' extension cords on one hand vs "you must not oversize your breakers" because it can burn your house down at any time. The latter is a few orders of magnitude more dangerous than the former. – Dan Neely Nov 23 '16 at 14:31
  • @Mast: There are some exceptions to that rule, e.g. allowing individual sockets on a luminary to use 18ga wiring even though that would normally require a breaker smaller than 15A. I would think in some cases it might not be a bad idea to have e.g. a 5-amp self-resetting breaker on a fixture with 5 candelabra sockets, but I've never seen any UL-approved devices for such a purpose. – supercat Nov 23 '16 at 17:34
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Was the bozo that wired those circuits trying to burn your house down?

Assuming that the wires are 10AWG (i.e. 30A), this is a major problem indeed as the wires can overheat badly from excessive current draw before the breaker ever notices something is wrong! Think of what a live toaster element inserted into your wall would do...

As to the Code, your issue violates 210.19(A)(1):

(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Conductors shall be sized to carry not less than the larger of 210.19(A)(1)(a) or (b).

(a) Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

(b) The minimum branch-circuit conductor size shall have an allowable ampacity not less than the maximum load to be served after the application of any adjustment or correction factors.

and 240.4 (the exceptions in A-G do not apply to your case):

240.4 Protection of Conductors. Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G).

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    Alternatively, a reasonable guy wired the house & a bozo retro-added a range & heat pump larger than the wires could support? – curious_cat Nov 23 '16 at 12:55
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    @curious_cat that was my initial thinking. At least for the range. However, the heat pump I had replaced 2y ago. The company that installed it brought out an electrician to do "all necessary electrical changes". Apparently they decided to not even inform me that they were leaving this crap fest for me to deal with later. I'll be calling them in 30mins when they open. – kinar Nov 23 '16 at 13:31
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    Presumably they just replaced the 30A breaker with a 50A one without changing the wiring. 30A should be plenty for a reasonable-sized heat pump. They probably sold you a much larger one than you need that will run at very short duty cycles, which means you get basically zero dehumidifying with your AC. More profit for them, worse AC for you. If so I'd make them refund the difference and replace it with an appropriately-sized unit. – R.. Nov 24 '16 at 2:06
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    @R.. nah, they actually installed a smaller unit than was there before. After talking to them today, they claim the max draw for the unit is 27A and they simply missed the existing oversized breaker. They are coming out Monday to swap it out for free. – kinar Nov 24 '16 at 6:16
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    While it is of course a code violation and a certain risk, the risk in this particular case isn't that high because the breaker protects a dedicated machine with known amperage rather than a couple outlets with unknown devices plugged in. Any short-circuit would still trigger, and normal operation is safe. The dangerous scenarios hence are an insulation or machine failure which does not short-circuit but increases the load beyond the 30A limit. (Admittedly, a pump may over-draw when it is blocked though, so the risk is real.) – Peter A. Schneider Nov 24 '16 at 15:45
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Breakers and fuses are designed to be the weakest parts of the circuitry. It is their feature. Period.

They are designed to fail safely. Fuses burn literally, breakers safely discontinue the circuit.

If they are oversized, they may not be the weakest points anymore. In case of failure they won't be the first to burn - it may be the most expensive device you own or, even worse, it may be a conductor in the wall.

In that situation, instead of an annoying blackout (breaker) or burnt $8 fuse, you have lost your vintage $500 stereo or you have set your house/flat on fire.

tl;dr Buy 25A or, if really necessary, 30A breakers ASAP. Preferably yesterday.

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    I once heard an electrician explain it as: "If the capacity of the breaker is greater than the capacity of the wire, then the breaker isn't your circuit breaker anymore; the wire is. And that leads to house fires." – Mason Wheeler Nov 23 '16 at 15:25
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    By what means would an oversized breaker or undersized wiring destroy a $500 vintage stereo except by starting a fire which would likely have far worse consequences? – supercat Nov 23 '16 at 17:35
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    @supercat I think what the answer means is that the wiring inside the stereo might be the breaker. But that wiring is unlikely to be sized for 30A anyway, so having the correct breaker in the breaker panel wouldn't help. – immibis Nov 23 '16 at 21:09
  • @immibis: Even there, fuses and circuit breakers are seldom effective at protecting electronics from electrical damage. Fuses are primarily intended to protect against thermal damage and fires. – supercat Nov 24 '16 at 16:26
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    @Crowley: Are you agreeing or disagreeing with me? There are many cases where, in the absence of a fuse, a failing part could overheat and cause thermal damage to nearby parts. Fuses are often effective at preventing such thermal damage. – supercat Nov 24 '16 at 22:27

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