NYC apartment building. Post-WWII construction. Wiring last updated 20 years ago in our apt. ( 3 pin grounded outlets, etc. )
The entire apartment is on a single 15 amp breaker. Till a few weeks ago, it meant we could not run the microwave and air conditioner. Now it does appear to me that the breaker is weakening. With nothing big pulling amps, it blows.
Here is my question. Is there a compelling argument against my desire to pull the 15 amp breaker and put in a 25 or 30 amp one? The wiring is not so ancient that I fear fire.
This is a whoosh, right? Without checking the wire sizes, that would be pretty stupid. Why not replace the old 15 amp breaker with a new 15 amp breaker? Not a long-term solution, but if your existing breaker is “weakening,” that should bring you back to where you were.
If the wires are big enough, a larger breaker would be OK, but don’t neglect this step. It’s hard to believe you are running an entire apartment on one 15 amp circuit, especially if it was updated 20 short years ago.
If wired to code, a 15 A breaker is connected to 14 ga wire. A 20 A breaker would use 12 ga wire. You could pull more current than the wire is rated for which would then get too hot and possiblely cause a fire inside the walls. Not a good situation at all.
Breakers wear out after tripping too many times, if you have 12ga wiring a 20 amp breaker will be ok. This should be done by an electrician if you are not absolutely sure you know what you are doing. Be darn careful, wire/ breaker size charts are readily available online. Make sure you know what you are doing before you do it.
if you put in a larger breaker than the wiring can accommodate then you risk a fire, the age of the wiring is not a factor in this.
also you can not determine if the circuit might take a larger breaker based on just the wire in the breaker box; you need to know about all the wire and devices in that whole circuit.
the owner might be willing to hire an electrician and see if it is feasible to make the apartment into more than one circuit.
Indeed. I wouldn’t do anything to the breaker box without first consulting the landlord or apartment manager. Keep in mind, though, that re-wiring the apartment is going to be expensive, so unless there is a real code violation (a distinct possibility) or some other safety issue, you’re probably not going go get them to do it.
As was already said, it’s the size of the wire that matters, not the age. 14 gauge wire is not designed to handle 25 or 30 amps no matter how old or new it is. From a safety point of view, replacing the breaker with a higher amp breaker is an extremely foolish thing to do.
There are also potential liability issues. If you cause a fire, you will be legally responsible for all damages you cause. If you burn down the entire apartment building, since you touched the electrical system you are financially responsible for it. Even if you replace the breaker with the right same size breaker, you still open yourself up to liability issues. If there is a problem in the future, they will try to blame it on you. The building manager will have paperwork showing that it was built to code. You don’t even have an electrical license. Legally, if there is any other electrical problem later, you’re screwed. Basically, if you touch it, you own any problems that occur later with it.
You don’t own the building. The correct course of action in this case is to notify the apartment manager of the problem and let them deal with it. They will probably just replace the breaker. If you ask nicely, you might be able to convince them to run a separate outlet for the air conditioner. It’s worth a shot, especially if you let them know that you keep having problems with it.
If for some reason you do feel a need to bypass your landlord, hire an electrician to do the work. Then he will be financially responsible for any problems that might occur later. That’s why electricians have insurance.
It’s not really an issue with the size of the wire, but the connections, most likely, since even 18 gauge wire can handle 16 amps (and 32 amps for 14 gauge, and the article notes that these are still very conservative ratings; you’d be amazed at how much current the leads of a power transistor can handle for their size). Not that I’d put a 20 amp breaker on a 14 gauge circuit.
The real issue is the temperature rating of the insulation.
The insulation used with newer “Romex” wire (e.g. NM-B, THHN) is rated for 90 °C. The actual temperature of the insulation is a function of the current, ambient temperature, and the number of conductors in the bundle. So at higher ambient temperatures, the amount of current the wire is allowed to carry must be decreased via a derating factor.
According to the NEC, 14 AWG wire with a 90 °C insulation can be used to carry 25 A when the ambient temperature is 30 °C (or less). But the NEC also states that the circuit breaker for a circuit that uses 14 AWG wire must be 15 A. So even though the wire can theoretically carry up to 25 A, no more than 15 A will be carried by the wire due to the circuit breaker.
As mentioned, the current ratings in NEC Table 310.16 are for an ambient temperature of 30 °C. Let’s say you run 14 AWG NM-B inside the attic of a house located in southern Florida, and the attic is not ventilated. If the temperature inside the attic reaches 132 °F, then you must use a de-rating factor of 0.71 according to Table 310.16, which means the wire should not carry more than (0.71)(25) = 17.75 A. If there’s old wire in the attic (e.g. NM wire manufactured before 1984), it will only have a temperature rating of 60 °C, and you would have to de-rate it even more.
The current ratings in NEC Table 310.16 are for the wires inside the sheath of the NM-B cable. The sheath itself has a temperature rating of 75 °C.
In addition to wire, a circuit also consists of switches, wire nuts, fixtures, receptacles, and circuit breakers. These items are usually rated for 60 °C or 75 °C. So even though the wire itself is rated for 90 ºC, it’s kind of a moot issue since the connection points are rated for 60 °C or 75 °C.
IANALE, but kitchens have required two 20 amp circuits for only the kitchen receptacles for more than 20 years, so there is most definately a code violation if it was rewired only 20 years ago.
From personal experience, 28 AWG wire can handle 5 amps (the table I linked to says 1.4 amps for chassis wiring, note again it is a conservative rating) and will only feel warm to the touch, I’d say maybe a 10-20°C rise (calculations show 1.6 watts per foot of power loss; note that power loss rises with the square of current, so it will be much cooler at 1.4 amps, with only 0.12 watts dissipated per foot, the value for power transmission gives only 3 mW/ft; the latter is based mainly on acceptable voltage drop over very long distances).
You need a extra circuit run. They can put in a subpanel right next to your main panel. Get that microwave on its own circuit. Really the AC should be on one too.