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Short version: When there is a high load on the power grid in general, does it make it more likely that my fuse will blow?

Full version: I'm renting an apartment in Rome, where we are currently experiencing a heat wave. When running the air conditioning unit on max, the circuit breaker will regularly trip after an hour or so, taking out the power in the apartment. Since I have to go down to reset it, I know that my apartment is the only one affected, i.e. my power is lost, but no other apartments in the building are affected.

When asking my landlord if he can rectify the situation (e.g. by installing a circuit breaker that can handle a slightly higher current), he says that the power grid is overloaded by people using their AC in the warm weather, and there is nothing he can do.

I intuitively find it hard to understand that an overloaded grid will lead to my circuit breaker tripping easier, but I don't have a super strong grasp on alternating currents and building/city level grids. Can anyone help me understand, or alternatively make my case?

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  • $\begingroup$ I'm sure there are folks here that can answer this but it's more of a question for an electrician than a physicist imo. $\endgroup$
    – pentane
    Commented Aug 4, 2017 at 20:27
  • $\begingroup$ I see what you mean! Is electronics stackexchange the best place for this, or is there a more targeted one? $\endgroup$
    – olagjo
    Commented Aug 4, 2017 at 20:33
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    $\begingroup$ Your landlord doesn't know what he's talking about. He just doesn't want to pay to upgrade your circuit breaker. $\endgroup$
    – Myridium
    Commented Aug 5, 2017 at 3:08
  • $\begingroup$ The fact that the circuit breaker trips after an hour or so suggests to me that as it warms up, its capacity drops. This may indicate a faulty circuit breaker, or it may be that you are taking more than the nominal maximum load, but that the CB can handle this when it is not too hot. $\endgroup$
    – Dr Chuck
    Commented Aug 5, 2017 at 8:09

2 Answers 2

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First of all, fuses blow when the current they receive is higher than what they are expected to handle. The main reason for that is either the fact that you have contracted a certain amount of power to the energy company and they are limiting the current you can receive because, otherwise, you would be getting more than paid or because, otherwise, the amount of current that would be going through the circuit could be dangerous to you.

That being said, if the flat circuit connections are well done, what the other neighbours do should not affect you -or, at least, should not affect just you- because the connections between flats -and also between rooms inside flats- are made in parallel so that one does not affect the others.

In other words, the amount of current that you receive in "your part of the flat's circuit" should be independent of the one the others receive.

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  • $\begingroup$ Brown out conditions with weird stuff happening with the phases and lots of inductive loads can play havoc with circuit breakers. $\endgroup$
    – Jon Custer
    Commented Aug 4, 2017 at 20:18
  • $\begingroup$ Thanks! Of course, we will not ask the landlord to upgrade the circuit breakers above what the actual circuits can handle :) My main concern was to identify whether the heat wave or the apartment's circuitry was to blame - and I'm reading your answer as "circuitry"? $\endgroup$
    – olagjo
    Commented Aug 4, 2017 at 20:22
  • $\begingroup$ @JonCuster That is true, but there are many other things that could be happening there. If they are renting the apartment and that is really happening once and again, they should be assisted because though it may be something stupid, it could also be because there were some current derivations, which could be dangerous. $\endgroup$
    – ccorbella
    Commented Aug 4, 2017 at 20:24
  • $\begingroup$ @JonCuster: Cheers! But would a brown-out affect only my circuit breaker? Would that be because I have more load on it than my neighbors? $\endgroup$
    – olagjo
    Commented Aug 4, 2017 at 20:27
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    $\begingroup$ @olagjo Just to be sure, if I were you, I would ask an electrician. I would tell you of a great forum, but it is in Spanish... but I am sure you can find one Googling a little. $\endgroup$
    – ccorbella
    Commented Aug 4, 2017 at 20:35
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The explanation could be partially true if

  1. The heavy city-wide load causes a drop in overall line voltage;
  2. Your air-conditioner, attempting to supply the right energy to the air-conditioner motor, responds to the low supply voltage by increasing the current drawn through your circuit-breaker. See this article https://en.wikipedia.org/wiki/Brownout_(electricity) for details...
  3. Your circuit-breaker, being triggered on the low side of the stated value, triggers...

You may have other high loads in your apartment, or possibly creative wiring adding someone else's load on your breaker...

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    $\begingroup$ Can you explain why a drop in voltage would increase the chances of a fuse burning out? I guess you would need more current for a lower voltage to draw enough power but I am not sure if devices would draw more current just because the voltage is low. $\endgroup$
    – Yashas
    Commented Aug 5, 2017 at 4:14
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    $\begingroup$ They could.. See edit... $\endgroup$
    – DJohnM
    Commented Aug 5, 2017 at 4:51

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