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Is ok to use 60amps breaker to AWG12?

  1. Jan 22, 2010 #1
    My parents house use to have 40amps fuse and awg12 solid wires on all the house wirings, including 1x 1/2watts ac, 1x ref, 1x 20inch crt tv, 10x large florescent lighting, 1x pc with 300watts psu and maybe some ironing once a week, i changed the main fuse box to 60amps breaker thinking its enough, the main breaker is still connected by 2 sets of 40amps fuses the first set is for the lighting and the other is for the ac and refrigerator, the breaker is connected now and i recently checked some websites and it says that if your have 12awg you need atleast 30amps of fuse, so you think my 60amps breaker would still trip off?
  2. jcsd
  3. Jan 23, 2010 #2


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    If I understand your post correctly, your main breaker (at the top of the breaker panel) is 60 A, and downstream from that there are 40 A fuses (i.e. breaking the 60 A breaker means that no electricity flows through the fuses). The specifics of the following pertain mostly to Canada (and for the most part, the US), but the generalities are used throughout the western world.

    You don't mention what feeds this panel (is this the primary one for the house?) I hope it's not being fed by 12 gauge cable, since that's a violation of at least the Canadian Electrical Code and probably the National Electrical Code as well (the NEC is used in the US). The recommendation (at least in the CEC, which is what I'm familiar with) is that you use 12 gauge wiring for 20 A max. If you put more current than this through this cable (and the cable is buried in insulation, or in still air, or otherwise can't dissipate heat), there's the possibility that the insulation or conductor itself could get hot and/or melt and/or start a fire!

    I don't know how things are wired up at your fuse panel. Are most of the loads you mentioned on separate circuits (i.e. lights on one, AC on another, etc.) that are tied together only at the fuse panel, or are these just in two really big chains controlled by the 40A fuses?

    If it's the first case (you can tell because there'll be lots of wiring coming from your panel), you can (depending on jurisdiction, check with your local electrical inspector, if applicable--some places require the electrician to do this, in part or in whole) replace your fuse box with a breaker panel with appropriately sized 15 or 20 A breakers on each of your circuits. Hopefully, wiring for things like your stove or dryer (assuming you have these) are sized appropriately: if they are, you just need to find the right breaker ampacity.

    If it's the second situation (you can tell because there'll only be two cables coming from your panel, along with whatever feeds the panel), in order to become compliant, you'd have to rip open walls to replace wiring (along with your panel). In many jurisdictions (again, you need to check), although your house may violate current electrical code, it may still be grandfathered in (as long as it was compliant at the time of installation / rework and re-inspection) and thus acceptable. However, unless this is a really, really old house, I don't know of too many legitimate electricians that would do anything like this, and a homeowner somewhere in the past probably did this work without consulting the code book, pulling permits, or getting an inspection.

    EDIT: You might think that you're okay, for the loads you've listed (after all, they each draw very little current--except for the AC: I'm not aware of too many that are 0.5 W; 0.5kW maybe--and my intuition thinks that'd be sort of anemic), but the danger is when things aren't working properly, and you have a short, or rats gnaw through the wiring, or any other number of non-normal situations that fuse panels and breakers are meant to protect against.
    Last edited: Jan 23, 2010
  4. Jan 23, 2010 #3


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    I'm thinking your "1/2watts ac" refers to 1/2 ton (6000 BTU). Most 1/2 ton air conditioners will require around 5 to 7 amps at 115volts. If you are having problems "blowing" fuses, then for sure you don't want to just up the fuse size in your case. The rated ampacity of 12 gauge solid copper wire is, according to the National Electrical Code, 20amps. The best solution is to either add another 20amp circuit or split the loads (move something to another outlet). As MATLABdude says, "there's the possibility that the insulation or conductor itself could get hot and/or melt and/or start a fire!"

    Here's a http://www.cerrowire.com/default.aspx?id=46" [Broken].
    Last edited by a moderator: May 4, 2017
  5. Jan 25, 2010 #4
    my current setup


    what do i need to change? here any suggestions?
  6. Jan 25, 2010 #5


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    Can you confirm that the TV, AC and refrigerator are all daisy-chained together (meaning that it's a single cable coming back to the box, instead of a bunch of cables that are tied together through a bus bar or with wire nuts.) I'd have to advise you to actually down-grade both fuses to 20 A ones. You want the fuse to blow instead of allowing your wiring to burn up. That or rewire some of these onto different circuits (each fluorescent tube, for instance, only uses up 1/3 A or so, neglecting the ballast).

    If this is a feeder panel, and the blue wire is ten gauge (check the jacket), you should use a smaller breaker at the main panel (or at the top of the feeder), probably a 30 A one, and not the 60 you have.

    The important thing to remember is that a 20 A fuse (or 20 A breaker) won't blow the moment it hits 20 A; they're designed to blow depending on how much more current they're carrying than they should. If it's 200%, it'll probably blow fairly quickly. If it's only 125%, you might have half an hour. If it's right at 100%, it probably won't actually blow.
  7. Jan 25, 2010 #6
    can i just change both 40amps fuses to 20 or 30amps breakers? would this be ok? i dont want to change the 60amps breaker because its coming directly from the power lines and i had a hard time installing it because i dont have any gloves to hold those live wires.
    iam always welcome for any suggestions here. just dont let me change those 60amps breakers.
    Last edited: Jan 25, 2010
  8. Jan 25, 2010 #7


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    Yikes, you were (almost) literally playing with fire there... Here, we're required to get a certified electrician to do the main breaker installation. At the very least, you should get power shut off so you're not worrying about 2 or 3 different things simultaneously, or heaven forbid, you short something out (the next breaker up from you is probably sized for a few thousand amps and is located at the substation).

    Maybe we should back up a step here... Is the breaker actually housed in a breaker panel? I'm presuming that your 60A breaker is the main breaker which could--but isn't--supplying current to other breakers. Actually, do you have inline fuses, or something entirely? Most of the panels I'm familiar with don't really give you your choice of fuses OR breakers. If you have a panel, great! Plug in the 20 A breakers, and you should be good to go. Again, you do not want to be exceeding 20 A on 12 gauge wiring.

    I don't mean to condescend, but have you got a copy of the electrical code book for your area? You don't need the full one: there's usually a simplified one for homeowners, available at your local hardware store for not very much money. These tell you what is legally required in your area, but there are other ones (say, the Black and Decker Electrical Projects, or 1001 Electrical Projects, etc.) that don't go into the code so much as basic electrical safety and how to do certain projects (e.g. panel replacement). These should also be available at your local public library.

    EDIT: Sorry, I just looked at your past posting history and realized you're from the Philippines (I just assumed you were American). I have no idea what the electrical code is like there, but in general the advice that I and dlgof have given still stands from a safety standpoint.
    Last edited: Jan 25, 2010
  9. Jan 25, 2010 #8
    yes, i bought my 60amps breakers with a solid metal panel housing

    i think the tv has a voltage regulator connected to it same with the PC that must have inline fuse, the ref and aircon doesn't

    thanks for the advice i will replace my 40amps fuse with 20amps breakers i will do that when i visit my parents house.
  10. Jan 27, 2010 #9
    just went to the hardware and bought 3x 20amps breakers and some 12awg's
    i want to setup these in my parents house, is this schematics ok?

  11. Jan 28, 2010 #10


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    That looks reasonable--I'm glad you didn't have to pull extra wiring to split the circuits like this. I'm a little confused as to how you have 10 gauge wire between the 60 and 20 amp breakers, though. What brand / model are the breakers? All the breakers I'm familiar with plug or screw into the breaker panel.

    EDIT: Nevermind, it looks like you are running extra wiring. If you've never done that sort of thing before, please, please consult a home wiring book or better yet, someone that's done this before. On the other hand, 20 A breakers with your current setup would pobably still work.

    Yes, having done it before, I'm distinctly not a fan of ripping open walls and running wiring. Suspended ceilings aren't too bad, but you still usually have to run into walls.
    Last edited: Jan 28, 2010
  12. Jan 28, 2010 #11


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    Looks good chrisalviola. It's nice that you took the time to check out the details. Now all you have to do is be careful and double check that anything you are going to touch is not energized.
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