What is the reasoning behind certain electrical breakers?

July 6, 2005 8:07 AM

Changing Electrical Circuits

When I purchased my home last year, part of the deal was that the seller had to install a new electrical breaker system to replace the antiquated 30 amp fuse system.

What was installed was a system of 2 panels of 100 amps each, covering 2 units of my duplex.

On Unit 2, the electrician who did the work (done well before I moved in) installed 4 20 amp breakers. On unit 1, he installed 2 20 amp breakers and 2 15 amp breakers.

The wiring throughout the house is old, but works well.

I have run several additional plugs in my basement from unit #2 box.

On the Unit #1 box, one of the 15 amp breakers keeps tripping, most likely due to appliances.

Is there a reason why a 15 amp breaker was used instead of a 20 in that wiring, but 20 amp breakers were used on unit 2. Could I just punch in a 20 amp breaker to allow more electrical power to that part of the house?

posted by benjh to home & garden (13 comments total)

It's not likely that you could safely swap the breakers.

The difference is probably in the gauge of the wire on that circuit - for a 20A breaker, you need 12 gauge wire. For a 15A breaker, you only need 14 gauge (thinner) wire. If you up the breaker to 20A and the wire is only 14 gauge you run a pretty decent fire risk as devices you hook up to the circuit can overload the wire connecting them to the box.
posted by true at 9:15 AM on July 6, 2005

Can you ask the electrician himself why he made this choice?
posted by winston at 9:19 AM on July 6, 2005

are you sure it's total current that's tripping the breaker? maybe something has an intermittent fault? if i were you i'd try using a long extension cable to connect one item at a time through to another circuit. if any item transfers the problem over then you know it's a problem with that, and not the fuse.
posted by andrew cooke at 9:53 AM on July 6, 2005

Sometimes it makes sense to save money and do it yourself; sometimes it doesn't. While folks that have never seen your wiring/house can make guesses, a licensed electrician can tell you the definitive answer, for not a ton of money, especially considering the potential consequences.
posted by bemis at 10:19 AM on July 6, 2005

I second true and andrew cooke. Can you also be sure it isn't a faulty breaker? Does it trip when several appliances are running stably or instead when certain appliances start up or shut down?
posted by fatllama at 10:35 AM on July 6, 2005

It's probably a wiring capacity issue, as true states. You really don't want to swap in a bigger breaker unless you want to significantly increase the chances of the units burning down. More seriously, swapping breakers probably violates your building code and likely will allow your insurance company to ignore fire claims. If you want to upgrade the breaker, you probably want to talk to an electrician about rewiring your circuit. That will cost a lot of money and be fairly disruptive.

Constantly tripping a breaker is bad. Every time a breaker trips, the connecting wire heats up and cooks the insulation. Eventually heat-damaged insulation, romex, asbestos or paper will degrade enough to create a serious fire hazard. If it's a wall plug circuit that doing this, seriously consider installing GFI plugs. Ground-fault plugs essentially put a breaker in every socket and protect your house wiring from damage. If you do it yourself, and it's very simple, and changing your plugs will only cost $10 each.
posted by bonehead at 10:40 AM on July 6, 2005

Two points:

1) Generally, electricians wire outlets to 20A circuits, and light fixtures to 15A circuits. I don't know why you got all 20A circuits in Unit 2. Winston is correct that the breaker difference is matched by a wire gauge difference, so be extremely careful if you decide to swap out a breaker for a larger capacity.

2) If you're at the bitter edge of capacity on a breaker, it can trip because of a temporary surge (as when an electric motor starts, for instance). In addition, a breaker's capacity lessens after many trips. You can try replacing the breaker with one of the same capacity and see if that helps.
posted by Daddio at 11:22 AM on July 6, 2005

You really have to diagnose what is causing the breaker to trip. Read the nameplates on the appliances and add up the current requirements. If you don't know how to do that post the info here and we will help you.

If you are trying to run too many things off of one breaker you have to stop. If the breaker trips regularly it will wear out.
posted by Chuckles at 11:37 AM on July 6, 2005

One more thing that occurred to me - if your wiring was not upgraded when the breaker box was, the electrician probably just replaced the existing fuses with breakers. A reasonable electrician would have replaced 15A fuses with 15A breakers, etc leaving the number and capacity of the circuits the same. This is further suggested by the fact that your total max load is 150A and you have 200A service - so if you were on the edge of tripping every circuit in the house your main breakers (the 100A boxes) would be nowhere near tripping.

This could mean a couple things, depending on what kind of fuses you had.

1) If you had the kind of fuses that only allow the correct size fuses to be inserted (later fuseboxes), your system is probably correct as now. The 15A breakers replaced correctly sized 15A fuses, etc.

2) You had a much older system where any capacity fuse would fit into any fuse socket. If that's the case it would be hard to tell - you could have 20A capable circuits everywhere, but the old homeowner only had a 15A laying around one day and that's what they put in. Or, in a worst case scenerio, they could have replaced the 15A (or even 10A) fuses with 20A as they started to use more electrical appliances, which would be quite unsafe.

Without seeing your system in person, I can't comment more. I'd definetly pay for an hour of an electrician's time on this one.
posted by true at 12:23 PM on July 6, 2005

I am planning to replace the breaker tonight with the same amp breaker. I figure this would be a quick check to see if maybe it was the breaker, with minimal risk since I'm not upping the power.
posted by benjh at 12:46 PM on July 6, 2005

As has been said, one would expect the lower rated breakers to protect your lighting circuits. Do you notice the breaker tripping when you turn on lights (low voltage spots, maybe?). Do you notice it trip when you turn on a particular appliance? Do you have any unusual equipment in your home?
posted by nthdegx at 2:18 PM on July 6, 2005

along that route, i'm assuming if you're sucking a lot of power it must be cooling or heating. does it trip when the airconditioning starts up, or a fridge? alternatively, a laser printer?
posted by andrew cooke at 2:39 PM on July 6, 2005

You should still figure out what the rated loads are for everything you are connecting to that circuit. Since you know exactly which plugs are on which breakers you should be able to do the calculation quite easily (or post the details), so do it!
posted by Chuckles at 12:19 AM on July 7, 2005