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I am having 2 new lines run in my basement to power a workbench's tools and an unrelated computer station.

I have room in my panel for additional breakers, and rather than tie into existing wiring, I think this is a good move.

I plan to add 2 single pole 20 amp breakers, the panel clearly says stab lok on it and I recall from a friend's upgrade that he matched the brand of the breakers that were already in the panel.

Is this a best practice, a requirement or just fussiness? Is it labelled somewhere on the panel what type I should pick up, or should I just remove the cover and see what's already installed?

I have seen advice that says avoid Federal Pacific breakers, the locally available brands seem to be Federal Pioneer, Eaton-Cutler, Schneider Electric, Siemens.

Is 20 amp single pole stab lok breaker enough information to purchase the parts I need, or do I need the installed brand information?

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2 Answers 2

up vote 6 down vote accepted

Running 20amp for your workbench is a good idea (and be sure to use 12/2 wire), but overkill for a computer circuit: most residential circuits are 15A and are run on 14/2.

You don't have any choice in the breaker: Siemens panels only accept Siemens breakers, and StabLok panels only accept StabLok breakers (and of course there are several other brands). The bus design in each panel is different, and so other brands of breakers won't fit. This isn't the full truth: there are other companies that make breakers that are compatible with Siemens panels, but they'll be marked that way. Just realize there are different designs of panels with different designs for how the breakers physically connect in, and they're not all cross-compatible.


There are some known problems with the design of StabLok panels (which are made by Schneider Electric, and sold as Federal Pacific, Federal Pioneer, StabLok). InspectAPedia has some pretty dire warnings against using FPE StabLok panels - I was actually not aware of the extent of problems until just now. According to the article, it's actually a fire hazard as they can come loose, and that's aside from the apparent defects in the breakers themselves (they can fail to trip, and even fail to shut off when you manually turn them off).

I personally am not a huge fan of StabLok, the connection is just not as solid as you get with, eg, SquareD panels, and most StabLok panels are ugly for that reason: all the breakers are skewed in random directions.

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@gregmac My computer(s) will have a fairly heavy max draw... the main box will probably draw about 8a (1000w x 120v), add 3 monitors (say an amp each?) not including any other devices. For the difference in cost between a 15amp circuit and a 20amp, why not? –  Stephen Jun 23 '11 at 2:48
    
@gregmac Thanks for pointing out that Stab-lok is a brand, I rechecked the site I was shopping on, and notice that all the Stab-lok breakers are Schneider, so that answers that. I was really unclear if it was a brand or a configuration identifier. –  Stephen Jun 23 '11 at 2:52
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I just installed 2 Siemens subpanels, and used 3 different brands of breakers. There are companies besides Siemens that make compatible breakers. The quality isn't quite as good, but they work & are code compliant. –  Jay Bazuzi Jun 23 '11 at 3:53
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It's unlikely that a desktop computer would draw 1000W for any length of time. It's more likely that you have a PSU rated at 1000W, but most of the time you'll draw much, much less. My laptops normally draw 20W. Measure it on a Kill-A-Watt. –  Jay Bazuzi Jun 23 '11 at 4:31
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Side note on FPE breakers. A FPE panel with stab-loc breakers from the 1970's is an automatic write up on my home inspections. There have been numerous advisories and warnings because of problems with this design. Primary problems stemmed from poor fitting breakers and possible corrosion issues. Although they were never recalled, it was advised to change out the original breakers with updated ones. You may find several manufacturers that make compatible breakers for your panel. Before you install a new breaker, inspect the buss for evidence of corrosion. Put breaker in and out several times. –  shirlock homes Jun 23 '11 at 10:52

Your panel should have information printed on it about what breakers are acceptable. My Siemens main panel / meter base has a big sticker on the inside of the door with a lot of useful info. For example, it says the left side can only take 50A maximum with aluminum conductors, while the right side can go to 150A.

However, while the panel maker only recommends its own-branded breakers in its panel, there are 3rd-party manufacturers, like Connecticut Electric that make compatible hardware. In my experience, they work fine but the quality isn't as good. For example, while torquing screws on a 3rd-party ground bar to the Siemens-recommended level (35 in lb), I destroyed the screw.

The easiest way to get a matching breaker is to pop one out and take it to the store with you. It's a good idea to turn off the main breaker while you do this.

I've had a very difficult time getting exactly the right electrical components at hardware stores. If there's an electrical supply house in your area, you may have more luck there.

14ga copper conductors are normally the minimum for a 15A circuit, and 15A is plenty for most computers, unless you run a rack of servers. Many electricians use 12ga for both 15A and 20A circuits, since it's easier to stock just one size of wire. If you do that, you may as well stick with your plan of a 20A circuit to your computer area.

Minimum conductor size is determined by ampacity - the amount of current you can safely draw without worrying about the wire overheating. However, over long runs, the resistance of the wire becomes a factor, causing voltage drop. The amount of voltage drop depends on the size of the wire, copper vs. aluminum, stranded vs. solid, the length of the run, the load, and heat. As current increases, voltage drops (V=IR).

Note that we're talking about actual load, not rated load. That is, if a computer is plugged in to a 20A circuit but only drawing 5A, the voltage drop is based on the 5A.

Voltage drop is particularly concerning for motors, especially when they start, as the starting current is extremely high. If you are running large saws in your workshop, you can protect the motors by oversizing the conductors.

If both circuits are running to the same location, consider using a multi-wire branch circuit (MWBC). You run 4 conductors (hot/hot/neutral/ground), and treated it like two separate 3-conductor circuits, so you use much less copper. You can just buy a roll of 12/3 + G cable and run it from the panel to all your receptacles, which is pretty convenient. If the loads are well-balanced, it can also reduce voltage drop.

Between either hot and the neutral gives 120V. Between the two hots gives you 240V, so make sure the breaker is off when working on it. You'll need to use a 2-pole breaker (not two separate 1-pole breakers) so that both hots get shut off at the same time.

You can even wire the top & bottom of each receptacle to be on different sides of the MWBC, so it's easy to balance out the load. That's the goal: get half the load on each side of the circuit, as well as you can. The recep will have two screws on each side and a tab you can break off to separate them - do that on the hot side.

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Thanks for the very thorough answer, really helps clear things up. –  Stephen Jun 23 '11 at 10:47

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