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My 100 Amp service already has about 180Amps worth of breakers — but still has 4 empty slots. I checked another box just for comparison and their 200Amp service had almost 350 Maps in breakers. When do you know you’ve reached “full” — how do you calculate “full”?
I’d like to add a few outlets and lights in the basement and it’s either time to upgrade to 200Amps (a cost I’d rather delay) or maybe I’m still OK?
Any guidance would be appreciated
Replies
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You asked two different questions.
The pannel is FULL when there are no more LEGAL spaces. Look at the label on the box. That should tell you the number of spaces for breakers. Note, that even if 1/2 breakers are available you can not use more than the number allowed on the label.
However, what you are wanting to know is if the pannel is overloaded. The most basic test is if you are having problems with the mail breaker tripping.
The code reconizes that you are not going to be running a stove with all burners on high, the oven, the diswasher, the clother washer, the clothes drier, even light with bubs of the max rating, and every outlet at it's max rating at the same time and for a period of time.
Thus they use a demand factor. Certain equipement is used at it's listed ratings, others allow a certain derating and the total amount is derated.
*Thanks Bill,You are correct the question centers more around overloading. I thought there might be a general rule of thumb for the common home. Maybe 1.7X the Amp service...know there is no such thing as the common home, but I live in something pretty close - 40 years old, 1400 s. ft and all the common plug in appliances. I'm not a big risk taker, I'm happy to hover at the safe level or upgrade if required.Thanks for the tip on the label, I'll have a look when I get home tonight!
*JamesYou might want to go to the library and look at a basic wiring book. I think that even the Black and Decker Advanced Wiring has the tables.It is simple, but it is too long to post all of the rules.
*"My 100 Amp service already has about 180Amps worth of breakers -- but still has 4 empty slots" Like, "I can't be out of money. I still have blank checks left."But seriously, as Bill said, there are limits to both number of breakers and the total, derated amps. If there are standard width breakers now, I would expect that you can certainly put in 4 more into the empty spots. Possibly more than that using 1/2 width breakers, but check the limit for that particular panel.Also, are you adding all the breakers, or just each leg of 120 volts? Your 100-amp panel, gives you 100 amps on each leg or, for instance, 10 20-amp, single-pole breakers, (plus a bunch more because of derating).If a lot of the breakers are for convienence circuits, you're fine. Only if you have lots of fixed, electrical appliances, could be close to 100-amp rating (or if you have much electric heat). -David
*i > "Box still has 4 empty slots."Reminds me of the time I had to install 2 new circuits in a remodeling job. The box was a Federal Pacific (my first mistake....their breakers are EXPENSIVE), I opened the door and saw several slots remaining for use in the box. I didn't take the cover off (my 2nd mistake). I noticed and was amused by the fact that all the wires running to the box were crammed through the few top knockout locations. None of the knockouts on the box's left hand side side were in use. This seemed a bit strange, and because the box was located in a corner and the right hand side was against a wall; no wires were routed through this side either. I made a mental note of it and decided that I would route my new wires through one of the knockouts on the box's left side(My 3rd mistake!)When it finally came time to remove the panel cover and begin the wiring, I was shocked! The reason no wires were run through the box's left side, was because the box's Neutral Bus Bar had been mounted in this location on the inside. It was physically impossible to route a cable through an existing knockout on that side. Furthermore, the existing wiring was in such a mess, that there were no available openings left remaining in this bus bar. This bar was TINY! Many Neutral and grounding wires had been twisted together and bonded to the bus bar through the same set screw openings. It was a spaghetti nightmare!I had to rewire the entire box; cutting, forming, and reshaping the cable wires in an orderly fashion so that I could make enough room to use the few remaining bus bar openings that had been physically impossible to get to a while earlier. Three hours later (all the time with a flashlight held in my mouth) I was finally done. All this work just for two new circuits!( The wiring had been routed over to the panel box a few days earlier). I remember the customer pointing to the box and saying, "You should have plenty of room. Look at all the unused slots remaining in the box." I remember looking at those same slots and agreeing with him. I also remember him saying that his father had wired that box nearly 40 years ago. His father was not an electrician by trade. No alarm bells went off in my head at that moment (THAT WAS MY BIGGEST MISTAKE OF THEM ALL.)Live and learn.Davo.
*A 240 volt 100-amp panel is capable of delivering 24,000 watts of power (ignoring power factor). The chance of all circuits being energized at full potential is extremely unlikely, so code makes allowances for this. The one thing you must be careful of when adding new circuitry is the balance between the "A" and "B" leg of your panel. Overheating of the bus can occur if one of the legs is more heavily loaded.
*Rules of thumb? The one I've read is 60% of the total of all of your normal loads (appliances, lights, etc) excluding heater and AC. As Paul noted, this assumes the panel legs are load balanced. How often has anybody encountered their main breaker opening? This may account for there being a liberal fudge factor in service size. Though you may want to plan for the teenager factor -- "there's an endless supply of water and electricity, according to my sheltered upbringing," you should be able to recognize trends and be prudent in electricity use. You may not wish to be running the dishwasher while cooking or drying your hair while vacuuming -- those things. These can temper your need to upgrade.
*Thanks for all the help and advise. Except for Davo (who's story was very interesting but..:-) I think y'all provide insight into my issue...
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My 100 Amp service already has about 180Amps worth of breakers -- but still has 4 empty slots. I checked another box just for comparison and their 200Amp service had almost 350 Maps in breakers. When do you know you've reached "full" -- how do you calculate "full"?
I'd like to add a few outlets and lights in the basement and it's either time to upgrade to 200Amps (a cost I'd rather delay) or maybe I'm still OK?
Any guidance would be appreciated