# Newbie Service Panel Question

I just read Black & Decker's Home Wiring Guide in an effort to understand how the service panel distributes electricity, but they use the word "circuit" to mean the wall socket / receptical sometimes, and alternately to mean circuit *breaker* and it isn't clear to me when they mean one or the other. Consequently I am not clear on the following concept:
Simplistic Hypothetical: ------------------------------------------
Circuit Breaker #1 on the service panel is a 20amp 120v circuit.
It's wired to *four* wall circuits [recepticles]. Each recepticle is now a 120v 20a outlet. -----------------------------------------------------------------------------------
Confusion point: The book states that a full load for a 120v 20amp circuit is: 120v x 20a = 2400 watts x 80% (safe capacity) = 1900 watts
Does that mean each one of those recepticles can have up to a 1900 watt load on them *simultaneously* without tripping the breaker, or that *collectively* at any given time their load in summary shouldn't exceed the safe capacity of 1900 watts total?
The reason I ask is this... the book also says that microwaves and large appliances should have a "dedicated circuit." Do they simply mean a dedicated wall outlet, or a dedicated circuit *breaker* -- meaning no other outlet is wired to that circuit breaker but the one the appliance is plugged into...??
Because the way I read it, is I need a separate *circuit breaker* for my washer/dryer outlet... one for my 1700watt treadmill (which can also run a TV and lights in the garage, but then reaches the 1900watt safe mark)... one for my garbage disposal and one for my microwave...
and the circuit breakers just keep adding up...!
Or do they mean a single circuit breaker can *share* outlets with major appliances because each outlet it services has a *simultaneous* capacity for a 1900 watt safe load?
Was that confusing enough??? :)
Jane
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No.

Yes, and no. it means that at any given time, collectively that circuit cannot exceed 2400 watts. Since there's no way you can control the total wattage on any given receptacle circuit, the 1900 watt "limit" is only a design limit.

Right, dedicated to that one appliance, either directly wired or via 1 single dedicated receptacle.

Yes.
No - A treadmill load is not considered a constant load, it won't be on longer than 4 hours.

Yes
and one for my microwave...
Yes

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On 19 Nov 2003, snipped-for-privacy@no.spam.com wrote:

Collectively. They are sometimes call "convenience outlets", and the thinking is that you will never use them all at one time, or even if you do, they will all be low load devices. You could load up all 4 of those receptacles (8 spots) with things like stereo systems, lamps, cordless phone bases, chargers for your cell phone, etc, etc and never come anywhere near drawing 1900W. But change those things to toaster ovens, coffee makers, hair dryers, etc, and you get to your next question...

Exactly. One breaker, one outlet.

Actually, your usage will determine this. Your Treadmill/lights/ TV example is a good one. If you don't have a dedicated outlet for those heavy drawing devices, you need to play the "I-can't- run-this-thing-while-my-treadmill-is-running" game, effectively creating a dedicated outlet, even though there are other duplex receptacles on the same circit. People have been doing this since we've had indoor electrical service, and as long as you do it in a -SAFE- manner, it's OK. "SAFE" being not sticvking pennies in the fusebox, propping a breaker handle in a closed position with a chunk of wood, etc. That kind of stuff burns your house down, the trial and error "learning" of your circuit limits gets you a workout running to the breaker box.

Not a bit. You knew how to voice your questions, that's better than half of the (cough)dim bulbs who show up here!
--
Baisez-les s'ils ne peuvent pas prendre une plaisanterie
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A circuit is actually a complete loop through which electrons can flow. Nobody in residential wiring really means that when the use the word though.. :) It typically refers to the wiring hooked up to an individual breaker, at least around here.

The 80% rule is for resistive loads, and even then it's only applied to special circuits (heating, water heater, other dedicated resistive load circuits). For everything else there is a "12 box rule". That is you can have any combination of light fixture and receptacle boxes (excluding boxes for switches and splices only) as long as the total of that combination is no more than 12. Most electricians like to keep it at 8 or 10. i.e.:
Circuit 1: 4 recessed light fixtures in the bedroom plus 5 receptacles = 9 Circuit 2: 6 receptacles in the living room, 2 in the hallway, 8 in the den = 16
Circuit 1 is ok because it only has 9 "outlet boxes", however circuit 2 is a violation, because it has 4 too many boxes.
The reason being is because you have no idea what someone will plug in some day. Someone might plug in two 1200 watt heaters. If the electrical installation is sound a 20A circuit will handle it

For branch circuits it's always collectively. A 20A circuit can run 20A collectively. ie: 10A on one outlet, plus 10A on another. 20A on only and 10A on the other would be pulling 30A through a wire (12gauge) that's only meant for 20.

Unless your treadmill is hardwired in (no plug) or attached to the house it doesn't need it's own circuit. The reason being is because it's portable, and will probably be moved around.

They do so blazingly fast! When I bought my 200A, 40 position Square D panel a year ago for our 2200 sq.ft house I never dreamed I would get close to filling it. Yet I am now close-- at 5 spaces left.
Every motor load circuit will need it's own breaker (code). This includes the microwave, refrigerator, dishwasher, washing machine, furnace, garburator, AC units, pumps, central vac, etc. Most small fans (ceiling fans, range hood, bathroom exhaust) can be placed on regular lighting circuits. If you have a lot of cool toys(like a garburator, hot tub or central vac) you'll fill up a panel quick.
The stove, dryer and electric water heater will all need separate breakers as well.
Most panels come as a 'kit' with a bunch of breakers included. It's almost a sure bet that you'll be buying extra.
If you are replacing an existing service, and using the existing wiring, the rules are often relaxed (sometimes even ignored) in many localities, you should call your inspector. (And for a service upgrade you WILL need to be inspected, the utility won't touch you otherwise).

Nope, major appliances and outlets that have a purpose to serve things like microwaves and washing machines need their own dedicated breaker. That's the code.
-- Steve
p.s. the 12 box rule is based on my knowledge of the CEC, I understand it's the same for the NEC but I may be corrected.
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Thanks to everyone for the answers! I really appreciated that.
So it was what I thought but when the electrician kept telling me the 100 amp panel would be fine and that it would be impossible for me to trip a breaker even with everything turned on, I thought I must have it wrong.
1 - Garbage disposal 2 - microwave 3 - washer/dryer in garage (both gas) 4 - treadmill in garage (heavy duty stays in garage, 17 amps when running and I want to use it when I'm doing laundry), can also use this outlet for light fixure, 113 watt TV, CD. VCR = just about 1926 watts 5 - gas stove/energy-saving fridge 6 - desktop computer
So that's already 120 amps without another two breakers for wall outlets in the 2 bedrooms, living room and bath.
Yet a 150 amp panel is \$450 more than a 100 watt panel. The job's already costing \$1800 to switch out the panel and wire seven new recepticles.
decisions decisions...!
Jane
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You're missing three things. First, you have a 240V, 100A service. This means you can run 200 amps of 120V eqipment if everything is perfectly distributed across the two incoming power legs. Next, just because a circuit has a 20A breaker doesn't mean it counts as 20A of load (washing machine may be 10A, microwave may be 12A, etc). Finally, there is a huge factor for "load diversity" in a dwelling. This means you are most likely not using all of this stuff at exactly the same time. The fridge and microwave cycle on and off when being used. Can you use the garbage disposal and treadmill at the same time (assuming only you live there)?
So all of these things are factored in when your total electrical demand is calculated. It would not be unusual to add up all the breakers and get 300 amps worth in a 200 amp service (and that's 300A per side or 600A if couning a double pole breaker twice).

From what I've seen, 100A and 200A are the cheapest services to install. Some of the 200A equipment is even cheaper than 100A since 200A is the most common service installed today. If the electrician says you don't need to upgrade past 100A, believe him. Houses that are all gas rarely go over 100 amps unless you have a welder, kiln, or huge air conditioner. If you want to increase anyway, I'd consider going to 200 amps.
-- Mark Kent, WA
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THANK YOU. This was the part of the puzzle I wanted to clear up. I know 2 lines come in at 120v but I didn't understand how it gets distributed if you have (say) only (5) 20amp circuit breakers. Is each CB wired to each leg, to actually deliver 40amps power each? (If wired correctly.)??

No, but no one wants to wire a house for one person. Someone may move in later, someone may be staying over... there are certain sacrifices that are no big deal (like don't use the microwave while running the garbage disposal) but otherwise I don't want to worry about it.

Wow. Okay... this part of the puzzle wasn't in the Black & Decker book, or if it was, it wasn't written clearly.

Thanks so much for this info!
Jane
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kindly wrote:

A 20A breaker will deliver 20 amps. In most modern panels, the incoming power legs alternate with each row. So the top two breakers could draw 40A from leg 1, the next row of breakers could draw 40A from leg 2, the third row of breakers could cause 80A to be drawn from leg 1 (rows 1 and 3), and so on. You have 100 amps available on each leg.
A 240V device uses a double pole breaker. This gives you 240V with each side of the circuit breakered at the amp rating. A 30A double pole breaker would provide two 120V circuits at 30A, or 1 240V circuit at 30A.

at
My example wasn't very good, but the code knows you can't use all your circuits at once. A service calculation takes most of your receptacle outlet circuits and adds up the load. The first 3000 watts are counted at 100%. Each watt over that is only counted at 35%. It is similar with fastened in place appliances. If you have 4 or more, then you can apply a .75 factor to each appliance load. Certain things must be kept at 100%, such as heat/cooling, clothes dryer, motors, and a special demand rating for electric ranges/stoves. Add all of these values up and that is how many watts your service must provide.
-- Mark Kent, WA
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Thanks very much for your explanation. I don't quite grasp the mechanics though. The electrician says that a 100amp panel is really like a 180 amp panel,(b/c of the two legs which you brought up) but I don't understand how the circuits utilize the two legs to make an electrican say that. It seems to fly in the face of the basic advice of needing a circuit breaker for: garbage disposal, microwave, desktop, etc... which all adds up to a 100amp panel very fast. If I go by the advice in the book, I would get a 150amp panel to satisfy all the equations of load, etc. for the house, yet he tells me the 100 amp is like a 180 and I'll never trip it even with everything on. And he's probably right b/c of the "two-legs."
I wish I knew of a book I could read that detailed how a service panel works. Black and Deckers book is more about how to wire stuff up, than the mechanics of how the service panel handles the (2) 120v lines and how the breakers distribute it. Their explanation does not take into account the two legs in terms of "so your 100 amp panel is really like a 180 or 200 amp panel because of this and this and this."
Sorry to be so dense. I know you gave an explanation but as with anyone who is new to a concept, I am missing the basic understanding that lies at the foundation of the thing. It's something that people (who already know it) take it for granted that someone would understand, because it's so basic. So that if that piece were filled in and I did a "EUREKA!" they would say, "Well DUH, of course THAT's blah blah blah!" KWIM? :)
I'm going to search the Web some more for something to read that will enlighten me. If anyone has a link to offer, I'm all ears. (eyes?)
Jane
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I'm in kinda the same boat as you are Jane...
I've gotten a great 'education' reading "Wiring a House" by Rex Cauldwell. It is one of Tauntons' "For Pros by Pros" series of books. Clearly written and supported with excellent color pictures and drawings.
If you have no luck finding this locally or online, you are welcome to order it from my employer, Craftsman Book Company
http://www.craftsman-book.com/cgi-bin/SoftCart.exe/cbcstore/prodpages/wah.htm?E+cbcstore
copy and paste if necessary...
Rick

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Yeah, when you know this stuff well, you forget how to explain things to people who've never looked inside a panel before. Try this link:
http://www.homewiringandmore.com/homewiringusa/2002/maindwelling/meter/100as ubpanel.jpg
This is a 100A panel without a main breaker. The incoming 100A feed comes in on the red and blue wires (100A available from each). There is 240V between the red and blue feed wires, and 120 between either the red or blue and the white feed wire. There are three single pole breakers in this panel, and lets say they are 20A each. The bottom two breakers get their current from the incoming red feed wire. If both those circuits are on and using their full rating, 40A will be sucked off that red feed wire.The higher breaker on the rights gets it current from the blue feed wire. This could suck 20A from the blue wire irrespective of what the bottom two breakers are doing. Put in another breaker on the right side above the two that are there, and it will get its current from the red feed wire making the total potential draw from the red 60A. Put in another above that one, and the blue feed could be loaded to 40A and the red line to 60A. This is 100A, but you still have 40 more available on the red and 60 more available on the blue.
So a 20A breaker doesn't utilize both legs, it is on one or the other. The layout of the panel makes it such that a column of breakers alternates between the red feed and blue feed wires. So as long as you're not putting your breakers in just every other row, you'll be able to suck current from both incoming lines. This means you effectively have 200A available if you're only using single breakers.
A 240V double pole breaker, like you'd use for a water heater, range, or dryer, sucks it current from both lines. So a clothes dryer rated at 25A at 240V would allow only 75 amps to be available on the red and blue legs to serve your 120V loads (which really means 150 total amps since there are two legs to choose from on 120V loads).
-- Mark Kent, WA
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>> Thanks very much for your explanation. I don't quite grasp the >> mechanics though. The electrician says that a 100amp panel is really >> like a 180 amp panel,(b/c of the two legs which you brought up) but I >> don't understand how the circuits utilize the two legs to make an >> electrican say that. It seems to fly in the face of the basic advice >> of needing a circuit breaker for: garbage disposal, microwave, >> desktop, etc... which all adds up to a 100amp panel very fast. If I go >> by the advice in the book, I would get a 150amp panel to satisfy all >> the equations of load, etc. for the house, yet he tells me the 100 amp >> is like a 180 and I'll never trip it even with everything on. And he's >> probably right b/c of the "two-legs." >> >> >> I'm going to search the Web some more for something to read that will >> enlighten me. If anyone has a link to offer, I'm all ears. (eyes?)
Yeah, when you know this stuff well, you forget how to explain things to people who've never looked inside a panel before. Try this link:
"
http://www.homewiringandmore.com/homewiringusa/2002/maindwelling/meter/100asubpanel.jpg "
This is a 100A panel without a main breaker. The incoming 100A feed comes in on the red and blue wires (100A available from each). There is 240V between the red and blue feed wires, and 120 between either the red or blue and the white feed wire. There are three single pole breakers in this panel, and lets say they are 20A each. The bottom two breakers get their current from the incoming red feed wire. If both those circuits are on and using their full rating, 40A will be sucked off that red feed wire.The higher breaker on the rights gets it current from the blue feed wire. This could suck 20A from the blue wire irrespective of what the bottom two breakers are doing. Put in another breaker on the right side above the two that are there, and it will get its current from the red feed wire making the total potential draw from the red 60A. Put in another above that one, and the blue feed could be loaded to 40A and the red line to 60A. This is 100A, but you still have 40 more available on the red and 60 more available on the blue.
So a 20A breaker doesn't utilize both legs, it is on one or the other. The layout of the panel makes it such that a column of breakers alternates between the red feed and blue feed wires. So as long as you're not putting your breakers in just every other row, you'll be able to suck current from both incoming lines. This means you effectively have 200A available if you're only using single breakers.
A 240V double pole breaker, like you'd use for a water heater, range, or dryer, sucks it current from both lines. So a clothes dryer rated at 25A at 240V would allow only 75 amps to be available on the red and blue legs to serve your 120V loads (which really means 150 total amps since there are two legs to choose from on 120V loads).
-- Mark Kent, WA
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to
boxes
The NEC has no "12 box rule". In non-dwelling installations, each receptacle counts as 180 VA, so that can limit a circuit. In dwellings, there is no limit at all. The 80% rule applies to a lot of things -- continuous loads, motors, and the other items you mentioned.

furnace,
Under the NEC, multiple motors can be on a single 15A or 20A circuit. This would be most common if the motors were small (1/2 HP and less such as three garage door openers that have a nameplate rating of 6A each).
-- Mark Kent, WA
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On Wed, 19 Nov 2003 20:03:39 GMT, Jane ( snipped-for-privacy@no.spam.com) wrote: <snip>

<snip>
Yes, it's a bit confusing. It's the circuit breaker that limits the maximum power that can be used by everything connected to it, whether you have one outlet connected to a single breaker or 6 outlets, or 4 outlets and 2 ceiling lights, etc. Generally, a dedicated circuit refers to a circuit breaker connected to a single load, whether it is directly wired to it, as would be done for a dishwasher, or whether it is wired to a single outlet, such as would be done for a microwave.
In new construction today, there would indeed be a separate circuit breaker for the microwave, disposal, dishwasher, refrigerator, and other large, dedicated appliances. Those separate breakers would either each be wired directly to the appliance or each wired to a single oulet serving each appliance.
The treadmill is a marginal case. Technically, you could get by without a dedicated circuit if you were careful not to turn on any other large loads connected to the same circuit while you were using the treadmill. So if you had an electic heater plugged into an outlet connected to the same circuit breaker as the treadmill, you would be ok as long as you didn't use the heater and treadmill at the same time.
The circuit breaker is there to limit the maximum power that can be drawn from all the wiring connected to it. This prevents overloading the wiring which can cause a fire. Generally, if you are not tripping any circuit breakers, then you are OK. I say generally, because circuit breakers are not precision devices. If the overload is large, they will trip quickly. But if the overload is small they may run for hours before they trip. This is usually not a problem because there is enough safety margin to prevent problems from small overloads.
Still, if you know when you use your treadmill that you are going to want the TV on and all the lights in the garage on, then you may want to consider having a dedicated circuit installed.
HTH,
Paul
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[...]

See, this was the part I understood, but what I was missing was how the useage of a 100a panel can really be more like 200amps because of using both legs. In my mind then, the "20 amp curcuit breaker" should be called a "40a" then... But I guess it's only a 20a because it distributes 20a per leg... or in an older house where there's only a single 120v line... 20a period.
Jane
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" snipped-for-privacy@no.spam.com" wrote:

Re 'dedicated' circuit. Agree the terminology can be confusing. To illustrate; There some rules in this jurisdiction that a kitchen shall have a certain number of 'dedicated' outlet/receptacles. This means that there is only one 'dedicated' outlet wired directly from one particular circuit breaker; for each dedicated circuit. I'm not sure what the requiremnt is now; but when we built this house some 30 years ago it was, I believe, a minimum of two dedicated and and also a certain number of 'convenience' outlets per 'X' feet of counter space! This requirement has come into use as more and heavier appliances have become common. Microwave ovens for example, a steam iron or electric kettle can each require sufficient power that to plug two such items into the one circuit (and use them at the same time!), would exceed the total current capacity of say 20 amps. Also for example non-dedicated (normal) outlets are around the walls of rooms or adjacent rooms. Usually such 'convenience' outlets are limted by local jurisdiction to some maximum number; such as eight or ten on the one run of wiring from one circuit breaker). Sometimes such outlets or half of them are controlled by a wall switch in order to turn on/off coffe table lamps. Dedicated outlets would normally NEVER be switched like that. One example of a dedicated outlet, in our case is the one wired specifically for an older style, large, microwave oven, on its own trolley, to 'it's own' circuit breaker. Any help? Terry.
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