Electrical Q

Hi Folks -
In a residential house is it normal to have the total max amps of all installed circuits (breakers in the breaker box) to excede the available amps for the whole system, creating a theoretical situation where if you ran every line to capacity, you'd blow the main? In our old colonial (90 yrs old) we recently upgraded our line from 60 amps to 150 amps. As we've been adding new circuits to handle air conidtioners etc... throughout the house, I've noticed that the total in my circuit box will likely go into the 220 - 250 total amp range at some point. Is this ok?
Tom
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031130 1530 - Tom Newton wrote:

You may have several circuit breakers in your panel and the total may exceed the 150 Amp Main breaker. That doesn't mean that the Main will trip out. The house system works on a demand basis. Hardly ever will you have everything in the house running at the same time, and even if this was the case, your Main breaker may not see 150 amps. You certainly wouldn't have the Air Conditioning system operating while the electric baseboard heating was on (of course, there are exceptions); and etc.
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Yes. First, are you counting per leg so you have over 150 per leg (300A total)? Even if so, you should do a demand load calculation to see if you're taxing your service -- this is how you size your service for what you have installed. If you trip the main breaker, then you're obviously over. My old 200A panel added to 220A on one leg and 235A on the other.
-- Mark Kent, WA
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A long time ago I had a 150 amp service and was worried about the same thing. I turned on every thing and even simulated some loads that were not going to run at the same time. Measured 50 on one leg and 53 on the other.
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Thanks SQ
Actually, with Gas heat, Gas hot water, Gas stove etc, and only one little window mounted a/c unit... I'm quite sure I'll never ask for more that 100 amps at any one time let alone 150!
One question, what does the term "leg" mean. My main breaker -- the line from the power company -- says "150" on it. I recently upgraded to 150 amp service, so this makes sense. But what are "legs" ??
I wonder, is my 150 actually broken down to two legs? like 75 each? It also reminds me of a funny thing that happened during the east cost blackout this year... my wife swears that at some point either when power was being restored or when it originally wnet out ... some of the house was up and running with power, and other parts of the house were not --- I told her she was crazy. Was she right? Was it possible to have a temporary condition where there's a partial outage -- however short lived -- within the house itself?
TN

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you get 2 hot wires into your house plus a ground. the main breaker is actually a double breaker, each breaker controlling one hot wire. you get 150 amps per wire and if your house system is well balanced you'll get a theoretical 300 amps total.
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A "leg" is a phase; on a North American residential 150A feed, you have two 150A phases ('"legs") - so in fact your house's total power consumption in volt-amps can be 2 x 120V x 150A. That's lots. (A DC volt-amp is a watt, but in AC a watt is less than a volt-amp, as I recall by a factor of the square root of 2, for simple loads like incandescent lamps and heating filaments. If Turtle explains it, believe him.)
Each 120V circuit is on one "leg" or the other. Each 240V appliance is wired "across both legs". There is only one neutral which is used by both legs, which does not get overloaded because - and this is actually very cool - the current from the two phases cancel out!
One phase live and one dead usually means a major wiring fault in your panel, or in an older panel, one of the main fuses out (new panels use linked breakers so both phases cut if either is overloaded - also true of each 240V appliance circuit). Conventionally both phases are taken from one transformer somewhere in your neighbourhood, so the utility *ought* to have no way of feeding you one phase only ... but the utilities *ought* to not let half the continent go dark, either, so that logic goes only so far.
My guess is that as the power came back, the current supply ramped up slowly, so the effective voltage was low for a while - and if the two phases are unequally loaded in your home, or your neighbourhood (the utilities hate this), one leg might have been at a lower voltage than the other. Plus, some things (incandescents, some electronics) work ok with low voltage, some things (fluourescents, some other electronics) don't, which would contribute to the observation.
If your wife says it happened, it probably did. Lots of fascinating phenomena have been denied because they were initially unexplainable!
Chip C Toronto

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On 02 Dec 2003, Chip C wrote:

You poor, misguided soul! Turtle has been hit in he head by SEVERAL falling trees in his lifetime, he's admitted it in other newsgroups. His is truly an elevator that doesn't even come close to stopping on every floor. He and 50cents, er, 50volts?, fancy themselves big time electricians, but neither know a damned thing about residential electric. Wait, check that, they know how to wire up a "whip" from a safety disconnect to a condenser. Beyond that, they look it up on the internet and try to bluff their way through it.
--
Baisez-les s'ils ne peuvent pas prendre une plaisanterie
--------------------------------------------------------
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Tommy, tell us again how you like to take out cartridge fuses and put in pieces of copper pipe?
You paid $80 to have your furnace filter changed?
You said there is no difference between a neutral and an equipment grounding conductor?
You told us that it is OK to use PVC pipe instead of B-vent on your waterheater?
Your name is published on the Pennsylvania Megan's Law sexual offender list?
Tell us again how you are an expert to be taken seriously?
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Generally speaking, the two legs are derived directly off a single HV line via a transformer that feeds at most a handful of homes. Which means that having the legs behave differently due to things upstream of the transformer is exceedingly unlikely. Different leg voltages in a residential system usually is caused between you and the transformer (ie: pole pig). Ie: loose neutral. Bad connection on the local transformer.
However, this phenomena is certainly common enough with three phase systems if a phase drops out. These are split much less often, such that any problem between you and the substation can do it.
But, notice the "usually"s and "generally"s. Some systems are different.
In a residential system, I'd take it to indicate that something is about to go bad on your local drop. The power failure just made some marginal connections misbehave.
Could also have been an illusion, with different things going on and off, your brain may not be the most accurate indicator of whether some "offs" were at the same time as some "ons".
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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reason it is ok, is that you are very unlikely to ever power up all of the circuits in your home to the maximum at once. You may have several outlet circuits at either 15 or 20 amps, but the usual load on these is probably only a few amps. You were wise to upgrade- 60 amp service is very outdated. The minimum on new residentail construction in my area is 150, I paid an extra $50 to get 200 amp service. As you add to your panel, you may want to do a demand load calculation, just to be sure. This is a pretty easy formula, and can be found at homewiringandmore.com. With 150 amps you should be pretty good, but the demand load calc. will tell you how much breathing room you have. Dave
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Thanks Dave!
Yes, I have a bunch of 15's and a few 20's... most of them never have any load. Because of the old system (60 amps) the entire upstairs (3 rooms and full bath) were on a single ancient 15 amp circuit! I guess this was common back in the good old days ...
Anyway, now I have separate 15 amp circuits in each place, and I even ran 60 amps to the garage. Probably more than I'll ever need their but what the heck (I was digging a long trench either way)
150 amp service looks to be fine for my demand load.
TN

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this is Turtle.
What the breakers are rated at is no where near what you would draw if everything in your home was turned on. First the breakers are the top of the draw to turn off at and the load would or can be only 805 of the breaker size or it will start to pop. this would make your 220 amp breaker amount go to no more than 176 amps at the very most. Then you don't run everything in your home at one time like air conditioning and heating at the same time, in the kitchen -- run the microwave/ ignitor on the stove or all elements on the electric stove / toaster/ cake mixer/ vent fan/ coffee pot/ refrigerator/ can opener/ all the lites/ garbage desposal/ radio and clock/ dishwasher/ and the list goes on. You usely will never turn on more that 1/2 the stuff in a kitchen to start with and this will not be counted as a real load on the system. You take the other parts of the house and you will find out you don't run everything in that room at one time.
Most home with all electric does not draw more than 100 amps to 125 amps at any one time. Most all homes with a lot of gas appliances will run about 50 amps to 75 amps. the only way you may get to the 150 amp servivce main limits is you turn on everything in your house heating and cooling at the same time and have straight electric strip heaters and you might be able to get near the 150 amp main limitand be at about 125 to 130 amps. Now in this crazy mode of operation it would still fall short of the 150 amp limit.
Now with all this said. you should have a amp draw load test run on your home to be sure of not getting to the limits in anyway. This can be done with a amp meter and someone running around and turn on everything in the house at one time. Now you could do it by look at every appliance in your home and get the max. amp draw off them and get it by the stated amp draw of all appliances. What the amp draw that they state on them, it will never draw that amount and you would have to account for that.
i really just thought about it here and i don't know why i'm explaining all this in detail with your ok by no breaker are popping right now and you can just run what you have and if your over the limits and the electrical system is installed correctly. the breaker or the main will pop if it is too much. You can't run more than 130 to 135 amps through a 150 amp breaker main or it will pop before it get to 150 amps. A lot of breakers will pop way before the 150 amps at maybe 125 or 130 amps.
I have a good mine to delete all this but well i'll let it go.
TURTLE
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