Hi folks,
This may seem elementry, but the dumbest questions are the unasked ones…
I’ve got a 1930 home with updated electrical. The main breaker is 100 amps. The total amperage of all the breakers in the box however is 240 amps. Call me crazy, but this seems wrong.
Question 1: Should I upgrade the service to 2 or 300 amps?
Question 1a: if so, is this as easy as replacing the main breaker with a larger one? (I realize that I’d need to cut power at the meter box before attempting this).
Question 1b: if I do upgrade to a higher amp box, will I also need to run new service wires from the meter to the box?
Now, I’m thinking about this because I’m installing a hot tub with 220v service, and I’m going to wire in a sub panel. There’s a space for the dual breaker to go to the sub panel in the main box, but again I wonder about that old 100 amp main breaker.
Question 2: Assuming for the moment that the service wires from the meter are only big enough to run the 100 amp main box, is it possible to install a second panel, using a second set of service wires from the meter box to power it? It seemed that I could then transfer over a few of the circuits from the main box to this box to drop the load a bit, even though I’ve never had problems that I’m aware of with the panel in its current (pun) state.
I have many books, so I can get proper wire sizing and such, and am a safe and handy guy. Is this truly a job for a pro?
Thanks in advance,
Tom
Replies
This is not ment as a put down, but from your guestions, you should hire an electrician.
Could you just run new wires to the meter base(?), indicates you don't know enough about electrical wiring to even get started.
Spend the money and have a pro wire your new tub or upgrade your service if needed. Enjoy your tub with the full knowledge that it is wired to code and your family and house are safe.
No offense intended.
Dave
Dave,
thanks for the feedback, but here's where I got that idea. Quoting from Rex Caldwell's book "Wiring a House" (Taunton Press, 1998):
"If the load will be over 200 amps, it's best to install two smaller main panels wired in parallel, as opposed to one larger one... I install all panels next to each other, with SE cable for each coming straight out of a large meter base, which has extra lugs or extra-large lugs provided for the parallel-service wiring required."
It made sense to me...
Tom
That concept will work, but you still need to know a lot more before you even think about this.
First the requried size of the service is not based on the total size of all of the breakers. It is based on a the total of the fixed loads, plus a square footage factor and some demand factors.
Next, it is most likely that they service drop and meter (and meter base) are limited to 100 amps. They all need to be upgraded.
Bill and Dave (and others who wrote directly)-
Thanks for the feedback (and no offense taken Dave)... I've come to trust that there are bunches of folks smarter than me about these things (and many of them put in their time on this board) and it's looking more and more like I'll need to hire a pro for this one. Guess I'd rather be sipping homebrew in my hot tub than lying in the ICU with electrical burns. Call me crazy...
Tom
Some reasons that Rex Caldwell recommendation (two 200-amp distribution panels in a McMansion) makes sense are that 200-amp panels are CHEAP (like $150 including a mess of breakers) and 400-amp equipment is NOT. And for that large an installation, the number of Romex runs and their lengths coming to a single point can get to be a bit much.
Bill is correct. Service size is not the total of all breakers. In my own house I have sixteen 20-amp breakers and six 15-amp breakers total = 380 amps. All of which is fed by a 100-amp breakers at the service entrance (typically would be 200-amp, and could be at any time, but there were advantages with the utility to do it that way).
To explain a bit: None of your circuits pull their maximum (or they'd pop). Most circuits pull very much less most all of the time. Code takes that into allowance as Bill describes. Base loads like the heating system and (if electric) hot water heater count fully. But convenience circuits and lighting are figured on square footage - only so many people will be using appliances/lighting at the same time in a given size house.
Do you even have a problem? It doesn't sound like it. Unless you have electric heat; or an electric hot water heater and lots of portable space heaters; or some other huge amp draw (are you a welder?), 100 amps is fine.
Write down all of your fixed electric appliances (HWH, space heat, stove, etc). And the proposed hot tub current rating. Take that and your house's sqaure footage to the building department. In my town, they'd run the numbers for you (for free).
-David Thomas Overlooking Cook Inlet in Kenai, Alaska
Edited 8/24/2002 1:25:03 AM ET by David Thomas
David,
Nope, not welding, and definitely not a McMansion; crackerbox palace is more like it. I've hardly got any serious stable electrical loads, aside from a dishwasher and washing machine. Everything else is gas, and I've rarely if ever popped a breaker. Except for the time that I created a living monster from the stitched-together body parts that Igor would bring me... but the lab's pretty much in mothballs these days.
So, it's looking like I'll either take my load tally down to the building department or have a local electrician come and give me his .02 on the advisability of upgrading.
Tom (overlooking a dumpster filled with my back porch)
I've got a 1930 home with updated electrical. The main breaker is 100 amps. The total amperage of all the breakers in the box however is 240 amps. Call me crazy, but this seems wrong.
You'd be hard-pressed to find a house panel where the total current for the branches didn't exceed the main. The code recoginizes that not all of those branches will be loaded with maximum current simultaneously. There are some rather byzantine calculations involved in the code to figure out how much one can put on the branches, based on the type of load involved. This isn't a safety thing so much as a good practice thing -- it would be bad to install a panel where the main breaker keeps tripping.
Question 1: Should I upgrade the service to 2 or 300 amps?
Maybe. 200 is commodity and pretty cheap; 300 is still niche and expensive, and it's highly unlikely you need it.
Question 1a: if so, is this as easy as replacing the main breaker with a larger one? (I realize that I'd need to cut power at the meter box before attempting this).
Probably not. If you look at the label in the box, you'll find it's probably only rated for 100 amps -- things like the bus bars inside are only rated to carry 100A. Also, the main breakers alse protect the wires from the meter base to the panel, and they're probably only sized for 100A as well.
Question 1b: if I do upgrade to a higher amp box, will I also need to run new service wires from the meter to the box?
Probably. This will involve the power company, who will need to come out and pull the meter. Then they'll probably require an inspection sticker on any work you do, before they'll re-install the meter. Worst-case, the pwer company would need to update the meter base, and the service entrance cable.
Now, I'm thinking about this because I'm installing a hot tub with 220v service, and I'm going to wire in a sub panel. There's a space for the dual breaker to go to the sub panel in the main box, but again I wonder about that old 100 amp main breaker.
The quick-and-dirty thing to try is just install the branch for your hot tub (Plan A). If you use it and the main breaker never trips, you're fine. If the main starts tripping when the hot tub and toaster are turned on at the same time then, well, you'll need to go to Plan B. Plan A isn't unsafe, since the breakers on the branch and main ensure that nothing gets overloaded. It just may not work real well.
Question 2: Assuming for the moment that the service wires from the meter are only big enough to run the 100 amp main box, is it possible to install a second panel, using a second set of service wires from the meter box to power it? It seemed that I could then transfer over a few of the circuits from the main box to this box to drop the load a bit, even though I've never had problems that I'm aware of with the panel in its current (pun) state.
If you go with an extra panel, I'd install a new 200A main panel, and run a 100A feeder over to the existing panel which would become a subpanel (ground and neutral would then need to be separated at the 100A panel). In any case, this still involves getting the power company and code authority involved.
That is an idea of just trying it and seeing.
I have a friend that just got a house that was built around 1950, but with addition(s) as late as 1980.
It has an 100 amp CH pannel, that was upgraded at some time, and I figured the load at 95 amps. Now she wants to get an electric stove. Knowing her and how she lives I suspect that she could get by with adding that to the existing pannel. But the service is old "romex" that with bad insulation and it looks like it might only be 60 amps.
So I am talking her into going ahead and getting a 200 amp pannel and serive. That way I know that the main pannel and stove are OK and it will give me time to start working on the other "issues".
In the garage there is a junction box with no cover. No legal, but it is on ceiling and not a real problem. A 2nd one does have a cover, a plastic lid from a coffee can.
Now here are some of the more interesting "issues";
Like the sub-pannel in the addition that bonds the neutral bus bar to the ground (no neutral was run from the main).
Like the 30 amp branch circuits with #12 (and maybe #14) wire. Not any big loads, just convience outlets.
Like the GFCI outlet that they added to have a "grounded" outlet for the refigerator.
Like the #14 that they tapped off of the 240/30 amp dryer circuit to feed a dishwasher.
"Issues" are what makes this fun.
3 way light switch in a small, maybe 12 cu in metal box, that used 12-3 in the run to the other switch (load was 240 watts), was fed by 12-2, and also had two #14's from the older K&T receptacle nearby, plus the pig tails. Box wasn't grounded as the 12-2 was fed off 1950's cloth braid romex from the 50's. Was inspiration for a new rule, only open boxes or switches for the first time on Saturday morning, in case it takes 2 full days to get the wires packed back in.
GFI outlet in new bathroom add-on. Outlet was spliced into 50's romex that ascended the wall to feed all the K&T lights on the first floor. Ironically, we assumed this GFI was a dedicated 20A circuit and used it to power tools to put in other boxes. Ground for the GFI was a copper wire from the screw on the GFI that was jammed between the ears and the metal box. A screw on the box connected a wire to the cold water pipe feeding the bathroom.
The house was split long ago into an up-down duplex. The upper kitchen had a fridge that ran off an outlet on the same circuit as the first floor lights (see above). So one circuit had a bathroom GFI, a refrigerator, and all the first floor lights.
First floor refrigerator ran off outlet that supplied all basement lights as well, and also the first floor stair light. 3 way switch in this circuit used 12-2, and the ground WASN'T used for the neutral!
1 outlet in a 900 sq ft basement, on same circuit as refrigerator and lights, and it was ungrounded.
Conduit to garage that consisted of 12-2 romex in 3/4" plumbing pipe. Romex entered the pipe as it emerged from ground under the porch at an angle. The pipe was from 3-6" under the soil to about 6" from the garage, where it emerged from the pipe and entered through the wall to feed a 2 circuit fuse box. Regular romex.
Speaking of neutrals, the house didn't have one. Ground was to a very corroded water pipe (gee, wonder why). And this was a place with 2 electric ranges, 2 electric watr heaters, an electric dryer and 2 refrigerators. I figured if it hadn't burnt down yet, there was no need to panic until the electricians got there to put in the new 200A 30/40 box.
I happened to come across some video footage that was shot right after we closed. Now I understand where all my weekends went, and boy am I glad. I sleep better now. Ironically, when we go to gas for dryer, hot water and range, I calculate the NEC load on the house will be less than 60 amps.
go to http://www.doityourself.com amd go to the electrical section, there is a electrian on there that is very good.
I agree most with BarryO. Install the tub. If it trips the breaker you could control your usage. Turn of the space heater. Have the wife join you in the hot tub instead of her doing her jewelry crafting in the toaster oven. If this seems impractical or overly inconvenient, some people have no problem with this sort of thing while others want to be a able to run everything at once and feel constrained if they can't, you can start to think of upgrading the panel and/or, as required, the service.
There is one step you could try before upgrading. It sometimes can help to look closely at the 120v loads that are run at the same time and check where the breakers for these loads are located in the panel. Sometimes most of these loads will be drawing power from the same leg in the panel.
If you have a situation where the main keeps tripping have an electrician put a ammeter on the neutral while you recreate the problem. A significant load on the neutral indicates an unbalanced panel. By rearranging the placement of the single pole breakers you may be able to balance the load and make it so that the load is not carried by only one leg of the main breaker.
You can do the same thing by noting what 120v loads are running and counting even/odd in the panel. A little experimentation can yield meaningful results and save some money. The method using an ammeter is quicker, surer and more exact. Both to identify the circuits loaded and to check the balance. While your in there have the electrician check the connections for tightness and heating.
You can do the same thing by noting what 120v loads are running and counting even/odd in the panel. A little experimentation can yield meaningful results and save some money. The method using an ammeter is quicker, surer and more exact. Both to identify the circuits loaded and to check the balance.
So by balancing the load on my panel I can save money? How is this measured over a 24 hour period to take into account changes in lighting, heating, refridg demands? I have to assume that all my 220 loads (A/C, shop tools, etc) are already balanced.
Please explain.
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So by balancing the load on my panel I can save money? How is this measured over a 24 hour period to take into account changes in lighting, heating, refridg demands? I have to assume that all my 220 loads (A/C, shop tools, etc) are already balanced.
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Sorry, power is power and you'll pay the same either way. What you'll get by balancing your load is evenly distributing how that power flows through the two sides of your main breaker. By doing this, you'll lessen the chance that you'll pop the breaker by overloading a single side.
Tom
Did you ever get this resolved?
For the shop (detached building), I'll need up 320A (400 Amp) meter anel. Still looks like splitting it into two 200 Amp panels wired off the main looks like the best bet. Need to check with the Power Company about disconnects at the pole. (Rural area, meter is set on a pole... lines trenched to the building).
Large 3000 sq. ft. Building. 30' x 50' Shop downstairs. Upstairs is for storage, but eventually to convert into a small apartment for the kids when they come home from college. Welding, three phase (rotary
convertor), and lots of low duty cycle power equipment. Still would be nice to plan for future A/C (4 ton upstairs), small electric kitchen, etc. and have it wired out long before I need to do it.
As to "balanced loads", the old "ELI" (Current lagging Voltage in an inductive circuit) has bitten me on the inductive loads. My 100 Amp welder will trip 125 Amp breakers due to the inductive nature of the load. Adding in a bank of capacitors parallel across the inductance (factory option) will insure that a 100 Amp breaker works fine. (Actually I had a 100 Amp breaker wired in, when I went above 60% of the current setting the breaker would trip. Bank of capacitors brings the current and voltage back into synch deliverying more power to the welder). [Dean -- this is different from your question about balancing the two sides of the 120V branches]
Tom W
What TomD said. It won't save you any money on your power bill. It is a way of squeezing a bit more power out of the main before it trips. A marginal solution in most cases but it can be the difference between an hour of labor costs and having to upgrading the panel and possibly the meter. $65 vs $500+.
When it works out your a hero for the day.
This is what I expected, but the thought of saving power/$$$ here in California just by rearranging my load sounded too appealing to pass up!
Tom's question about adding a second breaker panel makes me wonder -
I was in a new house recently that had 2 panels - A 100 amp (I think) panel in the garage right behind the meter, and a 200 amp panel in the basement.
I've never seen that done before, and was curious - Do you have to run a separate set of "supply" wires to the meter from each box, or take the wires to one service and use it to feed the other one? Everything was covered up when I saw it, so I don't know how it was wired.
Just curious.....................
You say "psycho" like it's a bad thing.
Boss, typically (at least in my area) the panel closest to the meter will have the main disconnect for the house and the other panel will be a subpanel wired from the main panel. This is based on the requirement that the main disconnect for the system be within a reasonable distance from the meter ("reasonable" being subject to interpretation - of course, as we all know from Breaktime, if there's any question on what's reasonable you can just ask me, right?.)
Also, there can be no more than 6 switches to throw to turn off all current in a house and I'm 99% certain they have to be in the same place, so I doubt if each of the panels you saw runs back to the meter.
Thanks for the explanation, Bob.
But I'm also curious about something. If the first panel has to be able to kill the 2nd panel, do you have to have a panel with a double main or something?
Take the panel in the geerage in this case, and assume it's 100 amp. You couldn't use the 100 amp main breaker to kill the 200 amp panel in the basement, could you? And I'd assume you couldn't stick a 300 amp main in the 100 amp box in the garage to kill both with, either.
So what's the "reasonable" explanation ???
I never forget a face, but in your case I'll be glad to make an exception.
Ummm, errrrrr, ahhhhh.....
Tough to say, now that you mention it you couldn't (shouldn't?) run a 200A through a 100Amp box: for one thing the connectors in the 100 amp box wouldn't be big enough.
Was/were there main disconnects outside at the meter? In some areas of the country I believe it's common for the main disconnect to be outside at/near the meter, and then the distribution panels become subpanels.
Of course, there's always the possibility of a screw up, too!
Edited 8/27/2002 9:49:52 PM ET by Bob Walker
"Was/were there main disconnects outside at the meter?
"
Heck, I don't know. But I really don't remember one. The possibility of a screw-up is definitely there - Small town, no codes, etc.
NORMEL: No, I'm not at all sure that the panel in the garage was 100 amp - Just that it looked smaller than the other one, and had breaker spaces in it.
When you talk, you only hear what you already think. When you listen, you hear what others think
> In some areas of the country I believe it's common for the main disconnect to be outside at/near the meter, and then the distribution panels become subpanels.
That's the way it is here in L.A. The service drop is required to run in conduit strapped to the outside of the building, you can only bring wires inside after the main breaker.
-- J.S.
Are you sure that garage panel was 100A? It could have been a small 200A panel that had a few breaker spaces and lugs on the bus bars for a feed to the other panel. The main at the garage would then also be the service disconnect.