Electric Service Rating vs Reality

[Tom Bender]

At one time some houses had only 15 amp electric service This has been increased over the decades to the point where 200 amps is common. That's 240 volts x 200 amps which is in the neighborhood of 48kw. (someone will please inform us about the power factor an whatever other mistakes I have made to this point)

When I estimated the loads that my generator would need to support it came to 11kw The 16 kw unit we installed has been fine

I think the biggest load a normal house will put on a system is if it has electric resistance heating That might be around 20 kw (presumably A/C will not run at the same time)

An ordinary one man workshop might draw up to 4 kw though it could go higher

Motor starting loads may double some individual loads briefly but these would be a small percentage of the total

Adding up my house plus electric resistance heat plus electric stove and water heater and a substantial shop load

11 + 20 + 8 + 4 = 43 kw if it all runs at the same time, 200 amp service (48 kw) is more than adequate but 100 amp (24 kw) would be borderline

or without the electric heat it would be 23 kw, 100 amp service (24 kw) would be good and 60 amps (12 kw) would be borderline

So here's my question; Who has had main circuit trips and under what circumstances?

[Mike Kees]

The only time my main circuit has "tripped "is when I shut it off to install something in my panel.

[Mike Henderson]

I'm not sure what your point is. I expect the reason for 200 amp service is to make sure that very few people have to upgrade their service - which would be expensive for both the power company and the customer.

Additionally, the power company cannot predict the future and wants to make sure that if power demands continue to grow - as they have in the past - that they won't have to upgrade their local grid and the connection to your home.

I've seen posting here on the forum where people who had 100 amp service were upgrading to 200 amp service but I don't remember why. Maybe they purchased an electric vehicle. Many electric vehicles require a 50 amp circuit.

Obviously, you would not want your main circuit breaker to trip from excessive current. If it did, it would indicate that your service is not sufficient, or you have some major wiring fault.

Mike

[Timothy Thorpe Allen]

Add a pottery kiln or welder (or both), either of which can require a 50-amp circuit. Further, pottery kilns typically run continuously for hours on end when they are fired.... (so even though on a 50-amp breaker, the wiring has to be uprated as if for a 65-amp circuit - something like that).

In answer to the OP's question, no, I can't recall the main breaker ever tripping... IIRC, we have a 150-amp service (odd, I know)

[Andy D Jones]

I have never had my main breaker trip. I bet it very rarely happens today, unless a fire or flood (of/in the main panel) occurs. Individual breakers will usually trip first, shedding load, and preventing the main breaker trip. This is by design and by code.

How long ago are you going back when homes had just 15 amp main service? The smallest I've ever seen was 50 amp service (fuse box), but I'm not an electrician.

Andy - Arlington TX

[Andy D Jones]

Add a pottery kiln or welder (or both), either of which can require a 50-amp circuit. Further, pottery kilns typically run continuously for hours on end when they are fired.... (so even though on a 50-amp breaker, the wiring has to be uprated as if for a 65-amp circuit - something like that).

In answer to the OP's question, no, I can't recall the main breaker ever tripping... IIRC, we have a 150-amp service (odd, I know)

A 50 amp pottery kiln does not draw 50 amps continuously once it is up to temperature. If it did, it would take forever to get up to temperature.

Electric services are also often upgraded if the original service did not provide for Air Conditioning, and the house used gas heat.

Andy - Arlington TX

[Dan Friedrichs]

As Mike said, it's future proofing that costs much less at install. Just a few years ago, few people would have anticipated a situation where someone had 2 electric cars charging in their garage drawing 60A, each, for hours, continuously. That plus some A/C and you're suddenly drawing a LOT of amps.

[Patrick Kane]

I have 100amp service, and i have tripped the main breaker. I think the breaker was old and lost its full load rating. I tripped it twice, replaced the main breaker, and no longer have an issue. If I planned on staying in this house for years to come, i would upgrade to 200 in a flash.

[Lee Schierer]

The only time my main circuit has "tripped "is when I shut it off to install something in my panel.

This is the only reason my main breaker has ever been used, even when I had baseboard electric heat in every room of my house.

You would get some pretty good amps if you are running the washer, dryer, dishwasher, oven, cook top, water heater, well pump and electric heat at one time. I've seen that many loads in my house. Not to mention tv and lights.

[John K Jordan]

...How long ago are you going back when homes had just 15 amp main service? The smallest I've ever seen was 50 amp service (fuse box), but I'm not an electrician.


50 years ago I had a house with a 60 amp fuse box. All the fuses were warm to the touch. I taught myself electrical wiring and installed a 200 amp service, rewired much of the house, and fed my first small shop with an underground cable. I learned then to love underground wiring.

I'm not an electrician either (except in Mexico) but I've done all our wiring since, upgrading a 100 amp service to 200 amps in the second house we bought as well and rewired 1/2 the house.

This (and our final!) house came with a 200 amp service fed from the meter next to a 7200 volt transformer on a concrete pad in the woods near the house. When I built the shop I rewired at the meter to keep 200 amps to the house and provide 100 amps to the shop. (I have four things in the shop that want 50 amp receptacles, never .)
There are four other sub panels fed from various places to elsewhere on the farm. (Every bit of the power is underground starting at the pole at the street. There are wires and pipes everywhere!)

I think it's far better and not much more initial cost to have more capacity than needed.

And also, never had a main breaker trip. And I'm happy about that.

JKJ

[Justin Rapp]

I never had the main breaker trip in my current house with 200 amp service. I have never had the 100amp shop sub-panel circuit break trip either. Like others stated, if your main is tripping, your electric has some major problem. Heck, even when lightening hit between my house and my neighbor's house, individual breakers went and so did gfci's that were affected by the zap.

Also if any break trips too many times, it does weaken the breaker and once you fix the reason for the breaker being tripped, you should also replace the breaker.

Electric kills - if you are not sure, hire a licensed electrician to fix the issue.

[Roger Feeley]

My understanding of it is that they must assume that everything in your house is going to start up all at once. All ovens and electric stove burners, all motors and compressors. Then they add in a safety factor. They they go up to a handy round number. When we built our little in-law quarters, we were fortunate that the main house already had a 400A service. They added a 125A breaker and gave us that which was overkill. But then I put a 70A breaker in our box and wired up a subpanel for my shop. Now the 125 doesn't look so crazy.

In my shop about the most power I would draw would be the 3hp table saw and a 1.5HP dust collector + about 700watts of lights. I seldom run more than one thing at a time since it's just me.

[Tom Bender]

One of our wood netters was considering upgrading his service so I thought it would be good to get a reality check.

Roger
If 'they' required a service equal to the greatest conceivable connected load very few would pass. A healthy diversity factor is applied. So it is possible to trip the main breaker under unusual circumstances (everything starts up at once).

When the power goes out some loads do not start up instantly. An electric clothes drier and some motors in your shop must be restarted, a gas furnace will have to heat up before the blower comes on, not everything else will be on. Still it's a good idea to switch off some things to reduce the startup current when it does come back on.

[Patrick Kane]

Depends on your friend's ultimate plans too. Im a unique situation in that i have a very small home service(100amps), and ive tripped a main breaker. It was a faulty breaker, but still. More so than the faulty breaker, ive passed on things and been limited because of my service. If I had 200-250 amps, i would have more than likley gone over to 100% 3 phase equipment off a converter. As it stands, im limited to to 5-5.5hp, which is on the low end for most bigger/better equipment. I wont tolerate another 100amp service if i continue in the craft and move.

[Jim Becker]

We originally had 200 amp service and bumped that to 400 amp service when I put a full panel into my shop building back in 2005. The house and the shop are on the same meter but have separate feeds from the meter with separate main breakers. (this work was all done by a licensed electrician and code inspected) However, the power company refused to change the aerial feed wire from the transformer. They said it was adequate...despite it looking "small" to my eyes...for anything we would be able to throw at it. My generator is a 22Kw, only powers the house, and is more than adequate to run both HVAC systems and everything else we normally use. We've never sprung either the main breaker on the house or the main breaker for the shop.

[Jared Sankovich]

I have 200amp that really should have been 400amp for the size of the house (needed a sub panel just to fit all the circuits) Never tripped the main though.

[Jacob Reverb]

Never tripped my 200A breaker, but if you have an "instant" electric HW heater, or if you like tig welding heavy aluminum, as I do, you're gonna occasionally gobble up some beaucoup kW, and 300A service is probably more prudent than 200.

[John K Jordan]

... or if you like tig welding heavy aluminum, as I do, you're gonna occasionally gobble up some beaucoup kW, and 300A service is probably more prudent than 200.

Yikes, I use TIG but I haven't welded aluminum. My Miller TIG and MIG machines both plug into a 50 amp circuit. Are you saying AL welding will use more current than I do for mild steel or do you mean using a much bigger machine? What kind of machine do you use?

And to further hijack this thread, what's a good way to learn aluminum TIG welding, is it considerably different than steel? Any particular type of electrodes? I have an argon cylinder.

Would an aluminum spool gun for the MIG be an easier way to get started? I'm mostly interested in smaller things, 1/4" or less.

JKJ

[Andrew Seemann]

I think part of the reason for 200A vs 100A is that the cost difference isn't that great to go from 100A to 200A in parts at installation, but upgrading from 100A to 200A after the fact is rather expensive. 200A boxes typically have more breaker spots in them as well.

My shop has a 100A subpanel and 100A wire, but I have just a 60A breaker feeding it in the main panel, mostly because I had one handy at the time. I've never tripped it.

I've never tripped a main breaker, although I lived in a 12 unit apartment building that had 100A service that blew one of the cartridge fuses in the 1930's vintage knife-switch service main. And that was only a on a hot day when everyone had window ACs running. I remember having to explain what was wrong to the maintenance guy and how to fix it. He was confused why only half the power was on in the the building. I was quite furious (and hot and sweaty) at the time and laid into him about the wiring being inadequate and a fire hazard. My tirade must have made it to the owner (or his insurance company) because the service was soon upgraded to more llke 400A and the place rewired.

[Alex Zeller]

I'm not an electrician either but I do lots of electrical work at my job. I work with people who are also not electricians but think they are. I wired my house after taking the time to learn the codes (we have plenty of sub contractors at work who are electricians). Here's a story I often tell people who think about trying to wire their house or shop without any knowledge.

A coworker (who will remain nameless) wired up his barn. At the back of the barn was a metal gate. While he never had a problem both his wife and son said they kept getting a shock. That went on for 6 months (with me saying he had a real problem). Finally one day one of his bulls went to take a drink out of the water tank. It was winter and he had a device in it to keep the water from freezing. As soon as the bulls lips touched the water it dropped him to his knees. That's when he figured there was really a problem (apparently the bull was more valuable than his wife or son). After shutting off circuits one at a time until he figured out the one with a problem he found he put a staple through a wire and it was shorting out the hot and ground wire. He pulled the staple and said the problem was solved.

Now if you know electricity and basic electrical red flags should be going off. And this is my point. No matter how many times I tried to tell him he had a much bigger problem. He didn't believe me. It wasn't until 3 or 4 actual electricians were almost screaming at him how dangerous his barn was that he finally figured I was right again. He could not understand when I kept saying that he should have tripped a breaker the moment he turned that circuit on. Turns out he used an old panel he had, the screw in fuse type. Someone had put a penny behind a good fuse. Since it wasn't blown he never checked.

I'm a do it yourself kind of guy but I do try to listen and understand advice given. Most everything you will do at a house is very much common sense stuff. But if you aren't sure find out. If you think something isn't right then assume it isn't. Electrical fires are by far and away the 1# cause of houses burning down.

[Rollie Meyers]

The only time my main circuit has "tripped "is when I shut it off to install something in my panel.


A breaker only "trips" during a fault, or overload, merely turning it off is not tripping it, larger frame circuit breakers not normally used in residential commonly have a push to trip button on them though.

[Jason Roehl]

A breaker only "trips" during a fault, or overload, merely turning it off is not tripping it, larger frame circuit breakers not normally used in residential commonly have a push to trip button on them though.

And you should stand to the side when you push that button. We've shut down our 2000A main service breaker at work before. The first time I went to shut it down for the electrician, he all but shoved me out of the way before my finger hit the button. He's in his early 60s, and has plenty of good stories from doing lots of work in commercial/factory settings. I've learned a lot from him...

[Jacob Reverb]

Yikes, I use TIG but I haven't welded aluminum. My Miller TIG and MIG machines both plug into a 50 amp circuit. Are you saying AL welding will use more current than I do for mild steel or do you mean using a much bigger machine? What kind of machine do you use?

And to further hijack this thread, what's a good way to learn aluminum TIG welding, is it considerably different than steel? Any particular type of electrodes? I have an argon cylinder.

Would an aluminum spool gun for the MIG be an easier way to get started? I'm mostly interested in smaller things, 1/4" or less.

JKJ

John.

The reason welding aluminum takes so much more power and heat than welding steel is aluminum's thermal conductivity. The only metals more thermally conductive than Al are gold, copper and silver -- so the heat "wicks away" faster than you can dump it into the workpiece, so you need a machine that can really put the coals to 'er To weld 1/4" aluminum, 250A is about the minimum, and 400A is better. It you try to weld aluminum slow, or with a smaller machine, what happens is that the whole workpiece gets hotter and hotter until, instead of a tiny, focussed puddle of molten aluminum, you get a big pancake PLOP. The whole thing melts at once and collapses.

I use an old Miller transformer that puts out 465A of AC, but being a transformer, it gobbles up the current. It's on a 100A circuit, but 150A or more would probably be needed to dial it up to 465A (never have opened it wide-open). If you use an inverter-based machine, you can feed it considerably less power (they're more efficient) but those machines are a lot more expensive and generally not as long-lived. If you occasionally want to weld something bigger than your machine can handle, you can punch it up by using helium instead of argon. This makes the arc far hotter for some reason, and allows you to weld things that you couldn't manage with straight argon, at least not without a lot of preheat. But helium is expensive, and floats away, where argon is cheaper and mostly stays put.

The other thing about tigging aluminum is that al develops a protective oxide on its surface (alum oxide) whose melting point is something like 3500*F whereas aluminum melts at around 1700* ... and you need AC welding current to "clean" off this oxide layer. The + part of the sine wave cleans/lifts off the oxides and the - part of the sine wave melts the workpiece. On machines newer than about 1975, you can vary the % of the wave that is pos and neg and thereby change how much "cleaning" versus penetration the arc will have (this is called "AC balance."). You will also want continuous high frequency on an alum welding machine to help keep the AC arc lit (it tends to extinguish as it crosses zero V).

Don't know much about mig in general or spool guns in particular, but hope this helps.

J.

[John TenEyck]

My house was built in 1961 with 60 amp service. I limped by on that until I wanted to get central AC. I actually thought the service was 100 amps and ran a 60 amp subpanel to the basement to power my woodshop. Never tripped the main breaker, miraculously, but to Tom's point, as I was running at least a combined 4 hp sometimes. Anyway, upgrading to 200 amps was as much about having enough breaker spaces in the panel as available amps. I could have gotten by with a 150 amp panel, but 200 gives me some room to grow w/o having to add a subpanel. And I filled it some with a two welder outlets and a couple of new 120V circuits. I installed a 17 KW generator a couple of years after the new panel was installed. It can produce something like 75 amps and is just capable of running everything in the house, minus the welders. It's really curious how the power company tried to convince me to only go up to a 150 amp panel. They had to install new lines to the house anyway. Wouldn't they want me to use more power and pay them more money? The gas company had no qualms when the gas meter needed to be upsized to handle the generator.

I do remember my parent's 1924 house had a 30 or 40 amp service when I was little; wire and tube in some places, too. Yikes. Fuses blew regularly until they finally upgraded to 100 amp service and installed new circuits.


John J. , I've never welded Al but I'm pretty sure it takes a lot more power than for mild steel. The thermal conductivity of aluminum is far greater than steel so the heat wants to run away from where you are trying to weld. So you have to dump a lot more power into it to raise the temp. enough to weld.


John

[John K Jordan]

Thanks for the tutorial! I might be happy welding things considerably smaller than 1/4"! I'll check my manuals. I thought I read in one manual that that machine uses a reverse pulsed DC for Aluminum which is supposed to blast the oxide off the surface with every pulse. But it's been years since I read it and I might be totally confused, not necessarily a rare thing. :)

O do love the TIG for small things made from steel. I never tried it before I got the machine but I did previously weld thin sheet metal with a torch so maybe that helped.

Things like this little hand saw that fits scroll saw blades is my idea of fun.
425772
Repairing farm and shop things is my justification for the little weld shop (and the plasma cutter).

Thanks again.

JKJ



John.

The reason welding aluminum takes so much more power and heat than welding steel is aluminum's thermal conductivity. The only metals more thermally conductive than Al are gold, copper and silver -- so the heat "wicks away" faster than you can dump it into the workpiece, so you need a machine that can really put the coals to 'er To weld 1/4" aluminum, 250A is about the minimum, and 400A is better. It you try to weld aluminum slow, or with a smaller machine, what happens is that the whole workpiece gets hotter and hotter until, instead of a tiny, focussed puddle of molten aluminum, you get a big pancake PLOP. The whole thing melts at once and collapses.

I use an old Miller transformer that puts out 465A of AC, but being a transformer, it gobbles up the current. It's on a 100A circuit, but 150A or more would probably be needed to dial it up to 465A (never have opened it wide-open). If you use an inverter-based machine, you can feed it considerably less power (they're more efficient) but those machines are a lot more expensive and generally not as long-lived. If you occasionally want to weld something bigger than your machine can handle, you can punch it up by using helium instead of argon. This makes the arc far hotter for some reason, and allows you to weld things that you couldn't manage with straight argon, at least not without a lot of preheat. But helium is expensive, and floats away, where argon is cheaper and mostly stays put.

The other thing about tigging aluminum is that al develops a protective oxide on its surface (alum oxide) whose melting point is something like 3500*F whereas aluminum melts at around 1700* ... and you need AC welding current to "clean" off this oxide layer. The + part of the sine wave cleans/lifts off the oxides and the - part of the sine wave melts the workpiece. On machines newer than about 1975, you can vary the % of the wave that is pos and neg and thereby change how much "cleaning" versus penetration the arc will have (this is called "AC balance."). You will also want continuous high frequency on an alum welding machine to help keep the AC arc lit (it tends to extinguish as it crosses zero V).

Don't know much about mig in general or spool guns in particular, but hope this helps.

J.

[Rick Potter]

My reality:

In 2005, I rehabbed a rental my brother owns. It was a 750 sq ft house from maybe the '20's that had been moved to it's present location. I had a bit of trouble trying to run a benchtop table saw, and discovered it had a panel with no main, just three glass 15A fuses that fed knob & Tube wiring, some of which had been replaced by zip (extension) cord wires. And my bro wanted to install an electric stovetop.:eek:

Ended up putting in a panel with rewire.

I currently have a rental house with a 60 Amp panel, and 6 circuits. I really want to put in a big wall A/C, but it will have to wait until I can get the place rewired.

My house has a 225A panel that was put in when we did the solar. We also have 4 sub panels. Hard to keep track.

[Ole Anderson]

I would think that the reason for 200 amp panels has more to do with the number of available circuits rather than the actual total load on the panel. Theoretical load, yes. When I built my house in 1975, my buddy's dad was an electrician and he convinced me to go with a 200 amp panel in a 1550 sf house. So glad he did as that panel is now full. Wired it under permit myself.

[Ronald Blue]

And to further hijack this thread, what's a good way to learn aluminum TIG welding, is it considerably different than steel? Any particular type of electrodes? I have an argon cylinder.



Would an aluminum spool gun for the MIG be an easier way to get started? I'm mostly interested in smaller things, 1/4" or less.

JKJ

I'm rusty at this because it's been so long since I TIG welded aluminum John. You definitely need the Argon. Once proficient you can get much prettier welds with the TIG. At least in my experience. Aluminum behaves much differently as well. The "puddle" isn't so obvious. As I recall I used AC and continuous high frequency but it's been over 25 year so I could be wrong. Get some aluminum rod and some odds and end pieces to practice on. New metal welds much better than used. By this I mean a repair weld is challenging on used parts because it seems you never get the impurities all out of the weld area. A water cooled torch head is nice if you are doing a lot of it. It will be hotter than you weld steel at.

[Tom M King]

The best way to learn to weld aluminum is to pay someone to teach you, whether a school, or individual. You just can't do it well with cheap equipment. A cylinder of Argon is a very small part of the investment. A spool gun works, but still needs a good machine running it, and it gets heavy, and awkward pretty fast, depending on what you want to weld.

Talking about upgrading a service, I'm getting ready to upgrade a 1974 200 amp to 400 amp. The service entrance is coming in to the house with the 200 overhead, and we're changing that to feed the 400 underground. The second 200 amp panel will feed a couple of car chargers, other stuff like a couple of RV hookups, and a 100 amp sub panel that will be far enough away that the cable to it will have to be upsized enough that the conductors will be too large to go in the 100 amp breakers, so there will be junction boxes with pigtails from the breakers to the larger cable. That subpanel will feed another subpanel another 300 feet away, so there is some serious cable sizing calculations to do.

We already have four meters running here, and I don't want to run another main service where the 100 amp sub panel is going.

[Steve Demuth]

So here's my question; Who has had main circuit trips and under what circumstances?

Once, at the pole, when an idiot drove a steel post through the underground cable to the house.

[John K Jordan]

Once, at the pole, when an idiot drove a steel post through the underground cable to the house.

Ha, if we include the protection on the pole... My transformer at the house is fed by a 7200v line from the pole. On the top of the pole is a fuse. That fuse has tripped five times in 15 years.

Three time it was tripped when a squirrel shorted the hot wire to ground. We found a cooked squirrel on the ground. Once it was tripped in the dead of winter when termites bridged the connection from warm transformer to the ground. Once it was tripped when the insulation failed on cable 4' underground causing a pinhole path from conductor to earth.

Every time the fuse blew it sounded like a dynamite explosion..

JKJ

[Warren Lake]

speaking of baked wildlife years back I was driving to the lumber company. On the other side of the road where big towers and many serious power lines. I looked over to see an alfred hitchcock number of birds all flying in formation together swoop around like all on the same flight program then come in and land on the high power lines. As they did they picked different lines and some were between. There was a huge bang and birds dive bombed to the ground only didnt pull up. Lights were out for miles and when I came back there were cops at every intersection. I told one of the cops what happened and he just looked at me like i was nuts.

Fuses have blown a number of times here, a branch from a tree falls and ends up on the lines and bang. They finally come around and trim stuff regular now. People have had power out for a long time in the past and homes have flooded when sump pumps arent working and they didnt have generators. My own post had some sort of short on it, I told them a few times and they ignored me. A guy stopped one day at a neighbors and walked over and told me the post was wired wrong. I said Ive told them it sizzles when there is rain when its wet. He said stay away there is a charge in that post. I took a photo of burning and sent it to them and they finally woke up and next day a crew was there. Guy working on it said some days they dont pay him enough. Been fine ever since.

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[Tom M King]

A squirrel shorted out the transformer for our house. It made a tremendous arc, like a welding arc, that I told everyone not to look at. The arc continued to burn until the wires parted. I called the power company. It caught the pole on fire, I called 911, and it was too hot to stop burning before the fire department got there. They needed to wait for the power company to come, and in the meantime, the pole burned all the way down to the ground. We were only out of power for a couple of hours, while they set a new pole, and transformer, and fixed the wires.

[Mike Cutler]

I would think that the reason for 200 amp panels has more to do with the number of available circuits rather than the actual total load on the panel. Theoretical load, yes. When I built my house in 1975, my buddy's dad was an electrician and he convinced me to go with a 200 amp panel in a 1550 sf house. So glad he did as that panel is now full. Wired it under permit myself.

Exactly!
With all of the code requirements for dedicated circuits that have happened through the years in residential wiring, a 100 amp panel fills up pretty quick. The number of available/allowed poles in a 200 amp panel is typically greater. The ability to balance the neutral, based on expected daily loads is also more easily accomplished in a box with more poles/breakers.
I know, I know, that folks will say that you can just use tandems to increase breaker availability, but they were not always as widely accepted in use as they are today.In some jurisdictions they were flat out not allowed! I would also venture to guess that a great majority of them are installed in violation of the panel manufacturers literature. We did a lot of panel remediation/ upgrades in the late 80's for this particular issue, for pending house sales, probably two or three a week in Connecticut during the late 80's housing boom.

[Pat Barry]

At one time some houses had only 15 amp electric service This has been increased over the decades to the point where 200 amps is common. That's 240 volts x 200 amps which is in the neighborhood of 48kw. (someone will please inform us about the power factor an whatever other mistakes I have made to this point)

When I estimated the loads that my generator would need to support it came to 11kw The 16 kw unit we installed has been fine

I think the biggest load a normal house will put on a system is if it has electric resistance heating That might be around 20 kw (presumably A/C will not run at the same time)

An ordinary one man workshop might draw up to 4 kw though it could go higher

Motor starting loads may double some individual loads briefly but these would be a small percentage of the total

Adding up my house plus electric resistance heat plus electric stove and water heater and a substantial shop load

11 + 20 + 8 + 4 = 43 kw if it all runs at the same time, 200 amp service (48 kw) is more than adequate but 100 amp (24 kw) would be borderline

or without the electric heat it would be 23 kw, 100 amp service (24 kw) would be good and 60 amps (12 kw) would be borderline

So here's my question; Who has had main circuit trips and under what circumstances?

Main breaker should NEVER trip!

[Andrew Seemann]

Exactly!
With all of the code requirements for dedicated circuits that have happened through the years in residential wiring, a 100 amp panel fills up pretty quick. The number of available/allowed poles in a 200 amp panel is typically greater. The ability to balance the neutral, based on expected daily loads is also more easily accomplished in a box with more poles/breakers.
I know, I know, that folks will say that you can just use tandems to increase breaker availability, but they were not always as widely accepted in use as they are today.In some jurisdictions they were flat out not allowed! I would also venture to guess that a great majority of them are installed in violation of the panel manufacturers literature. We did a lot of panel remediation/ upgrades in the late 80's for this particular issue, for pending house sales, probably two or three a week in Connecticut during the late 80's housing boom.

And even if you could jam all them tandem breakers in without violating box fill requirements, they ain't cheap and you get to basically the same cost as doing it right with the right sized box and breakers:)

[Mike Cutler]

Andrew
In Connecticut it was hit or miss back then if the town you were in would allow tandems. Some just did not allow them at all, while the town next door would allow them.
Folks would go to sell their house, and fail the pre-inspection walk through due to the main service panel being overstuffed, and too many poles. It was an easy fail for the inspector. Look at the label on the panel and count. It was kind of a panic situation for the seller! :(
I have no idea what will pass these days. I always ask my friends that stayed in the trade, and then check with the inspector before I start any work. I can't imagine that anyone is installing a 100 amp panel in new construction housing.

[Mike Henderson]

Why do some places not allow tandem breakers? I expect there's some code problem but as long as you stay within the total box amperage it seems that it should be okay.

Mike

[Bill Dufour]

Why do some places not allow tandem breakers? I expect there's some code problem but as long as you stay within the total box amperage it seems that it should be okay.

Mike


A tandem breaker is fed from one buss bar. A panel should have the breakers arranged so there is about equal load on each buss bar. A 240 breaker is equal on both bars. A 120 breaker is only drawing from one bar.
A 200 amp panel is really rated for only 100 amps at a time on each bar.
My Zinsco panel had aluminum buss bars which corroded and made a poor connection. It buzzed so loud I had an electrician replace the buss bars and about half the breakers under a home insurance policy. The corrosion caused overheating at the spring connections of the breakers which made it worse and caused arcing. Reducing spring pressure and cascading into a fire if not caught in time. He had copper buss bar stock on his truck of the correct size. He just had to cut it to length and maybe drill a mounting hole or two.
Bill D.

[Mike Cutler]

Why do some places not allow tandem breakers? I expect there's some code problem but as long as you stay within the total box amperage it seems that it should be okay.

Mike

Mike

This was in the mid to late 80's.
The issue then was that panels, at least here in New England, were smaller 100 amp panels. The use of Tandems would quickly lead to over filling the box, and to many poles/breakers per the panel manufacturer. They were also installed in the wrong location per the manufacturers drawings and literature.
For instance I have a 40 pole/breaker, 200 amp service panel, and the manufacturers details that a maximum of 10 tandems can be installed in the lower six position only. The 5th pole position up from the bottom cannot have tandems on either side. It would not have been uncommon back then to have more than 40 poles/breakers.
I actually have 41 breakers installed, but three are not in use.
If the tandems are not installed correctly, it's pretty easy to pull a lot of amps through one back plane stave. You could split one pole into two and end up with a microwave, slow cooker, and an electric skillet, on one pole/stave and potentially have a "hot spot" on the back plane.
As I said though, this was many years ago.

[Jim Becker]

In addition to Bill's comments about balance, tandems bring the potential of "overstuffing" a box. While most folks might use one to solve a space problem for one or two circuits, there are other folks who would choose tandems to fill a box to avoid buying a correctly sized box for their application.

Interestingly, our main 200A box has a few tandems in it, actually installed by a licensed electrician. (work done in 2005 to upgrade both the house and my shop) He did this because some of the existing wires were at that length where they could only get so far into the box (old box was much shorter) but were still usable and all of the available physical space for j-boxes to splice was already being taken up by other circuits that couldn't even come close to getting into the new panel. It's only a few circuits and was kosher with the inspector here.

[Mike Henderson]

Thanks for your replies, Mike and Bill. I understand the problem.

I have a few tandems in my subpanel but they are ones that replace a 240V breaker with a package that consists of two 120V circuits and the one 240V circuit. With that package the two 120V circuits pull from different buss bars.

Mike

[Mike Cutler]

Thanks for your replies, Mike and Bill. I understand the problem.

I have a few tandems in my subpanel but they are ones that replace a 240V breaker with a package that consists of two 120V circuits and the one 240V circuit. With that package the two 120V circuits pull from different buss bars.

Mike

Mike
We used to call that a "laundry" breaker,or an "appliance" breaker. It would give you the 240/30 for the dryer, a 120/20 for the washer, and the 120/20 convenience receptacle, that were required for a laundry. There is a 240/50, with the two 120/20's, for electric ranges.

[Mike Henderson]

Mike
We used to call that a "laundry" breaker,or an "appliance" breaker. It would give you the 240/30 for the dryer, a 120/20 for the washer, and the 120/20 convenience receptacle, that were required for a laundry. There is a 240/50, with the two 120/20's, for electric ranges.

What happened to me is that I put in too small of a subpanel and then bought more 240 volt tools than I expected when I put in the subpanel. So I took two 120V breakers and replaced them with an "appliance" breaker. A magic way to add a 240 V bonded breaker to a box and still keep the two 120V individual breakers. I described it previously as replacing a 240V breaker to add 120V circuits but that was not what I really did - I went the other way, to add 240V circuits.

Still waaay under the amp rating of the box.

Mike

[Bill McNiel]

speaking of baked wildlife years back I was driving to the lumber company. On the other side of the road where big towers and many serious power lines. I looked over to see an alfred hitchcock number of birds all flying in formation together swoop around like all on the same flight program then come in and land on the high power lines. As they did they picked different lines and some were between. There was a huge bang and birds dive bombed to the ground only didnt pull up. Lights were out for miles and when I came back there were cops at every intersection. I told one of the cops what happened and he just looked at me like i was nuts.

Fuses have blown a number of times here, a branch from a tree falls and ends up on the lines and bang. They finally come around and trim stuff regular now. People have had power out for a long time in the past and homes have flooded when sump pumps arent working and they didnt have generators. My own post had some sort of short on it, I told them a few times and they ignored me. A guy stopped one day at a neighbors and walked over and told me the post was wired wrong. I said Ive told them it sizzles when there is rain when its wet. He said stay away there is a charge in that post. I took a photo of burning and sent it to them and they finally woke up and next day a crew was there. Guy working on it said some days they dont pay him enough. Been fine ever since.

425992

Warren,
Do you live in the NorthWest also?

[Warren Lake]

North of Toronto.