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So I know practically nothing about houses having rented for many years, just bought a house and was told by my inspector the panel is only a 70 amp panel and will need to be upgraded before I go to install AC.

I took him at his word, and had one AC consult, mentioning this to the guy he looked at my panel and agreed it needed an upgrade.

He gave a terrible quote ($5500 for a 3 ton goodman AC install without the electrical work, no ducting work necessary), so I got somebody else to give me a quote.

Now here's the problem: Fellow comes over and says I have a 150 amp panel and there's room (which I can see) for a couple more breakers on it, and gives me a considerably better AC quote (3500 for a lennox 3 ton 14 seer, all the same bells and whistles).

So now I'm thinking, considering how terrible the quote was from the first consult, perhaps he was just trying to squeeze even more money out of me? Why did my inspector tell me it was a 70 amp panel?

I look at the panel and there's like 6 or 8 15/20 amp breakers on it as well as a 30 amp double-breaker thingy (not sure if this is 30 per or 30 total) and a 50 amp double-breaker thingy.

I'll get a picture when I get home to post here, but off hand my question is:

Is it accurate to say I definitely have over a 70 amp panel due to the sum of amps on breakers in there right now? Is the sum of those little labels on the breakers make up my panels current amperage?

I look online for 70 amp panel and it's this tiny dinky thing with 3 breakers on it..

Edit: Here are the pictures, if this is not a 70 amp can anybody identify the amps?

Appearances to me are the diagram on the box does not match the actual panel, as the panel has 20 breaker spots (as I read it) while the diagram shows 14. And yes, I realize it's missing a main breaker, so I included the other two pieces I understand identify the max amp load; the conduit and the meter.

Panel Diagram Panel Conduit Meter

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I would recommend replacing that box -- it appears to be ancient and has almost no room for adding breakers. Put in a brand new 125 amp load center with plenty of room and 125 amps should still be sufficient unless you're putting in a beast of an AC unit and have a 50A electric stove and a 30A electric dryer all running at the same time. My house has a 100A load center, 40A A/C, gas dryer/stove. Nothing ever trips. –  Snowman Sep 11 '13 at 5:00
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Well, we found Jimmy Hoffa, whatever happens... –  The Evil Greebo Sep 11 '13 at 13:55

5 Answers 5

up vote 5 down vote accepted

I've labeled your photo, which might help you understand what's going on.

Labeled Panel

The Panel Rating

The panel is rated to support 125 amperes, when connected to a 120/240 volt 3 wire system. This means that 125 amperes can flow through each of the upper bus bars and each main lug, without anything melting or catching fire.

The Upper Section

The top two double pole breakers are before the "main" disconnect, which means they will always have power when the wires feeding the panel have power. I'm guessing there is a disconnect ahead of this panel, maybe at the meter or as a standalone disconnect. Based on their size, I'm guessing one (50A) is for an electric stove, electric heater, or maybe a subpanel. The other (30A) is likely for a dryer, water heater, subpanel, or some other appliance.

The Lower Section

The next double pole breaker (50A) controls the flow of electricity to the lower section of the panel. Unlike the double pole breakers above, this one should not have any terminals where wires can connect. The lower section is rated for a maximum of 100 amperes, so the breaker protecting it must be 100 amp or less (50A in your case).

Branch Circuit Section

The lower section (highlighted in purple) is where the branch circuit breakers connect, and has a maximum breaker size of 70 amperes. This means the largest breaker that can be connected in this section, is a 70A breaker.

Upgrade Required?

Since there is only a single available slot (3), it's not likely a central A/C system could be connected without moving things around (at the very least). Upgrading the panel might be your only option, but it would depend on the existence (or lack thereof) of a sub panel, and the existing service provided to the building (and availability of services in the area).

A subpanel may be an option, however, it would require more information than you have provided here.

Depending on the service provided to the building, upgrading the panel may include an upgrade to the service. Installing a new 125A panel is useless, if you don't also have the service upgraded to support 125 amperes.

To determine if an upgrade is required, contact a local licensed Electrician to do a load calculation on the building.

Breakers Protect Downstream Wiring

Short-circuit and/or overcurrent protection devices (breakers, fuses, etc.), are designed to protect the wiring downstream (after them in the circuit). For example. If your panel did have a main breaker, it would be sized to protect the panel wiring. The breaker would not be sized to protect the wiring feeding the panel or anything before the breaker, only the wiring after the breaker.

Summing Up Breaker Ratings Means Nothing

If you total up the rating of the breakers in the branch circuit sub-section, you'll find that you have 85A on leg A, and 105A on leg B. Which means... Well, absolutely nothing. The only limitations here are that there can only be as many breakers as will physically fit, and no one breaker can be larger than 70A.

If more than 15 amperes flow through the breaker in slot 4 , that breaker will trip (open). This protects the wiring connected to that breaker. If more than 50 amperes flow through any combination of breakers on either leg A or B in the branch circuit sub-section, the sub- section breaker will trip (open). This protects the wiring between the sub-section breaker, and the branch circuit breakers.

You could theoretically. have breakers totaling 1,000,000A. It still wouldn't matter, as long as you have proper overcurrent protection.


If I've missed anything, or haven't explained something properly. Feel free to ask additional questions, or point out mistakes in the comments below.

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This makes perfect sense and means I'm actually in luck; some more looking around last night I realized, that 30 amp breaker goes to a 240v wall-socket behind my dryer; which is unused because it's a gas dryer, it and my washer both run off independent 15-20 amp branch breakers according to their manuals. Considering I have a gas hookup there I don't suspect to ever change the dryer to a non-gas dryer so I should be able to simply repurpose that 30 amp breaker. Also I have a gas stove, furnace, and hot water heater, therefore it seems reasonable 125A may be sufficient. –  Jimmy Hoffa Sep 11 '13 at 14:51
    
@JimmyHoffa Just because the panel is rated for 125A, does not mean the service is. Check with your utility to determine the service capacity. Though, repurposing the 30A circuit should work. –  Tester101 Sep 11 '13 at 14:56
    
Right, I guess it will be worth it to have an electrician over to look at it for just 2 minutes so he can do a load calculation on the conduit and call the electrical company about the meter service. –  Jimmy Hoffa Sep 11 '13 at 14:59
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@JimmyHoffa: There is no such thing as a brief electrician visit. They charge a minimum of like $75 just to get to your house, plus 30 minutes minimum service. Based on what I see here, your electrical system has plenty of spare capacity. Sometime down the road you will probably want to upgrade the split bus panel (which have not been allowed in new construction for decades) with a newer master breaker panel. –  wallyk Sep 11 '13 at 17:31
    
So, assuming one adds a 60 amp subpanel to @JimmyHoffa setup, he should only consider upgrading his electrical service if the main breaker kept tripping, correct? That would indicate the house repeatedly trying to use more amperage than is safe. It's weird to think of it that way, seems backwards. –  BigHomie Apr 15 at 20:08

No, just because there are X amps of breakers in the panel does not mean the panel is X or any specific size panel. Indeed, in many services the sum of the breakers is more than the panel size simply because it is known that not everything is "on" at once. For example, electric heating and air conditioning are not usually operated simultaneously.

The panel capacity is determined by how much current it can safely carry through its bus bars. The panel must be sized not to exceed the utility meter nor the utility feed.

If the panel does not have a main breaker—which is usually the panel's rating—then you might have to open it up and look at the manufacturer's label.

By the way, the 30 amp double breaker is simply two 30 amp breakers mechanically tied together so that if either trips, they are both shut off. Same for the 50 double. It switches 100 amps, 50 on each leg. (I am assuming the double breaker looks similar to this:

enter image description here

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Thanks for this tidbit! I've added pictures if you have any idea what the load is on this panel or if it appears overloaded at present to you. Thanks for the answer! –  Jimmy Hoffa Sep 11 '13 at 1:10
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Correction: a 50-amp double breaker is 50 on each leg, but not 100 total. It's still 50 amps total (just twice the voltage between the legs compared to a single breaker, therefore twice the power). –  Henry Jackson Sep 11 '13 at 1:21
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@HenryJackson so a 50 amp double breaker is simply a 50 amp draw of 240v? In other words, it's the breaker for likely my washer/dryer etc? –  Jimmy Hoffa Sep 11 '13 at 1:37
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@JimmyHoffa, Yes. It draws 50 A at 240 V. The top 50 A and top 30 A breakers are likely for an oven, dryer, water heater, or other appliance. The lower 50 A breaker feeds the rest of the circuits. –  Pigrew Sep 11 '13 at 2:13

The circuit breaker is rated at 125 A, according to its label. It is a "split-bus" panel. It is currently configured to have three "main" breakers (that is, you have to flip three things to turn off your electricity) which are wired in parallel. Counting the used power is a little bit tricky since you must perform the count for each leg individually: You may have up to 125 A on L1 and another 125 A on L2. I count 130 A on each: 50A + 50A + 30 A double pole breakers.

So, your installation is currently not in compliance with its design specifications (by 5 A on each line). You should reduce the current rating of one of these three breakers by at least 5 A.

For the bottom sections (individual breakers), you have 105 A of breakers on one leg and 85 on the other. You may want to swap some of these to better share the load between the two legs. It is acceptable that this count be above the 125 A because its total current draw is being limited by the 50 A breaker that you have installed. To repeat, even though the bottom breakers add up to a very large current, the 50 A breaker (2nd down on the left) will limit the total current of the single pole breakers to a total of 50 A.

In addition, I don't know what size conductor your service uses. You may want to verify that the conductor is sufficiently large for a 125 A load.

If you do not have a large house and you mostly have non-electric appliances (such as natural gas), then 125 A is plenty. But, it looks like you do not currently have enough free spaces in the breaker panel for a new two-pole breaker for the A/C.

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So what you're saying is if any of the 3 double pole breakers kick it'll be line kicking the main and knock out the whole panel? Or is it that of those 3 any of them that kicks would only disable itself and those below it, so if the bottom 50 kicks, the 50 and 30 above it will stay live? Or am I misunderstanding, if the top 50 kicks or top 30 kicks will any/all of the individual breakers below them stay live? –  Jimmy Hoffa Sep 11 '13 at 3:09
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The 50, 50, and 30 are independent. Any of the three could trip while maintaining power to the other two. If the bottom 50 trips, then power will be removed to all of the single-pole breakers. If the top 30 or 50 trips, the single-pole breakers will remain powered. This can be determined by the wiring diagram on the breaker's label. –  Pigrew Sep 11 '13 at 3:19
    
So then the only balancing I can do is realistically the 125 amps per pole available coming off the bottom 50? Nothing can be placed according to that wiring diagram as a child of the 30 amp in the way that those single pole breakers are children of the bottom 50? –  Jimmy Hoffa Sep 11 '13 at 3:33
    
Yes, that is correct. –  Pigrew Sep 11 '13 at 4:42

In your first photo, under the section entitled "MAIN RATINGS", it clearly states: 125 AMPERE. That is the maximum capacity of your load panel. In most houses, the sum of the ratings of all of the circuit breakers will exceed this number. That is because it is assumed that not all of the loads will be on simultaneously. Above that section, under the "TYPICAL WIRING DIAGRAM", it states that there can be a maximum of 22 circuit breaker poles and that no circuit breaker can exceed 70 amperes. The latter may be the source of the 70 amp limit that your electrican mentioned. That said, 125 amperes is too small if you are going to add central air conditioning. Also, you should have a primary breaker equal to the capacity of your system so that if that capacity is exceeded (without exceeding any single branch breaker), the house will be protected.

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My panel is 100 amp and we have a 40 amp AC circuit. Works fine. –  Snowman Sep 11 '13 at 4:55
    
Depending on the size of the AC and other loads, 125 amp service might be just fine. –  Bryce Feb 4 at 20:10

The big question here is what gauge are the wires feeding the panel? That will tell you what service you have.

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This may or may not be true. –  Tester101 Feb 4 at 16:02

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