House/Garage

[foo1bar]

Why is it so hard for you to understand you can't draw any more than your main breaker. That's way you have overcurrent devices called breakers. The only power you will draw from the grid when you have solar is to make up for any load the solar isn't producing. It's either or and sometimes both but you cannot exceed the breaker size.

What they are talking about is NOT about what you draw from the grid.

When I have a 100A main breaker, a 40A solar breaker, and a dozen 20A breakers for loads, there can be >100A flowing in that bus-bar. There will be 100A flowing from the main into the bus bar. And 32A flowing from the solar into the bus bar. (And 132 amps being consumed by the various load breakers)
This can continue without any breakers tripping because none of the breakers are exceeding their rating.
If the bus-bar is only rated for 100A, there's more than 100A running in it - and it could fail (probably not because the manufacturers put enough of a safety margin in)
But let's say you increase it even more - and you have 100A of solar breakers and a 100A main. And you're still using a 100A busbar. Now you could have 200A worth of current in that busbar which was only designed to handle 100A (plus some safety margin). Will that result in the busbar failing? (maybe not - but I wouldn't bet my house or my life on it)

This risk of having significantly larger currents in the busbar than they were rated for is why there is the "120% rule"

BTW - even my first example would run into problems with code unless it's a 125A bus bar with a 100A main. 125A bus bar * 120% = 150A; So maximum of 150A for both. 100A main + 40A solar would be less than 150A, so would be OK. Doing same calculations with 100A bus bar shows us: 100A busbar * 120% = 120A ; And 120A < 100A + 40A, so that is NOT OK.

If you have the solar backfeed being attached *before* the main breaker, ie. a "line side tap", then this doesn't apply. And that is what PVAndy was mentioning - having some of these connections for the backfeed and/or garage be in between the meter and the main breaker, via a supply (line) tap.

[oregon_phil]

Section 64-112 refers to the breaker connect to the bus. My 7.7 inverter is rated at maximum output of 7660 watts, and according to SMA 32 amps should be the maximum output. However inverter s are mechanical devices and often are not subject to the laws of man. At 32 amps going by the 80% rule my over current device should be 40 amps, however my inverter was putting out 7860 this summer which means based on the 80% rule the 40 amp breaker is not large enough. So 64-112 64-112 tells me the overcurrent device (breaker) can be 120% or a 48 amp breaker which they don't make, so 64-112 (d) allows you to go to 125% which in term means a 50 amp breaker can be installed.

I hope I haven't made this to confusing.

That who article in the code deals strictly with installation, overcurrent protection, rapid shut down, grounding etc.

My house has a 100 AMP service. Based on the 80% rule I can draw more than 80 Amps without starting to overload the main breaker. Electricity is like water or air, it takes the path of least resistance, so when your electric supplier sends out power, it doesn't automatically come to your house, it waits outside on the street until you turn on a light and then it sends only enough power to run your light. So when you have solar and it's running in the day time anything you use in the house runs first from the solar and if it isn't producing enough then power from your supplier comes in to make up the short fall. Subsequently if you are producing more power than you are using the extra goes and joins your electric supplier and travels down the road to the next house.

The only way I can over load my system is if I had a solar array producing more than 80 AMPs.

Bi directional meters are mechanical devices which measure what's coming and what's going out and that's all they do, but if every house in the US put a 15K solar array on their roof I can guarantee you your suppliers lines would be toast.

Your 20% rule, is this in every state?

I believe 64-112 closely follows NEC 2020. 64-112 also covers more than just breakers.

Δ 64-112 Interactive point of connection (see Appendix B)

4c) notwithstanding Section 14, the sum of the ampere ratings of the overcurrent devices in source circuits supplying power to a busbar or conductor shall be permitted to exceed the busbar or conductor rating to a maximum of 120% of the rating of the busbar or conductor;

4d) notwithstanding Section 14, for a dwelling unit, the sum of the ampere ratings of the overcurrent devices in source circuits supplying power to a busbar or conductor shall be permitted to exceed the busbar or conductor rating to a maximum of 125% of the rating of the busbar or conductor

There is also an article on load side line side inverter connection pro's and con's at http://neighbourpower.com/blog/ce-co...us%20ampacity.

A screen shot of the panel overloading issue is attached. I know you are in Canada and most of us are in the US. In my particular jurisdiction, county inspectors are not liable for any faults, omissions or other acts. Proof of certified county electrical inspection does not make the county liable for code violations the inspector did not catch.

I have an SMA 7.7 -40 and also occasionally have AC power at 7860 watts. During these 7860 watt episodes, almost without exception, line voltage is running on the higher side 124/125VAC with inverter current at or slightly below 32 amps.

[SunEagle]

Why is it so hard for you to understand you can't draw any more than your main breaker. That's way you have overcurrent devices called breakers. The only power you will draw from the grid when you have solar is to make up for any load the solar isn't producing. It's either or and sometimes both but you cannot exceed the breaker size.

Listen. Do whatever is legal in Canada. It is your issue to explain to your local inspector. If they approve your installation then this discussion is mute

I am just trying to make sure others on this Forum follow the legal electrical installation rules put in place to protect the homeowner.

Oh by the way. I have seen way too many circuit breakers pass more amps then they are rated for. It really comes down to their tripping mechanism which is not always foolproof.

[nosbod]

Why is it so hard for you to understand you can't draw any more than your main breaker. That's way you have overcurrent devices called breakers. The only power you will draw from the grid when you have solar is to make up for any load the solar isn't producing. It's either or and sometimes both but you cannot exceed the breaker size.

[SunEagle]

Every panel is protected by the main breaker. You cannot draw any more power than the breaker will supply or it will trip, and you cannot send any more power out to the grid than the main breaker size or it will trip. There is no way you can melt the bus or burn your house down. You are either using power from the utility or you are using solar and sometimes you are using both if your solar is not enough for your load draw, but under no circumstances can you draw more than your main breaker without it tripping.

But if you add what you draw from the grid to what you produce from a large solar array you can exceed the panel rating. It has nothing to do with the main breaker. Why is that so hard for you to understand?

[nosbod]

Every panel is protected by the main breaker. You cannot draw any more power than the breaker will supply or it will trip, and you cannot send any more power out to the grid than the main breaker size or it will trip. There is no way you can melt the bus or burn your house down. You are either using power from the utility or you are using solar and sometimes you are using both if your solar is not enough for your load draw, but under no circumstances can you draw more than your main breaker without it tripping.

[SunEagle]

The only way electricity comes into your house from the utility is if you turn on a light. Turn off everything in your house take the cover off your panel box so the wires going to the main breaker are exposed and put an amp probe over one of the wires. If everything is turned off in the house the amp draw will be zero, which means there is nothing from the supplier coming into your house. If you turn on a light then you will see the amp gauge move. If you have solar then nothing will be coming in from the utility unless the solar is not enough to supply the load.

I can't explain this any simpler. The only way you can burn your house down or melt your bus is if you are producing more than 80% of your main breaker. If you have a 200 AMP breaker then you would need a 45000 watt solar array.

Most of what you said is true but unless you have a way of automatically reducing your house load you run the risk of sending too many amps into the panel buss. Solar will send what it can and the house will use what it wants. Add that up and the total can exceed your panel rating.

The NEC does not presume you have any automatic load reduction equipment so it states how much solar amps can be sent onto the panel. Those are the rules like it or not.

[Mike90250]

......
I can't explain this any simpler. The only way you can burn your house down or melt your bus is if you are producing more than 80% of your main breaker. If you have a 200 AMP breaker then you would need a 45000 watt solar array.

Nope, it's not the breaker that's in danger, it's the bus bar, if you are pulling too much load from the grid ( maxed out 200A breaker) and then start adding solar from the PV to supply the rest of the heavy loads, the PV amps are added to the grid amps to supply your 250A of load, via your 200A bus bars. Smoke

[nosbod]

The only way electricity comes into your house from the utility is if you turn on a light. Turn off everything in your house take the cover off your panel box so the wires going to the main breaker are exposed and put an amp probe over one of the wires. If everything is turned off in the house the amp draw will be zero, which means there is nothing from the supplier coming into your house. If you turn on a light then you will see the amp gauge move. If you have solar then nothing will be coming in from the utility unless the solar is not enough to supply the load.

I can't explain this any simpler. The only way you can burn your house down or melt your bus is if you are producing more than 80% of your main breaker. If you have a 200 AMP breaker then you would need a 45000 watt solar array.

[bcroe]

Thanks for the response. I neglected to mention I am in Canada. My main service is 100 AMP. I Have installed a 9.2 KW system with the 7.7 sma inverter and have no problems. My system has been passed by Fortis, and hydro inspectors. I think the reason you have so many restrictions in the US is because of GRID Capacity which is unfortunate. Our roof mount systems require Rapid Shut Down which is done through the AC disconnect after the inverter.

The theory is that with both 100A available from the PoCo input breaker and 40A
available from solar, turning on enough loads to approach 140A would overheat the
distribution box 100A busbar. One way to make that impossible is to downsize the
input breaker to say 80A, so the total supply current possible is limited to 120A.

Another approach is to put the solar feed breaker at the opposite end of the busbar,
from the input breaker. This causes the currents from the 2 sources to flow in
opposite directions, so they cancel instead of add at any common point on the
busbar. Max current at any point on the busbar is limited to the largest source breaker.

The belt and suspenders approach is to use both of these methods for safety. I
expect your installer used at least one of these, otherwise your are in real risk
of damage or worse. Bruce Roe

[solarix]

This has nothing to do with grid capacity. It has to do with not melting the busbar in your breaker box and burning your house down.
Most 200amp breaker boxes have 2 to 3 times that much in breakers loading it. Yes, virtually all the time (in a typical home) they never actually pull more than half of the rated 200amps. But, worst case it could. With a potential of 200amps from the grid, if you back feed 32amps (7.7kW or 40amps ampacity) into your busbar with solar and have more than 168amps of load, then your busbar is in danger of melting.

[SunEagle]

I would think a state like Montana with a million people would have enough grid capacity for any size array. That's unfortunate.

The NEC really doesn't care who is on the grid. The rules pertain to each individual home panel and what can be self generated back into it.

[nosbod]

I would think a state like Montana with a million people would have enough grid capacity for any size array. That's unfortunate.

[SunEagle]

Section 64-112 refers to the breaker connect to the bus. My 7.7 inverter is rated at maximum output of 7660 watts, and according to SMA 32 amps should be the maximum output. However inverter s are mechanical devices and often are not subject to the laws of man. At 32 amps going by the 80% rule my over current device should be 40 amps, however my inverter was putting out 7860 this summer which means based on the 80% rule the 40 amp breaker is not large enough. So 64-112 64-112 tells me the overcurrent device (breaker) can be 120% or a 48 amp breaker which they don't make, so 64-112 (d) allows you to go to 125% which in term means a 50 amp breaker can be installed.

I hope I haven't made this to confusing.

That who article in the code deals strictly with installation, overcurrent protection, rapid shut down, grounding etc.

My house has a 100 AMP service. Based on the 80% rule I can draw more than 80 Amps without starting to overload the main breaker. Electricity is like water or air, it takes the path of least resistance, so when your electric supplier sends out power, it doesn't automatically come to your house, it waits outside on the street until you turn on a light and then it sends only enough power to run your light. So when you have solar and it's running in the day time anything you use in the house runs first from the solar and if it isn't producing enough then power from your supplier comes in to make up the short fall. Subsequently if you are producing more power than you are using the extra goes and joins your electric supplier and travels down the road to the next house.

The only way I can over load my system is if I had a solar array producing more than 80 AMPs.

Bi directional meters are mechanical devices which measure what's coming and what's going out and that's all they do, but if every house in the US put a 15K solar array on their roof I can guarantee you your suppliers lines would be toast.

Your 20% rule, is this in every state?

The 20% rule is listed various versions of the NEC but as far as I know it is to be followed in every US state.

[nosbod]

Section 64-112 refers to the breaker connect to the bus. My 7.7 inverter is rated at maximum output of 7660 watts, and according to SMA 32 amps should be the maximum output. However inverter s are mechanical devices and often are not subject to the laws of man. At 32 amps going by the 80% rule my over current device should be 40 amps, however my inverter was putting out 7860 this summer which means based on the 80% rule the 40 amp breaker is not large enough. So 64-112 64-112 tells me the overcurrent device (breaker) can be 120% or a 48 amp breaker which they don't make, so 64-112 (d) allows you to go to 125% which in term means a 50 amp breaker can be installed.

I hope I haven't made this to confusing.

That who article in the code deals strictly with installation, overcurrent protection, rapid shut down, grounding etc.

My house has a 100 AMP service. Based on the 80% rule I can draw more than 80 Amps without starting to overload the main breaker. Electricity is like water or air, it takes the path of least resistance, so when your electric supplier sends out power, it doesn't automatically come to your house, it waits outside on the street until you turn on a light and then it sends only enough power to run your light. So when you have solar and it's running in the day time anything you use in the house runs first from the solar and if it isn't producing enough then power from your supplier comes in to make up the short fall. Subsequently if you are producing more power than you are using the extra goes and joins your electric supplier and travels down the road to the next house.

The only way I can over load my system is if I had a solar array producing more than 80 AMPs.

Bi directional meters are mechanical devices which measure what's coming and what's going out and that's all they do, but if every house in the US put a 15K solar array on their roof I can guarantee you your suppliers lines would be toast.

Your 20% rule, is this in every state?