Difference between PV breaker and a circuit breaker?

[AngellottiPierson]

What is the difference between PV breaker and a circuit breaker? I am trying to learn and your input would be greatly appreciated.

 

[GoldDigger]

I am not sure that the term PV breaker has a commonly agreed meaning. The most likely distinction is one intended for use on the DC portion of a PV installation.

A breaker on the DC side of a PV installation must be rated to interrupt DC, which is a much harder task for a breaker, and some DC breakers can only safely interrupt current flow in one direction.

 

[AngellottiPierson]

I was told that the PV breaker is just a dedicated breaker in the panel for PV. Thank you for responding as I always learn more!

 

[jaggedben]

There is no difference. Breaker is always short for circuit breaker, and PV just names the circuit it's for. Same as Air-Conditioner breaker, oven breaker, family room breaker, and so on...

 

[GoldDigger]

One other interesting thing about the specific application of a PV breaker for backfeed from a grid interactive inverter is that the direction of power flow is from the terminals to the panel bus, but when open it has power only on the bus side. This leads to some disputes on whether you can use a breaker with the wire terminals marked as "output" for this purpose.

 

[JEFF MILLAR]

Abbreviations are no good in serious technical applications. Do you know what Load Factor means ? It also means how the mechanical engineer applies a load factor when sizing his electric motor. He typically sizes the motor to run most efficiently at. max. load of 75 %. Then we size according to NEC table and add 25 % of that continuous load when sizing the 3 / c. feeder. What is wrong with that picture ?

 

[BillK-AZ]

One other interesting thing about the specific application of a PV breaker for backfeed from a grid interactive inverter is that the direction of power flow is from the terminals to the panel bus, but when open it has power only on the bus side. This leads to some disputes on whether you can use a breaker with the wire terminals marked as "output" for this purpose.

Modern circuit breakers that are marked Line and Load are not tested and Listed for backfeed. Most special purpose circuit breakers, such as GFID, are not listed for backfeed. There are several threads on this.

 

[paulengr]

If you are referring to a DC breaker, a lot. An AC breaker merely has to open the contacts enough and cool the arc so that at current zero the are can’t restrike. A DC breaker has to totally quench the arc which is much more stable than AC. That’s why DC breakers are huge for their ratings.

 

[Andrew_L]

Hello AngellottiPierson,

Please see link for typical Solar system from Outback Power, https://www.outbackpower.com/downloads/documents/integrated_systems/flexpower_two_fxr/fp2_qsg_na.pdf. PV arrays normally go to a PV combiner box with cartridge fuses and from there to a circuit breaker ( PV Breaker) in the DC Panel. In DC panel, there are breakers for charge controllers, inverter, battery, and others systems you plan to integrate. The breakers are design to protect your components from overloading. To answer your question, it is most likely a circuit breaker in the DC panel that is designated for your PV array. Hope this helps.

 

[robertd]

If you are referring to a DC breaker, a lot. An AC breaker merely has to open the contacts enough and cool the arc so that at current zero the are can’t restrike. A DC breaker has to totally quench the arc which is much more stable than AC. That’s why DC breakers are huge for their ratings.

A while back someone posted a link to a youtube video showing the same knife switch opening AC and DC circuits with the same voltage and current. Very different results for the AC and DC circuits.
Found:

 

[gwr71]

I am a newbie and trying to understand solar pv ac disconnect switch. There is an interactive inverter that goes to the load in side (bottom) of the ac disconnect. There is the main ac coming to the top of the ac disconnect (line in), Ok I understand. Then there is a supply/line side tap (with insulated limiters) coming from the load out of ac disconnect (bottom). to the main disconnect to the meter side. Ok I understand. What I don't understand is how pulling the ac disconnect switch to off cuts the inverter ac to the main service panel. Can someone enlighten me? Is there another set of wires from the load out going to the main panel?

 

[jaggedben]

I am a newbie and trying to understand solar pv ac disconnect switch. There is an interactive inverter that goes to the load in side (bottom) of the ac disconnect. There is the main ac coming to the top of the ac disconnect (line in), Ok I understand. Then there is a supply/line side tap (with insulated limiters) coming from the load out of ac disconnect (bottom). to the main disconnect to the meter side. Ok I understand. What I don't understand is how pulling the ac disconnect switch to off cuts the inverter ac to the main service panel. Can someone enlighten me? Is there another set of wires from the load out going to the main panel?

Your question is hard to follow. It sounds like you are conflating two different things. An AC disconnect can be put into the inverter circuit anywhere. A supply side connection is one way of connecting the entire circuit to the rest of the premises wiring.

An interactive inverter is engineered and programmed only to output power when it senses being connected to another source. It will shut down output if disconnected.

 

[gwr71]

Let me clarify myself. The inverter regardless of what type will output ac energy to the critical load panel/main panel or both. It must adhere to NEC and therefore there is a fused solar pv ac disconnect on the outside of the building near the main disconnect /meter. Now as I understand it there is a line and load component to the ac disconnect. The line is fed directly from the main panel/ac combiner to the top of the ac disconnect. The inverter ac must be connected to the load (in) at the bottom of the ac disconnect. NEC requires overcurrent protection for the solar system and the ac disconnect provides this by running lines from the load (bottom) out of the ac disconnect to either the main disconnect box (breaker box) or meter itself. The connection is made to the supply side of the wires from the meter and insulated limiters are carefully attached to the positive and negative wires. So there are two types of ac currents connected at the pv ac disconnect. The purpose of the solar pv ac disconnect is to detangle the inverter ac energy from the grid ac energy. To disentangle you simply put the switch to OFF on the solar pv ac disconnect. It is supposed to prevent the inverter ac energy from flowing into the main panel etc. My question is how is this done? Is there another set of wires from the solar pv ac disconnect that goes to the main panel? In this way when the switch is locked onto the OFF position then the inverter ac energy does not flow into the main panel only grid ac energy can.

 

[jaggedben]

No there is only one set of wires on an inverter AC output. Also when it's AC there is no positive and negative, that's DC. Also the inverter can be interconnected various places, not just at the meter, and limiters are not required in most installations. Also systems that only interact with the grid are very different from those that provide backup power.

You are getting enough wrong that I suggest you look for a course that you can take from a local college or training company. You need to have a basic understanding of electrical power flow and how stuff gets wired up.

 

[gwr71]

I appreciate your input. I assume as a solar and energy storage installer I thought that you would understand the scenario and what information I needed to get. My scenario is practical not in theory. It assumes that the inverter is multimode not interactive mode ( I learned that in a forum with Mike Holt as moderator) Second it also assumes that there is a battery back up. It also assumes that there is a critical load panel/sub-panel. I can refer you to the following link

9 (wiring a pv a disconnect switch). It's a nice video demonstrating what I am discussing. I again assume that your are correct, then please explain where the wires for line side tap to the meter come from if not from the ac disconnect. Again the ac inverter output wires run to the load side and the main runs to the line side. Two sets of wires. I believe we are now on the same page. Then please enlighten me as to how the ac disconnect works if there is only one set of wires to the load side of the ac disconnect. Isn't this what I asked for originally?
I thank you in advance for taking the time to correct a newbie.

 

[jaggedben]

I still don't understand the question. The disconnect disconnects the wires, that's what it does. Therefore power can't flow from the solar inverter to the panel or anything else on the line side of that disconnect.

If you're trying to understand a system with battery backup then it's going to be more complicated. The video doesn't show a system with backup.

 

[BillK-AZ]

I think gwr71 is describing a low DC voltage standalone PV system with interactive capability such as the Xantrex/Trace SW series introduced in the 1990s that has multiple AC inputs and outputs. These systems could have many safety switches, fuses and circuit breakers.

His location 'Nevis' is Saint Kitts and Nevis, not USA for codes and standards.

 

[paulengr]

Look at UPS systems and generators. There are several ways of detecting loss of utility.

In an engine generator system this is normally dealt with by the transfer switch. Unless the line break happens right at the service entrance loss of utility causes a massive sag, sudden decrease in impedance, and sudden increase in load as the generator attempts to pick up everything even outside loads. Power flow (directional) exceeds limits and the transfer switch shuts off the utility breaker in short order. At that point voltage sensors on the utility will detect nothing. The transfer switch will not close in again until the utility is stable and the generator is synchronized.

It might seem like you could “island” forever with an inverter and with some you can (that have an offline mode) but without a utility signal to synchronize to eventually the inverter will drift to the point where it will be out of frequency and trip itself.

There are many other ways to do it. A good book on paralleling or protection relays will quickly get deeply into many ways of doing this.

 

[gwr71]

I must admit that the video I posted did not have a battery backup. So it is not exactly what I was describing. I also admit that I didn't understand the flow of electricity as was suggested. I then began looking at the flow of electricity and came into contact with backfeeding and realize that the reason why there is no other wires from the pv ac disconnect to the main panel is that there is backfeeding into the main panel through the line wires (top) leading to the main panel (fused). This is when the grid is down. The supply side tap is something independent from the working of the pv ac disconnect and although the wires are taped from the ac disconnect to the meter side wires, depending on the system there may not be any need for the supply side or load side tap. My apologies.
The laws of St Kitts and Nevis may be different but the the principles under our laws are up to a point comparable to the NEC. So learning to comply with the NEC helps us here how to comply with our laws and future amendments that will eventually happen.
The reason I was confused is that the system I had in mind has a double pole double throw switch inside that can allow the homeowner to run the house on grid alone or to the inverter ac ( which has grid in, solar and generator in and has multimode capabilities) there are two connections to this bypass and safety switch. One is from the grid and the other is from the inverter ac. I thought that the inverter ac goes from the inverter to ac combiner box and then to the pv ac disconnect and then out to the bypass switch. I was wrong. My apologies for not explaining the situation properly.

 

[kwired]

One other interesting thing about the specific application of a PV breaker for backfeed from a grid interactive inverter is that the direction of power flow is from the terminals to the panel bus, but when open it has power only on the bus side. This leads to some disputes on whether you can use a breaker with the wire terminals marked as "output" for this purpose.

Most general purpose circuit breakers don't have a specific line and load side either though. Some with integral electronic functions however might as those functions might be powered by the line side or the load side and need to be connected accordingly.