Otis Singleton
When connecting a solar photovoltaic (PV) system to the larger electric grid, it can be done through a line side tap or a load side tap. A line side tap, also known as a supply side connection, involves connecting the solar inverter to a PV service fused disconnect and/or a solar-only circuit breaker panel, which is then linked to a junction box. On the other hand, a load side tap involves wiring the solar inverter directly to the electrical panel via a circuit breaker. While load side taps are commonly used for residential and smaller commercial systems, line side taps are becoming more prevalent with large solar systems due to their lower cost. Understanding the differences between these connection methods is crucial when designing and installing solar systems, ensuring compliance with electrical codes and regulations.
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What You'll Learn
Line side tap vs. load side tap
The physical connection between a solar system and the grid can be made using either a line side tap or a load side tap. The current could be on the line side or the load side of an electrical system, depending on its location. If it is between the main meter and the main electrical panel, it is on the line side. When it comes out of the main panel and into the building, it is considered the load side.
With a load side tap, the solar inverter is wired directly to the electrical panel through a circuit breaker. When there is excess power, it flows from the breaker through the bus bars, the main breaker, the meter, and then out to the grid. Working on a live system is dangerous, so the electricity must be shut off when connecting the solar inverter to the panel. Load side taps are common for residential and smaller commercial systems. When designing a solar system, the provider must consider the 120% rule, established by the National Electrical Code (NEC) to identify how much power can be safely back-fed through the load side of the existing electrical panel.
Line side taps, also called supply side connections, are a more complicated process. The solar inverter is connected to a PV service fused disconnect and/or a solar-only circuit breaker panel, which is then connected to a junction box. This approach avoids de-rating the existing service panel and the back-feed limits of the panel. However, it may need approval from the local building authority and the utility.
In summary, the main differences between line side taps and load side taps are in the complexity of the process, the equipment used, and the regulations that apply. Load side taps are simpler and more common for residential and smaller commercial systems, while line side taps are more complicated and becoming more common for large solar systems as a cheaper alternative.
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Connecting a solar PV system to the grid
A load side tap is a common approach for residential systems and smaller commercial systems. With a load side tap, your solar inverter is wired directly to your electrical panel through a circuit breaker. When you have more power than you need, it flows from that breaker through the bus bars, the main breaker, the meter, and then ultimately out to the grid. The load side tap is made after the main breaker. The electrical panel receives a new circuit breaker or breaker. The dual-pole or double-space circuit breaker will be put in the place that is farthest away from the main breaker. The PV solar system wires are then attached to this new solar breaker.
A line side tap, also called a supply-side connection, is becoming increasingly common with large solar systems as a cheaper alternative. With a line side tap, the solar inverter is connected to a PV service fused disconnect and/or a solar-only circuit breaker panel, which in turn is connected to a junction box. The line side tap is made before the main breaker.
Before connecting your solar PV system to the grid, you may be required to get pre-approval from your electricity distributor. Your distributor will advise you of your 'export limit', which dictates how much excess solar generation you can feed back into the grid. This process will vary depending on your specific electricity distributor.
When connecting the solar inverter to the panel, the electricity must be shut off. It is recommended that homeowners always hire a licensed electrician to work on electrical components in their home, especially any work in the electric panel due to the safety risks involved.
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Double taps and safety
Double taps, also known as double-tapped circuit breakers, are a common electrical defect found in electric service panels. They occur when two wires are connected to a single circuit breaker designed to accept only one wire. This defect can lead to loose wires, causing overheating and arcing, which can potentially result in electrical fires. As a result, double taps are considered a fire hazard and should be addressed as soon as they are identified.
Double-tapped neutrals, a type of double tap, refer specifically to the termination of two neutral wires (the white wires) under the same screw on the neutral bus bar. This practice is unacceptable as it prevents circuits from being isolated when work is performed on them. While double-tapped neutrals were once a common practice among electricians due to a lack of specific guidelines in early editions of the National Electrical Code (NEC), they are now explicitly prohibited by the 2002 NEC and subsequent versions.
The presence of double taps in electrical panels is more frequently observed in older homes with outdated panels. This is because newer panels are typically designed to accommodate additional circuits as needed. When discovered during home inspections, double taps can be easily and inexpensively remedied by a licensed electrician. The most common repair involves adding another circuit breaker to the panel and connecting one of the wires to it. However, if the panel is excessively old, a panel upgrade may be necessary, which can be more costly.
To ensure the safety of your home and family, it is crucial to address double taps as soon as they are identified. Homeowners should consult a licensed electrician to evaluate and rectify any double-tapped circuit breakers in their electrical panels. By doing so, you can mitigate the potential fire risk associated with this defect and ensure the proper functioning of your electrical system.
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Insulation-piercing tap splice connectors
The NSI IPCS1002 IPCS Series Easy-Tap Insulation Piercing Connector is an example of a product that can be used for insulation-piercing tap splice connections. It is suitable for a wide range of electrical line tapping and splicing applications, with the appropriate conductor sizes. This connector is rated for 600V and 90 degrees Celsius, meeting the American National Standards Institute (ANSI) requirements and is Underwriters Laboratories (UL) listed. It is important to note that this connector is not recommended for extra-flexible cables or submersible applications.
Another option is the KUP-L-Tap Insulation Piercing Copper Connector, which is dual-rated and has a main conductor range of 4/0-4 and a tap range of 6-14. This connector is tin-plated and meets UL and CSA standards. There are also other variations of the KUP-L-Tap connector available with different conductor ranges to suit specific requirements.
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The 120% rule
To calculate the 120% rule for solar panel systems, you must first determine the main breaker's rating in your electrical service panel. Once you have this value, multiply it by 120% (or 1.2). The result is the maximum allowable back-fed breaker size for your solar system. For example, if your panel has a 200-amp busbar rating and a 200-amp main breaker, the 120% rule calculation means that the solar breaker can only be 40 amps. This value is generally fine for residential systems but insufficient for most commercial solar arrays.
If your system exceeds the 120% rule, one solution is to downsize the main breaker. For instance, a smaller main breaker of 175 amps instead of 200 amps means that your connected solar system can safely output 65 amps of power. However, if your load exceeds 175 amps, you will need to upgrade to a higher-rated panel, which can be costly.
To avoid exceeding the 120% rule, some have suggested upgrading the service panel to one with space for multiple service disconnecting means or installing a new meter and tap box ahead of the existing one.
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Frequently asked questions
A side tap is the physical connection between a solar PV system and the larger electric grid. This can be done in two ways: a line side tap or a load side tap.
With a load side tap, your solar inverter is wired directly to your electrical panel through a circuit breaker. With a line side tap, the solar inverter is connected to a PV service fused disconnect and/or a solar-only circuit breaker panel, which in turn is connected to a junction box.
Line side taps are becoming increasingly common with large solar systems as a cheaper alternative. Load side taps are more common for residential systems and smaller commercial systems.
