Shunted Tombstones vs Non Shunted Tombstones

Are you unsure if your light fixtures require shunted tombstones or non shunted tombstones? Telling these lighting tombstones apart is more than a matter of compatibility. It is essential for the efficient and safe operation of your fluorescent or LED lamps. This guide clarifies the selection, enabling correct choices for optimal performance.

What Are Lighting Tombstones

Lighting tombstones, also known as lampholders or sockets, are components within a light fixture. They physically support fluorescent or LED tubes and provide the electrical connection points necessary for the lamp to illuminate. Their design varies based on lamp type and electrical requirements.

Understanding Shunted Tombstones

Shunted Tombstone Definition

A shunted tombstone features internally connected electrical contacts. This internal bridge means both pins on one end of a tube receive power from a single electrical input path within the tombstone itself.

Electrical Current in Shunted Sockets

In shunted sockets, electrical current flows from a single origination point within the lampholder and is distributed simultaneously to both contacts that connect with the lamp pins.

Common Fluorescent Applications

Shunted tombstones are typically required for fluorescent fixtures utilizing instant start ballasts. These ballasts provide a high initial voltage to start the lamp without preheating the cathodes.

Understanding Non Shunted Tombstones

Non Shunted Tombstone Definition

A non shunted tombstone has separate, electrically independent contacts for each lamp pin. Power must be supplied to each contact individually from the fixture's wiring.

Electrical Current in Non Shunted Sockets

For non shunted sockets, each contact provides a distinct, isolated pathway for electrical current. This requires two separate wire connections to power both pins on one end of a tube.

Fluorescent Applications

Non shunted tombstones are generally used with fluorescent rapid start, programmed start, and pre-heat ballasts, which involve preheating the lamp cathodes before ignition.

Role in LED Tube Retrofits

Non shunted tombstones are frequently essential for direct-wire (ballast bypass) LED tube retrofits. Many such LED tubes are designed for power input to separate pins.

How to Identify Tombstone Types

Determining whether a tombstone is shunted or non shunted involves visual checks and a simple electrical test. These methods help confirm the internal wiring configuration of the lampholder.

Visual Inspection Cues

Visually, non shunted tombstones often present four wire insertion points, allowing for two separate circuits. Shunted versions might show only two wire insertion points, or have visible internal jumpers connecting pairs of contacts if four points are present. However, appearances can vary, making electrical testing more reliable.

Using a Multimeter for Confirmation

A multimeter set to the continuity test mode provides a definitive way to identify tombstone types. With power disconnected, place one probe on each of the two metal contacts within a single tombstone. If the multimeter indicates continuity (usually with a beep or a zero reading), the tombstone is shunted. No continuity signifies a non shunted type.

Shunted vs Non Shunted Sockets Comparison

What truly separates shunted from non shunted sockets? The table lays out the essential distinctions for quick understanding.

Core Distinctions Chart

Application Guide for Tombstones

You can now tell shunted and non shunted tombstones apart. But which one does your fluorescent fixture or LED tube actually need? Getting this right ensures your lights work correctly; here’s how to match them.

Tombstones for Fluorescent Lights

For traditional fluorescent lighting systems, the tombstone choice is dictated by the type of ballast for fluorescent lighting used in the fixture.

• Matching with Instant Start Ballasts Instant start ballasts provide a high voltage surge to ignite the lamp without preheating its cathodes. These systems require shunted tombstones. The shunted design ensures that the single high-voltage output from the ballast is correctly delivered across both pins at each end of the fluorescent tube. Using non shunted sockets here can prevent the lamp from starting or lead to ballast issues.
• Matching with Rapid Start or Programmed Start Ballasts Rapid start and programmed start ballasts preheat the lamp cathodes before ignition. This process generally extends lamp life and allows for dimming capabilities. These ballast types necessitate the use of non shunted tombstones. Each contact within the non shunted tombstone provides an independent connection point. This setup allows the ballast to manage the preheating current circuit to each cathode filament separately. Shunted sockets would create a short circuit in these preheating circuits.
• Considerations for T8 and T12 Tubes While both T8 and T12 fluorescent tubes often use a G13 bi-pin base, the required fluorescent light tombstone type depends on the ballast. Many T8 fixtures with electronic instant start ballasts will use shunted tombstones. Conversely, older T12 fixtures, often with magnetic rapid start or pre-heat ballasts, typically employ non shunted tombstones. Always verify the ballast type. Do not assume compatibility based on the tube (T8 or T12) alone.

Tombstones for LED Tubes

When retrofitting to LED tubes or installing new Светодиодные светильники, the choice of led tombstone is determined by the LED tube's internal driver and power requirements.

• Non Shunted Sockets for Direct Wire LEDs Most direct-wire (also known as ballast-bypass) LED tubes, particularly single-ended power (SEP) types, require non shunted tombstones. In these SEP tubes, line voltage (live and neutral) is connected to the two pins at one end of the tube only. Non shunted sockets ensure these two pins receive their distinct electrical inputs. The use of shunted sockets with SEP direct-wire LEDs would cause a direct short circuit.
• Shunted Sockets for Plug and Play LEDs Plug-and-play LED tubes are designed as direct replacements for fluorescent tubes. They are intended to operate with an existing, compatible fluorescent ballast. If these LEDs are designed to replace tubes used with instant start ballasts, they will consequently require shunted tombstones. This requirement mirrors the fluorescent system's needs. Always confirm LED tube compatibility with both the existing ballast and socket type.
• Double Ended Power LED Tubes Some direct-wire LED tubes are designed for double-ended power (DEP). This design means power is applied to both ends of the tube. The specific tombstone requirement (shunted or non shunted) for DEP LED tubes can vary significantly by manufacturer and design. Some DEP LEDs are versatile and can work with either shunted or non shunted tombstones. Others have specific requirements. Consulting the LED tube manufacturer's installation instructions is essential for these types.

Importance of Correct Tombstone Selection

The choice between shunted and non shunted tombstones is not arbitrary. An incorrect match can lead to immediate problems or long-term damage.

Potential Risks of Mismatch

An incorrect tombstone type can result in several negative outcomes. These include the lamp failing to illuminate, flickering, or immediate burnout of the lamp or ballast. In more severe cases, an electrical short circuit can occur. Such a short poses a fire hazard or can damage the light fixture tombstones and wiring. The UL listing of components may also be voided.

Ensuring Lamp and Ballast Longevity

Proper tombstone selection is a factor in achieving the expected lifespan of both lamps and, where applicable, ballasts. Correct electrical connections prevent undue stress on components. This prevention reduces premature failures and ensures the lighting system operates as designed by the manufacturers.

Modifying Tombstone Setups

Sometimes, a lighting fixture's existing tombstones may not match the requirements of a new lamp or a planned conversion, such as an LED retrofit. In certain situations, modifications are possible, though replacing tombstones is often the more straightforward approach.

Converting Non Shunted to Shunted

It is technically possible to make a non shunted tombstone behave like a shunted one. This typically involves creating a small wire jumper (usually #18 AWG solid wire) to connect the two separate contacts within the non shunted lampholder. While feasible for those comfortable with detailed wiring, purchasing new shunted tombstones is generally recommended for consistency and to ensure UL compliance, especially for multiple fixtures.

Replacing Shunted with Non Shunted

Converting a shunted tombstone to a non shunted one is not practically achievable by modification due to its internal construction. If a non shunted setup is required—for instance, when installing most direct-wire LED tubes into a fixture that previously used shunted sockets with an instant start ballast—the existing shunted tombstones must be completely removed and replaced with new non shunted tombstones. This ensures each contact has an independent electrical path.

Installation Safety

Working with any electrical components, including light fixture tombstones, requires careful attention to safety to prevent electrical shock or damage to equipment.

Power Disconnection Protocol

Before attempting any inspection, replacement, or modification of tombstones or fixture wiring, always ensure the electrical circuit supplying power to the light fixture is completely turned off. This should be done at the circuit breaker or fuse box. Confirm power is off using a reliable voltage tester before proceeding.

When to Seek Professional Assistance

If you are unfamiliar with electrical wiring practices, unsure about any step of the process, or encounter wiring that does not match diagrams or expectations, do not proceed. It is always best to consult a qualified electrician. Incorrect wiring can be dangerous and may void warranties or insurance.

Labeling Modified Fixtures

After any modification to a light fixture, such as bypassing a ballast for an LED tube installation that requires different tombstone wiring, it is good practice to apply a clear warning label. This label should indicate that the fixture has been modified and is no longer suitable for its original lamp type (e.g., "Fixture Modified for Direct-Wire LED Tubes Only. Do Not Install Fluorescent Lamps."). This alerts future users and maintenance personnel to prevent incorrect lamp installation.

Conclusion

The distinction between shunted and non shunted tombstones, while seemingly a small detail in a light fixture, dictates how electrical current reaches the lamp. As we've explored, shunted sockets create a common electrical path suitable for instant start fluorescent ballasts or specific plug-and-play LEDs. In contrast, non shunted sockets provide separate pathways, essential for most direct-wire LED conversions and fluorescent systems with rapid or programmed start ballasts.

Ultimately, matching the tombstone type to both the lamp and the ballast (or lack thereof in direct-wire LED setups) is not just a recommendation—it's a requirement for safe, efficient, and reliable lighting. Armed with the knowledge to identify these components and understand their applications, you are better equipped to maintain or upgrade your lighting systems effectively. Always refer to manufacturer specifications for lamps and ballasts, and when in doubt, professional electrical advice ensures a correct and secure installation.

Часто задаваемые вопросы (FAQ)

Q1: Can I use shunted tombstones for all LED tube lights?

A: No. While some plug-and-play LED tubes designed to work with instant start ballasts may use shunted tombstones, most direct-wire LED tubes, especially single-ended power (SEP) types, require non shunted tombstones to prevent a short circuit. Always check the LED tube's specifications.

Q2: What happens if I use a non shunted tombstone where a shunted one is needed for a fluorescent lamp?

A: If a fluorescent lamp system with an instant start ballast (which needs shunted tombstones) is fitted with non shunted tombstones, the lamp likely will not start or will operate erratically. The ballast may also be damaged due to an improper circuit.

Q3: Are T8 and T12 tombstones always interchangeable?

A: Physically, T8 and T12 tubes use the same G13 bi-pin base, so they can fit into the same size tombstones. However, the critical factor is whether the tombstone is shunted or non shunted, which must match the ballast type (for fluorescent) or LED tube requirements, not just the T8 or T12 designation.

Q4: How can I be absolutely sure if my existing tombstone is shunted or non shunted?

A: The most reliable method is to disconnect power and use a multimeter set to continuity. Test between the two contacts of a single tombstone. Continuity (a beep or zero reading) indicates a shunted tombstone; no continuity means it is non shunted.

Q5: Is it safe to convert a non shunted tombstone to shunted using a wire jumper?

A: While technically possible for those experienced with wiring, it is generally safer and often recommended to purchase new, purpose-built shunted tombstones. This ensures proper construction, maintains UL listings, and offers greater reliability, especially for multiple installations.