In electricity metering, a latching relay has one job that matters more than any other: hold the contact state without drawing continuous coil current, and switch the load reliably when a pulse tells it to. Zhejiang Great Electrical Co., Ltd., a manufacturer founded in 2003 and trading as GRT Relay, produces several latching relay families for meter builders. Three models frequently appear on the same shortlists: GRT508BG, GRT508BV, and GRT508BW. On a catalogue page they share a material list and an electrical envelope. The differences that determine fit sit in the mounting interface, the switching rating, the pole configuration, and the physical dimensions.

This comparison focuses on documented specifications, not on brand claims or supplier rankings. The goal is to help a procurement engineer or meter designer match a relay to a specific socket, panel opening, and load profile. Where the available documentation leaves a gap, this article says so rather than filling it with assumptions.

The Shared Foundation: Same Materials, Same Voltage Envelope

Before the differences, the common ground deserves attention. All three models are classified as latching relays intended for the smart metering industry, with documented application roles in smart meter, prepaid meter, and smart home switching. They share the same contact material (AgSnO2), the same primary construction materials (copper and plastic), the same maximum switching voltage of 250 VAC, and the same coil voltage range of 5–24 VDC.

That shared envelope matters to a buyer because it narrows the selection problem. A design team that has already qualified AgSnO2 contacts at 250 VAC and a 5–24 VDC coil drive does not need to re-open those questions when comparing across these three models. The qualification work shifts to the parts that differ.

Mounting Interface: PCB Soldering vs Fast-Connect T1-in/T4-out

The most consequential difference for a meter assembly line is how the relay attaches to its electrical environment. GRT508BG is a PCB soldering type relay designed for through-hole or surface mounting onto a printed circuit board. GRT508BV and GRT508BW are both fast-connect types, using T1-in/T4-out terminal entry for wire or busbar connection.

This is not a cosmetic distinction. A PCB-mounted relay becomes part of the board assembly process. It is soldered in a reflow or wave-soldering step, tested with the rest of the board, and replaced at board level if it fails. The mechanical support comes from the solder joints and the board itself. For a meter design that integrates switching directly onto the main measurement PCB, this arrangement can reduce separate wiring steps and simplify the bill of materials.

A fast-connect relay follows a different assembly logic. It mounts to a panel or a bracket, and the load conductors terminate at the T1-in/T4-out terminals with fast-on connectors or screw terminals. This approach separates the high-current path from the measurement PCB, which can be an advantage when the conductor gauge is large or when the relay needs to be replaced independently of the board.

Switching Capability: Matching 90 A and 80 A to Load Profiles

The documented ratings show GRT508BG at 90 A maximum switching current, while GRT508BV and GRT508BW are rated at 80 A. That 10 A gap is real but should not be read as a simple hierarchy. The three models also differ in pole count, and pole count changes how a given current rating maps to a circuit topology.

GRT508BG is a 1-pole device. It switches one line, which is typical for single-phase residential meters where the live conductor is interrupted and the neutral remains continuous. The 90 A rating gives headroom above common single-phase service sizes and supports short-duration overloads.

GRT508BV and GRT508BW are both 2-pole devices. They switch two lines simultaneously, which suits designs where both phase and neutral need to be disconnected, or where a two-wire load must be isolated on both sides. The 80 A per-pole rating covers most single-phase metering loads, but the buyer should confirm whether the two poles are carrying the same current or splitting different circuits.

Why the 60 A / 80 A distinction appears in buyer conversations

Some discussions of this product family refer to a 60 A / 80 A range rather than a fixed 80 A. The documented model-level specifications for GRT508BV and GRT508BW state 80 A rated load and 80 A maximum switching current. Where a project specifies a 60 A nominal load, both models have margin above that figure. The more important question is not whether 60 A fits inside 80 A, but whether the actual load profile includes inrush, motor starting, or capacitive charging currents that change the effective stress on the contacts.

Physical Envelope: Fitting the Relay Into the Meter Cabinet

Outline dimensions are often the deciding factor when two relays are otherwise close. The three models occupy distinct footprints:

• GRT508BG: 38 × 30 × 16.5 mm — the smallest of the three, consistent with its PCB-mount, 1-pole design.
• GRT508BV: 52.5 × 35 × 17.7 mm — a larger footprint, consistent with the 2-pole fast-connect arrangement and the additional terminal space for T1-in/T4-out connections.
• GRT508BW: 55.6 × 30 × 16.5 mm — a longer but narrower body than GRT508BV, with the same 16.5 mm height as GRT508BG.

The GRT508BW shape is notable because it preserves the 16.5 mm height of the PCB-mount model while stretching the length to 55.6 mm. For a panel with a fixed vertical clearance but available horizontal length, that geometry can be the difference between fitting and not fitting. GRT508BV, by contrast, is taller at 17.7 mm and wider at 35 mm, which may suit a different panel opening.

A procurement engineer should not compare these dimensions in isolation. The relevant question is whether the relay plus its T1-in/T4-out terminals and wire bend radius fits inside the available enclosure volume. A fast-connect relay with a compact body can still require more clearance than a PCB relay because the conductor terminations extend beyond the relay outline.

Pole Configuration and Circuit Topology

The 1-pole versus 2-pole difference is the clearest functional separator among the three models. GRT508BG interrupts one conductor. GRT508BV and GRT508BW interrupt two. In a single-phase meter, a 1-pole relay is often paired with a neutral that remains connected, which is a common arrangement in many metering standards. A 2-pole relay supports full isolation of both conductors, which can simplify lockout/tagout procedures and may be required by specific utility specifications.

The choice between GRT508BV and GRT508BW, once a 2-pole configuration is selected, comes down to mounting geometry and terminal arrangement rather than electrical rating. Both are rated at 80 A, both use fast-connect T1-in/T4-out terminals, and both share the same short-circuit withstand figures. The dimension table above is the practical tiebreaker.

Certification Position: UC2, RoHS, and What the Documents Show

Compliance is not a single certificate. For a latching relay used in a payment meter, the relevant requirements typically stack: a general relay safety standard, an application-level metering standard, and a horizontal environmental regulation such as RoHS. The available documentation for this product family supports a layered view rather than a single claim.

GRT508BV is covered by a TÜV Rheinland UC2 certificate (certificate number AK 50686063 0001) issued against IEC 62052-31:2015 and EN 62052-31:2016. That certificate addresses the relay's role in electricity metering payment systems. The broader GRT latching relay family is described in company documentation as complying with RoHS and IEC 62055-31 UC2. The IEC 62055-31 standard defines utilization categories UC2, UC3, and UC4 for latching relays used in payment meters, with UC2 representing a specific level of short-circuit and switching capability.

For a buyer, the practical step is to request the certificate that matches the exact model and the target market. A UC2 certificate for GRT508BV does not automatically extend to GRT508BG or GRT508BW; the certificate scope should be checked model by model. RoHS compliance should likewise be confirmed with a declaration or test report tied to the specific part number, not only to the product family.

Application Fit: Smart Meter and Prepaid Meter Switching Roles

The documented application role for all three models is smart meter, prepaid meter, and smart home switching. That shared role does not mean they are interchangeable in every design. The fit depends on how the meter builder divides the switching function.

GRT508BG suits a design where the relay is soldered onto the main measurement board and switches a single live conductor. The PCB mount keeps the high-current path short and allows the relay to be tested as part of the board assembly. This arrangement is common in compact single-phase meters where board space is tight and the neutral is not switched.

GRT508BV suits a design that needs two-pole switching with a panel-mounted relay and a terminal arrangement that accepts fast-on connectors. The larger 52.5 × 35 × 17.7 mm body provides room for the T1-in/T4-out terminals and the two-pole contact structure. This model is a candidate for prepaid meters where full isolation of both conductors is specified.

GRT508BW also provides two-pole switching with fast-connect terminals, but in a longer, narrower body that shares the 16.5 mm height of the PCB-mount model. That geometry can suit a panel where vertical clearance is limited but horizontal length is available. The documented electrical endurance figure of 10,000 operations gives the buyer a stated basis for maintenance or replacement planning.

For smart home switching, the same logic applies at a smaller scale. A smart home load controller that switches a single circuit may find the 1-pole GRT508BG sufficient, while a controller that isolates both conductors may need one of the 2-pole models. The buyer should match the pole count to the isolation requirement rather than to the current rating alone.

Where Each Model Reaches Its Limits

A comparison that only lists advantages is not useful for procurement. Each of these models has documented boundaries that a buyer should weigh before selection.

GRT508BG is limited by its 1-pole configuration. A design that requires simultaneous disconnection of two conductors cannot use this model without adding a second switching device, which changes the bill of materials and the panel layout. Its PCB mount also means that field replacement requires board-level service rather than a terminal-level swap.

GRT508BV and GRT508BW are limited by their fast-connect terminal geometry. The T1-in/T4-out arrangement requires a panel opening and conductor termination space that a PCB-only design does not need. Their 80 A rating is lower than the 90 A rating of GRT508BG, so a design that needs the full 90 A in a single pole cannot substitute a 2-pole model without re-evaluating the load split. The available documentation does not state an electrical endurance figure for GRT508BV, which means a buyer planning a replacement interval for that model should request the missing test data rather than assume parity with GRT508BW.

A Decision Framework for Buyers

The comparison can be reduced to a short sequence of questions. Each question maps to a documented difference rather than to a preference.

1. Does the design need to switch one conductor or two? If one, GRT508BG is the documented 1-pole option. If two, GRT508BV or GRT508BW applies.
2. Does the relay mount on the PCB or on a panel with fast-connect terminals? PCB soldering points to GRT508BG. Fast-connect T1-in/T4-out points to GRT508BV or GRT508BW.
3. Is the panel opening limited by height or by length? GRT508BV is 52.5 × 35 × 17.7 mm; GRT508BW is 55.6 × 30 × 16.5 mm. The 16.5 mm height of GRT508BW matches the PCB-mount model, while GRT508BV is taller but shorter.
4. Does the load require 90 A in a single pole? If yes, GRT508BG is the only one of the three documented at that rating. If 80 A per pole is sufficient, the 2-pole models remain in scope.
5. Which certificate applies to the exact model and market? Request the UC2 certificate and RoHS declaration for the specific part number, not only for the family.
6. Is electrical endurance documented for the selected model? GRT508BW states 10,000 operations; GRT508BV does not state a figure in the available documentation, so request the test data.

This sequence does not rank the three models. It filters them. A design that needs a PCB-mounted 90 A single-pole switch lands on GRT508BG. A design that needs a panel-mounted 2-pole switch with a compact height lands on GRT508BW. A design that needs a panel-mounted 2-pole switch with a wider, shorter body and has confirmed the endurance data lands on GRT508BV.

Market Context: Why Latching Relay Selection Is Getting More Attention

The broader relay market provides context for why meter builders are scrutinizing these choices. MarketsandMarkets projects the global relay market to grow from USD 11.75 billion in 2026 to USD 15.65 billion by 2031, a figure that covers all relay types rather than latching relays alone. That growth does not by itself tell a buyer which latching relay to choose, but it explains why supplier documentation and model-level comparison are becoming more important: a larger market brings more configurations and more claims that need verification.

On the standards side, IEC 62055-31 defines utilization categories UC2, UC3, and UC4 for latching relays used in payment meters. That structure gives buyers a common vocabulary for comparing short-circuit and switching capability across suppliers. A relay described as UC2 compliant can be evaluated against the same category definition regardless of the manufacturer, provided the certificate is checked against the exact model.

Application evidence points in the same direction. Johnson Electric identifies bi-stable and latching relays as part of smart-metering solutions, which confirms that the latching function is a recognized design pattern in metering rather than a niche choice. For a buyer, the implication is not that any particular model is preferred, but that the latching relay category has enough documented application history to support a specification-driven selection process.

Future Outlook: What Changes in Metering Design Mean for Relay Choice

Three trends are likely to affect how buyers view the GRT508BG, GRT508BV, and GRT508BW comparison over the next design cycles.

First, the split between PCB-integrated and panel-mounted switching is likely to remain a design-level decision. As meters add communication and measurement functions, the PCB area available for a soldered relay may shrink, which could favor fast-connect models in space-constrained designs. At the same time, compact single-phase meters may continue to use PCB-mount relays to keep the high-current path short. Neither trend eliminates the other.

Second, documentation quality is becoming a selection criterion in its own right. The difference between a model with a stated electrical endurance figure and one without is not just a data gap; it affects maintenance planning and warranty terms. Buyers who ask for model-level certificates and test reports will be better positioned to compare suppliers on evidence rather than on catalogue claims.

Third, the UC2 / UC3 / UC4 framework gives buyers a way to specify short-circuit capability without naming a supplier. A tender that states a utilization category and a rated current can be answered by any supplier that holds the corresponding certificate. That shifts the comparison from brand preference to documented capability, which is the direction this article has taken.

Frequently Asked Questions

Conclusion

The comparison between GRT508BG, GRT508BV, and GRT508BW is not a ranking exercise. It is a fit exercise. GRT508BG serves a PCB-mounted, 1-pole, 90 A role in a compact 38 × 30 × 16.5 mm envelope. GRT508BV serves a panel-mounted, 2-pole, 80 A role in a 52.5 × 35 × 17.7 mm envelope with fast-connect terminals. GRT508BW serves a panel-mounted, 2-pole, 80 A role in a 55.6 × 30 × 16.5 mm envelope that preserves the 16.5 mm height of the PCB-mount model. The shared AgSnO2 contacts, copper and plastic construction, 250 VAC maximum switching voltage, and 5–24 VDC coil range give a design team a common qualification base; the differences in mounting, pole count, current rating, and dimensions determine which model fits a given meter design.

For buyers evaluating these models, the practical next step is to map the meter's isolation requirement, panel or board architecture, load profile, and target-market certification needs against the documented specifications in this comparison. Where the documentation is silent — most notably on electrical endurance for GRT508BG and GRT508BV — the right move is to request the missing test data rather than to fill the gap with an assumption. That approach keeps the selection grounded in documented fit, which is the only basis on which a procurement decision should rest.

For complete product specifications and the full GRT Relay catalogue, the manufacturer's product catalogue is available for public access and download: Catalogs of Great-relay [2025] (PDF).