Line Voltage vs Dry Contact

Line-voltage relays (ZEN52, Shelly Wave 1) switch power to a light or fan. Dry contact relays (ZEN16, ZEN17, ZEN58) just open or close a circuit, which is what garage openers, gates and boiler thermostat terminals need.

Current Rating

Match the relay to the load: 15 A covers most lighting circuits; motors and heaters need headroom. Never exceed the listed rating.

Neutral and Power

In-wall relays generally need a neutral. Low-voltage relays like the ZEN16 run on 12–24 V or USB-C instead, which suits garage ceilings.

Power Metering

Shelly’s “PM” models report energy use, useful for pumps, heaters and confirming a load actually turned on.

Size and Mounting

Behind-switch modules must fit with the switch. DIN rail relays mount in a panel. Measure box depth before buying.

The ZEN17 offers two relays with both normally open (20 A) and normally closed (10 A) contacts, so it handles fail-safe wiring that the ZEN16 can’t. It’s popular for awnings, gates, garage doors and boilers, and each relay accepts an optional wall switch. The listing names Z-Box, Home Assistant and Hubitat compatibility. It averages about 4.5 stars from 180+ ratings.

The ZEN52 controls two 120 V loads independently from one small module, ideal for a double-gang box or splitting a fan and light in a canopy. Unlike the ZEN51, it’s not dry contact, and a neutral is required. Zooz says it supports single-pole and 3-way installs. It averages about 4.3 stars from 100+ ratings; only 13 were left when we checked.

The ZEN58 is a tiny low voltage dry contact relay for on/off control of garage door openers, gate controllers and similar low-voltage inputs, with an analog input for a wall switch. Zooz notes you should be familiar with dry contact relay function before buying. It’s new with 16 ratings averaging about 4.8 stars.

The ZEN55 wires to the last detector in an interconnected, hard-wired smoke alarm chain and reports smoke and CO alerts to your hub separately, according to Zooz. Its optional 120 V relay output can switch on lights or a siren during an alarm. Zooz is clear that it’s not a life-safety product and shouldn’t be used for other low-voltage applications. It averages about 4.9 stars from 60 ratings.

Shelly’s Wave 1 US LR is a compact UL-listed 15 A single-channel relay for lights, fans or small appliances behind an existing switch. It supports Z-Wave Long Range and averages about 4.5 stars from 20 ratings.

The Wave 1PM adds power metering to the 15 A Wave 1, so you can track a pump, heater or dehumidifier and confirm it’s actually running. It averages about 4 stars from 13 ratings. See our Z-Wave energy monitoring guide.

Shelly calls the Wave 1PM Mini the world’s smallest Z-Wave smart switch, and its size makes it ideal for tight spaces and small switch boxes where other relays won’t fit. It keeps power metering and LR. It averages about 3.9 stars from 13 ratings.

The Wave 2PM controls two lights or loads from one device with power metering on both, the Shelly counterpart to the Zooz ZEN52 but with energy data. It’s UL listed with a 16 A rating per the title, and averages about 4.5 stars from 17 ratings.

For panel builders and facility automation, the Wave Pro 3 is a professional 3-channel DIN rail relay that mounts inside a breaker box or control panel. The listing description also mentions power metering, so confirm the exact variant on the listing before ordering. It’s very new with 4 ratings, and installation belongs to a licensed electrician.

Enerwave’s Z-Wave Plus micro switch has been around for years and installs behind an existing wall switch to control lights or ceiling fans, with a wide 120–277 VAC range per the listing. It’s an older design without Long Range or S2-era features, but it has a large review base (260+ ratings, about 4.1 stars) and works with classic Z-Wave Plus hubs.

Garage door opener

ZEN16 for multiple doors, ZEN58 for one.

Keep designer switches

ZEN51 for one switch, ZEN52 or Wave 2PM for two.

Boiler or gate

ZEN17 for NO/NC contacts.

Pump or heater

Shelly Wave 1PM to switch and measure it.

Hard-wired smoke alarms

ZEN55 DC Signal Sensor.

Control panel

Shelly Wave Pro 3 on DIN rail.

What’s the difference between a dry contact and a line-voltage relay?

A line-voltage relay passes mains power through to a load such as a light. A dry contact relay simply opens or closes an isolated contact with no voltage of its own, which is what garage door openers, gates, boilers and many control inputs expect. Wiring the wrong type can damage equipment.

Do Z-Wave relays need a neutral wire?

Most in-wall line-voltage relays do, including the ZEN51 and ZEN52. Low-voltage relays like the ZEN16 avoid the issue by running on a 12–24 V supply or USB-C. If your switch box lacks a neutral, consider installing the relay at the light fixture where neutral is often present.

Can I keep using my existing wall switch?

Yes, that’s the main appeal. Behind-switch relays wire your existing switch to an input on the relay, so the switch still works locally while the hub controls the load. Some, like the ZEN52, also let you disable local control when the switch feeds smart bulbs.

Will relays inside metal boxes have signal problems?

Metal boxes and panels attenuate radio. Mains-powered Z-Wave relays act as mesh repeaters, which helps, and Long Range models can talk directly to an LR controller. See our best Z-Wave Long Range devices guide.

Relay or smart switch?

Choose a smart switch if you want a new switch with built-in Z-Wave and a clean install. Choose a relay to keep your existing switches, control non-lighting equipment, or automate something with no switch at all. See our best Z-Wave light switches guide.