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Dwyer TR-7 Safe-T-Ground

Explosion proof, Intrinsically Safe. Ground and Continuity Control. UL Approved Class I, Group D.

TR-7 Safe-T-Ground provides continuous monitoring of a truck's ground connection throughout loading operations. Static electricity is often brought in by tank trucks entering the loading area. The Safe-T-Ground Model TR-7 instantly stops loading operations if a tank truck loses its ground. The simple but rugged Model TR-7 circuit continuously measures resistance through the truck by applying a small voltage to one terminal of the truck grounding contactor. The other terminal is connected to the loading rack ground. If the Safe-T-Ground detects a resistance of more than a few ohms across the contact terminals, the relay opens, breaking the control circuit. The relay will not close until the grounding contactor is properly connected.

To safeguard loading operations, the Safe-T-Ground circuit can be wired into your pump control - and to an audible alarm or signal light.

The double wire TR-7 system provides an extra safeguard against explosion, compared to single wire grounding, which cannot measure the quality of the electrical ground connection durring loading. The transistorized TR-7 circiut generates little heat - an added safety feature.

The Model TR-7 Safe-T-Ground is simple and easy to install. Removal of the cover on the explosion-proof aluminum housing reveals the easily accessable terminal strip for relay and ground control wiring, and a complete schematic wiring diagram appears on a label next to the terminal strip for easy wiring. Coiled grounding cable/contactor-handle assembly is easily replaced via mil-spec connector on housing.


Housing: 356-T6 Cast aluminum alloy (copper free), explosion proof - Class I, Group D.
Size: 6-5/8" wide x 10-3/8 high x 5-5/8" deep.
Power Requirements: 105-125 VAC 60 Hz 7.75 watts - with light, 1.75 watts - without lights.
Electrical Rating, Relay: DPDT, 10 amps, 125 VAC 60 Hz contact rating. Optional 220-240 VAC, 50/60 Hz - call factory.
Wiring hookup: On terminal strip.
Conduit Connection: 3/4" NPT
Installation: 7/16" mounting lugs, integrally cast.
Contactor: (Grounding clamp) molded polyethylene with berylium copper contact clips. 16-2 type SO coiled cable; retracts to 3', extends to 16'.
Grounding Studs: 2 supplied. Order a pair for each truck.
Shipping Weight: 20 lb with contactor and cord
Options: Integral pilot lights; 30' coiled cable; temporary contactor assemblies,clamp connectors, and other supply voltages.

Model TR-7
Model TR-7L (Integral Pilot Lights)
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