The isolation barrier has to hold, and the fault path has to close fast
In high-voltage equipment, operator protection rests on an isolation barrier between the HV rail and every exposed metal surface, and on the ability to remove that voltage the instant a fault appears. That requirement is the same for distribution gear, test fixtures and handheld probes: under a fault, the HV feed has to be opened without delay.
In practice the sequence is two actions at once — the HV circuit is disconnected and, in the same motion, tied to ground so stored energy can bleed off. One set of contacts opens the rail while another set closes onto ground, a make-before-break safety sequence whose reliability is only as good as the switching device carrying it at kilovolt levels.
Why a sealed reed contact fits this duty
High-voltage reed relays use hermetically sealed tungsten contacts, which suit the role for a few concrete reasons. In a typical build the reed switch operates in under 6 ms and is offered with breakdown voltage to 15 kVDC depending on capsule type; contact switching current is 3 A with a 5 A carry ceiling, and the available contact forms let one relay combine the HV-opening and the grounding functions. It is worth keeping the two voltage figures separate: breakdown voltage is a withstand limit, not the voltage the contact is meant to switch continuously — the HVR line switches to 10 kVDC even though capsules break down at 15 kVDC.
Mounting covers both board-level and rack wiring: PCB through-hole for an integrated design and high-voltage lead-wire for point-to-point builds in power racks. Operate time runs about 3 ms and release about 1.5 ms, fast enough to follow a fault signal. Epoxy encapsulation holds insulation resistance at 1012 Ω and creepage above 32 mm, the two parameters that keep the barrier intact over service life.
HVR series coverage for power supplies and test systems
The HVR series spans 4 kV / 5 kV / 6 kV / 10 kV / 15 kV / 20 kV withstand versions. Headline figures:
- Contact switching voltage to 10 kVDC
- Switching current 3 A; maximum carry current 5 A
- Pulse current options of 5 A / 10 A / 20 A
- Insulation resistance 10 TΩ and above
- Multiple contact forms; PCB through-hole or HV lead-wire mounting
- Operate 3 ms, release 1.5 ms
In an HV power supply these relays switch the output, route it among loads and, on a fault, open and ground it. In an HV test system they connect and release the DUT, isolate the measurement front end and provide the discharge path that lets an operator touch the fixture safely once the cycle ends.
The tungsten contacts are chosen for what happens at break. Tungsten stands up to the arcing of a reactive HV load, and the hermetic seal keeps the contact face from oxidizing or eroding in air, so the contact keeps breaking cleanly at kilovolt level after a large number of cycles — where an air-exposed electromechanical contact would drift. That repeatable break-and-ground behavior is the property that matters in a safety interlock; raw speed alone does not help if the open contact cannot hold back the rail.
Selection takeaway
For both HV supplies and HV test stands the relay decision comes down to matching four numbers to the design: the continuous switching voltage (not the higher breakdown figure), switching versus pulse current, the creepage and insulation resistance the barrier needs, and the operate/release time the fault-response budget allows. Specified against those, a sealed tungsten reed relay carries both the routine switching and the fault-time disconnect-and-ground sequence without a second device in the path.
About SHR AUTOSENSOR
SHR AUTOSENSOR TECH LIMITED (SHR AUTOSENSOR) manufactures high-voltage reed relays, mercury wetted relays and high-voltage DC contactors. Contact: [email protected] | +86 13761571029 | www.reed-relay.com