Would a pir sensor cause a low insulation reading

Thread Starter


Joined Jan 22, 2020
hi, Ove just had an eicr carried out, the engineer found a low insulation resistance reading on a circuiit with a pir sensor controlling a lamp.
He queried whether those sensors can cause such a reading even if they arent faulty.
Can anyone please tell me if thats the case ?


Joined Jan 22, 2019
Gary111, all devices such as PIRs should be removed from in circuit (by shorting the switched live to live, and isolating the neutral)) when carrying out a test as the voltage used to test them can often be 500v, and would damage the circuitry. You have to remember that the PIR is always on and that the mains feed is transformed/reduced down so there is power supply circuitry across the L/N. That circuitry varies according to manufacturer but is likely to offer lower resistance in operate at 230v. An insulation test is purely to test the fixed wiring system for an EICR, not component insulation.


Joined Dec 4, 2015
PIRs for controlling lighting are usually mains powered or sometimes mains powered with the sensor on low voltage like 12-V DC.
Cheap units can be transformerless and cause problems.
If removing the PIR from the circuit removes the low insulation reading, then the fault lies with the PIR or its internal/external wiring.
On an insulation test which can be up to 1000-volts, anything in circuit when the test is done could be fried.
I isolate any electronic stuff before insulation tests, by fitting a fused spur or double pole switch.
On decent quality PIRs, the lamp switching is done with a relay.
Provided the PIR is not subject to the wiring insulation test (use a separate appliance tester), then tracking down the low insulation cuplrit is a section by section series of tests.
For what it's worth, I always use either Timeguard or Steinel PIRs, both on RCD (Ground Fault) circuits and have never had a problem as you describe