Chauvin Arnoux C.A 742 IP2X Notice De Fonctionnement page 32

If the test probe is in fact on the phase, the Ph (phase) indica-
tor flashes and the device beeps.
Warning: if the Ph indicator is not flashing, that does not mean
that there is no hazardous voltage on the outlet.
3.5. USING THE C.A 751 (OPTION)
If you have purchased a C.A 751 2P+T adapter, you can test
for the absence of voltage between the phase and neutral
on an outlet.
Attention: Pairing the C.A 742 with the C.A 751 derates
the combined product to measurement category
II, 250V.
3.6. Connect the C.A 751 to the terminals of the C.A 742, then
refer to the operating instructions of the CA.751.
+
600V
CAT IV
230
127
50
24
V
AC
DC
12
32
COM
690 AC
400
750 DC
Ph
Ω
ELV
+ -