IEC 62368-1:2014 has the following:
G.13.5 (page 240)
Insulation between conductors on different surfaces The requirements for insulation on the different layers of a multilayer board are specified below. For basic insulation there is no thickness requirement. Supplementary insulation or reinforced insulation between conductive parts on different surfaces in double-sided single layer printed circuit boards, multi-layer printed boards and metal core printed boards, shall either have a minimum thickness of 0.4mm provided by a single layer or conform with one of the specifications and pass the relevant tests in Table G.14.
Table G.14 Insulation in printed boards
Spec of insulation | Type tests (a) | Routine tests for electric strength (c)
Two layers of sheet insulating | No | Yes material including prepreg (b)
Three or more layers of sheet | No | No insulating material including prepreg (b)
a Thermal conditioning of G13.6.2 followed by the electrical strength test of 126.96.36.199. b Layers are counted before curing. c Electric strength testing is carried out on the finished printed board.
188.8.131.52 Test procedure for type testing of solid insulation
Unless otherwise specified elsewhere in this standard, the test voltage for the electric strength of basic insulation, supplementary insulation or reinforced insulation is the highest value of the following three methods:
Table 26 Test voltages for electric strength tests based on transient voltages
Required withstand voltage | Test voltage for basic | Test voltage for kV peak | or supplementary ins | reinforced ins | kV peak or d.c.
.33 | .33 | .5 .5 | .5 | .8 .8 | .8 | 1.5 1.5 | 1.5 | 2.5 2.5 | 2.5 | 4.0 4.0 | 4.0 | 6.0 ... etc ...
Table 27 Test voltages for electric strength tests based on peak working voltages
Peak working voltage up to | Test voltage for basic | Test voltage for kV peak | or supplementary ins | reinforced ins | kV peak or d.c. .33 | .43 | .53 .5 | .65 | .8 .8 | 1.04 | 1.28 1.5 | 1.95 | 2.4 2.5 | 3.25 | 4.0 4.0 | 5.2 | 6.4 ... etc ...
Table 28 Test voltages for electric strength tests based on temporary overvoltages
Nominal mains system voltage | Test voltage for basic | Test voltage for V rms | or supplementary ins | reinforced ins | kV peak or d.c. 250,