Step 10.19 — L, N and PE are isolated from each other¶
Step 19 of 80 · Chapter 10 — Wiring and Checkpoint #1
(no image — see text)
Parts:
- multimeter · tool
Do:
- Probe L→N, L→PE, N→PE at the WAGO blocks, rocker on, then again off.
- Probe the same three pairs at the PSU screws: 3 FG ↔ 1 L, 3 FG ↔ 2 N, 1 L ↔ 2 N.
Check
No beep on any of the nine. L↔N reads 100 kΩ or more, or OL, on the 2 MΩ range; L↔PE and N↔PE read OL.
What you're looking at
The mirror image of the previous check: the three buses must have no path between them at all. Live touching Neutral is a short across the mains; Live touching earth is what makes the metalwork lethal.
Why 100 kΩ
the PSU input bridges L and N whatever the rocker does, reading hundreds of kΩ or more, often climbing as its capacitors charge (verify on bench). A stray strand reads near 0 Ω; a shorted SSR reads the bed pad, tens of ohms. Write your L↔N number down for 10.78.
Tip
a momentary tick on 1 L ↔ 2 N as the PSU's input filter charges from the meter is normal; a steady beep is not.
If L↔N beeps or reads under 100 kΩ
something bridges the mains, a stray strand at a WAGO or a shorted SSR. Lift the brown lead off SSR LOAD 2 and re-measure. Silent now: the fault is on the SSR or bed side. Still beeping: a strand at a block. Refit the lead, PH2 tight.
Source: LDO wiring guide § Checkpoint 1