Rex C100 PID question: what is phase and what is neutral? - Beer, Wine, Mead, & Cider Brewing Discussion Community.

Help Support Homebrew Talk:


New Member
Apr 27, 2019
Reaction score
Hello all, newbie here. I have looked at most (not all) of the threads RE: the REX C100 PID on this forum and others. I understand that there are a bunch of them out there and this makes it quite difficult to know how to wire them. The manual is in Chinese but no wiring diagram is provided.

The model I bought is a BERM (not BERME) REX C-100 FK2-V*DN with a SSR 40 DA relay and thermocouple 0-400ºC.

So, according to the references above, I have a PID action with autotuning (F) with thermocouple input type (K, in my case 0-400ºC = 2) with voltage pulse (no internal relay) with first alarm (Band alarm= D) and no second alarm (=N).

So it is the most simple PID with no second alarm and that can control a SSR. The supply is 110-240V AC, 50/60Hz, so all is good here.

At the back of the unit, I have screws for:
1 and 2: AC input
3: empty
4(+) and 5(-) for connection to the relay (3,+ and 4,-)
6,7: empty
8: empty
9, 10: for the thermocouple, K type, 9 (-), 10 (+)

My issue is that there is no info about 1 and 2 on the side of the box so I do not know what is the neutral and what is the phase. I have seen that some have 1 with a + next to it or at least, the manual comes with a wiring diagram but I have no info.

When I open the box, 1 is connected to BD1 MB6S bridge connected to the (+) of the bridge. 2 is connected to a FR 1OR 1/2W resistor connected to the (-)of the bridge (I think).

So, I assume that my phase (hot, +) is the terminal 1 and my neutral (N) is my terminal 2?

Thanks for your help!

Cheers to all.

PS. Am I getting this right that it does not matter to power the instrument but I need to make sure I connect hot and neutral wires correctly to the rest of the circuit?
Last edited:


Supporting Member
HBT Supporter
Oct 25, 2007
Reaction score
On many, if not most, of these controllers, the AC input does not care which terminal is connected to L1 and Neutral. It doesn't matter.

In other aspects of panel wiring, your main concern is making sure you do not inadvertently make a wired connection between hot and neutral.