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Autofill controller switching neutral?

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HenryJavaJunkie

New Member
Hi,
Recently I was able to get an espresso machine dirt cheap as the previous owner said he forgot how it was wired after he took it apart for cleaning.
Well it looked like the cleaning was left off as well, as I cleaned out about 2 golf balls worth of hard scale rattling inside the boiler and a cumulative third from the other components.

Anyways back to the original problem, there wasn't much relevant information from the manufacturer or from third party sources on how it is to be wired to the control circuit. So after some careful investigation and scrutiny I reconstructed the circuit diagram, well the AC side of it at least. The DC side looks to be solely the Op-amp comparator that controls the relay switches.

The issue is that it looks like the only way to wire the machine's components correctly to the controller is so that the control circuit is Neutral switching. And I'm just not used to seeing this, so it's causing me some doubt, but I can't see it any other way. So I'm hoping someone can take a look at the schematic I drew up and/or educate me on why a circuit controller would be neutral switching.


To recap:
1. The machine is about 18 years old.
2. Circuit controller : Giemme MFC2SN
3. No manufacturers wiring diagram available. (Ive searched high and low for two weeks, in English and in ~ google translated Italian)
4. The CAD attached is what I've reconstructed.output.png


My questions:
1. What are some reasons a control circuit would be neutral switching?

I've done some researching and reading but can't find anything solid. Except that it might be to prevent live voltage keeping the control circuit components energized and therefore leading to possible overheating and degradation.

2. Does the wiring of my CAD make sense with neutral switching?

Thanks.
 

MaxHeadRoom78

Well-Known Member
Electrically speaking there is no difference it is generally because of the safety issue that the live conductor is switched.
The fact they have both lines being controlled you do not have much choice, the way the unit is wired.
Max.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
As already mentioned, it makes no real difference switching live or neutral, it's only a convention that live is normally switched.

Historically many items used two pin reversible plugs, so live and neutral didn't really exist anyway (as far as the products were concerned).
 

MaxHeadRoom78

Well-Known Member
In N.A. 2 pin plugs are prevalent now with the advent of double insulated equipment and appliances, but they are keyed in such a way that polarity is forced by design of the plug and socket.
It is still good practice to observe live conductor switching for safety reasons.
Max.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
It is still good practice to observe live conductor switching for safety reasons.
It still makes sod all difference :D

Although I must admit to been a little horrified a number of years ago to find some CRT TV's were only fitting single pole switches, and were actually switching the neutral not the live :eek:

Bear in mind that all UK plugs are three pin (although some double-insulated items have a plastic earth pin), so everything is polarised correctly.
 

tomizett

Active Member
Glad to hear it! Nice work drawing out the schematic be the way - very tidy.
 

MaxHeadRoom78

Well-Known Member
Bear in mind that all UK plugs are three pin (although some double-insulated items have a plastic earth pin), so everything is polarised correctly.
I will bear that in mind, however holding a UK Electricians license plus Industrial Electronics Cert., I was aware.:cool:
Max.:)
 
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