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This is a "wet" temperature sensor for a Boilermate 2000 thermal store. The pin connectors are inserted into a plastic plug that connects to the control board (see 2nd image).

The pins do not stick out from the plug (see 3rd image which shows that the main pins are on the PCB).

Are the pin connectors some sort of standard part? If so, what are they called?

Pin connectors Boilermate 2000 PCB connected Boilermate 2000 PCB disconnected

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up vote 24 down vote accepted

Those are called Bootlace Ferrules and, yes, they're pretty standard in electrical wiring. They come in many different sizes, and each size has its own colour.

enter image description here

There are also Twin Entry options, that allow two wires to be joined:

enter image description here

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I think OP means the connector/plug (the orange thing), not the ferrules. – Michael Jan 23 at 22:30
@Michael He's clearly asking about "pin connectors" that insert into the "plastic plug". – Armandas Jan 23 at 22:31
The ferrules aren't just pretty standard, they are the law in some countries :) – rackandboneman Jan 23 at 22:40
I did mean the ferrules. Thank you, great answer. – James Jan 24 at 9:10

The pins are bootlace ferrules.

The pins do not stick out from the plug (see 3rd image that shows the main pins on the PCB).

If I'm reading your photos correctly the wire ferrules are held in cage-clamp terminals on the PCB connectors. The ferrule pins do not stick out the other side of the connector.

enter image description here

Figure 1. Wago cage-clamp terminals.

These terminals can grip the ferrules or stripped stranded wire. They have become very popular as they are quick to install and are vibration-proof. The wet-sensor manufacturer probably uses them to prevent problems with stray strands, etc.

Cage clamp and wire

Figure 2. Cage clamp and wire showing excellent contact area.

Cage-clamp terminals actually work better on stranded wire than they do on ferrules. In Figure 2 you can see that the strands have formed a rectangular bunch and that contact is made between the terminal and many individual strands. When a ferrule or solid wire is inserted the contact will be tangential at top and bottom.

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Great answer, thank you. Yes, the PCB plugs have "jaws" that can be opened, to allow new wires to be added (which is what I need to do). It's interesting that you say the terminals can grab stripped wire. I'm hoping I can do that in this instance, as I don't want to have to buy a ferrule clamping tool! – James Jan 24 at 9:10
You can definitely avoid the ferrules for cage-clamp terminals. See my update (Figure 2, etc.). – transistor Jan 24 at 9:56

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