Protective Devices

[Marvo]

Nice!!! Pizza with a protective device for dessert...can't beat it

I'm impressed with the choices, this is another one I expected to be chosen only after the fuses and motor starter had gone.

These things can be found in just about every home, anyone with a domestic fridge or chest freezer has got them. They're specifically designed to be mounted hard against the compressor dome because as you said they not only measure current to protect against overload caused by failure to start (locked rotor) they also directly measure the temperature of the body of the compressor and protect against overheating due to blocked condenser or condenser fan failure or some other refrigeration problems.

Almost all of them are auto-reset and switch back on when they've cooled down. There are manual reset versions available of the same device but they look different to the one in the picture.

In domestic fridges and freezers these things actually switch the supply to the compressor so they're configured as direct-switching and their contacts are capable of disconnecting and reconnecting the full load current or even the locked-rotor current which could be 5 times higher than the normal load current.


Just for info, if you ever come across one of these that's gone faulty there's at least a 90% chance something else / another problem has caused it. They generally only fail if they've been cycling on and off frequently for a prolonged period, under normal circumstances these devices never disconnect. If you encounter a fridge where one of these devices is constantly opening and resetting closed every couple of minutes it generally indicates that the compressor is seized and needs replacing.


Nice work Pennychew that makes the score 7;3 and the remaining devices aren't sniggering any more

 

[Marvo]

Okay, I'm getting a bit bored so I'll do one of them whilst I'm waiting.:39::winkiss:

#3

1. What is the device generally called?
It would probably be called an automotive miniature circuit breaker. It's actually a newfandangled replacement for the old car fuses.

2. What does the device sense and how?
It senses current by thermal action.

3. Does the device provide direct or indirect disconnection?
It disconnects the full load current of the circuit so it's a direct disconnection device.

4. Is the device manual reset, auto reset, neither or could be both?
Could be either. There's two different types available, one type automatically recloses the circuit after it's cooled down, the other type stays open circuit until it's physically removed, then it recloses and it can be reinserted.

5. If the device has disconnected does it qualify as safe isolation of the supply?
No, it could reclose automatically but 'safe isolation' doesn't really apply the same to 12V DC car circuits.

6. In what application (where) are you likely to come across one of these devices?
Protecting 12v DC circuits in a car, it would be located in the car's fusebox.

7. What about this device makes it so suitable for its application?
It protects against overload but it's reusable after a fault has occurred so you don't need to carry spares or buy new ones as was necessary with the older type fuses.

8. Give at least one interesting piece of random info about this device.
It has an internal bi-metallic strip which facilitates the opening and closing of the contact.