Switching & protectionRebuild shelfTest and identify

Safety interlock

Also called lid switch, door switch, cover switch.

A switch whose job was to stop a machine from running with the guard open. Reuse the switch in a new machine. Do not bypass the one that is still in a working microwave, washer, or shredder.

If you are new to this category

A switch opens or closes a circuit. Some switches are for your finger. Some open when they get too hot and stay open. Those do not reset. A relay is a switch that a small current turns on so it can control a larger current. Use the rating printed on the part.

Click it and listen. Then use a meter on continuity, which beeps when the contacts touch. Do not guess that a small switch can run a motor.

The three legs of a snap switch

Common is the moving contact. NO means normally open: that leg connects only while you press. NC means normally closed: that leg is connected until you press. Click the button while the meter is on continuity and write down which beep matches which leg.

Mains voltage. Line voltage, and the DC bus just after the rectifier, both kill. A disconnected cord is not a discharged supply.

Specification. The right-hand column is what is typical. The label on the part in your hand wins if they disagree.
What to look for	Usual figure
Microwave	Usually three switches. One of them is a monitor switch arranged to blow the fuse if the others are defeated. Understand that before you call them 'spares'.
Rating	Often full motor current

Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.

What people actually use it for

Guard switches on a new tool
A robust door detector

Leave this one when

You planned to put the appliance back in service without it. That is not a salvage job.

Buying a new one is the better idea when

A purpose-made safety interlock with a forced-open contact, if a finger is what it is protecting.

How to tell if this one still works

Continuity map with the actuator pressed and released, written down, before you unplug the harness.

Tools you will want: Meter, Camera.

Words on this page

Short meanings, so the rest of the entry is readable if you are not already doing this every weekend.

continuity: A meter mode that beeps when two points are connected. It is how you map a switch: beep, then click, then see if the beep changes.

Where people actually find it

5 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.

Harvest at a glance
From	Call	How many	How often	Where it sits
Washing machine	Worth it	1	usually	Door lock.
Clothes dryer	Worth it	1	always	Door.
Blender	Worth it	1	usually	Jar detect.
Refrigerator	Worth it	1	always	Door.
Paper shredder	Worth it	1	always	Where the head meets the basket.

Worth pullingWashing machine1 · usually
In this particular machine
Mains, often with a solenoid latch.
Where to look
Door lock.
How to get it out
Map the wires.
The condition to expect
The lock is a common failure; test it.
Worth pullingClothes dryer1 · always
In this particular machine
Mains switch.
Where to look
Door.
How to get it out
Test it.
The condition to expect
Good.
Worth pullingBlender1 · usually
In this particular machine
A switch or a magnet and reed.
Where to look
Jar detect.
How to get it out
A reed version includes the magnet in the jar collar.
The condition to expect
Good.
Worth pullingRefrigerator1 · always
In this particular machine
Turns the lamp off. Sometimes a reed.
Where to look
Door.
How to get it out
Take the magnet too if it is a reed.
The condition to expect
Good.
Worth pullingPaper shredder1 · always
In this particular machine
Mains switch.
Where to look
Where the head meets the basket.
How to get it out
A good guard switch for a new machine.
The condition to expect
Good.