Device tags
Name the device from its tag. Get 10 right to finish.
On a US control drawing, what is PB7?
Why tags matter
A coil and its contacts are often far apart on a drawing, even on different pages. The tag ties them together: every contact tagged CR2 opens or closes when coil CR2 is energized.
US drawings
| Tag | Device |
|---|---|
CR | Control relay |
M | Motor starter (contactor) |
PB | Pushbutton |
LS | Limit switch |
OL | Overload relay |
FU | Fuse |
CB | Circuit breaker |
TR | Time delay relay |
T | Transformer |
SS | Selector switch |
PS | Pressure switch |
PL | Pilot light |
IEC drawings (IEC 81346-2)
IEC tags start with a dash, then a class letter and a number: -S1, -K3, -F2.
| Letter | Class |
|---|---|
-S | Pushbutton or manual switch |
-M | Motor |
-F | Protective device (fuse or overload relay) |
-K | Relay |
-T | Transformer |
-X | Terminal |
Two letters vary between drawings, so we do not test them: contactors appear as -K or -Q, and indicator lamps as -H (older practice) or -P (IEC 81346-2).
Questions
- What does CR mean on a control drawing?
- Control relay. CR1, CR2 and so on are separate relays. Their contacts carry the same tag as the coil.
- Is a contactor -K or -Q on IEC drawings?
- Both are used. IEC 81346-2 puts power-switching devices under Q, but many drawings tag contactors -K. Check the legend of your drawing set.
Explained in our own words and checked against several references. For the full rules, see the NEC (NFPA 70), NFPA 79, IEC 60617, IEC 60445 and IEC 81346-2. Your drawing legend always comes first.