# Parts identification: Y-cap, MOV or NTC?

I am having problems identifying whether a component is an Y-capacitor or a MOV. They are from my parts bin so I do not know beforehand what they are.

Is there a simple way to know the difference without searching for the part number or measuring them? If measurement is required, what is the capacitance usually for a "standard" MOV?

Two examples of the components I'm talking about. Resistance: inf

Resistance: inf

EDIT Some more...things that are probably different things but it a similar package: Resistance from top left: inf, inf , 11 Ohm, 5 Ohm, 55 Ohm

I think the middle one is a transient-voltage-supression-something but i don't know about the others.

• I measured the resistances, I hope that was what you meant. Jan 20, 2013 at 14:55
• OK, but the question is also how to find out what they are without actually measuring them, i take your comment as that is not possible? Also, none of them had an infinite resistance(or several M Ohms) The resistances are is the question now. Jan 20, 2013 at 15:08
• Yep, you are right, I am getting an infinite resistance now, thank you, I'll measure the high resistance parts again. Jan 20, 2013 at 15:27

## 2 Answers

Capacitors often have a safety rating of an X or Y class, also some logos of safety agencies. If you find X1, X2, Y1 or Y2 in the marking: EMI capacitor, intended for use at the input filter of a device. The other markings often state the capacitance (222 means 22*102 pF = 2.2 nF), the tolerance (e.g. J = ± 5%; K = ± 10%; M = ± 20%) and the rated voltage.

MOVs often have some logos of safety agencies. Their number is composed of the disk size (7 mm, 10 mm, 14 mm, ...) and the breakdown voltage.

Inrush current limiting NTCs often have a number composed of the disk size and the resistance at room temperature. Also, NTCs become very hot when "on". Their surface is not glossy (plastic/resin), but often rough (ceramic-like), because the epoxy dip used for caps and MOVs would burn at the temperatures the NTCs have when in use.

Especially for MOVs and NTCs, there are very many small and cheap manufacturers, so there is really no standard for the marking.

• Both the first and the second one have safety markings, the first one also has X1 and Y2. So the topmost two are caps, the low Ohm ones NTC inrush limiters and the two others unknown? Jan 20, 2013 at 15:44
• When there are numbers like 222 or 472, it's typically value of capacitance. Jan 20, 2013 at 17:37

It can be tricky to tell without measurement. There aren't any guarantees, but here are my guidelines.

Safety-rated X- and Y-capacitors will always have X# and Y# on the markings somewhere. As a general rule, the safety-rated capacitors tend to have many safety ratings on them: your top example has the UL recognized mark, VDE (Germany), DEMKO (Denmark), the Swiss S+ mark, FIMKO (Finland), NEMKO (Norway), etc.

X- and Y-capacitors usually don't explicitly have a voltage rating on the package, since the X- and Y- rating implies their use (mains circuits up to 250VAC nominal, for instance). These should be the easiest to identify of the three types you've mentioned.

Ordinary ceramic capacitors won't have a safety rating, and usually have some marking indicating their voltage rating. If the part is a capacitor (regardless of type), the part number will tend to be a multiple of picofarads as Zebonaut has explained.

A MOV part number usually doesn't 'look' like it corresponds to a capacitance value. They will have some safety marks on them as well. It will often have a 'smooth' case like a Y-capacitor.

An NTC can best be checked by measuring for resistance - a good Y-cap and a good MOV will appear open-circuit to a multimeter. Many MOVs won't have safety marks and part numbers that don't look like capacitor values. Most MOVs that I've seen have 'rough' cases - sometimes the only way I can quickly tell a MOV from an NTC is by the roughness of the case.

No matter what, once you've made your identification it's always best to try and look up the part number - putting the wrong part in an application can lead to spectacular failure.