Trouble identifying a MOV

[MyTechtime]

I have a mov that burned in half on a security system. The only letting on it is:
OS
33 NA
Anybody know where to find one/a modern replacement?

 

[dorke]

Please let us know in what part of the system is the MOV connected.
If it is at the line input area,then let us know what is the line voltage in your country.
If in another part let us know what are the voltages and/or devices involved.
A photo could help as well.

 

[MyTechtime]

The line voltage is 120. There's a transformer that steps it down to 18 before the mov. It is in series with one of the ac terminals

 

[shrtrnd]

First-off, they don't put MOV's in series with anything. It's probably wired in parallel (or this may explain why it was blown).
I too get annoyed at the markings on MOV's, everybody marks them using their own numbering system and it's tough tracking the mfgr down.
Here's my educated (barely) guess.
You've got 18VAC after the transformer (RMS), MOV's typically are chosen for Peak V (18V x 1.414 = about 25Vpeak)
But you have to consider voltage spikes, so MOV's are chosen slightly over the expected working voltage.
You probably have a 33V MOV.
The fact that it's blown would (depending on your application, how critical is it to maintain OEM specs on your security system),
I'd consider replacing it with a 50V MOV, so you don't see the replacement blow also in the foreseeable future.
You need to decide whether to go with a higher rating, or maintain the status quo.
If this device actually IS in series with one side of the AC line, you may not be looking at an MOV, it may be
some other component.

 

[MyTechtime]

I would probably go with the 33V one. It looks like a power surge occurred and the mov protected the system from damage. I attached a picture of the burned up MOV.


Could anybody recommend a part number for a good replacement?

 

[dorke]

Remove the MOV from the print and read the full writing on it.
If possible post a photo from the "Dark side".

 

[MyTechtime]

There's no other writing on it. Here's the bottom.

 

[shrtrnd]

Google one until you find what you need, a lot of mfgrs make them.
Bourns MOV-14D330K 33v 10% Tol,
Littlefuse V33MLA1206Am 33V
Epcos (TKD) makes them and many others.
If I were you, I'd replace BOTH of those MOV's, not just the one.
Good luck.