I had a bad plug-in transformer with a 3 wire output AC GRD AC, with following specifications PRI 120V 60HZ 0.24A , SEC 12VAC 20VA, I could not find a 3 pin transformer with same specifications instead find one on Ebay with little different specifications of PRI 120V 60HZ 0.31A, SEC 12VAC 25VA, My question is can I use this one instead of original specifications of the damaged transformer ? I would like to tell that the 3 wires goes to a Digital TIME TRACKER by FAST COMPANY. The timer gives a beeping sound at the end of the time set cycle
Original: PRI 120V 60HZ 0.24A, SEC 12VAC 20VA - 3 wire output AC GRD AC. Replacement: PRI 120V 60HZ 0.31A, SEC 12VAC 25VA.
Figure 1 (a) 12 V AC transformer. (b) Center-tapped, 12-0-12 V AC transformer. (c) Centre-tapped 6-0-6 V AC transformer.
You state that the original is three wire and that it is 12 V. What isn't clear is whether that's a 12-0-12 (Fig. 1b) or 6-0-6 (Fig. 1c). You need to double-check.
You don't state that the replacement is centre-tapped. Again, you need to double check.
Power rating is fine. You may find that the output voltage is slightly higher as the 25 VA transformer will be running at a lower percentage of its rated output.
The voltage is the same, which is what you want and the VA is slightly higher so if anything it has a little overhead. Will work fine.
Edit: Sorry misread the original question. You should try and source one with an earth as without knowing the purpose it would be difficult to make the call, may be performance related such as shielding, could be for circuit protection such as surge devices or may be for safety.
This can vary though. In Australia for example alarm panels have a provision for earth via the AC plugpack however direct bonding to communications earth (which is bonded to electrical earth also) is preferred.
So you may be able to also earth it seperately if you cannot source the exact plugpack.