RZ3A60D55 (DigiKey part number 1864-1251-ND) is a Solid State Relay made by Carlo Gavazzi that can handle 55A and a load of 42-660V. The part seems to have some details on the label that make it somewhat ambiguous on the current rating at a glance. Manufacturers may not always provide immediate context for ratings on a label. Here is a snippet of what the label may look like:
Keep in mind that the picture above is the A75 version, but as you can see it shows two markings:
- AC51: 75A 400VAC
- AC53a: 20A 400VAC
What are these calling out and how do we know what applies?
Nameplate Context
While nameplate ratings are often helpful, they don’t always provide the full picture. The datasheet for this part is more clear how ratings work for the series. Page 2 indicates a column named “Maximum Rated Operational Current.” RZ3A60D55 is listed under the column that reads “3 x 55AAC.” I would interpret this as a 3 phase type rating where each contact handles 55A of AC current.
We can also verify this information on page 6, too. The first table labeled “Output Specifications” lists a maximum operational current next to text labeled AC-51. There are three columns indicating part number formats with prefixes and suffixes. The second column would match up with RZ3A60D55 because it matches “RZ3A..55.” This explicitly says 55AAC which must mean 55A AC current.
What Are The Two Ratings Listed Then?
This is not as clearly explained in the datasheet, but it does briefly mention an IEC standard on page 6. The standard number that applies to the motor HP ratings is IEC 60947-4-2. It turns out the AC51 and AC53a are specifically calling out Utilization Codes used in IEC 60947. In short, they are special codes that indicate particular load types with specific duty cycles. AC51 is calling out “Induction-free or slightly inductive loads, resistance furnaces.” and AC53a is calling out “Control of a squirrel cage motor: 8-hour operation with starting currents for starting processes, maneuvering, operation.”
Relevant Resource
If you’d like to know more context, this post I wrote does help understand that standards sometimes define parameters: IEC Voltage Ratings: What Do I Go By?