Best practices for mounting Opto22 SSRs in Hammond polycarbonate enclosure

I'm a newbie to this forum so I appreciate the opportunity to ask for some help here!

I have five SSRs that will be switching < 1 amp each @ 120V AC. I plan to put them in a Hammond polycarbonate box. Is there a best practice for mounting these relays in the box? Neither Opto22 or Crydom provide any guidance on spacing, mounting material, or even off-the-shelf rails. Hammond only supplies details of the plastic's temperature and arc specs.

I am considering just a thin aluminum plate and ground it well. I also checked the NEC and did not find a section that gave much guidance there either. Mostly minimum bend radius for wiring.

Any help would be greatly appreciated.

Walter

Walter I have always found Opto22 give good data on their products. You don't specify exactly which model you are using apart from "Power Series" in your heading.
A bit of fossicking around on Opto22's site found this:

https://documents.opto22.com/0859_Solid_State_Relays_data_sheet.pdf

This does have a fair bit of information - refer to pages 3 and 5 which have information on mounting to finned heatsinks and to 1 degree/watt and 2 degree/watt heatsinks. An older version of this doc which I had on my PC gives a 6" x 6" plate as 2 deg/watt and a 12" x 12" plate as 1 deg/watt. Page 4 gives the dissipation in watts per amp of switched current that the device will generate. From this information you should be able to see if your plate will be of sufficient size for what you are doing.

As far as I know the metal tabs on the devices are isolated form the circuitry, but grounding your heatsink is a good idea. And use fuses or breakers to protect against any breakdowns, you don't want your heatsink going live!

Your idea of fixing the SSRs to back plate is a good idea as is your suggestion of earthing it. Indeed, earthing may be the electrical code in some places. I would think that you may be able to find a steel plate for the Hammond box.

The metal plate will also serve as a heatsink, although with the relatively low currents that you are using, I don't think heating will be a problem. You may want to contact Opto22 tech support with your questions.

However since your current requirement is low you may want to consider DIN rail mounted SSRs that will reduce your footprint considerably and simplify your mounting requirements. Look at the Phoenix Contact 2966634 (https://www.phoenixcontact.com/en-ca/products/solid-state-relay-module-plc-osc-24dc-24dc-2-2966634) to get the idea. However there are a multitude of options. Just go to digikey's solid state relay section (https://www.digikey.com/en/products/filter/solid-state-relays/183 ) and use the filters to narrow your search.

It is generally good practice to mount the SSRs on a surface that is electrically conductive, such as an aluminum plate, and to provide a good electrical connection between the SSRs and the plate. This will help to dissipate heat generated by the SSRs and will also provide a common ground reference for the SSRs.

In terms of spacing, it is important to consider the size and heat dissipation requirements of the SSRs, as well as any other components that may be present in the enclosure. You should also consider the airflow and ventilation requirements of the enclosure to ensure that the SSRs do not overheat.

In terms of mounting material, you can use screws or other mechanical fasteners to secure the SSRs to the aluminum plate. You may also want to consider using thermal adhesive or other materials to help transfer heat from the SSRs to the mounting plate.

It is also important to follow any manufacturer's recommendations for mounting and spacing the SSRs, as well as any relevant electrical codes and standards. The National Electrical Code (NEC) may provide some guidance on these issues, but you should consult a qualified electrician or engineer if you have any concerns about the safety and compliance of your installation.