Veyr new here. I am looking for some help. Want to use arduino and SSR to switch transformers, loading per transformer of about 3A max @240V. There are inrush currents to take into account, so probably at least 10A SSR required. Sequencing would be something that is fairly simple like a pattern to control lighting on and off in a flashing operation
SSRs require heatsinks. Does that fit within your plans.
The only device I know of that will have such inrush current is an electric motor. How does your design work with 10 amp inrush current using only 3 amp capable transformers?
Hi Jim, Heatsinks are fine
I am only going by the data sheets of the products supplied by the manufacturers. The inrush times are very short, but very high. The use of type C breakers is recommended for all of the products
You should have a look at the datasheet for this relay
Thanks for that Jim. just checking the heat sink for it, far more expensive than the relay ha ha!
At least a reputable make, although probably made in PRC like most things now
Transformers definitely have inrush, however it is proportional to primary current,,,in your design, if you can delay fully loading the transformer and let it “warm” up before, the inrush will be negligible … does not matter where the SSR is built just buy from good quality reputable company as SSR do not deal great with inductive loads, especially inductive loads with inrush.
Edit: forgot to mention, sometimes on smaller Tx people will use soft start to limit this. Simple way is use PTC thermistor rated for circuit current of course 
Hi and thanks for the input. I had considered using a current limiter, but finding one at a price that is not going to put the whole thing out of limits as a saleable item may be tricky
According to the data sheet if the current is less than about 6A and the ambient temperature is less than 40C, you won't need a heatsink.
However, I would at least mount them to some large metal surface.
What to you think happens to the voltage while the very high inrush current is happening? It approaches zero volts. Are you referring to inrush TO the transformer or inrush being supplied BY the transformer?
Inrush to the transformer
Yes, I was thinking an extrusion with fins that I could at least cut to the length required, fairly straight forward with sink compound.
Thank you. The inrush only happens if the switching on happens at the peak of the AC cycle. The impedance of the transformer limits the current which will lag the voltage increase of the cycle. All transformers have the inrush which only produces heat and the transformer can easily take care of that unless subject to long term very rapid on/off cycles.
I don't know anything about your installation but that's probably good enough
Be sure the mating surfaces are flat so they make maximum metal to metal contact. Heat sink compound is there only for places that cannot be forced into contact.
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Should we assume the transformers have a capacitive load? Might it be better to switch the secondary?
Hi John, probably not at 4000v 
For sure