# Can isolated circuits still share a heat sink?



## philistine (10/6/17)

Hey Dudes,
Thanks for all the help so far, I reckon Ive pretty much got it all squared away now.
I posted this question in my previous thread but it kinda plopped off the radar when the site updated etc.

Ive just got one pretty specific simple question this time -
If ive got two separate circuits with two separate power inlets wired up and isolated from each other in the same box, should I also use separate heat sinks?

As pointed out in my other thread, isolated circuits sharing a common earthing and/or neutral point is a bad idea - does that same caution apply for two isolated SSRs sharing a heat sink?

I would assume that it's a big no no (as in they cant share) but Im hoping that Im wrong....
Ive got individual heat sinks for them, but they're dicky and annoyingly shaped, so I'd prefer to use a flat rectangular larger heat sink that can accomodate them both together.

Thanks again for everything so far!
The build's coming along nicely - finished the stand the other night (sorry neighbours for all the grinding and stuff)
I'll get a pic up in a sec....


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## philistine (10/6/17)

IMG_3574



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IMG_3587



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IMG_3586



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## malt junkie (10/6/17)

2 Should be fine on one big heat sink or with fan just ensure you earth the heatsink.


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## Adr_0 (10/6/17)

Most SSRs I've seen have one of the mounting holes and the base connected, with the purpose of connecting the main earth so that the SSR body and heatsink are protected from a stray active or fault. 

You should connect one of the SSRs through this mounting hole to one of the earths to ensure you have this protection, but not both SSRs to your individual neutral/earth circuits.


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## Mardoo (11/6/17)

You are asking some very interesting questions these days Philistine


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## koshari (11/6/17)

The techdoc ror the ssr should tell you if the heatplane is actice or insulsted. Check with a multimeter the heatplane to any of the wiring connections on the ssr look for ohms. Then you will know if there is an electrical connection. I would suspect that no would be the case. In that sfenario a common heatsink wouldnt be an issue. If you choose the ground it only connect one earth.


If there is a connection you should use a mica gasket and insulated screw to mount the ssr.


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