On a NO only relay it doesn't matter about 30 and 87, but if you have a DT (double throw) with a NC contact it does, so it's a good idea to always use 30 for power and 87 for the device.
Likewise, on most relays, it doesn't matter if 85 or 86 is ground, BUT, if you happen to install a relay with diode spike suppression, then 85 has to be power and 86 has to be ground.
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