Does it matter which way current goes through a relay?

[Ripthorn]

I am about to wire up some relays and have noticed on the wiring diagrams that they don't specify + and - power pins, so I am thinking that I can pick either one, correct?  I just wanted to check here first.

[punkin]

true statement...

assuming the typical relay, the coil will create a magnetic field regardless of the polarity and pull in the contacts however...if it's equipped with a diode across the coil you may render the spike protection inoperative. Not likely with the type of circuits we're dealing with here but you should know before connecting it up...more good reading here;  http://www.bcae1.com/relays.htm

Same for the contacts...they simply act as a switch...there are some relays with more complicated configurations (normally closed and/or normally closed contacts or timer circuits etc.) in which case you do want to know where your lows and highs are connected but simply put, there usually arent any polarity sensitive component in the contact portion of a simple/typical relay pack.

[R.G.]

assuming the typical relay, the coil will create a magnetic field regardless of the polarity and pull in the contacts however...if it's equipped with a diode across the coil you may render the spike protection inoperative.

It's a little worse than that. If there is an internal diode and you get the coil polarity backwards, the coil is effectively shorted by the diode every time you try to turn it on. Relays with protection diodes internally simply must be fed the correct polarity or the smoke will come out.

Latching relays are, of course, polarity sensitive.

[Ripthorn]

How would I check about this internal diode?  I looked at the documentation for these relays and all they show are the pinouts.  They don't give a polarity indication, so I am assuming it wouldn't matter, but I don't want that to come back and bite me.

[German]

You can check for the diode with your multimeter.. Blah.. Simpliest thing.
But I think your relays dont have internal diodes. Manufacturer always place an information about that.

[R.G.]

Yeah, if they are polarized, the maker's literature will say so.