If there is an item that affect the wearer, say a Ring of Resilience that increases Soak, doesn't it need to penetrate Magic Resistance to affect the wearer?
A magus could suppress his MR (well, Parma) voluntarily, but what about a creature, such as a faerie or dragon?
I don't have a rules reference for you, but I 'd think that these creatures could also surpress their resistance temporarily.
Wouldn't your own spells and activated powers automatically penetrate your own Parma?
Your own spells, cast on yourself, do not need to penetrate. Items that you create do need to penetrate (with the exception of a talisman with a power invested at range personal).
I was thinking of an item made for another, at any rate.
According to the Magic resistance rules on pg. 85 in 5th edition rules any spell with touch or greater range must penatrate Parme even if cast on oneself. Only personal spell do not have to penatrate parma.
If a personal range spell is placed in an item it would affect the item only and not the wearer..
Thrumbar 
A most annoying state of affairs.
Oh well, them the rules.
Yair
Here are some options on a previous post that I made regarding this topic.
First, a magic item that is set up to effect its wearer/holder. The classic Ring of Invisibility, Belt of Strength, Cloak of Protection, or even Cursed Amulet. The wearer puts it on, and activates it (sometimes one and the same). The problem lies in the Penetration and if the user has Resistance. The item has to have a Range of Touch for it work, meaning it needs to affect the wearer, and Parma should resist it. The inconvenience of this cries out for a work around IMO. Some ideas I've had.
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The wearer must suppress his Parma, activate the effect, then resume his Parma again. Slightly dangerous, but the easiest way to do this. Still, many magi might want a workaround.
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Due to the Parma Ritual's genius, it allows the user to incorporate active magic effects already on the person, such as from an item. So when the user raises his Parma at Sunrise and Sunset he takes into account the items he wears and the Parma ignores them. This relies on interpretation and might not be suited for all players. An option would be to say that the Parma is slightly weaker, 1 lower than normal for example due to exercising this option.
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The item must be designed with Penetration in mind. This is potentially costly, but provides a surefire solution (and is most in line with the rules), until the wearer's Parma and Arts raise to a level too high for them to be Penetrated by the item. This option should always be exercised for the 'cursed item' magic items.
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An option during the invention process would be to add a special modification during the item's creation that would effect the creator only. For +5 (or perhaps more) to the item effect's total level, it would give the item the ability to automatically bypass the creator's Parma and Arts, so its effect always works on him, no matter how high they get.
I'm at work, and don't have my books with me, but I believe that if you check the "Talisman Attunement" rules in the core book you will find that the talisman is the single exception to this. As I recall, a magus' talisman is considered to be a part of him as long as he is touching it.
NCL
At work too, but I believe the familiar is also an exception.
Magi can get around the issue when making items for themselves, yes. But they can't make items for someone else, say a faerie or (in my case) a dragon, nor use that nifty wolfskin they just uncovered. Oh well, that's what companions are for...
Edit: The above house rule options are good, don't get me wrong. I'm just wondering if there is a solution in the rules, and apparently there isn't. (Options 1 and 3 are within the rules, IMO, but aren't much of a solution.)
Yair