Differences between electric & acoustic strings....beside what they are made from. Does one create more tension than another? Of course tone is a factor....but in a pinch, would it be harmful to put electric strings on a beater acoustic? Can you use acoustic strings on an electric hybrid (Michael Kelly Hybrid Special) in this case to get a better acoustic sound from the Fishman pickup.
The material they are made from is the obvious difference. Yes, steel strings place higher tension on the neck and bridge.

Would it be harmful to put steel strings on any acoustic? Depends on how well the beater guitar is built. In a pinch, meaning short term, it probably won't hurt.

The MK Hybrid Special is essentially a hollowbody (or semi) electric. It has humbuckers so using acoustic strings, like phosphur/bronze, may not work so well with them. The fishman bridge pickup is active so I would suggest sticking with steel strings and finding a brand that gives you the sound you are looking for. Try calling MK customer service. They should be able to point you in the right direction.
--- Joe ---
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Last edited by Auriemma at May 16, 2011,
The primary difference between "electric" strings and acoustic strings is that the gauges tend to be smaller.
Electric strings are often wound with nickle-alloys that are supposed to respond better in the magnetic field of a pickup...
However, the "gauge of the string refers to the diameter of the individual strings' music wire; in the case of wound strings the gauge of the core wire will determine the tension; the diameter of the windings will determine the mass/energy of the string.

Putting a set of super-slinky electric strings on your acoustic will probably not provide enough tension or mass to properly drive the top.
However, going up a couple of gauges might work just fine. A "medium" electric set would be about equivalent to a "light" acoustic set as I recall.