How Long Cables From Turntable to Preamp?

I want to add a turntable into my audio system. My equipment rack is maxed-out and cannot include the addition of a turntable. In addition, the second rack for the TT can't even be next to the existing one because it's in a walkway area. So, I have to place a separate stand for the turntable about 6' to 8' away from the preamp. Even further would work better still, but..... I'm concerned about line loss or other problems with long cable length.

What is the longest possible length of cables that would be allowable from the turntable to the preamp?
I think the correct answer will depend on the electrical parameters of the cables and the cartridge used, but in simplest terms the answer is "not very long at all". The signal generator in cartridges is not designed to push a signal very far at all. It might work but there will be degredation. BUT, if you can position a phono stage next to your turntable you should be able to that 6 to 8 feet with no problems.
1.2 meters is the standard tonearm cable length.

As Dan points out, longer can diminish already small cartridge output, and simultaneously increash RFI and hum pickip. So it's the worst of both worlds.

In addition to Dan's very good suggestion of locating the phono preamp near the TT and then not having to worry about the distance to the main preamp, you might want to consider mounting a TT wall shelf (like a Target) right over or next to your rack. IMO, unless you have a very solid rack and a concrete floor, this is the best way to install a TT anyway, and then you could have it close to your other equipment without adding another rack.
If I remember correctly, a few years back I read somewhere or was told by a dealer that once you go over 30 feet with RCA's interconnects then you should go with balanced IC's. I'm guessing you'll be using a decent pair of RCA IC's so as long as your under 30 feet you should be OK. I could be wrong, but this is what I remember. Uriah If you really want a professional answer, make a call to one or a few of the big Interconnect companies like Audioquest, Cardas, or Kimble and see what they think.
the first responses are the correct (and practical) recommendations, but since I had a similar issue last year I did some experimentation. I ran a 2 meter RCA connected in line with my phono cable using F/F rca adapters (which has to be the worst way to do this). This gave me a 3 meter length to the phono input on my preamp's inboard phono section. I was pretty content with it, but didn't do any really critical listening at the time, nor was I using a top line table/cartridge with this setup. It was a perfectly acceptable setup IMO, though if you listened carefully there was a little more noise. I was still pleased with my vinyl.

I also ran a similar setup but using an outboard phono preamp, with a 3 meter ic from the phono to the linestage preamp. Except for some special grounding I had to install, the result on this was better, and probably will stand up to more critical listening.

net/net - I suggest you try it out and see how satisfied you are with your own setup. I doubt you have anything to lose but the time it takes you to set it up. I certainly think you'll be more satisfied with the sound of a phono with 3M ic's than no phono at all.
I'll grant this one exception, which is: if you're using a high output moving coil cartridge (that means 2+ mV as opposed to 0.2 -- 0.6 mV), you could probably go six to eight feet without much problem.

MM cartridges, although they also have higher output, are susceptible to cable capacitance build-up over much more than 4 or 5 feet, so even though they have sufficient output voltage to drive a longer cable without noise, you will start to get non-linear frequency response problems unless you add capacitors to compensate.
Why not use a passive or battery phono step-up transformer?
OK, let me see if I understand this.
If I use, say 9'-10' of cable from my pre-amp to the phono stage... and the phono stage is right adjacent to the turntable... I should be OK?
Yes, you have it! Your phono stage is going to bring the signal up closer to what you would get from a CDP and will be much less susceptible to cable resistance and capacitance. Single ended will be fine. All things considered it is the easiest method short of the wall mount that Nsgarch suggested.
They need to be long enough to reach !

Sorry, could not resist.