Why would you use -48V instead of +24V to run equipment.?
Answer:
It was first done on telephone equip (maybe telegraph) for a very good reason. I used to work for the phone company and while I might say many things about them I hate to admit they got this one right.
Phone wires were often buried and galvanic action would corrode the copper away if the voltage was positive. Reverse the voltage and metals might accumulate at the joint but won't harm it.
Polarity of the solid state devices that are being used. The most basic answer is that this is the way it was designed because the designers wanted it that way. It also makes things difficult for "hackers" to use their own equipment versus what is being provided by the system suppliers. One voltage is as good as the other, it's just that -48 volt equipment is a bit more difficult to come by than +24 volt equipment.
The difference is the Polarity of the solid state contraptions that are being exercised. The most simple response is that this is the way it was created since engineers are mostly idiotic nerds. It's harder to find these but the currents are much more sharp and poignant towards their direct radial usage. In case you aren't following, -48's are excellent for Stage 1-12 rating electrical jobs, but if you want something a little more simplistic a +24v can work for stage 12-15 jobs if you make sure the surge charger has enough juice to carry the current for a decent time period.
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