It's a really nice voltage with lots of support for batteries and up/dn conversion hardware.
It's also right at the edge of what is human safe. You can burn yourself and blow up cables, but it's very difficult to electrocute yourself (afib or muscle seize) without lots of wet contact.
Indeed, I'm aware of only one recorded death by electrocution at 48V, iirc it was a Swiss radio amateur that had done a bunch of gardening sat down sweaty in a metallic chair and reached for the one switch of his set. Probably there were other contributory causes as well, I've been zapped multiple times from much higher voltage sources (that could have easily supplied the power required) and lived.
I can't find a reference for that Swiss case though. I'll keep looking.
It is with respect to ground, the positive pole of the battery is connected to ground.
The telegraph system figured this out very quickly. Most water in nature has at least a bit of salt in it, which is present as positive sodium ions and negative chloride ions. By making the outdoor wiring negative with respect to ground, the chloride ions are repelled, and such wires corrode much more slowly than those that're positive with respect to ground.
Since most of the telegraph network, later the telephone network, is outdoors, this is a pretty big deal.
You tie one of the leads to earth (literally grounding it)[1], leaving the other non-grounded. Depending on if you tie the negative or the positive lead to ground, you get 48V or -48V with respect to ground. As long as the potential between the most positive lead and the least positive lead is 48V, the circuit itself doesn't care.
As mentioned here[2], the reason for grounding the positive lead is to prevent galvanic corrosion[3] destroying the buried copper.
Generally with respect to ground. There are many good reasons to connect your power system to ground and so this is commonly done. (there are pros and cons to connecting to ground, but it gets complex fast)
kurthr|2 years ago
It's also right at the edge of what is human safe. You can burn yourself and blow up cables, but it's very difficult to electrocute yourself (afib or muscle seize) without lots of wet contact.
https://incompliancemag.com/article/experiments-of-dc-human-...
jacquesm|2 years ago
I can't find a reference for that Swiss case though. I'll keep looking.
firebat45|2 years ago
myself248|2 years ago
The telegraph system figured this out very quickly. Most water in nature has at least a bit of salt in it, which is present as positive sodium ions and negative chloride ions. By making the outdoor wiring negative with respect to ground, the chloride ions are repelled, and such wires corrode much more slowly than those that're positive with respect to ground.
Since most of the telegraph network, later the telephone network, is outdoors, this is a pretty big deal.
magicalhippo|2 years ago
You tie one of the leads to earth (literally grounding it)[1], leaving the other non-grounded. Depending on if you tie the negative or the positive lead to ground, you get 48V or -48V with respect to ground. As long as the potential between the most positive lead and the least positive lead is 48V, the circuit itself doesn't care.
As mentioned here[2], the reason for grounding the positive lead is to prevent galvanic corrosion[3] destroying the buried copper.
[1]: https://www.bicsi.org/docs/default-source/conference-present...
[2]: https://www.poweringthenetwork.com/uncategorized/negative-48...
[3]: https://en.wikipedia.org/wiki/Galvanic_corrosion
applied_heat|2 years ago
I see this more often on European stuff
bluGill|2 years ago
bloggie|2 years ago
dragontamer|2 years ago
Voltages are all relative. It's like saying 'How do you get a height difference of 10 feet by digging?'
Well, you dig and then label the initial level as +10 feet, and redefine the bottom of your hole to be ground.