transformers are smaller/cheaper at higher frequencies for one thing.
I would like to see higher voltages here in the US if we could start over. the 120/208 system is just on the lame side of things and has always bugged me a bit, a good 50% higher would improve efficiency and wire size a lot. I think utilizing ungrounded systems like a lot of the rest of the world does would greatly reduce shocks and make an increased voltage system safer. I have gotten probably hundreds of 120v shocks in my career but only maybe line to line shocks. There is the issue of the first fault though and Im not sure how those ungrounded folks deal with that in a residential setting?
Ok, that makes sense, but my understanding is capacitive inductive currents go up the higher the frequency?
IMO a line to line 240 volts system should be implemented in residential and light commercial while 240/415Y is reserved for larger applications. This would be a win-win combination. Both systems cover the same 240 volt loads while 415 volts covers big motors in industrial.
I would avoid a totally ungrounded system as arcing faults to ground would cause over voltages.
I would either go with a solidly earthed system or a high resistance ground where a resistor is sized to allow at least 20% more current over the normal capacitive to ground reactance preventing over voltages above 173% during a fault. This would also allow a GFI to trip if capacitive currents were not enough (like a small pole pig feeding one small home).
Employing GFIs on all circuits would enhance safety preventing a high resistance grounded system from having a perpetual ground fault.
From what I have heard about the situation in Scandanavia, the first fault is simply never dealt with. Any maintenance waits for the second fault to force the issue.
If I am recalling the statistics correctly something like 40% of the residential services (each on its own transformer) had a long term ground fault somewhere.
Norway screwed up what was supposed to be something elegant, an IT (unearthed neutral) system:
1. Older homes did not have RCDs, so a ground fault would remain unnoticed. A fault somewhere else would blow one or both fuses. Often changing the fuse would cause another circuit to blow, and then changing that circuit would cause the first circuit to blow... a dog chasing its tail. Good luck if the other fault is in a different building. The result is most IT systems inadvertently becoming TNs for decades at a time.
2. The grounding systems were not interconnected between homes. Worked well... until Phase A would fault to ground in one home, and then phase B would fault to ground in another home. The result was 230 volts between 2 homes, energizing both grounding systems to dangerous potentials.
This condition is believed to be responsible for many electrical fires in Norway.
What Norway should have done was started off with a 3x230 volt solidly grounded system having a ground wire delivered to each home. This would provide a low impedance path to clear the first fault in addition to preventing grounding systems from turning at opposing potentials.
As RCDs are quickly being fitted in existing installations the solid ground would be converted into a high resistance ground at the transformer. That way the benefits of an IT system while the RCDs prevent it from becoming a long term TN.
Of course, someone outsmarted themselves:happysad:
From what little I know of overseas wiring a lot of places use some form of low-current ground fault detection on the entire residence.
Many places in Europe apparently also have strict requirements that house wiring must undergo routine insulation-resistance tests, so this would help remove some of the ground-fault risk.
While all my experience is on ungrounded industrial and utility systems, I know that those do nothing to ameliorate the risk of electrocution due to cumulative leakage and capacitive coupling. It's possible on very small, routinely meggered house systems having them ungrounded might reduce the shock hazard, but that's a big "might."
In over seas wiring RCDs are mandatory in most circuits as well as insulation resistance testing of new and upgraded circuits. The standards in the EU are very strict with most electricians caring a multi function megger. If a circuit doesn't megger high enough, then it must be corrected before energizing.
I would never bother designing a system having leakage currents so small where it would be impossible to receive harm as every room would need an isolation transformer. However, having a high resistance ground with GFP on all circuits greatly enhances safety and reduces the incident energy at a fault.
Keeping the voltage below 150 volts to ground in residential and light commercial while having 240 volts at all utilization equipment would be the most optimal. A 3 phase 3 wire system fed by a 139/240Y transformer would not be a bad implementation.
