combination of TT&TN grounding system
- Thread starter zyhml
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bphgravity
Senior Member
- Location
- Florida
Get yourself the book,
"Overcurrents and Undercurrents", by Earl Roberts.
He discusses utility grounding configurations in great detail.
"Overcurrents and Undercurrents", by Earl Roberts.
He discusses utility grounding configurations in great detail.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Those designations are mostly european. If you were to google them, you would get a tremendous amount of info to sort through.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
Depending on what you mean by 'combining'. It only really makes sense if you have a TN-something supply and then add a TT distribution leg. As the fault current path is of unknown (and probably quite high) resistance, RCDs are mandatory.
I can't comment on how NEC compliant this would be, but in Europe it would generally be a permissible configuration.
There are disadvantages to this system, mostly around people not understanding it. Once you get past that, it's not inherently unsafe. The issue is that as fault current is limited by ground resistance a short circuit will never blow a breaker or fuse, so RCDs are needed. Mandatory, like I said above.
The only useful application of this system I advocate is when you have a temporary marquee or metal structure in a field being fed with power from a distant location with a "normal" grounded supply. If you take a feed out to the temporary structure using the normal ground arrangement, you end up with a potential gradient, leading to stray currents, and people can get tingles when touch the grounded structure elements whilst standing in bare feet in the wet grass. You know, the "stray current" thing. If you run the temporary feed as TT, with no earth wire, and just poke a rod in the ground next to the temporary structure, then you get no stray currents to tingle people. Sometimes, TT rocks.
I can't comment on how NEC compliant this would be, but in Europe it would generally be a permissible configuration.
There are disadvantages to this system, mostly around people not understanding it. Once you get past that, it's not inherently unsafe. The issue is that as fault current is limited by ground resistance a short circuit will never blow a breaker or fuse, so RCDs are needed. Mandatory, like I said above.
The only useful application of this system I advocate is when you have a temporary marquee or metal structure in a field being fed with power from a distant location with a "normal" grounded supply. If you take a feed out to the temporary structure using the normal ground arrangement, you end up with a potential gradient, leading to stray currents, and people can get tingles when touch the grounded structure elements whilst standing in bare feet in the wet grass. You know, the "stray current" thing. If you run the temporary feed as TT, with no earth wire, and just poke a rod in the ground next to the temporary structure, then you get no stray currents to tingle people. Sometimes, TT rocks.
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