AC voltage IN THE BEGINNING

[just the cowboy]

high voltage

high voltage

We all deal with capacitance coupling but I never heard of it being capable of a fatal sock. can you give me a example of this in a home and a biasness and industrial please ?

I worked on med voltage 4160v and the wires would build up a cap charge and I saw someone get knocked on there _by it just touching a (disconnected on both ends) wire , so i bet higher voltage more shock more chance of fatal.

 

[Haji]

HRG?

For three phase loads and not for single phase loads.

 

[fmtjfw]

"Lightning strikes on ungrounded distribution lines have a much higher potential (pun intended) for destroying equipment than strikes on grounded distribution lines."

Why doesn't anyone combine the advantages of an ungrounded system with the improved lightning safety of a grounded one by doing the grounding through a gas discharge tube or other lightning arrestor, something normally open but which will snub an overvoltage to ground?

This done on some consumer-side systems on farms.

 

[kwired]

For three phase loads and not for single phase loads.

Single phase loads would work fine - if they operate from ungrounded to ungrounded lines, you can not operate line to neutral loads with the resistor in the neutral on such systems, well you can but they will not work as intended.

 

[Haji]

Single phase loads would work fine - if they operate from ungrounded to ungrounded lines, you can not operate line to neutral loads with the resistor in the neutral on such systems, well you can but they will not work as intended.

It is not a matter operation- both line to line and line to neutral loads would work fine. It is a matter of safety when line to neutral loads are in operation in a HRG system.

 

[winnie]

With conventional HRG systems, one of the design goals is continuity of service, and ground faults are not immediately interrupted. During fault conditions one of the 'line' conductors becomes the grounded conductor and the 'neutral' conductor voltage is increased to the L-N voltage. Clearly this is a safety issue if the conductor you expect to be grounded is at 277V! So I absolutely agree that L-N loads are a safety issue in HRG systems as presently implemented.

IMHO, If the system _interrupts_ current to the faulted circuit when a ground fault is detected, then an HRG system would be no more dangerous than a solidly grounded system during a fault. In a solidly grounded system, extremely high fault currents flow, which will cause transient changes in neutral-ground voltage. The system will interrupt this current flow (hopefully...) and the neutral-ground voltage will return to approximately zero. If the HRG system were similarly designed to interrupt immediately on fault, then the raised N-G voltage would be transient.

In addition, the safety issue results from the expectation that the neutral conductor will be at ground potential. If you treat all conductors as 'hot', with all of the OCPD and insulation requirements, circuit common trip requirements, etc., then IMHO serving L-N loads in an HRG system is as safe as serving L-L loads.

Finally, iceworm asked 'HRG?' This stands for 'High Resistance Ground', where you have a grounded source, but grounded via a resistance. In the event of a ground fault, current flow is limited by that resistance. You get the 'voltage reference' benefits of a solidly grounded system, but because current flow is limited, you also can have the 'run with a fault' benefit of an ungrounded system.

-Jon

 

[iceworm]

winnie - bless your soul (yep truth - not facetious. You always have interesting comments)

This is offered as peer group conversation - not meant in any way demeaning to your knowledge.

Concerning your posts 20 and 26: I can't always tell when you are refering to NEC HRG, or "The New American Safety Electrical System - according to the worm" - Or "TNASESattw", pronounced "cess" (The "T" is silent:roll for short.

Either way, you got most of it right. But you got some holes. May I gently suggest you read my post 15 (about cess) and post 18 (about NEC HRG)

And no, I did not ask "HRG?". It was, "So why HRG?" as a retorical question - and then answered it. There is more than continuity-of-service and voltage reference at stake.

(edit to add ...)

ice

 

[winnie]

Pardon me while I deliver myself a dope slap.

iceworm: I totally read your HRG? as 'What is this term HRG?', even though you used the term in a post that I was replying to. I plead exhaustion related to 4 small kids and packing to move

I'll try to be more clear in the future, but I am in general not referring to HRG systems as currently permitted by the NEC, but rather TNASESattw. (Like that phrase) For purpose of this thread I also am discussing what is possible in terms of alternate approaches to safety in customer power distribution.

-Jon