ptonsparky
Tom
- Occupation
- EC - retired
How does the presence or lack of an EG affect the values of a L-L short circuit?
Extreme distance voltage drops
- Thread starter teh_engineer
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ptonsparky
Tom
- Occupation
- EC - retired
What I have, My VD spreadsheet is what I use. It works for real life situations that I am exposed to.
ptonsparky
Tom
- Occupation
- EC - retired
Utility Fault current above 1000 becomes less significant on L-L and L-N fault currents. I chose 4 Al because that should be available in a cablecon configuration. It allows for adequate voltage to operate a 1KW load @ 480v. I don't care what the voltage drops to on a SC as long as enough current flows to open the 20 amp fuses at my disconnect 6500 feet away.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
The only downsides are that some time later, another person checks and says "Why so low?", investigates, and curses the original installer for doing such a bad job; or that the client wants to install a specific voltage device and doesn't understand why they can't or they need to add an extra device to get the right voltage.
If nothing else, there needs to be some good documentation at the far end describing how it's being fed.
If nothing else, there needs to be some good documentation at the far end describing how it's being fed.
ptonsparky
Tom
- Occupation
- EC - retired
I put a new service on a building 35 years ago. Less than a 1000 amp, 120/208. About 10 years ago the building had a complete remodel, switched to all electric and added several large drive through lumber storage buildings. In excess of 1000 amp 277/480. The owner wanted to know why we didn't put in a large enough service previously. Hmmm.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
ptonsparky
Tom
- Occupation
- EC - retired
Good. We agree.
mbrooke
Batteries Included
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- United States
- Occupation
- Technician
But I hope that we can agree the bigger issue rests in a low impedance path, and not voltage drop. There are installations out there that get by on voltage drop, but will never trip an OCPD. I wish Mike Holt would do a video on the subject. And note that the CMP knows about this issue, but instead of limiting how far any one branch circuit may travel- they are gradually mandating GFCIs, SGFP AFCIs, and other means which will do little in the long run except secure $$$$ for the manufacturers.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I would revise tortuga's statement to say that if you were to design your circuit to function with a 20-30% voltage drop, you would need to use non-standard ($$$$) OCPD for proper function.
There is always a way...but reducing voltage drop is probably the simplest.
-Jon
There is always a way...but reducing voltage drop is probably the simplest.
-Jon
ptonsparky
Tom
- Occupation
- EC - retired
Why won't it? My Fault current calculator indicates 50 amps will flow at 6500 feet. That is more than enough to open a 20 amp fuse. At that distance how fast does it need to open on a short circuit? Nothing will be damaged by the 50 amps. The damage was already done when the SC occured. Granted I did use line to line and not L-EG.. That will take a longer depending on the fuse type but still no damage done
ptonsparky
Tom
- Occupation
- EC - retired
Aren't fuses standard?
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Railroads have many signals and shacks were there is no commercial power, typically some kind of propane, so that may be an option
Also there are some good options on fuel cells, and that technology is mature, can integrate with solar. I looked into fuel cells there are some systems in a box, so to speak.
Also there are some good options on fuel cells, and that technology is mature, can integrate with solar. I looked into fuel cells there are some systems in a box, so to speak.
This is just academic discussion at this point with the 6500 FT and 1kw load as givens.
ohh right I did not look at a 20A breaker I was figuring a 60 I think.
It still would be interesting to look into the trip time/current curve of say a Siemens or Eaton bolt on 480V breaker.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
It would be a much slower trip than usually expected for a short circuit, and something other than a solid fault might not trip.
-Jon
ptonsparky
Tom
- Occupation
- EC - retired
I looked at various curves for fuses. Range from well ok they will work to the water in the conduit won’t freeze.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Perhaps this?
Redirect Notice
www.google.com
Typically 0.4 seconds for over 120 volts to ground, 0.8 seconds 120 and under.
ptonsparky
Tom
- Occupation
- EC - retired
Well other than that guy with a bad heart...or soon to have one, if it’s a L-EG fault.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Or a child... people have died from this. But you'd be surprised the lawyers can't find anything...
ptonsparky
Tom
- Occupation
- EC - retired
We do see it often enough with a smaller voltage ranges and generally with animals involved. I‘ve told the story before about the farmers wife being shocked at the sink in their small dairy. Neutral VD. The fix was going to be expensive but once he found out the cows were not being bothered, he dropped the project.
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