Extreme distance voltage drops

ptonsparky

Senior Member
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
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.
 

ptonsparky

Senior Member
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.
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

Senior Member
Good. We agree.

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.
 

tortuga

Senior Member
I'd be curious to know if the equipment being fed is all multi-voltage capable. Sometimes these types of equipment can be fed any 50-60HZ voltage between 120 and 277 with no ill effects. Voltage drop is a FPN in the code anyway...so 5% is not a hard requirement....just a suggestion. So if the load is, say, all electronic equipment and LED lighting with the multi-volt type power requirements...then a 20-30% drop may still get the job done. Am I missing something here?
No, you’re not.
20-30% drop would violate 110.10 as the OCPD would not function.
 

winnie

Senior Member
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
 

ptonsparky

Senior Member
20-30% drop would violate 110.10 as the OCPD would not function.
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

Senior Member
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
Aren't fuses standard?
 

tom baker

First Chief Moderator
Staff member
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.
 

tortuga

Senior Member
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.
This is just academic discussion at this point with the 6500 FT and 1kw load as givens.
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
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.
 

ptonsparky

Senior Member
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.
I looked at various curves for fuses. Range from well ok they will work to the water in the conduit won’t freeze.
 

mbrooke

Senior Member
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

Perhaps this?



1585357237637.png


1585357295313.png


Typically 0.4 seconds for over 120 volts to ground, 0.8 seconds 120 and under.
 

ptonsparky

Senior Member
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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