Tripping Breaker - Long electric lines 1

[RememberTheAlamo]

Hi,

Have temporary 20 amp AC circuit serving no more than 700 watts of DC transformers for Fiber Optics modems. The breaker is in the center of a 3,000 ft line of #8 and #10 wire. 200 watts are at one end 1,600 ft away and 500 watts are on the other end 1,400 ft away.

Facts
-----
(1) Cable is buried in conduit
(2) All receptacles show 120+ volts
(3) Either side will run solo . . . no problem
(4) Throws 20 amp circuit breaker in box when both are attached (after about 15 minutes)
(5) All GFCI receptacles
(6) Circuit breaker sits 10 ft from 1000 AMP transformer
(7) Only panel on 1000 Amp transformer
(8) Only circuit in 200 AMP panel
(9) Both sides have 10 amp power strips which don't throw

700 watts draws far less than 20 amps so, what else could be load related that would throw the breaker? Voltage drop due to the line lengths? Does the circuit breake understand voltage drop?

Any ideas?

Thank you!

Larry

 

[waross]

If you are using a GFI breaker then the vector combination of resistance leakage to ground and capacitance current to ground may be close to the tripping point of the GFI rating of the breaker.
If you are in North America the ground current trip of the breaker is probably about 15 milli-Amps. If you are very close to tripping, a small voltage surge on the supply line may be enough to cause tripping. Leakage currents may increase over time.
Buy a second breaker. It sounds as if there is lots of room for it.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[RememberTheAlamo]

Hi Waross,

Excellent tip . . . yes, am using a GFI breaker . . . didn't realize the ground fault was as little as 15 milli-Amps . . . have seen small voltage surges during voltage tests . . . power company said the variations were related to having so much amperage so close and using so little . . . didn't think about the related ground-fault potential when I approved it.

Yes . . . will add another 20 AMP circuit and separate the two lines.

Was worried that I might actually be using 20+ amps due to unintended resistance somewhere in the long runs.

The usage is temporary while we construct the ranch . . . VOIP, internet, surveillance.

Appreciate the help!

 

[waross]

Thank you for the feedback.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

No, I think Bill is all wet on this one.

I think you have installed your U-Ground receptacles upside down with the open end of the U facing down, and all the electrons are leaking out all over the floor, causing the GFI to trip when it hears them scream.

Bad: If the ground slot makes the receptacle look like a frowny face, the electrons leak out.

Good: The ground slot "U" is up and thus retaining the errant electrons!

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[PHovnanian]

Replace the GFI breaker with a standard 20A thermal only type. You have GFCI receptacles at the load ends.

 

[RememberTheAlamo]

Hi PHovanian,

Thank you! . . . electrician is on his way this afternoon to add a standard 20A breaker and we will plug the longer underground line into that. We do have single GFCI recaptacles every 250 feet.

Realised last night that the long underground line parallels the deeper high voltage line bringing power into the ranch (8 ft apart?) . . . makes ripe conditions for inducing the low amperage ground fault which it would appear we have.

Thanks again!

 

[waross]

LOL Jeff. Actually the electrons leak out either way, but in the wrong configuration they leak right on to the U-ground terminal.
grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[RememberTheAlamo]

Hi All,

Closure . . . placed a regular (non-GFC breaker in the box) . . . and turned it all on . .. works great . . .2.8 amps of current flow, under load . . . precisely as designed . . . no evidence, measurable, of current flowing through the ground.

Thank you!

Larry

 

[TheBlacksmith]

In all seriousness, I saw some code (state or laboratory) that the ground lug had to be on top. The explanation was twofold, that since the ground prong is longer, it was easier to see to insert it and guide the plug into the receptacle and if the plug was not fully seated and a conductive material fell on the plug, it would contact the ground prong and not a blade at potential.

 

[waross]

In the Canadian Electrical Code, Section 72 -- Mobile home and recreational vehicle parks.
Rule 72.110, Sub rule (3) Receptacles, when mounted in other than a horizontal plane, shall be oriented so that the U-ground slot is uppermost.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[PHovnanian]

Receptacles, when mounted in other than a horizontal plane,

Wouldn't a vertical plane be called a rocket? ;-)