UF Cable to Dock has Fault

[mkgrady]

Customer reports he has a DB cable run to a boat dock and the GFI that feeds it is tripping. The run is over 100 feet across a well kept lawn. I suspect it is not buried deep enough and landscapers may have cut into it during lawn edging. If that is the case I will recommend he run a new cable and bury it 24 inches or run PVC and bury it 18 inches.

If I am wrong, and it is buried deep enough, is there a way to find the fault? I am familiar with thumpers but I would not use that on 600 volt cable.

 

[nakulak]

TDR /cable fault locater

 

[480sparky]

Progressive (now Tempo Electronics) 2003.

 

[aline]

I used this....

Amprobe AT-2005

to find this short circuit in an underground feed.

located here. The breaker would trip when the ground was saturated with water.

I traced the wire from both ends to make sure of the location before I dug it up.

 

[480sparky]

I used this....

.................

I traced the wire from both ends to make sure of the location before I dug it up.

I get the distinct feeling this question should be in the FAQs.

 

[Pierre C Belarge]

Is the GFCI a circuit breaker or a device located out towards the dock?

If it is a circuit breaker, that is a long run for a GFCI CBer to supply, which may cause tripping. Once the fault is found, I would suggest the GFCI protection be relocated closer to the load.

 

[ultramegabob]

I would megger the cable first

 

[mcclary's electrical]

megger the cable at 1000 volts,,,,if it's ok, replace the GFI breaker at feeed with regular breaker. Then install GFI's at end of run.

 

[surf more]

I used this....

Amprobe AT-2005

to find this short circuit in an underground feed.

located here. The breaker would trip when the ground was saturated with water.

I traced the wire from both ends to make sure of the location before I dug it up.

went service call the other day and i encountererd the same problem--fountain outside plugged in to gfci----
it would trip breaker(afci)only when ground was saturated also..
wish i had your tool then,but i got lucky-- crappy install--someone layed uf on top of ground and then landscapers put grass on top of it.....
DANGER----i gotta get me one of them

 

[GUNNING]

That looks like its been spliced before! What kind of megger do you suggest?

 

[ultramegabob]

What kind of megger do you suggest?

I have a cheapie that I bought on ebay, I think I payed about 40 bucks for it, I dont know what brand it is, it came in a plain white box....

 

[mkgrady]

I get the distinct feeling this question should be in the FAQs.

Why?

Is the GFCI a circuit breaker or a device located out towards the dock?

If it is a circuit breaker, that is a long run for a GFCI CBer to supply, which may cause tripping. Once the fault is found, I would suggest the GFCI protection be relocated closer to the load.

I assume I could do that if the cable is buried deep enough (24" UF or 18" in conduit)

I would megger the cable first

I bought my megger a year ago and hope to get to use it.

megger the cable at 1000 volts,,,,if it's ok, replace the GFI breaker at feeed with regular breaker. Then install GFI's at end of run.

I didn't know distance was an issue. I'll try that.

Thanks to all that responded.

 

[bradleyelectric]

Originally Posted by 480sparky
I get the distinct feeling this question should be in the FAQs.

Why?

It comes up about every other month.

 

[TOOL_5150]

megger the cable at 1000 volts,,,,if it's ok, replace the GFI breaker at feeed with regular breaker. Then install GFI's at end of run.

I dont believe you should meg a 600V cable at 1000V.

~Matt

 

[quogueelectric]

One more cheerleader rant for the amprobe 2005!!

 

[mcclary's electrical]

You HAVE to meg 600 volt cable at 1000 volts,,,,,you won't prove anything at 500,,,,,,you might as well use a multimter set on "beep"

 

[Pierre C Belarge]

I agree that changing out the GFCI breaker is upon the fact that the cable is buried deep enough as per Table 300.5

The industry standard is to meg 600V cables at 500v.
Try NETA's website or Megger.com, for more info.


The leakage current of just about any insulation type may cause tripping of the GFCI CBer when the conductor lengths start reaching approximately 100ft.

 

[mkgrady]

Today I found two circuits feeding the dock. The panel that feeds the circuits is over 100 feet away.

One 20 amp cb is dedicated to one duplex gfi receptacle at the dock. The gfi was tripped. It had two LV lighting transformers plugged in under an in-use cover. The only line voltage down stream of the gfi was inside the receptacle box, the short cords to the transformers and some minimal line voltage controls for the lighting within the transformer enclosure and the primary of the transformer. I reset the gfi receptacle and the lights came on. I'm wondering what could have tripped the gfi. I'm assumming everything on the low side of the transf will not affect the gfi. Maybe it is the splices in his cords but they were taped up pretty good.

The other circuit is fed by a 20 amp gfi circuit breaker. Because it feeds the end of the dock it is more like 200 feet long. It runs directly to a 30 amp 3R disconnect. The disconnect feeds a switch to a flood light and a 30 amp 125 volt twist lock receptacle. I assume to plug in a boat. The gfi cb was tripped. The green wire was cut and not connected to anything. All the metal enclosures were ungrounded! Of course I'll reconnect the ground wire and meg the wires to see if the feed to the dock is bad. I'm wondering why this particular feed even has gfi protection. Does it need it? If it does I could put a gfi receptacle just before the disconnect and eliminate false tripping??

 

[mcclary's electrical]

Idustry standard to meg 600 volt cable at 500 volts??? YOU ARE WRONG, WRONG, WRONG, WRONG, WRONG!!! When's the last time you used a megger? If you're not going to meg at 1000vdc, You might as well use dmm set on "beep"

 

[mcclary's electrical]

anybody care to back me up on this?