Ground Fault Issue

[Opie11]

480V 1phase circuit feeds 11 exterior locations. At each location is a hand hole with splices to feed an equipment box. The first component in the box is a breaker then on to a 480v to 120v step down transformer to the rest of the equipment in the box. At all 11 locations we opened the breaker. When we energized the circuit it popped the 400A breaker at the MDP. When reset, the 400A breaker stated a GF had occurred. There is @ 20 feet of EMT inside the building before this circuit goes outside into the ground routed through PVC pipe. Other than the EMT what would cause a ground fault to occur when all the loads are opened per their respective breaker? Full disclosure - all 11 hand holes are subject to filling up with water completely. 1 equipment box location had its bare ground wire severely corroded and the hand hole that fed it the bare wire was discolored red and broken in multiple places with approximately a 1 foot section of the ground rod having broken off.
Thanks.

 

[mtnelect]

Are these eleven location RXR crossings ?

 

[hillbilly1]

It could be anywhere, just because it’s in pvc conduit doesn’t mean it’s immune to ground faults. Fault can be between a phase and the egc in the same pipe. Time to break out the megger, and divide and conquer!

 

[Opie11]

Not RR crossings.

Where I am confused is isnt current needed for a ground fault?

 

[mtnelect]

Not RR crossings.

Where I am confused is isnt current needed for a ground fault?

Please describe more fully the type of structure.

 

[Opie11]

There is no structure per se. The equipment box houses a breaker, transformer, ups, convenience receptacle, a power supply, and a router. The total load calc for all 11 locations is less than 20A.

 

[Sea Nile]

Not RR crossings.

Where I am confused is isnt current needed for a ground fault?

What concerns me is all these splices and devices in hand holes that fill with water and the corrosion you mentioned. Looks like the elements have won. But I think what you are asking is why does it trip when all 11 are open? Are you saying that it doesn't trip when the 11 are closed?

 

[mtnelect]

There is no structure per se. The equipment box houses a breaker, transformer, ups, convenience receptacle, a power supply, and a router. The total load calc for all 11 locations is less than 20A.

Still, I don't know what type of structure you are talking about. Is it out in the field ?

 

[hillbilly1]

Not RR crossings.

Where I am confused is isnt current needed for a ground fault?

The feeder to those boxes would still be energized, even with their breakers off? The ground fault would be before them.

 

[Opie11]

Sea Nile - breakers open or closed trips a GF.
Mtnelect - each equipment box is for a camera. Yes, it's in the field.
Hillbilly1 - yes of course but there should be no load on the circuit if all the loads are de-energized by their local breaker and the circuit is working properly. Obviously it is not.

 

[Opie11]

That is my confusion, doesn't there need to be current for a GF event to occur? If all the loads on the circuit are open by their local breaker doesn't this potentially mean that something else is creating a load and hence the GF?

 

[mtnelect]

When you say "Hand Hole" to me that means a standard access for wiring connection/splicing.

 

[Sea Nile]

There is current. You are correct. One or more of the conductors have a break in the insulation allowing current to travel back to the source.

 

[hillbilly1]

Sea Nile - breakers open or closed trips a GF.
Mtnelect - each equipment box is for a camera. Yes, it's in the field.
Hillbilly1 - yes of course but there should be no load on the circuit if all the loads are de-energized by their local breaker and the circuit is working properly. Obviously it is not.

A ground fault does not need a load, it is a voltage that is faulting to ground through bad insulation.

 

[mtnelect]

When you mentioned water, then that is your problem.

 

[Opie11]

Mtnelect - correct. I believe I stated such in my original blurb.
Hillbilly1- so you are saying i do not need current for a GF?

 

[Sea Nile]

No one is saying that there is no current.

 

[mtnelect]

Mtnelect - correct. I believe I stated such in my original blurb.
Hillbilly1- so you are saying i do not need current for a GF?

A Ground Fault Circuit Interrupter (GFCI) has current coils that monitors the incoming and outgoing currents. When they don't match, the current is going elsewhere, so it trips.

 

[hillbilly1]

Mtnelect - correct. I believe I stated such in my original blurb.
Hillbilly1- so you are saying i do not need current for a GF?

The current is in the voltage leaking to ground! Example: you have a water hose connected to a sprayer, the sprayer is off (load) you put a hole in the hose, water comes out (current) because you still have the spigot on (main, or breaker for the feeder)

 

[Sea Nile]

Not trying to be .... Don't know the word for it. But if its been a while, this is a great refresher.