Stray current on grounding systems

[TEC1991]

I have a multiple-part question.

1. How much stray current is acceptable before saftey becomes a concern?
2. At what level does stray current begin to degrade the grounding system?
3. Are there any public documents or papers that elaborate on the topic of stray current and grounding systems?

Thank you.

 

[djd]

djd

djd

stray current, yes is a problem, how much wheres the current, there is a problem to equipment, potetial fire, and maybe blackened bolts

 

[don_resqcapt19]

As long as we have grounded systems there will be "stray" current on the grounding system. The use of a grounded system creates parallel paths and current will travel on all available paths. There is no way around this. The only thing that limits the stray current on the grounding paths is the relative impedance of the paths with the most current on the lowest impedance path and the least on the highest impedance path.
In areas with a common underground metal water piping system it is not uncommon to find 20% or more of the total grounded conductor current flowing on the water piping system.

 

[dereckbc]

1 & 2. There is no specific answer to your question. As Don explained it is normal in any grounded system. Now with that said there are non compliance issues that will cause excessive current on equipment bonding conductors most notable is bonding the grounded circuit conductor down stream from the MDJ at the service. So if you are seeing load currents on equipment ground conductors you need to find the source and correct it. However if you are referring to the GEC, some current will always be flowing on it. Excessive current on the GEC indicates your service grounded circuit conductor has trouble like a bad connection.

3. Yes IEEE 1100 and 142 are what many consider the Bible of grounding. At least i do as I am a contributor of 1100 chapter 9. :grin:

 

[hornetd]

Source of the stray current

Source of the stray current

Determining the source of the stray current can be very important. If the stray current is coming from the premise wiring system then the owner will have to have it cleared but if as sometimes happens, the stray current is from off premise and is actually causing harm you may be able to get the utility to clear the source. On stock farms such as dairies the utility sometimes installs special transformers to prevent the flow of Multi Grounded Neutral current over the farm's Equipment Grounding conductors on it's way back to the substations distribution transformers. If you can measure a substantial current on the Grounding Electrode Conductors or the main bonding jumper when the Service Disconnecting Means is open then the source of the stray current is off premise.

 

[brian john]

I have a multiple-part question.

1. How much stray current is acceptable before saftey becomes a concern?

depends on the size of the system and the source of the stray current.

2. At what level does stray current begin to degrade the grounding system?

At the point where it overloads the conductors or connections. But this does not mean it is causing other issues at lower levels.

3. Are there any public documents or papers that elaborate on the topic of stray current and grounding systems?

Thank you.

As many as you care to read, do a web search and search the IEEE, NETA, also any construction type bookstore.

 

[brian john]

Determining the source of the stray current can be very important. If the stray current is coming from the premise wiring system then the owner will have to have it cleared but if as sometimes happens,

This is not necessarily true, depends what is the source of the stray current leakage current is had to rid a system of. Neutrals grounded downstream a must to fix.