Objectional Current in Grounding Conductors.

[pattbaa]

What effect or "symptom" would reveal the existence of Grounding Conductors conducting a "Objectional Current"?

 

[xformer]

What effect or "symptom" would reveal the existence of Grounding Conductors conducting a "Objectional Current"?

IMHO... A OCPD that activates below its rated current could be a symptom. Then depending on the objectionable current level, GFCI nuisance tripping.

 

[__dan]

Put a current clamp on the EGC. If you get a reading, it's objectionable (imo).

However, it may be something that is to be avoided but not necessarily fixed. Depends on if you understand what is happening and if you can avoid it or fix it.

If you want to share the details of your instance, it may get looked at.

 

[petersonra]

Any current on an EGC at all is "objectionable" IMO. But, sometimes it is also unavoidable.

 

[Smart $]

Any current on an EGC at all is "objectionable" IMO. But, sometimes it is also unavoidable.

The would be no point to installing any EGC if it were "any" current. :happyyes:

If we consider the simple definition of objectionable as undesired, fault current is desired... so not objectionable. Some other currents may be unavoidable, simply because grounding methods typically result in multiple parallel paths and to conducting means outside the directly associated electrical system. Currents could originate (and return) to a completely separate electrical system and be undesired.

 

[jap]

fault current is desired... so not objectionable.

There have been a few Fault Currents I've witnessed, that have been very undesirable....

 

[Smart $]

There have been a few Fault Currents I've witnessed, that have been very undesirable....

I said fault current on an EGC is not objectionable...

I didn't say [or mean to imply] the fault current or fault itself was desirable. :happyno:

 

[al hildenbrand]

What effect or "symptom" would reveal the existence of Grounding Conductors conducting a "Objectional Current"?

I have never heard or read anything that pins this down. The reason it is so hard to quantify, in my opinion, is that the power company grounded service conductor is tied to a grounding electrode system along with the equipment grounding conductor. Also, many power companies connect their primary distribution system grounded conductor straight through to customer grounded service conductor. Also, many occupancies are supplied potable water by a common conductive piping system that is bonded to the grounding electrode system.

All that is a web of parallel paths for any unbalance currents either from the occupant's loads, or from the connected neighbor's loads or from the power company's primary distribution network.

NOW, considering your question and a single equipment grounding conductor (EGC) of a branch circuit. . . if your single branch circuit EGC is not incidentally re-grounded downstream from where you are observing . . .good. There should be no current on the EGC and any might well be objectionable, with the exception of things like switches and other electronics that deliberately use the EGC as if it were a neutral (with UL's blessing).

BUT, if the single EGC of your branch circuit is incidentally in contact with grounded conductive surfaces, the EGC itself becomes another parallel path for the unbalance currents. . . These currents are "intended" by the required main bonding jumper and the grounded service conductor's connection to the grounding electrode system.

What is "objectionable" gets real hard to pin down. . .

 

[david]

Objectionable Current: any current other than fault current on conductive surfaces or conductors not designed to be part of the normal circuit

 

[al hildenbrand]

Objectionable Current: any current other than fault current on conductive surfaces or conductors not designed to be part of the normal circuit

So, when I run a 14/2 NMB to a residential forced air furnace, a furnace with metal ductwork and a metallic gas piping system, a furnace that is incidentally connected to building steel by the ductwork, building steel that is in contact with earth through its footings, the unbalance currents that are likely to be present on the 14/2 EGC, once they get into the metal of the furnace are "objectionable"?

 

[david]

So, when I run a 14/2 NMB to a residential forced air furnace, a furnace with metal ductwork and a metallic gas piping system, a furnace that is incidentally connected to building steel by the ductwork, building steel that is in contact with earth through its footings, the unbalance currents that are likely to be present on the 14/2 EGC, once they get into the metal of the furnace are "objectionable"?

some objectionable currents can not be avoided. But the thrust of the rule is to take corrective action to remove the objectionable current.

 

[al hildenbrand]

some objectionable currents can not be avoided. But the thrust of the rule is to take corrective action to remove the objectionable current.

OK. My point, I guess, is that some objectionable current is not objectionable and some objectionable current is objectionable. . . Your definition seems to exclude current on the equipment grounding conductor. That, in part, answers the OP, maybe. . .

How are we to determine what objectionable current can not be avoided? I could avoid it with increasing amounts of money.

 

[david]

OK. My point, I guess, is that some objectionable current is not objectionable and some objectionable current is objectionable. . . Your definition seems to exclude current on the equipment grounding conductor. That, in part, answers the OP, maybe. . .

How are we to determine what objectionable current can not be avoided? I could avoid it with increasing amounts of money.

For me when I am looking at electrical plans and the design calls for the utility transformer to have equipment grounds land on the utility XO and the service equipment. I consider that an objectionable current path that can be removed. And when portable generators are designed as separate derived systems and the neutral is not transferred a consider that an objectionable current path. In both of these I think corrective action should be taken to avoid creating a path for objectionable current

 

[__dan]

If you're running an EGC, you are required to provide an effective fault current clearing path back to the source breaker. You have no or limited choice of the path or method. Intercepting an existing circulating ground loop current that reads on your current clamp, the current is objectionable and unavoidable. It would be the owner's discretion and owner's money as to your spending more time studying and planning what to do. Doing nothing may meet code as you may not be able to change the EGC materials or methods.

If you are running a GEC to the grounding electrode, the earth is a giant low impedance busbar that provides a zero voltage reference point in a manner that all points on the earth are equal. Effectively you have your choice of many paths and methods to connect to the earth. IMO, 250.6 would require you to connect to the earth in a manner that avoids existing circulating ground loop currents. You are bringing a clean zero voltage (zero current) earth reference to the system bonding jumper, effectively giving you the opportunity to clean up noisy grounds and neutrals that may exist elsewhere in the facility. If you fail in this, 250.6 would apply.

 

[kwired]

For me when I am looking at electrical plans and the design calls for the utility transformer to have equipment grounds land on the utility XO and the service equipment. I consider that an objectionable current path that can be removed.

Please enlighten us more on what you are getting at here.

Though the EGC's of branch circuits and feeders typically "end" at the service disconnecting means, they are still bonded to the grounded service conductor and ultimately the goal is to have as low of impedance possible back to the X0 terminal of the transformer to allow high level of current during a ground fault to help insure the overcurrent device opens rapidly during such fault events. No connection or a higher impedance to the X0 terminal is counterproductive to that goal.

 

[david]

Please enlighten us more on what you are getting at here.

Though the EGC's of branch circuits and feeders typically "end" at the service disconnecting means, they are still bonded to the grounded service conductor and ultimately the goal is to have as low of impedance possible back to the X0 terminal of the transformer to allow high level of current during a ground fault to help insure the overcurrent device opens rapidly during such fault events. No connection or a higher impedance to the X0 terminal is counterproductive to that goal.

the neutral passes through the CT cabinet with a main bonding jumper bonding the metal CT cabinet enclosure The equipment grounds originating at the utility company XO land directly to the Ct cabinet enclosure and from their both the neutral(s) and the equipment ground(s) continue on to the service. Am I wrong that current would be found between the larger neutral conductors and the smaller equipment grounds by way of the main bonding jumper and the metal Ct cabinet. I would consider any current on that path as objectionable.

Be sides you may as well call the equipment grounds neutrals when they originate at the XO of the utility transformer when the neutral and the equipment grounds bond together at both the xo and the service enclosure.. In my opinion the circuit current flowing on the equipment grounds as described above during normal conditions is objectionable

 

[al hildenbrand]

the neutral passes through the CT cabinet with a main bonding jumper bonding the metal CT cabinet enclosure The equipment grounds originating at the utility company XO land directly to the Ct cabinet enclosure and from their both the neutral(s) and the equipment ground(s) continue on to the service. Am I wrong that current would be found between the larger neutral conductors and the smaller equipment grounds by way of the main bonding jumper and the metal Ct cabinet. I would consider any current on that path as objectionable.

Be sides you may as well call the equipment grounds neutrals when they originate at the XO of the utility transformer when the neutral and the equipment grounds bond together at both the xo and the service enclosure.. In my opinion the circuit current flowing on the equipment grounds as described above during normal conditions is objectionable

Your experience is interesting to me. What you describe, in your posts in this thread, causes me to believe you are talking about, only, certain Premises Wiring (System) connections to the electric power utility either AT or on the utility side of the Service Point. I suspect that each specific XO, you are thinking of, with respect to "objectionable current," that you have authority over, is a small group of all of the electric power utility transformers within your jurisdiction.

Can you exert the same control over the utility transformer XO for a grouping of customers connected overhead to a single transformer (120 / 240 single phase) where, because of the distances between buildings, there is utility owned spans of 120 / 240 Volt secondary between several utility owned poles? Let's say there is SINGLE overhead utility primary wire running across the top of all the poles, and this is the source for the single, wye-connected transformer supply to this grouping of customers.

I am not describing an overhead Single Wire Earth Return electric power utility primary distribution to this transformer. The low side of the wye will be bonded to earth at the base of the pole, along with bonding to the transformer can and XO, and along with bonding to the overhead secondary side 120 / 240 Volt grounded conductor which is generally continuous and connected to other groupings of customers connected to other overhead transformers and, ultimately, connected back to the electric power utility substation and yet another transformer. I believe this to be a rather common urban situation. Mix into this scenario, a municipal domestic water system delivered in conductive metal piping to all the customers connected to this one overhead transformer. -------------- The end result --------------- Many parallel paths for unbalance currents from both the customer loads and from the electric power utility primary distribution unbalance. Lets say that most of the homes in this one grouping of customers have fan forced hot air furnaces, each served with a 15 Amp 120 Volt NM-B branch circuit, and the HVAC systems have metal ductwork and are supplied by metal gas piping systems. All the HVAC systems are incidentally connected to Earth and the EGC in the furnace branch circuit is not the sole conductive path to Earth.

Changing the wiring at the overhead transformer XO for this group of customers will affect the "objectionable current".

 

[kwired]

the neutral passes through the CT cabinet with a main bonding jumper bonding the metal CT cabinet enclosure The equipment grounds originating at the utility company XO land directly to the Ct cabinet enclosure and from their both the neutral(s) and the equipment ground(s) continue on to the service. Am I wrong that current would be found between the larger neutral conductors and the smaller equipment grounds by way of the main bonding jumper and the metal Ct cabinet. I would consider any current on that path as objectionable.

Be sides you may as well call the equipment grounds neutrals when they originate at the XO of the utility transformer when the neutral and the equipment grounds bond together at both the xo and the service enclosure.. In my opinion the circuit current flowing on the equipment grounds as described above during normal conditions is objectionable

If the EGC's in question are connected to both the service equipment grounded conductor either directly or via a bonding jumper as well as in the CT cabinet I agree with you, you basically have a parallel neutral conductor here.

If there is no bonding jumper in the service disconnecting means or any upstream service enclosures, you will not have objectionable current on the EGC's, but may have other violations regarding the grounding and bonding. As a general rule there must be a bonding jumper at the service disconnect, I did not look to see what exceptions there may be to that rule, but if there are any exceptions to that they would have to be fairly limited.

 

[david]

If there is no bonding jumper in the service disconnecting means or any upstream service enclosures, you will not have objectionable current on the EGC's, but may have other violations regarding the grounding and bonding. As a general rule there must be a bonding jumper at the service disconnect, I did not look to see what exceptions there may be to that rule, but if there are any exceptions to that they would have to be fairly limited.

This comes up when these are pad mount transformers, the utility owned transformer has the XO bonded by the utility to the enclosure as you know. Connections on the customer side are customer owned. The design calls for neutral (s) and equipment ground(s) to originate in the pad mount transformer bonded through a main bonding jumper, pass through a CT cabinet (costumer owned), to the service disconnect, neutral grounded and bonded article 250.

Besides 310.4 Conductors in Parallel violations, if you consider the neutral and grounds parallel conductors since they are bonded together at both ends and at the Ct cabinet.

I was discussing objectionable current paths this creates and can be eliminated by removing the equipment grounds originating in the pad mount transformer

 

[Smart $]

This comes up when these are pad mount transformers, the utility owned transformer has the XO bonded by the utility to the enclosure as you know. Connections on the customer side are customer owned. The design calls for neutral (s) and equipment ground(s) to originate in the pad mount transformer bonded through a main bonding jumper, pass through a CT cabinet (costumer owned), to the service disconnect, neutral grounded and bonded article 250.

Besides 310.4 Conductors in Parallel violations, if you consider the neutral and grounds parallel conductors since they are bonded together at both ends and at the Ct cabinet.

I was discussing objectionable current paths this creates and can be eliminated by removing the equipment grounds originating in the pad mount transformer

A grounding conductor is not required between a service transformer and the service disconnecting means of a grounded system, regardless of who owns the transformer. Non-current-carrying metal parts must be bonded to the grounded conductor.

That said, what usually establishes a path for [objectionable] system current on or through non-current-carrying metal parts on a grounded-system service is electrically continuous metallic raceway.