RV Park Bath House Shower Shock

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We have 2 bath houses in an existing RV park and there is a fluctuating voltage potential between the floor drain and the shower valve. We have measured from 4 volts to 12.5 and people were getting shocked. I am not very experienced with MV transformers and the ground methods. I am trying to clarify that the existing grounding and bonding methods are correct. Here is a summary of the installation. The main service is 4160V WYE system feeding multiple 2400V - 120/240V transformers connected to each phase. The conductor is 15kV rated direct burial with a concentric neutral. There is no grounding conductor ran between the transformers. Each transformer has the neutral on the primary bonded to the case, low voltage XO terminal and Ground rod. The transformers have internal distribution section with multiple OCDs feeding out to RV pedestals and bath houses. My question is should the primary neutral be bonded to the case and XO. It appears there is a defective neutral underground on the primary side and we have voltage traveling through the earth back to the source. If this neutral was not bonded to ground then there would not be a potential to earth correct? This transformer and bath house is at the end of the line. There is a EGC running to the bath house sub panel from the transformer, the EGC, neutral, cold water, bath house GRC all bonded at the bath sub panel. I believe this is incorrect and the neutral should not be bonded creating a parallel path back to the transformer. We have identified another problem from the same transformer, a 120/240V sub panel fed from this transformer, when disconnected at the CB the voltage potential falls to around 5 to 6 volts. This sub panel is direct burial fed with no EGC from the transformer and feeds multiple RV pedestals the neutral and Grounds from the RV pedestals are bonded together at the sub panel but isolated from the panel with a nice piece of wood. Each pedestal has its own ground rod. The pedestals GRC and EGC are isolated from the neutral. Last thing, when all OCDs at transformer distribution are shut off ther is still a 5 Volt potential in the shower. Also the under ground waste plumbing is ABS not cast iron. I can supply wiring diagrams and photos if necessary. I can provide more info but don't want to overload this post.

Thanks for any suggestions or recommendations.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Do spend too much time figuring out why there is a difference in potential from one point of "earth" to another. Just metallically bond the drain to water pipe first.
Once that is done you can go on to sticking two screwdrivers into the ground in different places and measuring the voltage difference. Actually, better to use one fixed screwdriver as remote as you can get it and one moveable probe.
A map of the voltage field should indicate where the related currents are flowing, and that will give you an idea of what needs to be done in terms of earth return versus metallic bond for MV and LV.
 
Thanks for your reply but bonding the drain to the water pipe may be a little difficult since it is in concrete and tile. This also would not repair the problem and a person would still be in parallel with the current. Depending on resistance, water and currents I don't know if just bonding the drain would be adequate protection. I am a little more interested in finding and repairing the problem because there may be other shock hazards associated with this problem that we are currently unaware of.

Thanks
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Is there a metal drain grate in the shower stall? Are you somehow measuring the voltage between the shower head and the pool of water in the bottom of the shower?
Or perhaps is the stray voltage coming through the earth through the conductive concrete?
In that case, in addition to correcting the underlying problem you might try putting a ground wire in a circle around the perimeter of the shower and bonding that to the water pipe.
You would not need/want to bury it much deeper than the bottom of the slab. You would be trying to establish an equipotential plane rather than a "ground".
Can you provide a schematic or plan view of the installation and the showers?
Just some screwdriver measurements in all directions 10-20 feet from the showers to see which direction the ground current is flowing.
 

ceb58

Senior Member
Location
Raeford, NC
Is there a metal drain grate in the shower stall? Are you somehow measuring the voltage between the shower head and the pool of water in the bottom of the shower?
Or perhaps is the stray voltage coming through the earth through the conductive concrete?
In that case, in addition to correcting the underlying problem you might try putting a ground wire in a circle around the perimeter of the shower and bonding that to the water pipe.
You would not need/want to bury it much deeper than the bottom of the slab. You would be trying to establish an equipotential plane rather than a "ground".
Can you provide a schematic or plan view of the installation and the showers?
Just some screwdriver measurements in all directions 10-20 feet from the showers to see which direction the ground current is flowing.


Also the under ground waste plumbing is ABS not cast iron

Digger is on the right track. Sounds like voltage leakage on a direct bury cable. Had a near by community that several homes were receiving shocks from above ground pool ladders. POCO had a bad UG cable from a 4 way pad mount transformer.
 

kwired

Electron manager
Location
NE Nebraska
Is this 2400 volt transformer NEC covered or is it a utility transformer? I guess you said service is 4160, if that is the case and the feed to these transformers are covered by NEC then they need to have separate grounded and grounding conductors supplied to them.

But that aside if they were POCO owned/controlled they would typically have the neutral bonded to the transformer both primary and secondary. Outside of bonding issues make sure the voltage you are seeing isn't just voltage drop on the neutral - primary or secondary. The floor of the shower is at true earth potential. If you have metallic water piping and it is bonded to the electrical grounding system - you are effectively extending that neutral that has voltage drop on it to the shower head, faucet, etc.

If the transformer case is not bonded to primary in any way, there may be capacitively coupled voltage on it. On under 600 volts this voltage would be more of a phantom voltage, and it easily shunted but at medium voltages it may have more behind it to be problematic.
 
Thanks for everyone's response. I have been away for the holidays. I have created a couple of drawings for the RV park and electrical systems. As I mentioned in my original post I too think we have a problem with a 15kV DB cable on the concentric neutral side. This is why I am questioning the primary bonding of the concentric neutral. I was also able to run a test lead from the bath house transformer T2 housing to the previous transformer T1 housing and got sparks and measured 5 volts. If the concentric neutral was not bonded and if the concentric neutral became defective wouldn't this just create an open circuit instead of current traveling through the earth? These are not POCO owned transformers.

Thanks
 

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No, no other replies. I have suggested to remove the primary bond jumper in all the transformers then there would be no way for a parallel path for current to travel through the earth from the primary side. We are currently awaiting an engineers blessing on this.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
If you remove the bond from H2 to the case, then what happens in the event of a high voltage fault to the case?

In general the NEC requires all conductive enclosures to be bonded to the source which could energize that enclosure. In this way a fault to that enclosure will open a protective device.

It used to be common to use the earthed conductor for purpose of bonding in many situations, in particular between different buildings. (The earthed conductor being the circuit conductor which is intentionally connected to earth at the source.) As you note, this sort of bonding can inject current into the earth, causing shocks.

Under current code you would be required to have a separate earthed conductor and equipment bonding conductor ('neutral' and 'ground'). The ground wire would provide your bonding to the chassis, and the H2-chassis connection would be removed.

I don't think that simply removing the bond would be acceptable; IMHO you will need to provide some sort of replacement bonding.

-Jon
 
I understand what you are saying. This is an existing installation where they have used the neutral grounded conductor for H2 and bonded it to the case and also the secondary neutral is also bonded to the case along with the secondary grounding conductors. The problem we have is the neutral primary conductor (Direct buried) has somehow become compromised and now 4160V is seeking a path to the source and is energizing the earth and secondary grounding conductors e.g. bath house plumbing which is bonded and to all other earth grounded parts. It is my opinion that if this primary neutral is not bonded the transformer and connection from H2 is lost no stray currents would be possible. I also recognize that a grounding conductor should have been ran with the primary conductors and this would have solved all the problems but it was not installed that way.

Let me also give this example: If the primary conductors were both hot legs say A and B phase you definitely would not bond one of these to the case so why the bond the primary neutral conductor? Just because it is a neutral grounded conductor?

I agree that if there was a short to the case it would become energized and would not trip any over current device since they did not run a grounding conductor. So being the current installation we have isn't the case essentially already in parallel with the primary feed and energized?

Thank you for your interest in this post and all recommendations are greatly appreciated.
 

kwired

Electron manager
Location
NE Nebraska
I understand what you are saying. This is an existing installation where they have used the neutral grounded conductor for H2 and bonded it to the case and also the secondary neutral is also bonded to the case along with the secondary grounding conductors. The problem we have is the neutral primary conductor (Direct buried) has somehow become compromised and now 4160V is seeking a path to the source and is energizing the earth and secondary grounding conductors e.g. bath house plumbing which is bonded and to all other earth grounded parts. It is my opinion that if this primary neutral is not bonded the transformer and connection from H2 is lost no stray currents would be possible. I also recognize that a grounding conductor should have been ran with the primary conductors and this would have solved all the problems but it was not installed that way.

Let me also give this example: If the primary conductors were both hot legs say A and B phase you definitely would not bond one of these to the case so why the bond the primary neutral conductor? Just because it is a neutral grounded conductor?

I agree that if there was a short to the case it would become energized and would not trip any over current device since they did not run a grounding conductor. So being the current installation we have isn't the case essentially already in parallel with the primary feed and energized?

Thank you for your interest in this post and all recommendations are greatly appreciated.
If this is covered by NEC then you must have a separate EGC and only bonding to grounded conductor should be back at the service equipment.

If this medium voltage portion of what you have is POCO owned they don't follow NEC, and it would be bonded to the grounded conductor at nearly every piece of equipment. Problem causing the stray voltage may not even be on site however, it could be on POCO side of things and could easily be voltage drop on their grounded conductor. If that is the case there are really only two solutions, better equipotential grounding in the bath house which doesn't get rid of the stray voltage it just shunts it around users, or for POCO to better balance their line to neutral loading so there is less voltage drop.
 
As I stated in a previous post. These Transformers are customer owned not POCO owned. I understand the requirement for a grounding conductor should have been ran with the primary. Since one was not installed my whole question is to make things safer wouldn't it be better remove bonding jumper from the primary conductor to the transformer case thus removing the path for current leakage.

I am also recommending to the park to just turn off all power to that section and just use it for group picnics, campfire story telling and marshmallow roasting.
 

iwire

Moderator
Staff member
Location
Massachusetts
wouldn't it be better remove bonding jumper from the primary conductor to the transformer case thus removing the path for current leakage.

Unless I am misunderstanding you .... NO, absolutely not.

That would leave a 4160 volt transformer floating in relation to earth. If the transformer faults the case will be live and nothing will trip the overcurrent device feeding it.
 

iwire

Moderator
Staff member
Location
Massachusetts
The more I think about this the more I think the only answer is to kill the compromised feeder until such time it can be replaced.

I would not want to be involved in any short cuts on this.
 
You are right it should be disconnected until feeder is replaced. Right now they will only make the bath house out of order. We are scheduled to replace feeder. The whole reason for my questions is because there are multiple transformers fed the same way throughout this park. Until the electrical is upgraded I was trying to eliminate any future problems that could be related to the same scenario. The park is slated to do a complete electrical renovation in a year or so.

I think this could be debated forever. When you talk about a fault to transformer case and a potential to earth if we remove bond jumper isn't it essentially this way right now by loosing the neutral primary conductor? I guess it just depends on how you want to look at it and determine which would be the lesser hazard since it wasn't installed correctly from the beginning.

Thanks for your recommendations on this.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
AVSparky,

I think that you've identified why this is somewhat debateable.

When the concentric neutral is used as the bonding conductor, then if you have a fault in the wire where the neutral opens then you will energize the case.

If you remove the bond at the case, and then you have a fault between hot and the case, you energize the case.

It seems to me that the former situation is more likely (damage to the cable rather than damage to the transformer), but that the latter case would impose a much higher voltage on the bonded chassis and its grounding system. In the first fault, the voltage would be dropped by the transformer primary.

I think that everyone is in agreement that the _proper_ fix is to fully replace the feeder to the transformer with a proper separated EGC, neutral, and phase.

For the damaged feeder IMHO it should be shut down.

I agree with you that bonding the floor to plumbing is a 'band-aid' with respect to the problems with power distribution, however I also think that this bonding should still be added. My reasoning is that there are other potential sources of current flowing in the ground, and these could present shock hazards. Bonding plumbing and floor would provide protection against other sources of stray current.

-Jon
 
Thank you so much for identifying my dilemma. I didn't look at the voltage potential being less through the primary. I was only looking at the two different scenarios. Now that you have shed some more light I guess there is really no way to make it safer the way it is installed. We will replace the cable and hope in the future there are no more open neutrals until the major upgrades take place. Thanks again for helping me see the 2 differences.
 
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