Bonded neutrals and grounds at existing nat. gas facility

[PetrosA]

This is a question about an older installation at a natural gas pressure boosting facility (along a pipeline).

Any of the subpanels I've seen in separate structures on the site have the neutrals bonded to the enclosure. Some have additional grounds run from gensets that have also been connected to the neutral bars. There are (obviously) ground rods all over the place and bonds between ground rods, structures, electrical pipes and gas pipes. Additionally, they use a sacrificial anode system that pumps DC current through the pipes to prevent corrosion. Since I'm not an expert in this kind of installation, I have the following question:

In spite of the fact that they may have been within code to not run separate ground conductors to subpanels and separate structures at the time of the install, doesn't the fact that neutrals are bonded to ground at all the subpanels mean that part of the neutral current is being carried by the gas pipe system on site and also getting mixed in with the DC current being used for the sacrificial anode system? Is this safe? Should I make a recommendation to separate the neutral/ground bonds?

Thanks

 

[mcclary's electrical]

This is a question about an older installation at a natural gas pressure boosting facility (along a pipeline).

Any of the subpanels I've seen in separate structures on the site have the neutrals bonded to the enclosure. Some have additional grounds run from gensets that have also been connected to the neutral bars. There are (obviously) ground rods all over the place and bonds between ground rods, structures, electrical pipes and gas pipes. Additionally, they use a sacrificial anode system that pumps DC current through the pipes to prevent corrosion. Since I'm not an expert in this kind of installation, I have the following question:

In spite of the fact that they may have been within code to not run separate ground conductors to subpanels and separate structures at the time of the install, doesn't the fact that neutrals are bonded to ground at all the subpanels mean that part of the neutral current is being carried by the gas pipe system on site and also getting mixed in with the DC current being used for the sacrificial anode system? Is this safe? Should I make a recommendation to separate the neutral/ground bonds?

Thanks

If there are multiple metallic paths, which in this case there are, the N/G bond should not be allowed past service equipment. If it is bonded, as you pointed out, the pipes become parallel with the wires.

Also, IT CAN AND WILL affect your cathodic protection. The pipes with protection need to be isolated from being used as a GEC, or EGC.

 

[walkerj]

I am no expert, but that sounds scary.
I would have a nice, well rehearsed speach prepared for the customer.

If any of the NG piping is bonded in an accesory structure AND in the main structure, there will be neutral current flowing on it.

 

[jmargolis79]

I have done a fair amount work in conditions like this. It sounds like trouble. The specs i have had to follow include pvc pipe underground or pvc coated ridig and a few feet of non-metallic sealtight on both ends of pipe to keep any stray currents off the gas line.

 

[PetrosA]

I have done a fair amount work in conditions like this. It sounds like trouble. The specs i have had to follow include pvc pipe underground or pvc coated ridig and a few feet of non-metallic sealtight on both ends of pipe to keep any stray currents off the gas line.

Do I understand correctly that any electrical pipe running out the buildings underground, if metal, should not be bonded to ground?

 

[mcclary's electrical]

Do I understand correctly that any electrical pipe running out the buildings underground, if metal, should not be bonded to ground?

I've seen a few of these systems. If the pipe is metal leaving the building, normally there is an isolation fitting somewhere to prevent the pipe from becoming a GEC.

 

[richxtlc]

There are two types of systems that I have seen in high pressure compressor stations:
1. The main gas line coming into and leaving the compressor station has an isolated flange and is cathodically protected. The cathodic protection on the transmission pipeline is independent of the cathodic protection in the facility. As far as the electrical conduit it is normally grounded and bonded as with any other facility.
2. The main gas line coming into and leaving the compressor station has the isolated flanged jumperred out and the cathodic protection protects the transmission line and the station equipment. In this case the cathodic protector is oversized in order to accomodate not only the gas transmission equipment, but also the metal piping underground. The newest trend is to install pvc coated rigid conduit to reduce the loading on the cathodic protector. In areas where additional cathodic protection is required, a sacraficial anode is place in the area to be protected.

 

[mcclary's electrical]

There are two types of systems that I have seen in high pressure compressor stations:
1. The main gas line coming into and leaving the compressor station has an isolated flange and is cathodically protected. The cathodic protection on the transmission pipeline is independent of the cathodic protection in the facility. As far as the electrical conduit it is normally grounded and bonded as with any other facility.
2. The main gas line coming into and leaving the compressor station has the isolated flanged jumperred out and the cathodic protection protects the transmission line and the station equipment. In this case the cathodic protector is oversized in order to accomodate not only the gas transmission equipment, but also the metal piping underground. The newest trend is to install pvc coated rigid conduit to reduce the loading on the cathodic protector. In areas where additional cathodic protection is required, a sacraficial anode is place in the area to be protected.

You're exactly right, I didn't realize he said electrical conduit. We wer talking about piping