Grounding Questions (Fuse panel, grounding rod, frame of panels)

[sdold]

Mike Holt seems really fired up about this! I'm running into the same thing here this month, we are installing a powder coating operation and the gun manufacturer wants us to drive a ground rod that will be connected only to the part being coated, the gun power supply, and the person holding the gun. At least we're not in Florida.

[Sunking]

Mike Holt seems really fired up about this!

Yes sir, Mike really dislikes ignorance and stupidity. If you watched the 60 minute video on 690.47 all of us were a bit stunned with Mike's opening statement. We knew he was going to say something strong as we are working from an Agenda/Script. As I think you know Mike is a straight up Bible Thumper Born Again Christian, (he was once a gangbanger and never graduated from high school), so he is usually very careful with how it expresses himself. So we were a bit taken back with his very STONG opening statements. He has never done that in the 17 years I have worked for and with him. In fact they had to edit out my Oh Chit comment after he said that. He just laughed and nodded his head. Wish they had left that in there.

FWIW for the rest of you although Mike Holt was a Gangbanger and did not graduate from high school fool you. When he was 18, got arrested for pushing drugs and attempted murder. It was a life changing event for him. He obtained his GED while in prrson, came out and went to Miami University and earned a MBA strangely enough. After college became an Electrician and worked his way up through the ranks to Master Electrician. In 1975 he started his own biz. Today Mike is considered the most knowledgeable NEC in the country. His biz teaches code and electrical fundamentals to all levels of the trade. If you are in the biz, you know Mike Holt. When he speaks, the NEC listens.

I'm running into the same thing here this month, we are installing a powder coating operation and the gun manufacturer wants us to drive a ground rod that will be connected only to the part being coated, the gun power supply, and the person holding the gun. At least we're not in Florida.

My advice is you get them to sign a letter relieving you of all responsibility. Then take their money and run. You know that does nothing, and if there is a utility fault, could injure or kill the operator. Get it in writing so you cannot be held liable. Make sure the plant manager and equipment manufacture signs off on it. If something happens, the lawyers will get money from their pockets first. If you were a PE, you would loose an investigation review by your peers and held responsible. So be careful, you are playing with fire.

EDIT NOTE:

Steve FWIW there is a way to give them what they want, be code compliant, and safe. NEC 250.30, Separately Derived System aka SDS. Exact same way you do a radio tower with DC Supply, Isolation Transformer, UPS, or Generator.

[SunEagle]

Mike Holt seems really fired up about this! I'm running into the same thing here this month, we are installing a powder coating operation and the gun manufacturer wants us to drive a ground rod that will be connected only to the part being coated, the gun power supply, and the person holding the gun. At least we're not in Florida.

Make sure that person that is using the paint gun is wearing rubber boots and is on a grounding pad.

[sdold]

Make sure that person that is using the paint gun is wearing rubber boots and is on a grounding pad.

I'm the guy doing the painting. I was thinking of standing on a piece of plywood. heh heh

Dereck, what I meant was that we are having the stuff installed for us. I work for the state of CA and the little part that I work in builds equipment for the state radio vaults. I wanted to add powdercoating for one-off stuff and occasionally, maybe once a year, ham projects

[sdold]

Some of our fine DC power distribution products My favorite is the last one, we used mosfets instead of relays for the low voltage disconnects. The two relays are the high voltage disconnects. These are DC distribution panels for radio racks. By the way that was an interesting story about Mike, looks like he really did good for himself once he got on the right track.

[max2k]

Max you do not understand Step Potential Difference.

Defined is: When current is flowing from Lightning or utility high voltage to the earth ground, the ground potential rises at the entrance point, and a voltage gradient will occur based on the resistivity of the soil, resulting in a potential difference between two points on the ground. This is called a Step Potential as it can cause voltage between a person feet.

I understand that . What I'm not clear about is how bcroe's installation can be made reliable if he has DC source 600' from the building? I understand that during lightning strike for very short time in microseconds range that 6 gauge grounding wire might be subjected to the difference in potential of 2 grounding points 600' apart. As a result the array site will inevitably 'jump' in potential which is OK by itself at array site as everything will be more or less equipotential there due to local GES. The problem IMO is with say one of the phase conductors coming from the array inverter into the building as suddenly it will be 'lifted' up in potential by may be thousands of volts from the building's AC system point of view due to voltage drop on the 600' run. The voltage drop can occur not only due to resistance but also due to inductance of so long wire in that time interval. I'm sure there's simple solution to all this as power distribution lines are used everywhere. Is he supposed to install some 'surge arrestor device' on both ends of this 'transmission line' to ensure no conductor wonders too far from the local ground?

[Sunking]

I understand that . What I'm not clear about is how bcroe's installation can be made reliable if he has DC source 600' from the building? I understand that during lightning strike for very short time in microseconds range that 6 gauge grounding wire might be subjected to the difference in potential of 2 grounding points 600' apart. As a result the array site will inevitably 'jump' in potential which is OK by itself at array site as everything will be more or less equipotential there due to local GES. The problem IMO is with say one of the phase conductors coming from the array inverter into the building as suddenly it will be 'lifted' up in potential by may be thousands of volts from the building's AC system point of view due to voltage drop on the 600' run. The voltage drop can occur not only due to resistance but also due to inductance of so long wire in that time interval. I'm sure there's simple solution to all this as power distribution lines are used everywhere. Is he supposed to install some 'surge arrestor device' on both ends of this 'transmission line' to ensure no conductor wonders too far from the local ground?

If 600 feet away you run a 3rd wire in direct contact with the soil called a Bonding Jumper. Use TVSS where it enters the building .

[bcroe]

If 600 feet away you run a 3rd wire in direct contact with the soil called a
Bonding Jumper. Use TVSS where it enters the building.

I don't have a picture of how that goes together. The situation is DC flowing up to 300' (mostly
underground) to inverters, then AC flowing 300' (mostly underground) to the main panel. The
ground runs the entire distance.

I don't expect anyone to be out by the array in a storm, and replacing lightning damaged equipment
doesn't worry me (did that once before). More likely to be directly hit is the 65' tower 150' away. Just
don't want the house burned down or anybody inside hurt. Bruce Roe

[max2k]

I don't have a picture of how that goes together. The situation is DC flowing up to 300' (mostly
underground) to inverters, then AC flowing 300' (mostly underground) to the main panel. The
ground runs the entire distance.

I don't expect anyone to be out by the array in a storm, and replacing lightning damaged equipment
doesn't worry me (did that once before). More likely to be directly hit is the 65' tower 150' away. Just
don't want the house burned down or anybody inside hurt. Bruce Roe

Is your grounding wire bare and in direct contact with the soil along those runs? I think the idea is to dissipate charge along the way. Where inverter's neutral is connected to the ground- at that intermediate site or on the building side only? I'm sorry I hijacked the thread and used your install as an example, I just think it is very representative example of the grounding challenges when remote sites are involved.

IMO your inverter's neutral should be connected to the ground at the building side only but all wires DC and AC including neutral should be protected by TVSS devices relatively to their respective local grounds, in your case- that 6 gauge ground wire going from site to site. In case of the strike those TVSSs will clamp and 'lift up' conductors towards ground conductor potential making sure all conductors in the system are within their voltage protection range. When this happens at your intermediate site inverters inputs would remain protected as their flying up ground would pull DC wires through those TVSS up as well. At the building side inverter's outputs would be clamped to the building's ground potential with AC TVSSs there. I think at that moment TVSSs at both intermediate site and at the building will be conducting part of the charge bypassing and protecting circuits they're connected in parallel with.

This is just my take on this, not experience in designing such systems.

[bcroe]

Is your grounding wire bare and in direct contact with the soil along those runs? I think the idea is to dissipate charge along the way. Where inverter's neutral is connected to the ground- at that intermediate site or on the building side only? I'm sorry I hijacked the thread and used your install as an example, I just think it is very representative example of the grounding challenges when remote sites are involved.

IMO your inverter's neutral should be connected to the ground at the building side only but all wires DC and AC including neutral should be protected by TVSS devices relatively to their respective local grounds, in your case- that 6 gauge ground wire going from site to site. In case of the strike those TVSSs will clamp and 'lift up' conductors towards ground conductor potential making sure all conductors in the system are within their voltage protection range. When this happens at your intermediate site inverters inputs would remain protected as their flying up ground would pull DC wires through those TVSS up as well. At the building side inverter's outputs would be clamped to the building's ground potential with AC TVSSs there. I think at that moment TVSSs at both intermediate site and at the building will be conducting part of the charge bypassing and protecting circuits they're connected in parallel with.

This is just my take on this, not experience in designing such systems.

I think you are right, remote sights could use more attention. My feeling is that the 48 concrete posts
with rebar should keep most lightning energy at the remote sight. In addition the panels are surrounded
by much taller trees that may provide both wind and lightning protection.

I use plenty of small scale protection devices (TVS) in equipment, but don't know the best way to
use such things on this scale. My feeling is that a TVSS may help protect equipment its connected
to, but may not do much to control where lightning goes. None of my ground is buried bare, only the
array uses bare 6 gauge. To better visualize this discussion, perhaps pics are in order. Bruce Roe

[Sunking]

Is it AC or DC at the house? I should have asked that question first.

You might be able to treat it just like your AC service. Just bond the neutral conductor to ground at the AC Service panel like you would a service.

[bcroe]

Is it AC or DC at the house? I should have asked that question first.

You might be able to treat it just like your AC service. Just bond the neutral conductor to ground
at the AC Service panel like you would a service.

AC when it gets to the house. I can't undo the concrete grounds at the far end. Bruce Roe

[Sunking]

AC when it gets to the house. I can't undo the concrete grounds at the far end. Bruce Roe

Your answer is found and determined by NEC 250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuits.

(A)Grounding Electrode. Building or Structures supplied by either Feeders or Branch Circuits SHALL have a grounding electrode or grounding electrode system installed.

That is pretty clear with no ifs, ands, or buts. The word SHALL means it has to be done that way. However there are a few options depending on the conditions.

(B) Grounded Systems
(1) Supplied by Feeder or Branch circuits. A Equipment Grounding Conductor SHALL BE RUN with the supply conductors, and connected to the Grounding Electrode or Structure Disconnecting means and to the Grounding Electrodes.

The B option is telling you to run a EGC with the circuit conductors like any Branch Circuit requires. An EGC must be ran and closely coupled to the circuit conductors In other words inside the same raceway with its circuit conductors. That is not a Ground Electrode Conductor laying in the dirt. That is an important distinction.

2 Supplied by Separately Derived System.
(a) With Over Current Protection provided where the conductors originate, the installation SHALL Comply with 250..32(B)(1).

Ok that is just a circle back to where we started. But the very next method (b) is your way out.

(b) Without OCPD provided where the conductors originate, the Installation Shall Comply with 250.30(A)

What that is saying if you go read 250.30(A) is you treat it just like a SERVICE. There is no Ground ran between the ground mounted panels and your house. Just like your AC Service the POCO does not give you a Ground. They give you L1, L2, and Grounded Circuit Conductor aka Neutral.

At the Panels you bond all the poles and frames together to its own Ground Electrode, and yes all the poles in concrete make a ground electrode. And just like the POCO you bond the Neutral to Ground, and that is all. So if you use an inverter, you bond the Neutral and send it one 3 circuit conductors to the house. If DC bond one Polarity, most likely Negative and then run your 2 conductors to the house.

At the house you treat it like a Service. You bond the Neutral Circuit Conductor to ground at the disconnect means which is part of the house Ground Electrode System.

[max2k]

Your answer is found and determined by NEC 150.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuits.

(A)Grounding Electrode. Building or Structures supplied by either Feeders or Branch Circuits SHALL have a grounding electrode or grounding electrode system installed.

That is pretty clear with no ifs, ands, or buts. The word SHALL means it has to be done that way. However there are a few options depending on the conditions.

(B) Grounded Systems
(1) Supplied by Feeder or Branch circuits. A Equipment Grounding Conductor SHALL BE RUN with the supply conductors, and connected to the Grounding Electrode or Structure Disconnecting means and to the Grounding Electrodes.

The B option is telling you to run a EGC with the circuit conductors like any Branch Circuit requires. An EGC must be ran and closely coupled to the circuit conductors In other words inside the same raceway with its circuit conductors. That is not a Ground Electrode Conductor laying in the dirt. That is an important distinction.

2 Supplied by Separately Derived System.
(a) With Over Current Protection provided where the conductors originate, the installation SHALL Comply with 250..32(B)(1).

Ok that is just a circle back to where we started. But the very next method (b) is your way out.

(b) Without OCPD provided where the conductors originate, the Installation Shall Comply with 250.30(A)

What that is saying if you go read 250.30(A) is you treat it just like a SERVICE. There is no Ground ran between the ground mounted panels and your house. Just like your AC Service the POCO does not give you a Ground. They give you L1, L2, and Grounded Circuit Conductor aka Neutral.

At the Panels you bond all the poles and frames together to its own Ground Electrode, and yes all the poles in concrete make a ground electrode. And just like the POCO you bond the Neutral to Ground, and that is all. So if you use an inverter, you bond the Neutral and send it one 3 circuit conductors to the house. If DC bond one Polarity, most likely Negative and then run your 2 conductors to the house.

At the house you treat it like a Service. You bond the Neutral Circuit Conductor to ground at the disconnect means which is part of the house Ground Electrode System.

Like this?

[Sunking]

You are not showing a bond to N at the Inverter.