2 service panels, 1 ground - InspectionNews

Jon Randolph · #1 (**permalink**) 10-11-2007, 05:53 AM

Home has one 300 amp supply, a 200 amp primary and a 100 amp secondary panel. Secondary panel was NOT a sub (auxillary) panel as it had it's own feed from one of the lugs off of the meter.

SEC was fed through panel # 1 (directly behind meter) to go into panel #2 (about 1 foot away from panel #1) using rigid metal conduit to bond the 2 panels together.

Panel #1 had #6 ground to grounding rod.
Panel #2 had no ground conductor attached to the bus bar from a ground source.

Questions:

1. Is this considered to be using panel #1 as conduit? (I say it does)

2. Is the bonding of the panels sufficient to ground panel #2? (I say no)

If not:
3. Can panel #2 be grounded to the same grounding rod as panel #1 or should it have a separate grounding rod?
4. Are you allowed to bond main panels?
5. If a separate grounding rod is used, does the 8' clearance between rods apply when the panels are side by side?

I did refer this service to an electrician for repairs of loose grounds, oversized breakers and an improperly wired GFI breaker and suggested that the electrician evaluate the grounding of these panels. Any information learned will be useful in the future.

Jon Randolph · #2 (**permalink**) 10-11-2007, 02:56 PM

30 views / 0 replies.

Anyone have any information for me?

Billy Stephens · #3 (**permalink**) 10-11-2007, 03:32 PM

Jon,

#31 Here any Pictures?

Jon Randolph · #4 (**permalink**) 10-11-2007, 04:47 PM

No pictures of the panels together, but the description (and the drawing that I added) above pretty much describes it.

Jerry Peck · #5 (**permalink**) 10-11-2007, 06:38 PM

Quote:

Originally Posted by Jon Randolph

Home has one 300 amp supply, a 200 amp primary and a 100 amp secondary panel. Secondary panel was NOT a sub (auxillary) panel as it had it's own feed from one of the lugs off of the meter.

Quote:

Originally Posted by Jon Randolph

30 views / 0 replies.

Anyone have any information for me?

That last post was a 5:56 pm, it is now 9:37 pm ... one reason is that your terminology may be wrong and is confusing people.

"primary" "secondary" "sub panel"

You are referring to "service equipment".

I just do not know what that is so hard for HIs to understand.

Think of them as they are: "service equipment", you will likely get your own answers and get them right.

Tom Munds · #6 (**permalink**) 10-12-2007, 09:21 AM

Quote:

Originally Posted by Jon Randolph

No pictures of the panels together, but the description (and the drawing that I added) above pretty much describes it.

Jon,
It does appear that what you are saying is a bit confusing but only perhaps because I am new. I submitted your question to a friend of mine that is an electrcal enginner and will let you know what he says. This site is really good, in my opinion, for accurate answers quickly. I saw that your qustion remains hanging so I thought I would offer some closure to your question.
Tom

Jerry Peck · #7 (**permalink**) 10-12-2007, 10:16 AM

Quote:

Originally Posted by Jon Randolph

Questions:

1. Is this considered to be using panel #1 as conduit? (I say it does)

Answer: The SEC running from the service equipment on the right in your drawing through to the service equipment on the left *are not allowed to be in there*.

Quote:

2. Is the bonding of the panels sufficient to ground panel #2? (I say no)

Answer: Maybe. *IF* the raceway (conduit) is metal, *AND* is not through concentric knock outs or has grounding locknuts or bushings and grounding bond jumpers (neither of which you showed) ... so ... "maybe", or "maybe not".

Quote:

If not:
3. Can panel #2 be grounded to the same grounding rod as panel #1 or should it have a separate grounding rod?

Answer: Yes, if done properly.

[quote]4. Are you allowed to bond main panels? [/quote

Answer: They are not "main panels", they are "service equipment", and, as such, *are required to be* bonded to ground (neutrals bonded to ground).

Quote:

5. If a separate grounding rod is used, does the 8' clearance between rods apply when the panels are side by side?

Answer: The separation clearance is 6 feet, and, yes, if more than one rod is used, they would need to be more than 6 feet apart.

Tom Munds · #8 (**permalink**) 10-13-2007, 08:15 AM

Quote:

Originally Posted by Jon Randolph

No pictures of the panels together, but the description (and the drawing that I added) above pretty much describes it.

Jon,
I spoke with a friend of mine and this is what he wrote:

These are some interesting questions. I think the referral to a qualified electrician is a wise one. Furthermore, when you can honestly call out enough sound reasons for the electrician to visit the site, it doesn't hurt at all to ask him to also look at some other issues that concern you which you don't pretend to be expert enough to call. That strategy keeps you looking good and doesn't make sellers angry that they had to pay for an electrician.

I find that electricians will often disagree a little on what is "code" or what "should be done" in situations like these. However, even when they do, the responsibility for the opinion or advice is no longer in the inspector's lap -- no matter whether the electrician is right or wrong. That's the best part.

Nonetheless, here's my take on your questions.

First of all, I imagine that a #4 bare, stranded copper ground wire should be absolute minimum in these panels. It's possible that two, #4 ground conductors should be used for a 300-amp service because of the possible greater load currents that could be involved at the neutral if the loads on each of the 120-volt legs are really imbalanced. (Remember that the ground conductor is set up to be a completely alternate path for the neutral conductor.)

Secondly, although I've seen many electricians try to get away with using metal conduit between panels as true ground connections, I believe the code does not accept threaded metal conduits in ground paths because the threads are not designed or rated as "bonded" connections. I believe that the code requires separate bonding conductors and bonding clamps or terminals designed for that purpose.

I further believe that with the two panels being so close together and so close to the meter that they could be essentially treated as the same panel -- not requiring isolation of the ground and neutral in the second panel.

The driving motive behind floating the neutrals in subpanels comes from the amount of voltage drop that can easily be developed along ground and/or neutral conductors when they are carrying current. Such a voltage drop can cause the case metal of a remotely located panel to be elevated above adjacent earth potential, thereby becoming a potential shock hazard under certain conditions. Usually those conditions would involve system voltage surges or nearby lightning strikes; but sometimes high neutral currents through long, undersized conductors can generate quite a voltage. If those return currents are shared with the ground conductors, the panels are no longer at ground potential.

I believe that you are not only allowed to bond main panels; but that you should, when they are essentially side by side.

Even if two ground rods were used for the two panels of which you speak, the two ground rods and their ground conductors should be bonded together, essentially bonding the two panels together.

However, if two "main" panels are located remotely from each other in buildings that are more than 6 feet apart, they should each have their own ground rods.

If two ground rods are driven to establish a satisfactory (or improved) ground for the service, they should still be driven far enough apart to be in contact with different possible current flow paths into the earth.

Just a side note: The codes have long supported the encouragement to drive multiple ground rods. However, I've taken measurements on ground rods all over the state of idaho and found them to typically offer anywhere from 100 to 1000 ohms or more of resistance to remote earth.

A far better connection to remote earth is always attained with the "made electrodes" (or UFR) grounds that consist of 20 feet of 1/2-inch rebar embedded in concrete foundations. This is because concrete is a wonderful conductor and foundations have large areas of effective contact with soils. Usually, UFR grounds offer from 5 to 50 ohms of resistance to remote earth.

I hope some of this makes sense or is helpful. Please don't think for a moment that I'm a code expert. I'm not. Most of this comes from memory and my understanding. When I need to know where to stand regarding specific code issues, I ask a local expert before putting my foot in my too deeply.
I would appreciate any thoughts on this as well.
Hope this helps!
Tom

Jerry Peck · #9 (**permalink**) 10-13-2007, 08:40 AM

Quote:

Originally Posted by Tom Munds

A far better connection to remote earth is always attained with the "made electrodes" (or UFR) grounds that consist of 20 feet of 1/2-inch rebar embedded in concrete foundations.

Not addressing other parts of the reply to keep from sounding to negative on too many things, but ...

While the above is stated correctly (almost), that "(almost)" part if key.

That only applies to when the concrete is in direct contact with earth. This is a problem almost everywhere in the country in that AHJ *are* enforcing that code section, but enforcing it incorrectly as most areas of the country with monolithic slabs have a requirement for a moisture barrier underneath the slab ... along with its thickened edge footing ... which means that there is a sheet of plastic separating the concrete encased electrode from earth, i.e., the concrete encased electrode is not in direct contact with earth - as required.

I've been poking at this issue for 5-10 years, and the IAEI News (The International Association of Electrical Inspectors magazine) even had a full article on this about 3-4 years ago explaining why it is 'not a good thing' to do when the concrete is separated from earth by a moisture barrier (sheet of plastic).

Nonetheless, it is still being enforced.

Now, if you have a footing and a basement wall or an inverted 'T' stem wall on a footing, the steel in those footings are do create a concrete encased electrode in direct contact with earth. *That* is when this code section applies and what makes the Ufer ground work.

Tom Munds · #10 (**permalink**) 10-13-2007, 08:49 AM

Quote:

Originally Posted by Jerry Peck

Not addressing other parts of the reply to keep from sounding to negative on too many things, but ...

While the above is stated correctly (almost), that "(almost)" part if key.

That only applies to when the concrete is in direct contact with earth. This is a problem almost everywhere in the country in that AHJ *are* enforcing that code section, but enforcing it incorrectly as most areas of the country with monolithic slabs have a requirement for a moisture barrier underneath the slab ... along with its thickened edge footing ... which means that there is a sheet of plastic separating the concrete encased electrode from earth, i.e., the concrete encased electrode is not in direct contact with earth - as required.

I've been poking at this issue for 5-10 years, and the IAEI News (The International Association of Electrical Inspectors magazine) even had a full article on this about 3-4 years ago explaining why it is 'not a good thing' to do when the concrete is separated from earth by a moisture barrier (sheet of plastic).

Nonetheless, it is still being enforced.

Now, if you have a footing and a basement wall or an inverted 'T' stem wall on a footing, the steel in those footings are do create a concrete encased electrode in direct contact with earth. *That* is when this code section applies and what makes the Ufer ground work.

Now we are getting some good meaty conversation! Awesome input, and Thank you!By the way how much electrical experience do you have and how much do you think is necessary to do the home inspection well?

Jerry Peck · #11 (**permalink**) 10-13-2007, 07:42 PM

Quote:

Originally Posted by Tom Munds

By the way how much electrical experience do you have ...

I started working with my dad, an electrical contractor, when I was old enough to crawl attics and crawlspaces and pull wire, I was probably around 10, give or take.

Quote:

and how much do you think is necessary to do the home inspection well?

Not that much.