Grounding for new Equipment Pad

[philly]

A new 480V Switchboard is being installed outdoors on a concrete pad. This new Switchboard and pad will sit right next to an existing Switchboard and pad. The existing pad is going to be extended in order to accommodate the new Switchboard.

I was curious to see what is usually required or best practice in terms of grounding the new pad extension and the new Switchboard?

Usually when a new pad or building is installed I typically see a ground ring having ground rods at each corner of the pad/building with the ground ring then connected to the equipment and the pad.

In this situation however where a pad is simply being extended I don't know if a new ground ring for jus the pad extension is required or even a good practice (unknown weather existing pad has a ground ring).

I was thinking that for this situation the best grounding options may be a combination of the following:

1) Use the rebar in the new foundation as an UFER ground and connect this ground to the new Switchboard.

2) Install a single ground rod (or multiple ground rods) at one of the corners of the pad and tie these rod's into the foundation rebar and connect to new Switchboard.

3) Connect to existing grounding system on existing Switchboard and pad (not sure how practical this maybe)

Curious to hear how others would approach.

 

[GoldDigger]

To have a UFER, you will need to have foundation or footings with a sufficient length of rebar under the switchboard, not just a flat slab.

 

[petersonra]

if you are extending the existing pad, IMO the new assembly is still just one structure. If so, one would use the existing GES.

Personally, I would not get real excited about trying to get a "better" ground. There just is not generally much in the way of any benefit to doing more than the bare minimum the code requires.

 

[Fulthrotl]

A new 480V Switchboard is being installed outdoors on a concrete pad. This new Switchboard and pad will sit right next to an existing Switchboard and pad. The existing pad is going to be extended in order to accommodate the new Switchboard.

I was curious to see what is usually required or best practice in terms of grounding the new pad extension and the new Switchboard?

Usually when a new pad or building is installed I typically see a ground ring having ground rods at each corner of the pad/building with the ground ring then connected to the equipment and the pad.

In this situation however where a pad is simply being extended I don't know if a new ground ring for jus the pad extension is required or even a good practice (unknown weather existing pad has a ground ring).

I was thinking that for this situation the best grounding options may be a combination of the following:

1) Use the rebar in the new foundation as an UFER ground and connect this ground to the new Switchboard.

2) Install a single ground rod (or multiple ground rods) at one of the corners of the pad and tie these rod's into the foundation rebar and connect to new Switchboard.

3) Connect to existing grounding system on existing Switchboard and pad (not sure how practical this maybe)

Curious to hear how others would approach.

if they are near, but not touching......

sink a ground rod under the new gear, stubbing it up underneath the gear.....

hypress a lug onto a piece of appropriately sized copper.... bolt to new ground bus.
use a C hypress to bond to new ground rod.
put a 1" GRC nipple between the sections of gear, run the copper ground unbroken thru that,
and use a C hypress to attach to the existing GEC.

if they are touching.... 1" chase nipple between them....

hipress is the same as continuous, in the eyes of the code.

 

[philly]

To have a UFER, you will need to have foundation or footings with a sufficient length of rebar under the switchboard, not just a flat slab.

This particular pad does have a 14" footing with #5 rebar on 12" center spanning the 8' x 9' lengths of the pad. Based on this I would think that it can be considered an UFER?

if you are extending the existing pad, IMO the new assembly is still just one structure. If so, one would use the existing GES.

When you say "one structure" I'm assuming you are referring to structure in the structural sense (building, foundation, etc...) and not in the electrical sense (Switchgear structure, MCC Structure, etc...)?

So if this is considered a single structure is there are requirement in the NEC to use the existing GES?

Personally, I would not get real excited about trying to get a "better" ground. There just is not generally much in the way of any benefit to doing more than the bare minimum the code requires.

O.k. so would you just tie into existing ground and be done with it? Any suggestions on how to tie into existing ground system on outdoor slab? Would you drive additional ground rod at new pad location and tie it in?

Now if we have a completely new pad located some distance away fed by a ductbank with the pad having large chiller equipment would it make sense in this case to install a ground ring around this new remote pad?

 

[petersonra]

A structure has but one GES. If you want to add GE to you can, but they have to all be tied together so there is no real reason to add anything if what is there now is already compliant.

IMO, adding on to an existing pad can't create a new structure (structure being as defined in the code).

 

[philly]

if they are near, but not touching......

sink a ground rod under the new gear, stubbing it up underneath the gear.....

hypress a lug onto a piece of appropriately sized copper.... bolt to new ground bus.
use a C hypress to bond to new ground rod.

The new gear and existing gear are several feet apart. So essentially what you described above is using a new ground rod at the new Switchaord and connecting it to the new Switchboard as well as tying it into the existing GEC via the existing Switchboard ground bus or location in the existing gear where the existing GEC is accessible? Would you connect new ground rod to new pad's rebar?

put a 1" GRC nipple between the sections of gear, run the copper ground unbroken thru that,
and use a C hypress to attach to the existing GEC.

So in addition to connecting new ground rod to new switchboard would you run the copper ground to the existing switchboard directly from the new ground rod or would you run it from the ground bus in the new Switchboard?

 

[petersonra]

if they are near, but not touching......

sink a ground rod under the new gear, stubbing it up underneath the gear.....

hypress a lug onto a piece of appropriately sized copper.... bolt to new ground bus.
use a C hypress to bond to new ground rod.
put a 1" GRC nipple between the sections of gear, run the copper ground unbroken thru that,
and use a C hypress to attach to the existing GEC.

if they are touching.... 1" chase nipple between them....

hipress is the same as continuous, in the eyes of the code.

how do you know that one rod is adequate?

 

[philly]

A structure has but one GES. If you want to add GE to you can, but they have to all be tied together so there is no real reason to add anything if what is there now is already compliant.

I have seen industrial sites where the GES's at different structures are all tied together via a ground conductor in a ductbank. Although there is no real requirement to tie these separate structures together I guess it makes sense to have every structure at the same ground potential.

 

[Cow]

Is this new switchboard a new service or is it being fed by the adjacent switchboard?

 

[philly]

Is this new switchboard a new service or is it being fed by the adjacent switchboard?

It is being fed by existing adjacent switchboard. Not a new service.

The existing adjacent switchboard however is a Service Entrance Switchboard.

 

[Cow]

It is being fed by existing adjacent switchboard. Not a new service.

The existing adjacent switchboard however is a Service Entrance Switchboard.

What makes you think you need to do anything more than run an equipment grounding conductor to this switchboard?

 

[kwired]

It is being fed by existing adjacent switchboard. Not a new service.

The existing adjacent switchboard however is a Service Entrance Switchboard.

What makes you think you need to do anything more than run an equipment grounding conductor to this switchboard?

+1

Now if there currently is no CEE and if the new pad qualifies as one might not be a bad idea to use it, but you must run the associated GEC back to the service not to the new gear.

 

[philly]

What makes you think you need to do anything more than run an equipment grounding conductor to this switchboard?

I don't necessarily. I agree that the minimum required in this case tis the EGC like you mentioned. I have just always seen additional grounding put in for new construction of pads and foundations. Especially since the GES at the existing pad is unknown I figured it wouldn't hurt to add extra grounding. Maybe its overkill?

+1

Now if there currently is no CEE and if the new pad qualifies as one might not be a bad idea to use it, but you must run the associated GEC back to the service not to the new gear.

The new pad does indeed qualify as a CEE and like I mentioned above I'm not sure if the existing pad qualifies as a CEE or even has one.

Why must you run GEC back to service gear and now new gear? Is this stated in the NEC somewhere? So would this go directly from the new pad CEE directly back to the ground bus in the service gear? How would the new gear ground bus then be tied in? Or would it simply only have the EGC connection?

 

[philly]

I cant seem to find anything in the NEC requiring additional grounding electrodes to be tied back to existing grounding electrodes or back to the service equipment. I only see requirements for having multiple GEC's from a single grounding electrode to multiple pieces of equipment.

Can anyone point to the requirement for tying additional grounding electrodes to existing electrodes or existing equipment? I guess the closest I see is 250.50 which requires all available grounding electrodes at a building (or structure I'm assuming) to be bonded together?

 

[kwired]

Yes you start in 250.50, all electrodes present that are mentioned there must be used as part of the grounding electrode system. I did ask earlier if there already was a CEE present. If not and you are now adding one then it must be use.

250.64 tells us where to run the GEC to. It says:

"Grounding electrode conductors at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system shall be installed as specified in 250.64(A) through (F)."

It must run to the first disconnecting means or in accordance with other instructions if you have situations that A through F apply to.

You have indicated your existing switchboard is the service - the GEC needs to go there. You have also indicated this second switchboard is to be supplied from the first switchboard, making it a feeder within the same building or structure, GEC,s should not run to this. If would happen to be a second (allowed) service then it must have a GEC but also must bond to the other service GEC.

 

[Sahib]

I agree that the minimum required in this case is the EGC like you mentioned. I have just always seen additional grounding put in for new construction of pads and foundations. Especially since the GES at the existing pad is unknown I figured it wouldn't hurt to add extra grounding. Maybe its overkil?

NO. It is there to provide extra safety. If earth leakage current on equipment enclosure is 0.5mA or more, it presents a shock hazard. Of course EGC eliminates that hazard. But if EGC were compromised, the local equipment ground still eliminates that hazard.

 

[philly]

After a little bit of searching I now see that 250.58 requires that the same grounding electrode shall be used to ground equipment located within the same structure. This tells me that all of the equipment at a structure (pad in this case) must be connected to the same Grounding electrode or Grounding Electrode System. This says to me that if any new grounding electrode is added it cannot simply be connected to the new switchboard as all equipment at this location must be connected to the same electrode or electrode system?

Yes you start in 250.50, all electrodes present that are mentioned there must be used as part of the grounding electrode system. I did ask earlier if there already was a CEE present. If not and you are now adding one then it must be use.

So if a new CEE is formed by pouring the new pad/foundation does this new CEE have to be used since it is now "present" at the structure as required by 250.50 regardless of weather an existing CEE already exists?

The customer also wishes to add a new ground rod with test well at the new foundation. 250.50 requires that all grounding electrodes at an area must be bonded together so this new ground rod cannot simply be connected to new Switchboard but rather must be bonded to existing Grounding Electrodes?

250.64 tells us where to run the GEC to. It says:

"Grounding electrode conductors at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system shall be installed as specified in 250.64(A) through (F)."

It must run to the first disconnecting means or in accordance with other instructions if you have situations that A through F apply to.

You have indicated your existing switchboard is the service - the GEC needs to go there. You have also indicated this second switchboard is to be supplied from the first switchboard, making it a feeder within the same building or structure, GEC,s should not run to this. If would happen to be a second (allowed) service then it must have a GEC but also must bond to the other service GEC.

I guess my main confusion is how to bond the new grounding electrode back to the existing grounding electrode system. 250.64 seems to discuss a common GEC for multiple pieces of equipment as well as the requirements for the individual GEC's at each piece of equipment. I do not see anywhere in this section where it requires any new Grounding electrode to go back to the service? Can you never have grounding electrodes connected to equipment located in the same building that is not service equipment? If for some reason the Equpiemnt Ground Conductor between the service switchboard and the new switchboard ever became damaged wouldn't you want to also have a connection to grounding electrode as a backup?

In order to bond new Grounding Electrodes to existing GES can you simply run the new GEC back to the ground bus in the service equipment?

 

[philly]

Expanding somewhat on my original question one of the feeders from this new Switchboard feeds a large chiller and auxiliary chiller pumps located on a new concrete pad some distance away.

I'm also trying to determine weather or not this new Chiller location requires a Grounding Electrode System per 250.32? Here's what I'm considering to make the determination:

1) Would this new chiller pad and equipment be considered a building or structure?

2) Is the circuit to the chiller considered a feeder ( or is this a branch circuit)? I would think its a branch circuit fed from the upstream switchboard since it only feeds a chiller starter. But what if inside the chiller enclosure there was other small distribution components that had further branch circuits to the individual chiller components?

If the answer is no to either of the above then I take it that a GES is not required? However would it be good practice to still install a ground rod, CEE, ground ring, etc....? I see lots of industrial designs that appear to have ground rings at locations like this weather its required or not.

 

[kwired]

Get it out of your mind that your new switchboard that is feeder supplied from the same building/structure needs a grounding electrode run to it, it doesn't. It does need an equipment grounding conductor run to it though, but that should be run with the feeder supplying the switchboard.

If you happen to create a new CEE and never had one to begin with, bring it to the existing grounding electrode system.