Equipotential grid

[FionaZuppa]

Why do you want to tie an EGC to the gutter?

EPB is it's own network. Any items in that network that also require an EGC, pool pumps or lights are just some common examples, is where an interconnection to the EGC typically comes into play.

typically for bodies of water, the bond grid gets tied to the egc at some point. so if a gutter is in the bond zone and you already had a egc wire running up to the gutter via some hidden path (wall, attic, roof rafter, etc) and tied to the gutter, the gutter then becomes part of the bond grid via egc. thus, if the grid near the pool became 500v, then so should the gutter and everything else that the egc lands on. so instead of a 500v "circle" you now have a bunch of 500v fingers.

a bond grid is great if you are in the middle of it, not so great if you are at the edge of it.

in the case of a fully isolated bond grid (not tied to egc), if the bonding gets energized by another ckt that perhaps does not have gfi, there is no egc on the grid to clear that fault and you end up with a potential shock hazard near the edge of the bond grid, like grid to earth, or grid to something else that is tied to egc, etc.

isolation is "bad" for pool scenarios. the grid should be good, tied to egc (perhaps in more than one place, like pump and disco/sub), and tied to a few ground rods.

perhaps NEC should simplify the 680 section, just call it an extended egc grid.

 

[blkmagik21]

I disagree, and the engineers and others on the NEC code panel have determined that it is unsafe to have them directly connected to each other. It is something an electrical inspector would write a correction on as well.


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[kwired]

replies within quoted content

typically for bodies of water, the bond grid gets tied to the egc at some point. so if a gutter is in the bond zone and you already had a egc wire running up to the gutter via some hidden path (wall, attic, roof rafter, etc) and tied to the gutter, the gutter then becomes part of the bond grid via egc.why would you have an EGC running to the gutter in the first place? thus, if the grid near the pool became 500v, then so should the gutter and everything else that the egc lands on. Everything already connected to bonding network is already going to rise to same voltage so instead of a 500v "circle" you now have a bunch of 500v fingers.

a bond grid is great if you are in the middle of it, not so great if you are at the edge of it. there is always an edge - by current rules it is at least three feet of perimeter surface away from the walls of pool plus other conductive objects that are within certain distances. the hazards are greatest when submerged in the water and touching something outside that zone - but the zone is big enough not many are contacting anything outside of it while in the pool.

in the case of a fully isolated bond grid (not tied to egc), if the bonding gets energized by another ckt that perhaps does not have gfi, there is no egc on the grid to clear that fault and you end up with a potential shock hazard near the edge of the bond grid, like grid to earth, or grid to something else that is tied to egc, etc. Even with no EGC most pools have enough concrete with metal reinforcements and other objects plus water standing on many of these surfaces while pool is in active use that they probably have low enough resistance to earth to allow the 4-6 mA of fault current necessary to trip a GFCI - yes a solid EGC would ensure it will trip and likely in less time. Equal potential is still more important to safety of pool users then GFCI. GFCI still needs current to make it work, equal potential means no significant current flows through a pool user.

isolation is "bad" for pool scenarios. the grid should be good, tied to egc (perhaps in more than one place, like pump and disco/sub), and tied to a few ground rods. Only thing bad is if there is a "hole" in the grid, then you have possible voltage gradient near that hole.

perhaps NEC should simplify the 680 section, just call it an extended egc grid.No, it is still bonding more then grounding that we are trying to accomplish.

 

[blkmagik21]

replies within quoted content

I second that


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[ActionDave]

No, it is still bonding more then grounding that we are trying to accomplish.

:thumbsup:

 

[FionaZuppa]

"it probably has enough low ohms to allow 4-6ma"? Direct tie to egc has zero ohms on meter, repeat, zero ohms. with one ez tie between bond grid and egc i just removed that "probably, just dont know" factor and pegged it to a for-sure zero ohms. the NEC doesnt need all the convoluted verbiage around pool pump, simply bond all the metal crud, including pool pump, and then tie bonding to egc, done.

 

[kwired]

"it probably has enough low ohms to allow 4-6ma"? Direct tie to egc has zero ohms on meter, repeat, zero ohms. with one ez tie between bond grid and egc i just removed that "probably, just dont know" factor and pegged it to a for-sure zero ohms. the NEC doesnt need all the convoluted verbiage around pool pump, simply bond all the metal crud, including pool pump, and then tie bonding to egc, done.

Pump is already supposed to be connected to the EGC of it's supply circuit, only time there is a problem is if you would have a situation of double insulated pump. Not sure how common that is, but suspect it isn't all that common.

 

[Dennis Alwon]

I disagree, and the engineers and others on the NEC code panel have determined that it is unsafe to have them directly connected to each other. It is something an electrical inspector would write a correction on as well.


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Are you saying that the nec states that the bonding grid is or should not be tied to the equipment grounding conductor?

 

[rcarroll]

It is something an electrical inspector would write a correction on as well.


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I can't. There is no code that prohibits the connection.

 

[FionaZuppa]

Pump is already supposed to be connected to the EGC of it's supply circuit, only time there is a problem is if you would have a situation of double insulated pump. Not sure how common that is, but suspect it isn't all that common.

1) agree, but tying another from bond to egc at disco/sub gives further protections.
2) a few ground rods on the bond grid is a good idea (not for clearing ckt faults).
3) seems to be some confusion by some, that the bond grid DOES get tied to egc under normal circumstances, the exception is dbl-insulated pump, which still gets bonded, and its why #1 is very valid for this special case.

With #1 AND #2, w/ a good egc the bond grid is tied to earth. if egc becomes compromised you get the next best thing, low ohms into the earth via ground rods + equi pot., and then if the ground rods go missing you get the last best thing, everything just sitting at the same voltage. The 1st two however has better probability of clearing fault via ocdp/gfi, but the last one will remain "bird on wire", and hopefully you dont bridge the gap at the edge, etc.

So, if NEC simply made the requirement to tie bond grid to egc then you kinda won't run into the "bird on wire" scenario, nor will that bonded gutter suddenly become 240v, etc.

 

[kwired]

1) agree, but tying another from bond to egc at disco/sub gives further protections.
2) a few ground rods on the bond grid is a good idea (not for clearing ckt faults).
3) seems to be some confusion by some, that the bond grid DOES get tied to egc under normal circumstances, the exception is dbl-insulated pump, which still gets bonded, and its why #1 is very valid for this special case.

With #1 AND #2, w/ a good egc the bond grid is tied to earth. if egc becomes compromised you get the next best thing, low ohms into the earth via ground rods + equi pot., and then if the ground rods go missing you get the last best thing, everything just sitting at the same voltage. The 1st two however has better probability of clearing fault via ocdp/gfi, but the last one will remain "bird on wire", and hopefully you dont bridge the gap at the edge, etc.

So, if NEC simply made the requirement to tie bond grid to egc then you kinda won't run into the "bird on wire" scenario, nor will that bonded gutter suddenly become 240v, etc.

You are not prohibited from exceeding what code requires if you wanted to do your installations that way, just like you can run a 12 AWG conductor where 14 AWG is minimum code compliant as a general rule.

 

[KnightPower]

I'm with Dennis. Are you trying to sell isolated ground snake oil?

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[cowboyjwc]

Are you saying that the nec states that the bonding grid is or should not be tied to the equipment grounding conductor?

It says it isn't required to.

 

[blkmagik21]

Upon further reading of 680 when I had a chance. I have discovered that I was wrong. I’ve been called for it on an inspection before but didn’t argue it with the inspector. But if he calls me in it again I sure will. I’m sorry for my misconception of the code in this instance.


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[Dennis Alwon]

It says it isn't required to.

Where does it say that?

 

[Craigv]

Then it needs to be bonded or somehow located in a place where bonding won't be required.

Exactly, and I don't see this as the huge problem some are making of it.

 

[Craigv]

It says it isn't required to.

I have never seen anything stating it isn't required to be connected to an EGC.

The requirement to bond the equipotential grid to the premises EGC is somewhat circuitous, but it exists. 680.26(B) has long stated that "metal parts of electrical equipment associated with the pool water circulating system, including pump motors, and metal parts of equipment associated with pool covers, including electric motors, shall be bonded." The only way this can be met without a connection to the EGC is with listed double insulated motors, and then a solid 8 AWG wire has to be provided at the location to allow bonding in the event of motor replacement. If there is no connection to the premises EGC elsewhere in the equipotential system, then this bonding conductor shall be connected to the equipment grounding conductor of the motor circuit.

Therefore regardless of having a double insulated motor, the equipotential grid is connected to the pool pump circuit EGC, or another connection to the premises EGC shall be made.

 

[Little Bill]

I think some may be confused with the fact that the code doesn't require the grid (or jumper) to extend to the panel or service.

 

[ActionDave]

I think some may be confused with the fact that the code doesn't require the grid (or jumper) to extend to the panel or service.

:thumbsup::thumbsup:

 

[Craigv]

I think some may be confused with the fact that the code doesn't require the grid (or jumper) to extend to the panel or service.

Agreed, the wording is circuitous and certainly doesn't convey the stated intent of ensuring that everything conductive be at the same potential. It would seem rather important that the EGC have as close to the same potential as the grid, so burying the requirement to bond them in such a mishmash of language is unfortunate.