Pool Bonding

[fmignella]

Article 680-22 of the NEC states " It shall not be the intent of this section to require that the number 8 solid copper bonding conductor be extended or attached to any remote panel board, service equipment or grounding electrode, but only that it shall be employed to eliminated voltage gradients in the pool area".

I was under the impression that the bond wire should start at the panel board and end near the filter? Is this not true? If so, I assume that the bonding wire just has to encircle the pool area and connect to metal ladder pockets, diving board jigs and the frame work of the pool then end at the pump.

[ April 24, 2003, 07:19 AM: Message edited by: fmignella ]

 

[russ]

Re: Pool Bonding

Write! the bond is to tie everything associated with the pool together including the motor frame.

It is not the same as an equipment ground, which is associated with the electrical supply circuit, but in most cases will end up bonded to the equipment ground through common contact with the motor frame and other items.

That way everything is at the same potential.
If there were to be a voltage induced, there is less a chance that a person would be come a conductor if everthing is at the same potential.

Russ

 

[fmignella]

Re: Pool Bonding

Thanks for the information Russ. I was just looking through the NEC handbook at article 680-22 and saw the same thing. The diagram in the hand book looks like you can use the walls of a vinyl lined pool (in ground) as a conductor by just bonding at one point to the metal frame, then from the frame work bonding to the ladders etc.

 

[spyder]

Re: Pool Bonding

The pool bond should not tie into the panelboard. During a fault condition (say another circuit not associated with the pool) it could actually cause the pool bonding grid to become energized!!

Only the pool and associated equipment, such as pumps, blowers, heaters, lights, ladders, diving boards should be bonded.

 

[iwire]

Re: Pool Bonding

Originally posted by spyder:
The pool bond should not tie into the panelboard. During a fault condition (say another circuit not associated with the pool) it could actually cause the pool bonding grid to become energized!!

How would this be different from the equipment grounding conductor that comes out with the feeds, tying the panel ground into the bonding wire?

 

[bennie]

Re: Pool Bonding

Bob: You got it. The pool conductive objects are directly connected to the neutral at the panel which is connected to the MGN of the distribution system.

Consider this... The active high voltage conductor, at the transformer, breaks loose from the bushing and falls on the neutral. The neutral burns clear back to its source. The pool metal is now at primary voltage.

 

[iwire]

Re: Pool Bonding

Thanks, Bennie

I got it I just do not know what to do with it.

Could we prevent what you described by feeding the pool circuits with an isolation transformer, have no ground conductors between panel and pool and use GFCIs to clear faults?

 

[bennie]

Re: Pool Bonding

Bob: The connection of the bonding conductor to the equipment ground of the pump motor, is a loop circuit.

The rebar becomes a big "stray voltage sucker"

Double insulated pump motors, with no bond to the pool equipment and no equipment ground conductor, will break the closed loop.

[ April 26, 2003, 07:17 PM: Message edited by: bennie ]

 

[don_resqcapt19]

Re: Pool Bonding

680.26(B)(4) Where a double-insulated water-pump motor is installed under the provisions of this rule, a solid 8 AWG copper conductor that is of sufficient length to make a bonding connection to a replacement motor shall be extended from the bonding grid to an accessible point in the motor vicinity. Where there is no connection between the swimming pool bonding grid and the equipment grounding system for the premises, this bonding conductor shall be connected to the equipment grounding conductor of the motor circuit.

Even with a double insulated motor, the code requires a connection to the service grounding system. I'm not sure why this is needed, but it was added in the 2002 code.
Don

 

[bennie]

Re: Pool Bonding

That section is a contradiction of the FPN in 680.26(A). The #8 may not run to the service but it is electrically connected. This is a very dangerous situation.

Read: Stray Voltage.org for reasons.

 

[bennie]

Re: Pool Bonding

Regrounding the equipment ground conductor is the same as regrounding the neutral. There will be some load current flow on the equipment ground conductor to the rebar and on to the transformer.

Transient current from other sources will flow on the rebar to the MGN of the utility.

 

[don_resqcapt19]

Re: Pool Bonding

Bennie,
The FPN to 680.26(A) does not say that the bonding shall not be connected to the EGC or other system grounding conductor, it just says that this section (680.26) does not require a connection to these items. Just because there is a current flow on the bonded items does not make an unsafe condition. As long as everything is bonded and the current flow does not create a large voltage drop across the bonded items there is no safety hazard. Even without a connection to the service grounding system, a fault on the primary system can produce current flow across the bonded items. The "stray voltage" problem exists between things that are bonded to the electrical system and the earth or things that are not bonded. The most common cure for the "stray voltage" problem on farms is making sure there is only one neutral to ground bond and that all conductive objects are bonded together and to the EGC. Yes, the additional connections to earth may actually increase the amount of current flowing on the grounding system, but the bonding produces an equal potential plane and eliminates the shock hazard.
Don

 

[don_resqcapt19]

Re: Pool Bonding

The substantiation for the change in 680.26(B)(4) was to prevent problems that may be caused by "stray voltage". If the pool bonding system is not connected to the electrical grounding system and someone, using a powered appliance with a 3 wire cord and metallic surfaces, comes in to the pool area, there would be a potential difference in voltage between the outer grounded surface of the appliance and the bonded surfaces of the pool equipment and deck.
Don

 

[bennie]

Re: Pool Bonding

The NEC is hell bent on grounding everything, NEMA is hell bent on insulating everything.

I can't think of any electric appliance with a three wire cord. I have an electric lawn mower, it has a two wire cord. Double insulated motor.

You can get shocked touching a grounded surface, you won't be shocked if you don't touch it.

Common mode voltage is the problem on dairy farms.
This voltage is between the neutral and the earth.
Creating a path for current flow on the pool bonding system will produce common voltage between the pool and the non-current carrying equipment ground of an appliance. The tie of the pool grid to the neutral does not provide a equal potential, it only assures there is a difference in potential.

 

[don_resqcapt19]

Re: Pool Bonding

Bennie,

Creating a path for current flow on the pool bonding system will produce common voltage between the pool and the non-current carrying equipment ground of an appliance.

This is the very reason that bonding is required between the EGC and the pool bonding system.

The tie of the pool grid to the neutral does not provide a equal potential, it only assures there is a difference in potential.

The only possible difference in potential between bonded objects is that caused by the voltage drop between the two bonded objects. It would take a combination of high current on the bonding path and high resistance on this same path to create a hazardous voltage potential.
Don

 

[bennie]

Re: Pool Bonding

Stray voltage from other sources will only appear on the pool equipment, not on the appliance enclosure. There will be a voltage difference.

This is what many call tingle voltage at a pool.

This voltage has been known to kill cows, according to some of the articles.

Leakage current in the human body must be less than 10 uA in medical diagnostic equipment.

 

[don_resqcapt19]

Re: Pool Bonding

Bennie,

Stray voltage from other sources will only appear on the pool equipment, not on the appliance enclosure. There will be a voltage difference.

This is not possible if the pool bonding system is bonded to the electrical grounding system. It is only possible when the connection between the two systems does not exist. The only voltage that can exist between two objects that are bonded is the voltage caused by the voltage drop in the bonding system between the two points of contact or measurement. The current involved in "stray voltage" is too small to create a hazardous voltage drop.

This voltage has been known to kill cows, according to some of the articles.

The most common correction for stray voltage on dairy farms is bonding all noncurrent carrying conductive items to the electrical grounding system. This is exactly what you would be doing when you tie the pool bonding grid to the electrical system grounding conductor.

Leakage current in the human body must be less than 10 uA in medical diagnostic equipment.

The key word is "in". This involves voltages applied to the body without the protection (resistance) of the skin. Very small voltages can be fatal when applied internally.
Don

 

[bennie]

Re: Pool Bonding

Don: The frame of the appliance is not bonded to the pool metal. It is connected to the same ground point. A bond is a short circuit, a long conductor is an inductor with a voltage difference at each end.

The only way there would not be a potential difference is if the frame of the appliance is connected (shorted) to the pool grid near point of contact.

A bonding jumper will equalize potential between two points, an inductor will not.

This is why the words bonding and grounding should remain the same. They are two different procedures.

 

[bennie]

Re: Pool Bonding

Measure the voltage difference between the neutral and ground at the appliance. This is common mode voltage.

Bond (short) the neutral to the equipment ground at the appliance, the common mode voltage will go away. Common mode current will then appear as a ground loop.

 

[don_resqcapt19]

Re: Pool Bonding

Bennie,

Measure the voltage difference between the neutral and ground at the appliance. This is common mode voltage.

The only voltage that you should read between the EGC and the grounded conductor is that caused by the voltage drop in the grounded conductor. The two condctors are connected together at a common point. One has currrent flow, the other doesn't. The voltage that appears can only be based on ohms law and the current and impedance of the grounded conductor.

A bond is a short circuit, a long conductor is an inductor with a voltage difference at each end.

Can you show me the math for this? Thanks.
Don