broadgage
Senior Member
- Location
- London, England
It is my belief that the code requirements for below ground swimming pools (if of steel reinforced concrete, as most are) are not adeqaute.
I believe that a code compliant installation could be dangerous under entirely forseeable fault conditions.
At present a relatively small wire for grounding or bonding is code compliant to the steel reinforcing of a below ground swiming pool.
A large below ground pool forms an excellent connection to the general mass of earth, of far lower resistance than any likely ground rod or array of ground rods.
(I have measured less than 1 ohm)
If therefore a fault occurs, such as an open neutral on the POCO service conductors, then very substantial currents will flow via the pool bonding conductor, and the general mass of the earth.
The ground connection could be so good that nothing would be noticed as being amiss, with almost the whole of the neutral current flowing via the pool, perhaps almost indefinatly.
Consider a ground rod resistance of 50 ohms, and resistance from the pool of 0.5 ohms.
With an open neutral and 100 amps of neutral current, about 99 amps will pass through the grounding or bonding connection to the pool, and about 1 amp via the ground rod.
The relatively small conductor permitted to the pool could therefore become dangerously hot.
It is therefore my belief that Code should require much larger bonding connections to in ground pools.
"No smaller than the service entrance neutral" might be reasonable and is simple, requiring no calculations or tables.
Similar arguments apply to other large structures in good contact with the general mass of earth, such as large buried tanks and pipelines and steel docks, wharves and pontoons.
What do others think ?
Is it worth someone making a formal proposal ?
Not certain how to do this.
I believe that a code compliant installation could be dangerous under entirely forseeable fault conditions.
At present a relatively small wire for grounding or bonding is code compliant to the steel reinforcing of a below ground swiming pool.
A large below ground pool forms an excellent connection to the general mass of earth, of far lower resistance than any likely ground rod or array of ground rods.
(I have measured less than 1 ohm)
If therefore a fault occurs, such as an open neutral on the POCO service conductors, then very substantial currents will flow via the pool bonding conductor, and the general mass of the earth.
The ground connection could be so good that nothing would be noticed as being amiss, with almost the whole of the neutral current flowing via the pool, perhaps almost indefinatly.
Consider a ground rod resistance of 50 ohms, and resistance from the pool of 0.5 ohms.
With an open neutral and 100 amps of neutral current, about 99 amps will pass through the grounding or bonding connection to the pool, and about 1 amp via the ground rod.
The relatively small conductor permitted to the pool could therefore become dangerously hot.
It is therefore my belief that Code should require much larger bonding connections to in ground pools.
"No smaller than the service entrance neutral" might be reasonable and is simple, requiring no calculations or tables.
Similar arguments apply to other large structures in good contact with the general mass of earth, such as large buried tanks and pipelines and steel docks, wharves and pontoons.
What do others think ?
Is it worth someone making a formal proposal ?
Not certain how to do this.
