Safety concerns of a 30 yr old swimming pool

Ravenvalor

Senior Member
Hello

if you bought a home that had a 30-year old inground swimming pool that had absolutely no bonding of metal parts would you let your kids swim in the pool? Home is in a suburban neighborhood with 1/4 acre to 1/2 acre lots.

thanks for your input
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
lots of 30 YO pools with no bonding out there.

problem is that the rare case where there is a problem gets all the attention and the millions of times there is no issue get ignored.

it is a risk you have to make an evaluation on.

personally, I would think a 30 YO inground pool is near the end of its useful life anyway.

my best guess would be that on the whole the risk of drowning or injury due to diving improperly is greater than the risk of electrocution.
 

drcampbell

Senior Member
Location
The Motor City, Michigan USA
Occupation
Engineer
Just reading the title scared me.
My answer is "no". Maybe if all the power to the pool area were disconnected during swim sessions, but I'm not even comfortable with that, given children's attention to detail. Maybe if a red revolving warning light were hard-wired in to the pool circuit without a switch.

... the risk of drowning ... is greater than the risk of electrocution.
The problem with that guess is that electrocution isn't the only (or major) danger. Electric-shock drowning is indistinguishable from any other kind of drowning. When someone drowns, there's no way to tell whether it was an electrical problem. So we really don't have good data about the relative risks.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Just reading the title scared me.
My answer is "no". Maybe if all the power to the pool area were disconnected during swim sessions, but I'm not even comfortable with that, given children's attention to detail. Maybe if a red revolving warning light were hard-wired in to the pool circuit without a switch.


The problem with that guess is that electrocution isn't the only (or major) danger. Electric-shock drowning is indistinguishable from any other kind of drowning. When someone drowns, there's no way to tell whether it was an electrical problem. So we really don't have good data about the relative risks.
If it is indistinguishable from other types of drowning, how would one know that it even happened?
 

Ravenvalor

Senior Member
Just reading the title scared me.
My answer is "no". Maybe if all the power to the pool area were disconnected during swim sessions, but I'm not even comfortable with that, given children's attention to detail. Maybe if a red revolving warning light were hard-wired in to the pool circuit without a switch.

That sounds like a good way to handle the situation. Wonder, should one be concerned about underground utility power lines leaking current? If for instance an underground neutral has a nick in it, will current leak out of it and possibly find its way to a swimming pool area?

Thanks,
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
That sounds like a good way to handle the situation. Wonder, should one be concerned about underground utility power lines leaking current? If for instance an underground neutral has a nick in it, will current leak out of it and possibly find its way to a swimming pool area?

Thanks,
Why would you be more worried about a leaky neutral than a leaky hot?
 

kwired

Electron manager
Location
NE Nebraska
Tuning off all power to the pool isn't going to gain much, GFCI's will trip for nearly all conditions that this will prevent.

The bigger problem that a GFCI will not protect you from is rise in voltage on service neutral which is also imposed on the EGC and everything bonded to the EGC. That voltage rise can simply be ordinary voltage drop on conductors that otherwise are considered to be functioning properly. It may be in the 120 volt to ground customer "service" portion of the supply or it could be a result of normal voltage drop on a portion of the grounded neutral of the primary distribution which is also bonded to the service neutral conductor at the transformer.

The whole concept of properly installing equipotential bonding network is that regardless what voltage level the EGC is in relation to "true ground" everything in the pool and immediate vicinity that a pool user can contact is always at same potential and pool user is in many ways no different that a "bird on a wire" that won't get shocked because it can not contact something that is at different potential.

If by "disconnecting power to the pool" you also disconnect the service neutral and any and all possible bonding paths between S/N and the pool then you have a reasonably safe from electrical events situation on a non properly bonded pool.
 

Ravenvalor

Senior Member
Is the traditional means of testing the bonding system of a swimming pool with an ohm meter still apply to a 30 year old pool? It seems that after 30 years those connections are highly suspect.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
That sounds like a good way to handle the situation. Wonder, should one be concerned about underground utility power lines leaking current? If for instance an underground neutral has a nick in it, will current leak out of it and possibly find its way to a swimming pool area?

Thanks,
A nick in the utility neutral is not really a problem...the problem with is neutral is where it has become a high impedance path and the neutral current is flowing in the earth
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Is the traditional means of testing the bonding system of a swimming pool with an ohm meter still apply to a 30 year old pool? It seems that after 30 years those connections are highly suspect.
In Mike Holts testing, he found that the quality of the connection is not very important...even connections with a resistance as high as 100k ohms worked to bond the pool.

His testing method is to put a small connection to earth, such as a long screw driver, or a short length of pipe, away from any known grounding electrodes. Then he measures the voltage from the service neutral to this temporary electrode. That number is his basis number for testing the pool. He then measures the voltage from the temporary electrode to everything at the pool, including the deck and the water. If the bonding is there, you will see approximately the same voltage as you read to the service neutral. There will be some variations in this voltage as loads change, but the voltage at the pool should match that from the neutral. I believe this method is shown on at least one of his pool videos.
 

kwired

Electron manager
Location
NE Nebraska
Is the traditional means of testing the bonding system of a swimming pool with an ohm meter still apply to a 30 year old pool? It seems that after 30 years those connections are highly suspect.
Simple ohm meter may not even give you results you are assuming to see on a new installation. What matters is whether voltage gradients can occur in/around the pool that cover short enough distance a user can place themselves across that voltage.

Testing for volts in a manner like Don mentioned (that MH has instruction on) would catch this sort of thing much easier than strictly an ohmmeter.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If it is indistinguishable from other types of drowning, how would one know that it even happened?
It is indistinguishable in an autopsy alone. But that is usually not all the information available.
At least two indicating factors:
1. Behavior of the person who drowned.
2. Complaints of shock by others before or after the drowning.
A conclusive indication would be measurement of an excessive voltage gradient in the water or between water and pool ladder or other metal.
 

Ravenvalor

Senior Member
In Mike Holts testing, he found that the quality of the connection is not very important...even connections with a resistance as high as 100k ohms worked to bond the pool.

His testing method is to put a small connection to earth, such as a long screw driver, or a short length of pipe, away from any known grounding electrodes. Then he measures the voltage from the service neutral to this temporary electrode. That number is his basis number for testing the pool. He then measures the voltage from the temporary electrode to everything at the pool, including the deck and the water. If the bonding is there, you will see approximately the same voltage as you read to the service neutral. There will be some variations in this voltage as loads change, but the voltage at the pool should match that from the neutral. I believe this method is shown on at least one of his pool videos.

Thanks for the great info Don. I see where you all were discussing this topic on this forum about 4 years ago at this link

 
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