Should a giant steel framed human aquarium be earth bonded?

[Deuce]

I have a large, portable steel framed tank. approx 6m x 2m x 2m. It is used for actors/models to perform in for a variety of productions.

For many years now, I have had conflicting advice about whether or not it should be earth bonded. The initial response is "it's a giant steel structure, bond it!!". But then invariably someone else comes along and points out that, should the tank itself become energised, the people in the water within the tank would become part of the return to earth - the current would flow through the tank and them. If it was not bonded, as it is by design insulated, they would be ok. At least until they tried to leave the tank.

To date our solution has been to be super cautious of anything that could even present the possibility of bringing current to the tank itself. But how do we make a once and for all decision on whether it should be bonded without any professional consensus of opinion?

 

[Leesparkykent]

I have a large, portable steel framed tank. approx 6m x 2m x 2m. It is used for actors/models to perform in for a variety of productions.

For many years now, I have had conflicting advice about whether or not it should be earth bonded. The initial response is "it's a giant steel structure, bond it!!". But then invariably someone else comes along and points out that, should the tank itself become energised, the people in the water within the tank would become part of the return to earth - the current would flow through the tank and them. If it was not bonded, as it is by design insulated, they would be ok. At least until they tried to leave the tank.

To date our solution has been to be super cautious of anything that could even present the possibility of bringing current to the tank itself. But how do we make a once and for all decision on whether it should be bonded without any professional consensus of opinion?

It would be site specific.

 

[chris gray]

Earthing and bonding as far as I’m aware as 2 separate things

 

[Deuce]

Earthing and bonding as far as I’m aware as 2 separate things

Maybe I'm wrong in my terminology. I thought bonding was the connection of two conductive systems, and in this case bonding the tank to earth = earth bonding. Feel free to educate me though - that's why I'm here asking

 

[Deuce]

It would be site specific.

Can you give me an example of a site where bonding the tank would not put those inside at risk if it were to become live?

We take site specific factors into account for a variety of reasons but I can't see how the tank being earthed would ever be a good thing for the people in the tank.

 

[Marvo]

Is Rcp ≥ (Uo/Ib)? What earthing arrangement does the electrical installation have?

 

[Deuce]

For clarity; my concern is that because the tank is full of water, it is the equivalent of forming a conductive shell around the occupants, and then passing current through it. It's not the same as earthing a fridge so that if the outer skin becomes live, anyone touching it doesn't carry the current. It's the equivalent of making them part of the earthed item itself.

 

[Deuce]

Is Rcp ≥ (Uo/Ib)? What earthing arrangement does the electrical installation have?

Varies! Our own kit (the filtration system) is bunded in case of leaks and all electrical fully isolated from the water passing through it. The environment alters as the tank is used at various studios and venues around the world.

 

[Marvo]

So the whole tank and its associated equipment is effectively portable? It plugs in? It's also used in a variety of building structures ie some will have metal building elements in reach of the tank others won't........ Lol, You might have mentioned this in the OP

 

[PEG]

Is this fixed or mobile? I would be tempted to do a risk assessment where it is filled,and keep all cable connections away from it. Well away.
In my opinion,depending on where it is sited,the least number of possible electrical connections to it - the better.

 

[markythesparky]

What is the tank sitting on/ in?

In the case of swimming pools, they are in or on the ground (earth). The idea behind pool bonding is that everything touchable is brought to the same potential and therefore minimises shock risk. TN-C-S earthing systems are not allowed due to the risk of a disconnected neutral and the consequence of mains potential within the pool area.

My view would be to TT it and have anything near it on a 30mA RCD.

 

[Deuce]

What is the tank sitting on/ in?

In the case of swimming pools, they are in or on the ground (earth). The idea behind pool bonding is that everything touchable is brought to the same potential and therefore minimises shock risk. TN-C-S earthing systems are not allowed due to the risk of a disconnected neutral and the consequence of mains potential within the pool area.

My view would be to TT it and have anything near it on a 30mA RCD.

The one constant is that wherever the tank goes, 30ma RCD is the standard.

The tank is always sat upon a butyl membrane, so it's isolated.

If it was TT'd, of course that is a sound path to discharge current. But if the clamp is at the base of the tank, and a live lamp collapses and hits the top of the tank, the current would flow down through the tank and the water and through the people inside it surely. In that scenario wouldn't it be better that it was left isolated?

 

[chris gray]

Surely bonding would create a path?

 

[Marvo]

So there's 230v lighting within zone 1? This just gets better....
Did the tank and its associated equipment come as a certified design or is it just something that was fabricated and that's evolved and been added to?

 

[Marvo]

Do you have some photos maybe?