Should a giant steel framed human aquarium be earth bonded?

[markythesparky]

If the tank was bonded I doubt anyone in side it would see any current flow in fault condition as the current would find the path of least resistance to ground though the nice conducting water.

But really this needs someone who a expert in the field of swimming pool safety

Don't run
Don't jump
Don't bomb
Don't spit
No petting
......

 

[PEG]

Don't run
Don't jump
Don't bomb
Don't spit
No petting
......

That's 5 out of 6 of my previous post's RA list

 

[Deuce]

The 30mA RCD is the key. It will disconnect the supply before the current gets to a dangerous level (50mA). If you didn't have the TT, then the tank would remain live and the RCD would not operate. That is until someone or something created the earth path.

Which do you think is safer?

You just opened up another sphere of debate we have had before. If isolated the performers remain safe, so long as they don't connect with the ground or some other earth point. So they will be ok if the fault is detected and power removed. However, if the tank is earthed they will definitely be subject to current until the RCD reacts, on the assumption that all RCD's are going to react - which isn't the case. It's a fact some have their breakdown moment after their most recent test.

 

[Marvo]

Don't run
Don't jump
Don't bomb
Don't spit
No petting
......

Just watched the video....Not sure we should rule out petting so quickly.....

 

[Deuce]

Nice clean water is not a good conductor

I think the additional information,increases my belief that this needs a specialist,risk assessment.

Next,we will be told that these performers are lowered in this tank,using an electric crane,and i can think of half a dozen RA issues,on that fact,alone.

To be honest all water is pretty crap as a conductor. "Clean" water isn't a conductor at all. The water in the tank is probably cleaner than your tap water, but will still conduct - albeit quite poorly.

 

[StephenRowley]

But the tank water I would hope have a chlorine or other water treatment in there. Which would massively increase its conductivity to better than that of human body.

What does the tank sit upon? It may all ready inadvertently have a path to ground though the ground it's self.

 

[Marvo]

I think the water conductivity is a moot point. This installation would be treated as a special location defined for bathrooms or swimming pools in the regs. I don't know the finer points of the UK regs but I'm inclined to agree with an earlier post suggesting a risk assessment and appropriate mitigation and management of risks be performed for every time it's used.

 

[Deuce]

But the tank water I would hope have a chlorine or other water treatment in there. Which would massively increase its conductivity to better than that of human body.

What does the tank sit upon? It may all ready inadvertently have a path to ground though the ground it's self.

It's dissolved solids, particularly minerals that increase conductivity. TBH I don't know to what extent chlorine does, but yes we use chlorine.

It sits on a 1mm rubber membrane.

It's not just about the water though. The performers could be in contact with the steel frame itself. Or the steel base of the tank.. Of course the steel is certainly a better conductor than us fleshy beings!! But adding the submersion in water of all parts does add an unusual angle to this problem.

 

[Strima]

Without seeing it set up and doing some testing we’re just stabbing in the dark.

 

[Deuce]

I suppose I should add, that clearly this is not a standard application or problem. It's a very unique thing - and the world is all the more richer for having such things.

My goal is to get to a point at which I'm confident that the best solution for safety is in place. As it stands, with the divide in opinion on this, that certainty isn't there. My personal view is that it should be earthed, as it minimises risk overall. Albeit, under certain unexpected conditions it could be said it would have been safer if it wasn't.

 

[Deuce]

Without seeing it set up and doing some testing we’re just stabbing in the dark.

What would you test for? I'm not asking if/how it could transmit current to earth, I'm asking if it should be allowed to in the first place.

 

[PEG]

I'm glad this has run to three pages...at last,i have some independent proof,why my 10 year old,cannot have a pet mermaid.

 

[Taylortwocities]

Sorry, couldn't resist this..

 

[Wilko]

Hi - just a couple of thoughts
- Has the installation been done in accord with BS7671 section 7 and BS7909 ?
- RA and full test prior to each use?

 

[littlespark]

I think we’re missing the big question here

Have you drowned anyone famous yet?

 

[Deuce]

Hi - just a couple of thoughts
- Has the installation been done in accord with BS7671 section 7 and BS7909 ?
- RA and full test prior to each use?

Hi,

The only part of section 7 which in spirit is tough to enforce is others placing/moving lamps closer to the tank than the regs would permit. I say "in spirit" as that requirement is specific to certain locations such as bathrooms, with specific rules for each defined special location.

Was there a particular requirement you were thinking of?

Regards BS7909, yes. That's the one that all event/studio sparks are well read up on. We don't have full control ourselves over what goes where in the layout of the temporary installations, such as the running of power cables and lighting in the area, but we do flag anything that is obviously a concern or may not have been given full consideration.

The sparks on site always ensure the following key areas:

- Every new electrical feed/cable is tested prior to being made available for connection, incl RCD

- All must be 30ma unless special equipment required a different solution.

- All third party electrical equipment is checked for testing within past 12 months and in general scrutinised for suitability of safety precautions.

- in potential wet areas (ie filming in a carpark where it could rain and water could pool) all portable distribution boxes are raised from the ground.

In general everything is considered, checked/tested ahead of each use, most of which last only a few days before being used for something else and being tested again. You could compare it to fully testing and reviewing the electrical installation in your bathroom everytime you take a bath.

The question of whether or not to earth the tank itself does remain a sticking point, but I can say sparks in charge of power on site do everything reasonable to make the surrounding electrical installation as safe as possible. They're 'on it'.

 

[johnduffell]

In terms of bs7671
Bonding - only if it can introduce a potential. The only way i can think is if it was sitting directly on the earth. In that situation the earth would be the extraneous conductive part.
Earthing - only if it is a part of the electrical installation designed to protect people from electricity eg class I appliance or fitting.

So it sounds like the answer is connection it to the main earthing terminal is like bonding a spoon.

If it's a temporarily installation other rules apply other than bs7671. In terms of common sender, to me, any conductive surfaces have a risk, and bonding them all just changes the risk to a different one.

 

[marconi]

Could you post ( I have only looked quickly over the previous posts so you may have done already) - a sketch of the set up including where the items of electrical equipment and their wiring are in relation(including distances) to the aquarium? Also, what voltage is the equipment and what is the electrical supply ie: generator, mains, TT/TNCS/TNS. Where is the water supply which fills it and include the pipework and whether metal or plastic?

 

[Wilko]

I can see why you've not reached a conclusion on this question. I can imagine setups where it may add safety, perhaps as performers enter and exit the tank and stepping onto GME while touching the tank etc. If you've a repeated system of installation (tank placement, access and egress, steps etc) that could be assessed perhaps and a conclusion reached. Personally, I want to TT the installation and connect all conductive parts, but it's not a cattle shed so I'm probably wrong

 

[marconi]

I can see why you've not reached a conclusion on this question. I can imagine setups where it may add safety, perhaps as performers enter and exit the tank and stepping onto GME while touching the tank etc. If you've a repeated system of installation (tank placement, access and egress, steps etc) that could be assessed perhaps and a conclusion reached. Personally, I want to TT the installation and connect all conductive parts, but it's not a cattle shed so I'm probably wrong

I have similar thoughts to you on this but still need to see a sketch - my early thoughts before seeing sketch are to make it a 55V-0-55V TT installation centre -tap earthed and the 110V passed through a 10mA double-pole RCD. 110V provided by a safety isolation transformer supplied by mains through a 30mA double pole RCD. Then bond all metalwork together and to terra-firma. OP - this is not a definitive answer.