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?

 

[Wilko]

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[Midwest]

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Thats the briefest of replies I've ever seen. Brief & to the point

 

[johnduffell]

If it's in a rubber mat then you can't touch it and true earth at the same time. Also it isn't touching true earth. Therefore no chance of an electric shock involving it unless you are touching a live conductor and another live conductor is touching it.
Therefore it doesn't matter if something falls in and lifts it to any voltage. True It won't trip any rcd or mcb unless the item falling in has an earth, but for the same reason no one can get an electric shock.
If you connect it to the MET, you are giving the potential to get a shock from touching the tank and a light that falls inside the matting but didn't touch the tank itself.

Summary: bond increases both the risk of getting a shock and the chance of something tripping.
On a single conductive item not bonding hugely reduces the chance of getting a shock, but also reduces the chance of something tripping.

This is precisely the argument for and against earthing neutrals (as opposed to an isolated ie earth free transformer outlet).
The reason we go for ADS is that it's impossible to guarantee that there are no earth faults in a system, therefore we create an intentional one and provide devices to detect a further one.
Since earthing and bonding (and conductive metal) are fundamentally dangerous, if there's little chance of a fault from a live conductor to the earth in your zone, it's much safer not to earth/bond.

We only "bond" the actual earth itself because it's so big and the electrical supply is also big and out of our control, that there's likely to be another fault elsewhere unnoticed. Is that likely in the context of the large tank which is probably earth free?

So id come down on the side of don't bond.

 

[Wilko]

Thats the briefest of replies I've ever seen. Brief & to the point

The reply was replete with the sum of my life experience.

 

[littlespark]

Nothing to add to the debate.

Just that I recall a group of synchronised swimmers appearing on Britain’s Got Talent a couple of years ago. They had a portable tank and performed the audition in the car park rather than in the studio.

How do escapologists manage when they’re hanging upside down in a tank of water trying to undo handcuffs with one hand and fill in a risk assessment in the other?

 

[Marvo]

It's not often there's a thread in the evening that I think about several times during the following day and even discuss it with others....but this thread is the exception. It's interesting, not just because the setup itself is novel or unique but also because all the usual perameters that electrical safety decisions would be based on are so fluid and change probably just about every time the thing is set up (supply earthing arrangements, surrounding accessories and electrical items etc etc). The whole tank could in fact be non-extraneous in nature one minute and, following a water splash as performers enter or exit, the classification could change immediately.

My gut feel is to earth the tank but I don't have any regs to back this up because of the ever changing physical and electrical environment. The driver behind my gut feel is I think that creating an area within an completely surrounded existing equipotential zone creates more unmanageable risks and potential problems than it solves.

 

[markythesparky]

BS7671 has regulations on ‘out of ground’ pools as well as ‘in ground’ pools. My view is, and this is directly from the regs, and we do lots of pools, and we’ve not been pulled yet in inspections, would be they this is an out of ground pool. Even if the pool has plant, which I would see no need for as it is temporary, but I stand to be corrected, and the plant is within the zones then the regulations for pool zones apply to that plant. If the plant is not within the zones then it does not as they are not in that area of special location.

It is after all a metal framed box with glass walls. We don’t even know if the metal is accessible from inside the pool.

The risk, as with most pools is when the occupant enters or exits the water.

As I said before, there are already regs on out of ground pools.

As for the lighting above or around this tank, in my view this lighting should be treated in the same way as lighting around an out of ground pool.

If it were to fall in, as some one previously surmised, then I would say, ‘if my granny had wheels, she’d be a bus!’

You cannot realistically take into consideration every possible eventuality as this in itself is unrealistic. The regs are designed to minimise most of the obvious dangers.

 

[chrisdungan]

Hell yes earth bond it.
One question ..... Is it exposed metal that has the potential to become live?
Another question....... Is it electrically unsafe? Note I ask "unsafe?" rather than "safe?" a subtle but I believe a significant difference
Last question....... What would be your response in front of the coroner??

 

[MFS Electrical]

If it’s sitting on an insulator then it isn’t extraneous and doesn’t have to be bonded a test would have to be carried out at each location it was used though as well as complying with the formula in the regs book

 

[Nigel]

Hell yes earth bond it.
One question ..... Is it exposed metal that has the potential to become live?
Another question....... Is it electrically unsafe? Note I ask "unsafe?" rather than "safe?" a subtle but I believe a significant difference
Last question....... What would be your response in front of the coroner??

No it is not exposed metal that has the potential to become live.

 

[littlespark]

Similar question here. I’ve just hired a storage container for my equipment. There’s 6 in an old farm shed, 13A sockets approx 2m from the door. The owners have plug in lights that the renters can carry into the containers.

Do containers need bonded or earthed?

They have bigger containers in another shed with installed lights inside them. I would think these will be bonded, but haven’t checked.

 

[Nigel]

Similar question here. I’ve just hired a storage container for my equipment. There’s 6 in an old farm shed, 13A sockets approx 2m from the door. The owners have plug in lights that the renters can carry into the containers.

Do containers need bonded or earthed?

They have bigger containers in another shed with installed lights inside them. I would think these will be bonded, but haven’t checked.

You really should start a new thread.

 

[littlespark]

I wasn’t going to start a new thread because I thought the situation was very similar- big lump of metal that people can enter with electricity nearby.

It’s just the water tank is more portable than a shipping container.

Are there regulations in place for containers, and can they be used for the OP of this thread?

 

[markythesparky]

I wasn’t going to start a new thread because I thought the situation was very similar- big lump of metal that people can enter with electricity nearby.

It’s just the water tank is more portable than a shipping container.

Are there regulations in place for containers, and can they be used for the OP of this thread?

It’s totally different. BS7671 doesn’t have a section devoted to metal shipping containers but it does for pools. I agree that you should start a new thread.

 

[Nigel]

It’s totally different. BS7671 doesn’t have a section devoted to metal shipping containers but it does for pools. I agree that you should start a new thread.

Portable and relocatable buildings - Section 7.