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working inside special places like tanks, etc

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martinrelayer

Electrical
Oct 26, 2007
68
Hello,

There will be temporary maintenance works in special places like metallic tanks or very humid places and our local code demands to fulfill some criteria.
It says that the lighting and the tools shall be of 24V or less, or shall have insulating class II (double insulation), or shall be connected through an insulating transformer.
Of couse our tools are of 220Vac and not insulating class II, and there will be major works so we will need all of our tools to match the needs of the workers, so we'll need the 220Vac inside the place.
In case of insulating transformers, which are the conditions tha they should fulfill? which connection is required and which kind of protection is demanded?
Any reference? (IEC, IEEE...)
I was thinking IT single phase distribution, and only short circuit and thermal protection but I would be grateful to hear your experience or some reference.

thanks in advance!!
 
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No mention of the Ground Fault Interupter approach?

I'm not an expert in this field, but I'd expect GFI to be better and cheaper than using a big transformer.

 
I daren't ask why you think this belongs in 'circuit engineering' but the short answer is that you need to buy the right tools for the application. Where are you working?

Lighting is 24V AC for the safety of the workers. Tools are 110V AC centre-tapped earth, which is the standard industrial tool supply voltage for Europe, for the same reason: to reduce the risk to the workforce. Isolation transformers in the UK are to constructed to BS 3535.

What's the reason why can't you provide 110V tools? Most portable tools are available as 110V, unless it draws more than about 4kW or so. That's a big motor for a portable tool, although perhaps not so big for a heater. If there is a 110V alternative - virtually regardless of the cost, within reason - and someone is badly hurt killed as a result of using a 230V tool in a high risk environment then the persons and company responsible for the works will have a very uncomfortable time in court, possibly before an even more uncomfortable time in prison.


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I think Martin is in Uruguay, and thus 230VAC.

 
PS: I'd never heard (until just now) about Europeans using 110V AC centre-tapped earth for tools. Neat idea.
 
It's somewhere with IEC influences from the 'insulating class II', and the 24V AC and 110V AC is common in Europe, as is 230V AC. Maybe he'll get back to us.

I'd have guessed that Uruguay would have been US-influenced, so I guess I'm learning something anyway! [smile]


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Yeah I don't know if it belongs to circuit engineering... not sure if it's circuit or power distribution, and I'm not an university engineer also!!
Yes, I'm in Uruguay, here the normal consumer distribution is 380V three phase 50hz, TN-S, if i'm not wrong, it's central europe influence. I once heard that our code is much influenced by spain but I cannot assure.
Same thing in Argentina, but Brazil is different.
Anyway here we have 400V three phase TN-S distribution for field panels, used by maintenance.
It is not possible to buy class II tools, and yes, we have 24V lighting. But for grinders, drilling machines and that kind of tools it has to be with the standard tools.
No worries about three phase, sicne the only three phase loads are welding machines and will be placed outside.
Ground fault interrupters I think not needed in IT single-phase systems, but that was part of my question also!!
By the way... what's centre-tapped?
 
'Centre-tapped' in the sense that I used the phrase means that the winding is a 110V winding, but there is a third connection to the mid-point of the winding. Either end of the winding is at 55V relative to the mid-point, but there is still 110V between the winding ends. By earthing the mid-point the maximum possible voltage relative to earth is 55V so the risk to personnel is reduced while still making a 110V supply available. It's a fairly standard type of supply in the UK and, I think, in Europe.


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I thought the 110V CTE was just about unique to the UK hence all the stories about Poles turning up on building sites with 230V tools
 
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