Electronics > Beginners

Lab with NO grd, what about gear?

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exe:

--- Quote from: station240 on October 14, 2018, 10:35:45 am ---Do you have any exposed metal water pipes you could clamp an earth wire to ?

--- End quote ---

Oh shi~, don't do it. Unless you want to electrocute somebody taking bathroom or something. Not to mention you don't know if part of the pipe was replaced with a plastic one.

I think some idiots did it in my previous appartment. Touching radiator was painful.

Brumby:

--- Quote from: station240 on October 14, 2018, 10:35:45 am ---Do you have any exposed metal water pipes you could clamp an earth wire to ?

--- End quote ---

You don't do that here any more - and it would be risky to suggest that, IMHO.

Doing so relies on there being very good and reliable earthing of the pipes all the way from the connection point to the soil in which they are embedded.  It only takes some dry dirt around a pipe or one gap in the electrical conductivity to send current in a direction that you don't want.

There is also the very real risk that someone working on a pipe somewhere up the line could find themselves between a fault current and the path it wants to take.  This is no joke - I have seen plumbers with a meter connected across a pipe that needs to be separated for whatever reason and if it measures a voltage above a certain limit, then they have to walk away from the job and get someone in to sort it out.

Separate earth stake is really the only safe way - which is a problem in units/apartments.


--- Quote from: exe on October 14, 2018, 03:43:44 pm ---Unless you want to electrocute somebody taking bathroom or something. Not to mention you don't know if part of the pipe was replaced with a plastic one.

--- End quote ---
Exactly

FriedMule:
You are all great, thank you!

I have found out that we use something called "TT systemet" does that mean anything to you?

helius:
TT stands for "Terra-Terra", and is the system where each premises is independently grounded (through a copper rod driven into the earth). The electric service connection does not contain a ground conductor, and the protective earth pins in the outlet sockets do not connect back to the power feed, only to the local ground rod.
https://en.wikipedia.org/wiki/Earthing_system#TT_network

The TT system has high ground fault impedance (since the earth between the local building and the utility transformer is part of the loop). That means that in the case of an insulation fault from phase to chassis in equipment, even if the equipment has a grounded plug, the fault current may be too low to trip a breaker. The RCD is what provides safety in this scenario.

Ian.M:
If you cant run an adequate ground connector to a ground rod for a TT system because you are on a high floor in an apartment building etc.  its possible to use a large isolating transformer (so the whole bench can be powered through it), then on the secondary side, set up an equipotential bonding zone for supply ground, with secondary side neutral tied to it, followed by a RCD.   Any fault currents are local to the bonding zone, so cannot cause the safety problem with unexpected potentials across any insulating joints or section in water pipes etc.   I must emphasise that *ALL* equipment that is on the bench or connected to it *MUST* be supplied by the same isolating method to avoid endangering plumbers etc.

N.B. This arrangement almost certainly doesn't meet local  electrical code for a fixed installation, so only build it as a plug-in setup.

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