Stray current in reinforced concrete 2

[Plantec]

Hello,

we are currently involved in a project where a big statue is to be constructed in concrete. (The foundation of the statue is a big plate (3m*40m*0.6m). The statue itself is in fact two semi-arcs in concrete (0.5*1.2m), total height 12m.) Now there is a tram passing next to this statue (approx. 5m). I heard that there is a danger that stray current could affect the steel in the reinforced concrete.

Is this wright? If there are problems concerning the stray current, is this only for the steel in the ground, or also above it?

I heard about a solution in which one should connect a diode to the tram rails to "catch" the stray current. Is this the only solution?

Many thanks,
Karel

 

[SlideRuleEra]

At electric generation stations there are many chances for stray currents. Foundations are encircled underground by heavy gauge copper wire (maybe 15 mm, or so, diameter) with ground rods (say 6 meters long) at several locations on this closed loop. Heavy copper wire "pigtails" come through the foundation and are connected to the steel. All electrical connections are usually thermal welded (Cadweld). This system is totally passive, very effective and may be suitable for your situation.

A "power" electrical engineer should be able to work out the details with you.

 

[Plantec]

Thank you for your response, SlideRuleEra. I contacted the tram company and apparently they always use the same method to deal with stray current, and we have to apply their method. So that part of the problem is solved now :-D.

The first part of the problem stays however: is it really necessary to provide such a system (not really cheap...)?

For instance, when I design a building along a tram railway, should I take precautions for my foundations, or for every beam and plate, or is this neglictible? What is the radius of influence of the stray current (maybe depending on the type of soil?)?

Many thanks.

 

[SlideRuleEra]

Dealing with the stray currents is necessary for safety. It is possible to get quite an electric shock. For example, since people with heart pacemakers are often advised to stay away from operating microwave ovens, they probably should not be exposed to preventable electric fields either.

It is usually not necessary to connect each steel member to a grounding grid. Most steel frame buildings (say typical pre-engineered buildings) are connected to a grounding loop on 10% to 20% of their columns. You do want a minimum two grounding connections to the loop for redundancy; this is also the reason that the underground loop is closed - if it gets cut a one location the structure is still grounded.

 

[letrab]

Another reason for grounding you statue would be lightning strikes. Without adequate electrical grounding the lightning current may exit your statue with significant spalling around the base, should it be struck.