Talk:Taking electricity outside

concrete resistance

"A concrete floor in a garage that has no extraneous metal parts in contact with earth and no other services like water pipes entering the building will offer a good isolation from earth,"

Experience with ufer earthing seems to indicate the opposite. NT 23:26, 4 June 2007 (BST)

Not been able to find much on this. Normal practice in new builds seems to suggest that a concrete floor is considered to pose no risk with a PME installation. Ufer earthing also seems to depend on quite a high rebar content in the foundation slab.

The conductivity of concrete also seems hard to pin down - but it is influenced by its moisture content. I have seen figures of 25K ohm / cm - which if true would place more than enough impedance in the earth reference to make this a non issue.

I might post another invitation to comment on the group since the first one seemed to generate somewhat less than the normal level of response.

--John Rumm 11:17, 7 June 2007 (BST)

Some comments on Ufer concrete earth resistance:

"When structural steel is bonded to the earth electrode system, the results can be quite dramatic. The author participated in one mountain-top project where the measured resistance-to-earth of a 20-rod, building earth electrode system — prior to bonding to foundation steel — was 150 ohms. After bonding foundation steel to the earth electrode system (all below grade), the resistance-to-earth was 1.0 ohm"

more here: http://www.psihq.com/iread/ufergrnd.htm NT 22:45, 7 June 2007 (BST)