Ground tails through slab

[bennie]

Re: Ground tails through slab

Dereck: You are correct, I was thinking of a contact with high voltage lines.

A low side surge can contain different frequencies on a DC fundamental. The magnitude of these frequencies can not create enough self inductance to impede the DC current flow.

The only white paper I have read, deals strictly with the e field and related charging by capacitance coupling. This voltage, when reaching the flashover stage, is a mini-lightning strike.

 

[dereckbc]

Re: Ground tails through slab

Bennie, lets try a different approach. Since you have some radio background I am sure you are aware of how to calculate the impedance of a inductive circuit using Xl=6.28*F*L. Now a 10 foot long piece 750 MCM cable in free air exhibits 3.8 micro- henries of inductance. The same length of a single 750 MCM in conduit exhibits 128 micro-henries of inductance.

Now pick some numbers for frequency like 1 Mhz, 10 Mhz, and 100 Mhz to represent lightning or any fast rise current and see what a difference in impedance you get between free air and conduit.

I hope you will see by bonding the conduit at both ends simply removes it from the circuit and makes it part of the cable.

Dereck

 

[websparky]

Re: Ground tails through slab

I tend to agree with Bennie.

If one were to place two Conductors side by side; one passing a steady Electric Current (DC); the other wire is unaffected. Although there are Magnetic Flux lines "cutting" the second Conductor, No E.M.F. is generated since there is No Relative Motion.
However, if the Electric Current is made to vary in Magnitude and/or Polarity, then there would be an Induction of an E.M.F into the second Conductor, i.e., this variation/change in Magnetic Flux has the same Effect as Relative Motion between the Magnetic source and the Conductor.

 

[bennie]

Re: Ground tails through slab

The explanation in the 1984 Handbook is even more bizarre. The author maintains that when the conductor is bonded at each end of the metal conduit, 97% of the current flows in the conduit meaning that only 3% flows in the conductor. With the conduit and conductor not in parallel, the current is reduced to the 3% by inductive reactance created by the conduit.

I may be in the goofy zone, but I have some company.