Tinned Ground Conductor

Though NEC doesn't specifically mention the type of coating indicated in the table 8 anywhere in the code but most probably it is for nickel coated. Because, whenever NEC indicates the coating of the conductor, it always mentions nickel coating (see NEC 2008 article 330.104 or 332.104 or 336.104 etc.). I think there will be negligible variation of DC resistance due to the type of coating (tin or silver or nickel). I would suggest you to see the manufacture's catalog and find the DC resistance and I don't think it exceeds the value indicated in NEC table 8.

For safety side and peace of mind, you can go for the higher size of cable (either 3/0 or 4/0) but it sounds to me 2/0 is good enough.

- MS

The coating from your point of view can be ignored as on dc the electron flow is via the core,

so select a core which will give you the required resistance

Not to sound like a moron..... but i thought AC and DC run along the surface of the conductor. That is why with the same mass of conductor per foot. You can get a higher amperage rating by making a bus then a circular conductor?

I'm about to get an educational ass kicking aren't I?

Transmission lines are hollow.

the ongoing thoughts are that electricity flows through the conductor at dc and as the frequency ie ac goes up the more the electricity moves towards the outer skin, Meaning that the centre part of the conductor is not used.

http://en.wikipedia.org/wiki/Skin_effect

http://encyclopedia2.thefreedictionary.com/Skin+effect+(electricity)

http://www.ehow.com/how_6058831_calculate-skin-depth.html

http://www.hmwire.com/skin_effect.html

Electrons are all the same polarity:negative.Like charges repel each other.The higher the voltage, the higher the repulsive force.High voltage insulated wires have special considerations when terminating and splicing(Called stress cones) that have a semiconductor membrane and a braided ground to bleed off any accumulated charge on the surface of the wire.If this is not done properly, the static can ionize the air around the conductor and create a short circuit condition as the resistance avalanches downward as the curernt increases.Big Boom! The higher the voltage, the furthur out on the conductor the electrons tend to travel. I once worked on a device that carried 300 amps, 120 volts, 50 Khz thru a 1/4 inch copper tube that had cooling water circulating thru it. DC can also ionize air at high voltages, creating the same catastrophic conditions. Insofar as grounding is concerned, since the job is pre-engineered, do not try to second guess the engineer.All grounds are not created equal.Even the best grounds contain resistive,inductive and capacitive elements in them.A good ground for AC 60 hz may be a poor ground for DC, and visa versa. Some computer rooms require a grid grounding structure,with copper wire forming a net like structure under the floor. The size of the grounding conductor is determined by the size of the upstream circuit breaker.It must be large enough to safely carry the full load needed to trip the breaker. CAD WELD of joints is recommended for security of connections.This is a Thermite type welding that will bond even dissimilar metals permanently. Hope this helps. HTRN

I think the TIN coat is more of a corrosion resistant issue. If oxides build up, and they are most likely with a floor installation, then the ground connection will be compromised. I would go with a bit heavier AWG and make sure that the ground connections are very secure. You might also consider applying some anti-corrosion grease on the connections. You can get it at an automotive store. It is used on the battery terminals in cars.

There are a couple of issues here.

First, if the drawings show 2/0 tinned wire for the ground, that is what should be provided. This was probably engineered to take many issues into consideration. I am fairly certain that the tinning is for corrosion resistance and was probably figured into the calculation of the required size.

Second, the difference between coated and uncoated wire is only about 4% resistance increase.

Third, the table deals with DC resistance which is only one aspect of grounding. With high frequency electronics, you normally need to look at providing a low resistance path to ground for high frequency as well. Due to the "skin effect" of high frequency current, you would want to have as many strands as possible. And with tinned conductors, you would eliminate the possibility of corrosion changing the "skin " resistance.

Friends,

I agree with MLHemmer on this one. I would also be very cautious before using any "hardware store" type of anti-corrosion materials on the connections (as another post suggested). I would want to see its certification for use in this environment, before using it.

--JMM