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Re: grounding - this doesn't make sense - wire size
Subject: Re: grounding - this doesn't make sense - wire size
Date: Mon, 05 May 1997 20:09:44 -0700
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization: Stoneridge Engineering
To: Tesla List <tesla-at-pupman-dot-com>
References:
1
Tesla List wrote:
>
> Subject: grounding - this doesn't make sense - wire size
> Date: Fri, 2 May 97 06:35:58 UT
> From: "William Noble" <William_B_Noble-at-msn-dot-com>
> To: "Tesla List" <tesla-at-poodle.pupman-dot-com>
>
> I read about the importance of a high current ground, and the use of
> heavy
> wire to connect to it. Yet the secondary wire isn't all that big. I'm
> using
> 24 gague on a 4 inch secondary - if I remember right the largest wire
> size on
> a secondary I've read about on the list is 18 gague??? What I don't
> understand is why the wire from the secondary to the ground rod (or
> whatever)
> needs to be more than one wire size (or 2) larger than the wire that the
> secondary is wound with. IT would seem to me that current is limited by
> melting the secondary wire. Can someone explain.
William,
The point of maximum current in the secondary is at the base of the
coil. In order to maximize performance of the secondary resonant system,
it's important to keep the total impedance in the ground path to a
minimum. This means minimizing the inductance and resistance in this
path. The AC resistance, in particular, can be much higher than the DC
resistance due to skin effect. Losses in the groundpath will reduce
power available at the top of the coil. This is why having a solid RF
ground is also important. While not as critical on a small coil,a good
grounding system becomes very important as you increase power levels.
Poor grounding will also cause inordinately high coil base voltages,
which can cause significant problems with flashover to the primary.
Round or strap type conductors are most effective, since they will have
BOTH low AC resistance and inductance.
-- Bert H --