# Re: Current Limiting and Impedence

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• Subject: Re: Current Limiting and Impedence
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• Date: Tue, 26 Apr 2005 19:46:07 -0600
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`Original poster: "Paul B. Brodie" <pbbrodie@xxxxxxxxxxxxx>`

Gerry,
It isn't confusing at all. I had completely forgotten that Z = sqrt(R^2 + X^2). That little reminder brought everything clear as can be. At least I can still adhere to Z total = Z1 + Z2 + ... Zn. Thank you very much for your explanation.
Paul
Think Positive

```----- Original Message -----
From: "Tesla list" <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
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Sent: Tuesday, April 26, 2005 11:33 AM
Subject: Re: Current Limiting and Impedence```

> Original poster: "Gerald Reynolds" <<mailto:gerryreynolds@xxxxxxxxxxxxx>gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Mark,
>
> This can be a confusing area.
>
> Rtotal = R1 + R2
>
> For parallel resistances, the conductances (G) add:
> Gtotal = G1 + G2
>
> or expressed as resistance:
> 1/Rtotal = 1/R1 + 1/R2
>
> Now the tough part:
>
> Impedance, in the general case, has resistive (R) and reactive (X)
> components (sometimes refered to as the real and imaginary parts). For
> series impedances, the resistive components add up and the reactive
> components add up (keeping in mind that capacitive reactance is negative
> and inductive reactance is positive) so you get the following:
>
> Ztotal = Rtotal + jXtotal = Rtotal + j(XLtotal -XCtotal)
>
> You can't linearly add the resistive and reactive components together. The
> impedance is a complex number denoted by the j prescript on the reactive
> part. What you can do instead is determine the magnitude of the impedance
> using:
>
> Z = sqrt(R^2 + X^2)
>
> You can think of the R and X terms being two sides of a right angle
> triangle and the Z being the hypotenus (sp?). Series impedances add
> similar to resistances in that:
>
> Ztotal = Z1 + Z2
> but one needs to keep to the rules of complex math.
>
> Parallel impedances also behave similar to parallel resistances in that:
>
> 1/Ztotal = 1/Z1 + 1/Z2
> and again one needs to keep to the rules of complex math.
>
> Hope this helps more than being confusing.
>
> Gerry R
>
>>Original poster: "Mark Dunn" <<mailto:mdunn@xxxxxxxxxxxx>mdunn@xxxxxxxxxxxx>
>>
>>I still don't quite get it.
>>
>>1. Not that it matters for this question, but I thought I could sum
>>series impedence. Could you re-confirm? Are you sure you haven't
>>confused with Z^2 = R^2 + X^2? I don't mean to question and I am not
>>an expert so I am just making sure.
>>
>>If it is Z^2 then my formula for parallel Z must be wrong. I'm using
>>1/Z = 1/Z1 + 1/Z2 + ... . Just like resistance.
>
>
>
>
>