# Why resistor will be used between two different grounds

#### pinkyponky

Joined Nov 28, 2019
309
Hi,

This is theoretical question but it will be implemented practically in many circuits (I don't have circuit to show). The question is why the resistor will be used between two different grounds and how that value to be calculated?.

#### ericgibbs

Joined Jan 29, 2010
16,345
hi pp,
As this is Homework, we need to see your attempt at answering the assignment.

E

#### Lo_volt

Joined Apr 3, 2014
275
What will happen if the grounds are not connected? In answering that question think about real world influences such as EMI (electromagnetic interference) and leakage current etc. that may affect your circuits.

Once you understand why grounds should be referenced together then take a look at what will happen if they are connected with a resistor and compare that with connecting directly without a resistor.

#### Fresnome

Joined Oct 13, 2021
1
Current limiting. If a short to ground occurs voltage drop across resistor would make the rest of path to ground ssfe

#### Papabravo

Joined Feb 24, 2006
19,244
There may be different reasons.
1. You might choose a low value resistor so that the grounds will be separated in the layout but electrically, approximately equal. An example would be an analog ground and a digital ground on the same PCB, mechanically separate, but electrically equal.
2. You might choose a high value resistor so that no current flows between the two grounds, effectively isolating them from each other.
It is easy to see the effects of these choices in a simulator.

#### pinkyponky

Joined Nov 28, 2019
309
If possible, Can you show me with the example circuit using low value resistor and high value resistor?.

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#### ericgibbs

Joined Jan 29, 2010
16,345
hi pp.
We are not here to do your Homework, post the circuit example yourself, then we will help.
E