What is chasis ground and why is it needed?

[magnetra]

What is chasis ground and why is it needed?

Magnetra

 

[SkyHigh]

Re: Grounding

Chassis ground is instrument or equipment ground where metal casing or enclosure is used, epecially when the equipment is using a high-voltage supply. The potential difference between high-voltage supply and the metal casing can create static potential that is leaky is the gap or distance is very near. Therefore chassis ground is required to provide the shortest return path to prevent electrical hazard.

 

[Kral]

Re: Grounding

In addition to the points mentioned by SkyHigh;
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A chassis ground provides a termination point for electric fields, thus reducing the effects of electromagnetic interference (EMI) and other stray electric fields.
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It also provides a termination point for eletrostatic discharge (ESD). If the chassis is connected to Earth ground, then the current due to ESD can flow to earth ground rather than through sensitive electronic circuitry.

 

[SkyHigh]

Re: Grounding

Kral,

Yes indeed, good facts made from outside the chassis. I only said from internal the chassis.

EMI and ESD can be terminated by chassis grounding.

One caution, grounded chassis can only effectively minimise E-field, depending on chassis thickness. However it doesn't minimise H-field because it has a far-field wave impedance.

Another purpose of grounded chassis is to reduce cosmic radiation (such as one caused by Solar Effect), especially in space equipment used on satellites, shuttles and even ones on aircrafts.

 

[FANT]

Re: Grounding

Look at the following link :

hXXp://bwcecom.belden.com/college/techpprs/capwmtp.htm

Not properly EDA, but worth the reading.

Mandi

PS = remember to change XX with tt

 

[sinbeloanthi]

Re: Grounding

Grounding and lightning protection is essensial for any communication system because the sensitive of electronic device

 

[epp]

Re: Grounding

In lighting protection systems for telecom towers/masts you have to had impedance (50/60Hz)<10ohm. But when thunder strikes our grounding system acts as an capacitor at high frequency which no one had measured till now.

 

[magnetra]

Re: Grounding

"Therefore chassis ground is required to provide the shortest return path to prevent electrical hazard."

Could really understand that? Would you please elaborate?
Thanks for the response
Magnetra

 

[SkyHigh]

Re: Grounding

Shortest return path is not a path of the shortest physical route measured by length or distance travelled. In electrical principles, shortest return path refers to the path that offers the lowest impedance for a leaky current to return back to its source. Therefore as commonly said, short-circuit is the return path with the least or zero impedance for a current.

In many metal-enclosed equipment, PCBs and other sensitive devices are not more than 3 to 5 cm away from the chassis. Should there be an electrical leakage in the PCBs or user interface panel (made of metal), the path taken by the leaky current seeks to travel via the shortest path, instead of paths that are connected to many sensitive devices, thus spared them from damages.

At DC, metal chassis provides very low impedance due to its large surface area.

At high frequencies, grounded chassis might not be useful because high-frequencies leakage use a different shortest path that as much as possible stay on the surface (due to skin effect), proximal and parallel to the incidental source of leakage.