Newbie- Wiring limit switches using schielded cable

[Action-KAT]

Hi Guys

just a quick newbie question about how to use shielded cable and limit switches.

When wiring limit and home switches up what do I do with the shield part of the cable,

Do I solder the inner part to the contacts & bob.
do I just leave the shield at the switch & bob end
or does one end or both need to be grounded some how.

Had a search but got even more confused as to what is needed.
cheers for any pointers
KAT

[neurofen]

dont quote me on this (im just in the process of doing the same thing myself). but i think what you have to do is leave the switch side of the shield as it is (do not connect it to anything), and then connect the shield on the other end (driver side) to your main ground earth point. earthing both ends of the shielded braid can cause feedback loops and undesired problems with your motor operation.

though theres different kinds of cable

[hemsworthlad]

Originally Posted by Action-KAT Hi Guys just a quick newbie question about how to use shielded cable and limit switches. When wiring limit and home switches up what do I do with the shield part of the cable, Do I solder the inner part to the contacts & bob. do I just leave the shield at the switch & bob end or does one end or both need to be grounded some how. Had a search but got even more confused as to what is needed. cheers for any pointers KAT

Just ground one end at the main ground point in you control box. All grounds should go to this one point, creating a star grounding.

[Al_The_Man]

There has been a recent reversal in the old method of grounding one end only.
See section 6 of the pdf. http://www.automation.siemens.com/do.../emv_r.pdf?p=1
concerning grounding shielding both ends.
Al.

[neurofen]

thanks al that was an interesting read..

can any of you recommend a contact grease that will stop aluminium from oxidizing (my main earth plate is made of aluminium)

[Al_The_Man]

What about automotive dielectric silicone grease?
Al.

[neurofen]

sorry action-kat, dont mean to hijack this thread, but i think its along the same lines..

going by the seimens guidelines you posted al.. they suggest putting a shield up bewteen the transformer and data carrying lines of the stepper motor drivers in the control box.. would an earthed metal plate in the attached photo act as a emi shield when placed between the 'victim' and the emmiter..?(the driver cables and the transformer toroid)

[Al_The_Man]

Historically the metal shield to prevent E.M. radiation has been mµ metal.
Mu-metal - Wikipedia, the free encyclopedia
But this is usually reserved for very sensitive applications such as medical equipment etc.
In the case you have shown, any metal that is electrically permeable should help.
One advantage of a Toroidal transformer is it does not radiate EMI to the extent a EI core type does.
The magnetic field tends to stay contained within the transformer itself.
Al.

[RCaffin]

What Siemens are describing is a rather sophisticated grounding SYSTEM that still relies on a central single point ground. You can do it their way, but you will need to know exactly what you are doing or it can go horribly wrong.

If you building or modifying your own system and do not have 10 - 20 years experience in this area, the standard ground-at-one-end rules are much easier and safer to follow.

Cheers

[neurofen]

you're right ground at one end is simpler, but the siemens guidelines arent that complicated they just go in for page after page.. they dont need 10-20 years experience to understand and implement them, dont be phazed.. keep youre cables as short as possible, seperate your power and signal cabling, be aware of the different electromagnetic fields that your components emmit and,, the componenets that they will effect the most, and you should be ok.

[Al_The_Man]

Also what they are espousing is uni-potential bonding. I don't think there is anything especially sophisticated about it.
It helps to be aware of the concept involved as to using Earth as a ground conductor.
The original concept was Early developers of electrical systems theorized that the earth was an electrically neutral body, i.e. an equal number of negative and positive charges are distributed throughout the earth at any given time. Being electrically neutral, earth is considered to be at zero potential and establishes a convenient reference frame for voltage measurements.
So simply put, the effort is, is to make all Earthed grounded parts of the system common to each other.
Al.

[neurofen]

taken from the guidlines