Junction box - how would you do?

[rQx]

Hi!

We currently have a junction box and everything works fine, but one thing just bothers me and that is how I handle the cablescreen for the analog signals in the junction box. I don't think it's wrong. But how would you do?

We have three cables to the JB. 24VDC power, 24VDC signals (screened), analog signals (screened).

In the cabinet the screen of the 24VDC signals cable is connected to the earth bar and so is the earth conductor. In the terminal box the 24VDC signal cable screen is cut and the earth conductor is wired to an earth bar.

In the cabinet the screen of the analog cable is connected to the earth bar. In the terminal box the screen is connected to a regular terminal and on the other side of the terminal the two analog sensors connect their screens.

This is working fine and nothing wrong.

BUT would it be more logical to cut the analog cable screen and then connect the analog sensors to the earth bar (the earth comming from the 24VDC signal cable).

How would you do?

/Tim

 

[parky]

A general rule is you only connect the screen to earth one end to help eliminate earth loops. so the way it is connected is normal. If there is an intermediate connection then it should not be grounded and use a through terminal, also at the sensor end leave the screen disconnected but the sensor should be bonded i.e. do not rely on screen for bonding use correct bonding this is one reason not to connect the screen both ends.

 

[OkiePC]

I normally ground the shields at one end or the other, but not at a junction point in the middle. My preference is to ground the shields at the terminals nearest to where the signal is consumed. I don't have this as a strict rule. There are sometimes practical reasons to deviate. There have been a couple of cases where I have had better results reducing noise by changing the ground location or leaving it floating.

Keep in mind the cardinal rule "if it ain't broke don't fix it".

 

[rQx]

Thanks for the input so far, I also lean towards "if it ain't broke don't fix it"