Well connected and teminated cable ladders? 1

[Jensdsds]

Hello,

For at motor powered by power cables coming from a converter setup.
The motor cables are being run in cable ladders which are all correctly connected to the earthing system.
Everything is well correctly connected to the earthing system.
My question is in regards to the common mode return current origination from the converter.

My question is:

At a point in the cable routing the cable ladder has to be disconnected, and the cable will be routed inn free air.
Before and after the cable ladder is well connects and terminated at both ends.
This means that the cable ladder is unable to form a uniform connected line of common mode return current back to the converter.

Considering this disconnection, is it still important to uphold the well connected cable ladder before and after the connected, or is it sufficient to just connect the cable ladders to earth and not worry about electrically connecting each piece of ladder?

Thanks in advance.
- Jens

 

[waross]

There is the code and there are engineering standards.
By the Canadian Code, ladder tray mounted on grounded structures is code compliant.
In much of the petro-chemical industry, the engineering standards require a grounding conductor to be run in the ladder tray and to be connected to each section of the tray. This is in addition to bonding jumpers across all expansion joints.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Jensdsds]

Thanks you for the answer!

Are bonding jumpers commonly used today?

https://www.goudaholland.com/SiteContent/files/H1E - EMC and cable ducts.pdf

Page 18 in the link.

Many of the sources i seem to find recommends not using bonding jumpers because of the impedance at high frequencies.
Is it worth using the jumper if the ladders are correctly grounded, won't the noise flow through the grounding instead of the bonding jumpers?
Thanks in advance

 

[waross]

While the information in the link is accurate, it may overlook some important points, and page 18 may not be applicable to expansion joints.
Re: The link.
1. The high frequency impedance of a very short cable may be negligible.
2. If the impedance of a short jumper is significant, how can useful power be transferred down the similar phase conductors?
3. The first purpose of bonding or grounding tray is to conduct short circuit currents an the fundamental frequency. Cable jumpers do very well for that.
4. While the original installation of tray on grounded structural surfaces is code compliant, with passing years, corrosion of both the aluminum and of the steel supports and hardware may compromise the bonding.
5. I have seen some ladder tray that has a specified rating or ampacity for short circuit current.
6. I have seen engineering standards that call for the jumpers across splice plates to be flat, woven or braided conductors. Possibly 3/16" x 1".
7. I have seen projects where only trays carrying high voltage cables used additional grounding conductors and jumpers.
The code is a minimum standard. Engineering standards, written by an engineering firm responsible for a project or by an industry group are often more stringent than the basic code.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Jensdsds]

Okay, great points.
Thank you very much!