Steel sleeve inductance effect

[alehman]

It is well known that an un-bonded ferrous metal sleeve or conduit surrounding a single conductor adds substantially to the inductance of the conductor. Does anyone know of any actual measurements of this effect, and the effect of bonding the sleeve to the conductor?

IEEE 142 (Green Book) mentions the inductance may be increased by a factor of up to 40, but there are no specifics provided, nor references to published data or calculations to substantiate this.

The question pertains specifically to grounding applications, so I'm not as concerned about heating effects.

Thanks,
Alan

Alan
The engineer's first problem in any design situation is to discover what the problem really is. Unk.

 

[FacEngrPE]

See this
thread238-114338

In a grounding application,

https://catalog.nfpa.org/NFPA-780-Standard-for-the-Installation-of-Lightning-Protection-Systems-P1367.aspx[/URL]]NFPA 780: Standard for the Installation of Lightning Protection Systems

requires bonding the ground cable to the conduit at both ends, as lightning wants to run only on the conductive surface. If the bonding is left out, lightning will jump the gap.

 

[alehman]

Thanks FacEngrPE. I did see the thread you referenced, but as someone in that thread also asked, I am looking for actual test data or even theoretical analysis of the effect ferrous raceways on inductance of a single conductor.

Alan
The engineer's first problem in any design situation is to discover what the problem really is. Unk.

 

[dpc]

Not directly on point, but Google "Let's Be More Specific About Equipment Grounding" by Kaufmann, et al. They did specific testing of ground wire impedances both inside and outside of steel conduit, IIRC.

Dave

 

[alehman]

Thanks Dave. I found the article! Will read to see how well it answers my question.

Alan
The engineer's first problem in any design situation is to discover what the problem really is. Unk.