Mixing Low Voltage And High Voltage In Handholes

WREC

Member
Location
Greenville NC
I have a electrical engineer on a project putting high voltage 480 volt, 12 volt control wire #12 xhhw-2, and twisted shielded pair for 4-20 ma in the same duckbank but also in the same handhole with no separation. He says this is allowed with the 600v jacket on the cables im still in question and cant seem to put my finger on it in the code book. I have never seen this and never installed this way. Any direction would be appreciated.
 

WREC

Member
Location
Greenville NC
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I have a reply from the engineer he is set on its ok and requiring me to install as drawn on prints. He has talked to the inspector and he is going to pass it.
 

tom baker

First Chief Moderator
Staff member
I have a electrical engineer on a project putting high voltage 480 volt, 12 volt control wire #12 xhhw-2, and twisted shielded pair for 4-20 ma in the same duckbank but also in the same handhole with no separation. He says this is allowed with the 600v jacket on the cables im still in question and cant seem to put my finger on it in the code book. I have never seen this and never installed this way. Any direction would be appreciated.
Your engineer and inspector are wrong. Read the informational note to 300.3(C)(1). The code is concerned if the there is a short between the 480 and 4-20 Ma cables the 4-20 MA equipment would not withstand the higher voltage and can start on fire.
What you and the engineer need to be concerned with is the induction from the 480 circuit causing noise on the 4-20 mA circuit. If the 4-20 mA has erratic operation the non separation would be a likely cause.
 
I agree with Tom. You need to have the engineer review article 725. What you have described is a violation of that article.

I concur that there is the possiblity of induced noise into the 4-20ma circuit.


Your engineer and inspector are wrong. Read the informational note to 300.3(C)(1). The code is concerned if the there is a short between the 480 and 4-20 Ma cables the 4-20 MA equipment would not withstand the higher voltage and can start on fire.
What you and the engineer need to be concerned with is the induction from the 480 circuit causing noise on the 4-20 mA circuit. If the 4-20 mA has erratic operation the non separation would be a likely cause.
 
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