4-20 ma Analog beside 480 Volt AC in Wire Tray

What would be a safe distance between Analog cables (4-20ma)and
120 & 480 volt multi conductor cables laying in a 12" or a 18"
Ladder Wire Tray.

Thanks and have a great day,

Coachman said:

What would be a safe distance between Analog cables (4-20ma)and
120 & 480 volt multi conductor cables laying in a 12" or a 18"
Ladder Wire Tray.

Thanks and have a great day,

Click to expand...

I remember IEC or ISA has specified That center to center safe distance is "Five times the diameter of the largest ac cable in the tray"
Regards,

Life's to short to take shortcuts that only cause momentary savings...

You will probably have problems, maybe not immediately but sometime in the future it will probably come around to bite you. Mixing high and low level is a great way to test your troubleshoot prowess in the future, just hope everything is grounded correctly. I never trust air to be a shield, at least put something metallic in between them, especially if there is any safety concerns/ risk.

Heck, you can have problem running 480VAC wires from one device runnning next 480VAC to another isolated device. We just blew out a VFD last week because of a 500mcm 3 phase/ 3 wire feed to a 50 hz generator in our Lab shared conduit with an air compressor (#3 3 phase/ 3 wire) for about a 60' run. A 30 to 40 year old air compressor was replaced with a new energy efficient one earlier this year. Good grounding wasn't required for the old compressor but that new VFD sure wanted to have a good ground (which we though we had). It was seeing over 700 volts to ground which the some of the silicon had an issue and it let some smoke out.

Make sure you use shielded wire that is grounded only 1 place. Then put the largest distance between it and the power cable. If you can use the 18" use it and put the shielded on one side with max air space to the power wire.

And be ready to sharpen your troubleshooting skills when you get some "noise" on the signal line. Some 0.1uf 100v non polarized mylar caps across the signal leads at the terminating end helps cut the noise.

By code, if the cables are in the same tray, the insulation level of the analog cable must be the same as your highest voltage cable. In other words, the analog cable must be 600 V insulation.

Never thought of that. Good point

brucechase said:

By code, if the cables are in the same tray, the insulation level of the analog cable must be the same as your highest voltage cable. In other words, the analog cable must be 600 V insulation.

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if they have to be together, i would also use dividers. i don't know which trays you are planing on using (we usually use hoffman F44 series with F44BK60 barrier)

Coachman said:

What would be a safe distance between Analog cables (4-20ma)and
120 & 480 volt multi conductor cables laying in a 12" or a 18"
Ladder Wire Tray.

Thanks and have a great day,

Click to expand...

Maybe You shouldn't be concerned with the safe distance
Current signal (4-20mA) is resistant to magnetic induction generated from current in high voltage cables, even without cable shield. Two year ago I've used two twisted pair cable as power supply and analog signal cable (4-20mA). One pair for power supply 220VAC/50Hz and another one for analog signal (4-20mA), all in one single 4 wire cable. There was no disturbance. So You can put analog cables together with power cables in the same tray.
But, if through analog cables is conducted voltage signal (0-10V, mV, signals from load cells or thermocouples) then You must use separated tray (min distance 30cm from power tray) and all shields must be grounded. Safe distance from power cables depends on current in the cable. If power cables are supplying motors then put analog cables as far as possible (1-2m).

Marino

If I had to do it and I was worried about it I would put the cable inside metal flexible conduit.

marinko said:

Current signal (4-20mA) is resistant to magnetic induction generated from current in high voltage cables, even without cable shield.

Click to expand...

I try to keep my signal wiring seperated from my power feeds whenever I can, but I was also under the impression that the whole point of using a 4-20mA signal was for noisy environments where the signal wires are going to be subjected to magnetic induction that would interfere with a 0-10Vdc signal.

One of my pet peeves is finding signal wiring run with twisted pair cable and a split pair is used.... Seriously why even bother paying for UTP if you aren't even going to take advantage it's noise cancelling properties? It ain't twisted cause it looks pretty.

Define "Safe"

If the insulation is adequate (600 Volt insulation is common and as stated above required by some standards) then you will probably not kill anyone or let the smoke out of any equipment.

You will probably have tremendous problems with EMI and RFI (Electro Magnetic Interference and Radio Frequency Interference) induced noise in the 4-20 mA signals unless the distance is very short.

Can you get away with this - yes, in the right circumstances and if you don't have a choice. I've tried it and done it, but always with great trepidation. Recommended practice is separate conduit or wireway for analog and power wiring, and it is the best way to go.