Hi All,

I need some clarification on signal segregation. I have an electrical actuator which has 3 cable entries. 3 signal types will be coming from the actuator, AI (1PR)/AO (1PR) /DO (3PR) plus power cable (total 4 cables).

So my question is, would it be possible to run the AI & AO signals through a two pair cable to reduce the amount of incoming cables (Power, DO, AO/AI combined = total 3 cables)?

also note there is no specific local standard covering this.

Any advice will be highly appreciated.

Regards
Max

 

Max,

Proper wiring usually requires the Analogs to be separate, shielded pairs to reduce interference from outside sources. The Digital wiring can be run it the same conduit. The power wiring should be run in a separate conduit.

You can reduce your wiring dramatically using a fieldbus of some sort, Ethernet, FF, Profibus, etc. This will give you more information for a lower cost and eliminate the need for home runs for all the devices. Can reduce wiring costs up to 30% with very little increase in actuator cost.

Bob

 

If the digital signals are low Voltage i.e. 24VDC they can also be run in the same multi pair shielded cable.

If solenoids are involved you may need to provide spike suppression (MOV for AC ir a flyback diode for DC) to avoid triggering digital inputs when the coil is switched.

 

Max,

The usual practice I've always tried to follow separated signals based on their voltage and/or current levels. "Low level" was considered to be anything like 4-20 mA; 24 VDC; 0-50 mA; 10 VDC; 48 VDC; thermocouple (millivolts); RTD (low DC voltage/current). Most low level signals were run in twisted, shielded pair cabling (single- or multi-pair cables). "High level" was considered to anything like 110 or 220 VAC; 440 VAC; 125 VDC; etc. Most high-level signals were run in multiple conductor cables (2, 3, 7, 19, etc.) which were not shielded (sometimes a multi-conductor (multi-core) cable would have an overall cable shield, but not always). These signals (low- and high levels) were never run in the same cable, conduit or cable tray/trench--except where entering a control panel, and there only for a short distance if absolutely necessary.

The concept is that anything that is high voltage or high current (like three-phase motor leads) or anything that was switched on/off frequently with currents above 0.5 amp or so, would not be run in the same cable or conduit or cable tray/trench as low level wiring so as to prevent inducing stray currents in the low level wiring (even when twisted and properly shielded).

You haven't defined the voltage/current levels of the various signals which would really determine what signals could be run in which cables, and in which conduits or cable trays/trenches. In general, AI and AO can be considered to low-be level and even run in the same cable using twisted, shielded pairs (with properly earthed shield drain wires). But, DI or DO signals above approximately 24-48 VDC--depending on current--are not run in the same cable, or even the same conduit or cable tray/trench as AI/AO wiring. There's just too much chance of "electrical noise" affecting the AI/AO signals.

Hope this helps!

 

Max
it is proper to run a 4 conductor twisted, shielded cable to take care of the analog signals.

If you bunch the cabling together with any low voltage digital signals in the same conduit or cable tray, make sure that the rated voltage is the same. If they are not you will be violating the NEC code.

 

You should have no trouble running AI's and AO's in the same cable. I would recommend shielded, twisted pair cable. You should also be able to put the DO in there too if it is 24 VDC and you are coming off of limit switches or an alarm relay contact (shielded, twisted pair cable). There are several standards that provide guidance on signal separation. They are a bit old but they are still provide good guidance.

IEEE 518-1982 IEEE Guide for the Installation of Electrical Equipment to Minimize Electrical Noise Inputs to Controllers from External Sources

API RECOMMENDED PRACTICE 552 - 1994: Transmission Systems

William (Bill) L. Mostia, Jr. PE
ISA Fellow, SIS-TECH Fellow,
FS Eng. (TUV Rheinland)
SIS-TECH Solutions, LP

"No trees were killed to send this message, but a large number of electrons were terribly inconvenienced." Neil deGrasse Tyson

Any information is provided on a Caveat Emptor basis.

 

The AI/AO can certainly be combined into a single cable if that is convenient. It may end up being less convenient than you might initially think though depending on where they end up being routed. Might actually be simpler to run two cables.

if the DO is 120V there is no reason it cannot be run inside the power cable for convenience sake. However, even if it is 24VDC you could likely still run it in the same cable as the power and not run afoul of any codes, depending on how this is accomplished.

The fact that you are running cables instead of conduit suggests it is not a US installation so that might make some difference.