Level Switch Cable

In Spain I would just use a bit of 3core 1mm 1000v cable! It's not data so no need for twisted stuff! The 1000v cable gives you a bit of external protection if the bobbin of the relay is a 230v bobbin! Are the relay and the level switch in close proximity? Another thing to consider is the environment! But first I would check my local regulations to see what they advise!!

I am going to activate 24 V DC relay in (IRP) Interpole Relay Panel, which in turn activates contactor for the motor to start/stop. I am going to activate alarm simultaneously. Level switch will be in tank and relay will be in relay panel.

Since it is a discrete signal, either 3 core control cable or instrument cable (shielded triad) will work. If your system is integrated with DCS or PLC, it is better to use instrument cable (shielded triad). But, yes, see the specification or the local regulation or the company culture if it restricts to use the the specific type.

See http://cr4.globalspec.com/thread/53830/Signal-Control-Cables for cable types.

- MS

What is the distance from the switch to the relay? What is the highest ambient temperature that the wire will be exposed to?The ambient atmosphere(corrosive,explosive,etc).

I presume the wire will be in conduit.

Not knowing these factors, I would gorilla-engineer it using AWG #14 THHN stranded wire, single strands(1 Green, and the others of your choice) because you are carrying a very low current and it is a simple contact closure, not a digital signal, shielding and or twisted pair is not required.

You can use a standard instrument cable (normally comes in 2 pairs) of 0.5 to 0.75 sq mm with an insulation capacity of 250V to 300DC. {normally used for drive cards to interposing relay (coupling relay) of 24VDC}.

You can refer to Lapp cable catalog for information.

http://www.lappusa.com/Spec_Template3.asp?nGroupID=200130

These types of questions really do annoy me. Nothing can replace having a knowledgeable person on site able to look at the logistics of the installation and the circuit topology. Instead of having a qualified technician or engineer do this simple engineering work, people post this type of question here with minimal information but still expect an engineers insight to solve their problem. So a wild variety of pertinent questions never get discussed before an answer appears. Silly little questions like:

• How big of a motor?
• Motor voltages and currents?
• Relay contact current and voltage rating?
• Motor control interface?
• Cabling path environment? (Cabling will have to flex 5000 times per day of operation.)
• Cable path length?
• Any hazardous environment? Are you really sure?
• Fire hazard concerns?
• Disconnect considerations?

I could go further on but I think I've made my point.

Follow the Cabling Standards in use at the installation.