Posted 29 Apr 2011 Hi, In one of my application, I am planning to implement Cat3 safety circuit with one E.stop controller and three E.stop buttons in series (dual channel). This sound simple but two of the buttons are placed 3500ft (1.1km) away. For 24 VDC system at 18AWG it should not be a problem. But as far as I know the controller would be checking the E.stop button wiring by sending pulses (I think at 5V but not sure). So would the length be too much and false tripping may result? If anybody has past experience with similar implementation please share. I am planning to use Allen-Bradley E.stop controller but any other brand that can handle this length is OK. Share this post Link to post Share on other sites
Posted 2 May 2011 You can find charts to calculate the voltage drop, but for those distances you will need to either use much (MUCH) bigger wire, or switch to a safety fieldbus that can handle the distance. There may be wireless solutions that are safety rated? I know it seems overkill for two EStops, but at over half a mile, you don't have many choices. All this begs the question. WHY do you need EStops 3500 ft from the controller!! Share this post Link to post Share on other sites
Posted 2 May 2011 24VDC on 18AWG, 3500 ft carrying 100mA would have 5.4VDC drop, still good for most instruments etc. I can boost the voltage at source if required. See, http://www.csgnetwor...gedropcalc.html Fieldbus and Wireless are not possible as restricted by customer. This application has hazardous liquid being transported 3500ft from controller. The operator at that end would like to stop pumping in case of trouble. My question is very specific, would the E.stop controller's power supply (that does frequent circuit check) be able to handle it or not.. Since I don't know it those pulses are 5V. 24V or any other weird number. Share this post Link to post Share on other sites
Posted 5 May 2011 I have several 900 ft lines in the plant with multiple e-stops along the path and I always go for a larger e-stop wire gauge. 14 AWG will only drop 1.3 V @ 24 VDC at your 3500 ft length. This means that it should have less drop for any 5VDC pulses that the system might do for checking as well. Your milage may vary, (pun intended) Susan Share this post Link to post Share on other sites
Posted 6 May 2011 I have some very long distance E-stops and we ran 12 ga. wire, never had a problem . A little math will make you feel better about the whole thing. I would pull 12 ga. in you situation. the price difference is negligible. Share this post Link to post Share on other sites
Posted 6 May 2011 Ken, By the discussion it looks encouraging. Do you know the length of cable and the controller (make/model) that you used. Few days back I was talking with Omron people, some of their controller has 5V pulse check and some has +24V, -24VDC on each channel. I would be interested in the current it draws (Omron didn't have definite answer at that moment) while doing this check so that I can calculate the voltage drop. As far as the cable price goes, I think 18AWG and 12AWG multi conductor cable would have significant price difference for this 1KM length. Share this post Link to post Share on other sites
Posted 7 May 2011 (edited) Voltage drop depend on the resistance of your wire X the current drawn by each input channel of your safety relay . Each of your loop would have 2.2km of wire. 18AWG wire has a resistance of about 21 ohm/km, so you have about 46ohm for a loop. G9SP has 6 mA consuption for each input. So the Voltage drop would be 46 x .006 = 0.28V (for 18AWG). 14 AWG has a resistance of less than 9 ohm/km. So it would give a drop of 0.12 V for 2.2 km. I have G9SA and G9SP at my job that i could test monday (measure "real life" input current). The number i used (6mA) were from Omron spec. for G9SP , i did not find it for G9SA. Edited 7 May 2011 by pfort Share this post Link to post Share on other sites
Posted 9 May 2011 pfort, G9SP is the Programmable safety Controller, I would be using a safety monitoring relay, similar to G9SB or G9SA. I assume that the monitoring ckt would have less then 10mA current ( as you mentioned 6mA for G9SP), but if you can check it I would appreciate it. The question here is how sensitive this monitoring ckts are to circuit resistance and voltage drops as a result. If it results into nuisance tripping, would be a trouble. Most instruments etc can handle 5-6VDC drop at least, but I am not so sure about safety monitoring circuits. Share this post Link to post Share on other sites
Posted 9 May 2011 (edited) Hi Ben, I tested with a G9SA. The current for a safety input, when the relay is energised, is 24 mA. So the drop with a 46 ohm resistance would be 1.1V. There is no problem at 1.1V, i tested with a potentiometer and about 4-5V drop before it trip. If you want a relay with less input consuption, i think you could try a G9SX. He is solid-state. Edited 9 May 2011 by pfort Share this post Link to post Share on other sites
