Unless you are intentionally floating the control voltage for reasons other than the obvious. You should tie OV to ground. If you don’t there exists the possibility of the control voltage floating to a potential that exceeds the capabilities of your plc and devices.
I think there is no standard as reference of your question, because it is meaningless to system. But in a real situation, the 0 VDC grounded helps us to determine which wire (Line or neutral) is broken. I believe it will decrease downtime unit for the system itself.
Yes - I normally provide terminals for 24 & 0V distribution, and connect the 0V to ground using a single link. This allows the 0V and ground to be isolated if you need to fault find etc.
You don't want your 24VDC to float relative to ground - most equipment and technicians will use ground during testing as a reference point for 24VDC fault finding.
Generally I connect 0 vdc to ground, particularly if there are comms involved. Have seen comm ports with different power supplies not grounded have problems with floating voltages and even disappear in a puff of smoke.
> Should 0v of 24VDC power system for PLC be connected to ground? <
In the vast majority of situations, the answer should be NO.
I can think of one exception, however. If your 24 volt system is uses a very low impedance power source, such as a set of batteries with a floating charger, and your loops may be exposed to lightning damage, then you may want to ground one side of the loop --AT THE POWER SOURCE AND NOWHERE ELSE. This will help mitigate induced static charges from lightning. Generally, I don't recommend such measures unless the loop travels a substantial distance (for example, between buildings).
A better solution, however, would be to use shielded instrument cable and to attach the sheild to ground at one end or the other but not at both ends.
For a working example of how such loops should be grounded and why, look at telephony standards. Note also that they tend to ground the positive side to reduce corrosion. I wish our industrial standards had been this forward thinking...
In general yes. An ungrounded power supply can float to high voltages. This will eventually cause problems when you need to interface with
other devices.
In general yes. An ungrounded power supply can float to high voltages. This will eventually cause problems when you need to interface with other devices.
I always design a PLC 24vdc power system to have the negative solidly grounded.
I have a client who installed an Allen-Bradley SLC PLC with 24vdc power. They said they "smoked" the processor, and asked me to find the problem. I found that they not only ruined the processor, but also melted a 3" hole through the plastic barrier in the rack that separates the processor from the power supply!
The cause of the problem turned out to be a missing ground for the power system. The power system included two 12-volt batteries connected in series. Everything worked fine with the power supply floating, until the mid point between the batteries became accidentally grounded. Since the PLC frame was grounded, this made the power supply positive 12 volts above ground, and the negative 12 volts below ground. Connecting a 12-volt battery between ground and the PLC power negative has disasterous results!
Generally I connect 0 vdc to ground, particularly if there are comms involved. Have seen comm ports with different power supplies not grounded have problems with floating voltages and even disappear in a puff of smoke.
Just had this problem on site because one cabinet hand its GND tied to OV (where the equiptment was supplied from) and the the other cabinet (where I ran the control cable to a different PLC) did. Now because there is no standard I am having a tough time putting it back on the installers for shorting out a very expensive peice of electrical equiptment :-/
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