Using 24v+ & GND to power a part-present prox sensor.

[unsaint32]

I have a 24v prox with three wires. I do not have COM available for 24v+. Can I just use the 24v+ & GND to power the sensor? It's not a critical input. It just sees a part. If the sensor fails, nothing will move after that.

 

[ASF]

When you say 24V+ and GND, do you mean 24V+ and (what we down under would call) earth? i.e. provide 24VDC and tie the 0V wire to the metal frame of [something]?

If I have the above correct, it will work if the DC power supply has the negative connected to earth (ground) also. If not, no.

As to whether you should...no. No, you should not. I've seen it done plenty of times in a pinch, to get a machine running at 3am, but it's not a good idea. You're forcing the metalwork and the earth conductors to be a part of your current path, and that's just not the right thing to do, unless you're doing auto electrics.

Run a new cable.

 

[DwSoFt]

If you have 3 wires that is typically all you need. 24vdc. Common. And signal return to the input. That is 3 wires. Then run a jumper from either 24vdc or common depending on your input type (sourcing or sinking)

Edit

Don't use ground as a 4th wire as it's meant for safety and not for carrying current. If the input is of different voltage the. You can use a 24vdc relayat the other end.

 

[GaryS]

Don't do it it's a very bad idea
While you may get it work for a while but if the ground loop changes you could end up with all kinds of problems intermittent operation
Also you could never get it inspected if they see it ground conductors may never carry any current
the Ground or Earth is there to make sure that all metal parts are at the same earth potential
If you cant run a simple 3 conductor cable to the Prox then maybe you should not be using it.

 

[parky]

Perhaps you could give us the manufacturer & part number of the Prox it would help

 

[Rson]

If I understand correctly, you are asking if you can use an earth ground instead of a 0VDC common terminal point.

If your 0VDC is bonded to your earth ground, I suppose you could. Having the neutral tied to earth ground in AC is pretty standard, but I have found having 0VDC tied to earth is not as automatic. Double check - It may not be connected/bonded to earth ground.

That said, even if it is, you will probably run into ground loop issues. Don't rely on the earth bonding to complete your sensor's circuit.

 

[OkiePC]

No. You cannot use ground as a current carrying conductor. Unless it's a '74 Duster, the answer is no.

 

[Mickey]

No. You cannot use ground as a current carrying conductor. Unless it's a '74 Duster, the answer is no.

I had one of those, Gold Duster. Only memory is a cracked exhaust manifold.

 

[OkiePC]

I had one of those, Gold Duster. Only memory is a cracked exhaust manifold.

Mine was (mostly) red. Slant 6 225. My dad picked it out, and I gave $200 for it. I had to walk to work past it for two more weeks to save enough for a battery and some retreads.

 

[alive15]

Question on grounds and commons, is it acceptable to tie the grounds between two different panels that have two different power supplies (AC or DC)? What about tying 24V common / neutral between two different power supplies?

From my understanding, it is okay to tie the grounds together. However, for the 24V common, the current will take path of least resistance, so most likely it will stay within the circuit of it's own panel anyways. I guess my question is, is there any benefit to tying the commons together, if it's allowed in the first place?

 

[parky]

If it is genuinely a two wire sensor then the +Ve lead will go to +24v of the plc input supply, the output will go to an input and the -ve will go to the PLC common, this is unusual to have two wire DC sensors and not sure if the load of the input will be enough for a DC prox.
https://slideplayer.com/slide/4468776/14/images/25/Sourcing+Two-Wire+Inductive+Proximity+Sensor.jpg

 

[daba]

If it is genuinely a two wire sensor then the +Ve lead will go to +24v of the plc input supply, the output will go to an input and the -ve will go to the PLC common, this is unusual to have two wire DC sensors and not sure if the load of the input will be enough for a DC prox.
https://slideplayer.com/slide/4468776/14/images/25/Sourcing+Two-Wire+Inductive+Proximity+Sensor.jpg

It's a 3-wire sensor, he said so. His problem is he only has 2-wires going to it.

 

[parky]

sorry I misread the post, I now understand that it was a 3 wire (well by the sounds of it a 3 wire + earth) with one broken off why not just say that. a statement like "I have a 24v prox with three wires. I do not have COM available for 24v+." is a poor English explanation in my book.
In that case Using the earth (if it is one) probably would not work unless it is internally connected to the -ve (com). For the cost of a sensor why not just buy one.

 

[Aabeck]

Question on grounds and commons, is it acceptable to tie the grounds between two different panels that have two different power supplies (AC or DC)? What about tying 24V common / neutral between two different power supplies?

For grounds it is usually a good idea to ground everything connected together into one common bonded ground point. There can be a potential voltage between 2 separate ground rods on panels at different locations, and if the panel and the machine have individual ground rods.

Always try for a single ground point and have good bonding throughout.

 

[alive15]

For grounds it is usually a good idea to ground everything connected together into one common bonded ground point. There can be a potential voltage between 2 separate ground rods on panels at different locations, and if the panel and the machine have individual ground rods.

Always try for a single ground point and have good bonding throughout.

Yes, I agree about the grounds. What about the commons / neutrals for 24VDC?