ground a limit sw in 24VDC application?

[emiller233]

there's a debate going on here...
whether it is mandatory or not to ground a limit switch (metal body with 1NO-1NC and a ground screw).
this is being used as a door switch for entering an area. Its a big industrial hydraulic unit with metal enclosure around it to keep the weather off of it.
The switch will turn on/off a 24vdc LED light fixture when the door is open, lighting up the area inside the enclosure. the LED light does not have a ground (2-wire).

crude sketch attached to show the wiring

Lights
PATLITE CLA12S-24-CD-30
https://www.patlite.com/product/index.php?Command=Index&method=Download&id=191&idx=4
https://www.patlite.com/product/detail0000000191.html#related


Limit switch
Omron D4B-2171N
http://download.ia.omron.com/download/page/D4B_2171N/OEI/D4B_2171N
https://www.ia.omron.com/product/item/9919/

 

[Jraef]

Are you asking if the body of the limit switch needs to be grounded, or are you asking if your entire 24VDC system needs to have a ground reference, and you want to do that at the limit switch?

If you are just asking if the limit switch body needs to be grounded, the answer is no. You CAN, but it's not required.

BUT, if you have grounded your 24VDC system, then you want to troubleshoot this circuit, having the body grounded makes it easier to test if you only have one side going through the switch (as you apparently do in that diagram) because you can just touch one meter probe to the body connection.

 

[emiller233]

I was talking about grounding the limit switch body.

The customer may or may not ground their 24VDC system? We are just wiring the devices back to a terminal box and they will integrate with it out in the field.

How do i prove to them that this does not need grounded. When they (my coworkers) see a ground screw the immediately demand it to be grounded.

They also demand M12 connectors on everything. But when we do this, then there is no green wire in the pre-made cables for them. It would be gray for the 5th wire in this case and we'd have to put green tape on it. So of course they get mad about that to.

 

[hbiss]

How do i prove to them that this does not need grounded. When they (my coworkers) see a ground screw the immediately demand it to be grounded.

That switch is manufactured for a great many applications. The ground screw is provided by the switch manufacturer so that it could be grounded in the event it is used in an application that requires a ground, such as high voltage or line voltage interlock that is referenced to ground. Since your 24V system is neither itself grounded nor of a hazardous voltage, a ground connected to the screw would be useless.

The lack of common sense by your co-workers amazes me.

-Hal

 

[LarryFine]

How do i prove to them that this does not need grounded. When they (my coworkers) see a ground screw the immediately demand it to be grounded.

Remove the grounding screw - problem solved.

 

[emiller233]

Remove the grounding screw - problem solved.

^^^ THIS :rotflmao:

 

[buffalonymann]

I was talking about grounding the limit switch body.

The customer may or may not ground their 24VDC system? We are just wiring the devices back to a terminal box and they will integrate with it out in the field.

How do i prove to them that this does not need grounded. When they (my coworkers) see a ground screw the immediately demand it to be grounded.

They also demand M12 connectors on everything. But when we do this, then there is no green wire in the pre-made cables for them. It would be gray for the 5th wire in this case and we'd have to put green tape on it. So of course they get mad about that to.

You have to explain to them the ground screw exists for high voltage applications, not necessary for voltages of 50 or less

 

[tom baker]

The correct term is bond, but we call it an "equipment grounding conductor" . I have 40 sites I maintain, all 24 VDC for inputs outputs to a PLC. I typically do not install a bond to the limit switches, pressure switches, etc, non of this equipment is in a classified or hazardous location.
There is no code requirement or safety reason to bond, and nearly all are protected by a 1 amp fuse.
However, one side of the 24 VDC power supply is bonded to the panel which is connected by an EGC with the 120V supply to the panelboard which is connected to an earth ground somewhere

 

[emiller233]

You have to explain to them the ground screw exists for high voltage applications, not necessary for voltages of 50 or less

I'll have to find this section of the code book and throw it at them...

 

[emiller233]

The correct term is bond, but we call it an "equipment grounding conductor" . I have 40 sites I maintain, all 24 VDC for inputs outputs to a PLC. I typically do not install a bond to the limit switches, pressure switches, etc, non of this equipment is in a classified or hazardous location.
There is no code requirement or safety reason to bond, and nearly all are protected by a 1 amp fuse.
However, one side of the 24 VDC power supply is bonded to the panel which is connected by an EGC with the 120V supply to the panelboard which is connected to an earth ground somewhere

Very true, maybe i need to start using correct terms when chatting with them about this. I do tend to say ground for everything with them

On a strictly 24vdc terminal box enclosure, do you bond the subpanel and enclosure?

 

[petersonra]

If it is a Class 2 circuit the answer is probably not. If it is not a Class 2 circuit I don't recall any code section that would exempt it from requiring bonding since it a is metal that encloses conductors probably doesn't serve any especially useful purpose but I don't recall that there's any exemption for lower voltages other than Class 2 circuits