shock from 24vdc control circuit

[gbeaker]

I've recently had reports of people getting shocked from a 24volt light curtain. I've checked everything out and I don't see any major issues. The machine appears properly bonded and grounded and the curtain does not have a ground, only a drain which I assume isn't connected inside the actual unit. I've never been shocked by 24volts before so I'm trying to figure out where the shock is coming from (they claim is repeatable when its happening and not static).

The only thing I noticed is the 24volt power supply doesn't have the 0vdc grounded. Is it possible the 0vdc is raising high enough to shock someone?

Thanks!

 

[Lancie1]

The 24 Volt power supply could have an internal fault that is allowing the higher AC voltage to ride on top of the DC. The higher voltage could be on either leg of the DC. I would ground the (-)24 VDC terminal of the power supply to earth ground. If that doesn't fix the problem, then replace the power supply with a better one.

Either that or it really is some type of static charge build-up on part of the machine.

 

[maxketcham]

I would look to see if the case is isolated from the machine it is mounted on. If the light curtain is grounded and isolated a short in the machine would track back to that ground when touched. You can get a shock out of a 12 volt car battery if your skin is wet.

 

[gbeaker]

the light curtain is isolated from the machine and doesn't appear to be grounded. there is only 24vdc, 0vdc, and a shield/drain connected. the shock comes from touching the machine and the light curtain at the same time. I suspect the light curtain case is connected to 0vdc internally and there is some kind of potential between this and the machine ground. I'll try grounding the power supply.

 

[shooter]

a PSU must be grounded or guarded.
so ground the curtain, and make the floor conductive, when i touch a shopping cart it happens to me. so no worries just tell the people to wear safety shoes etc. This was big problem in cleanrooms.

 

[The Plc Kid]

Also don't under estimate static shock. I have some applications where on our winders if you get within 24 inches of the material and plant conditions are right and operator have the static control system turned off you will get a blue arc to your skin that will take you to your knees.

 

[maxketcham]

Also don't under estimate static shock. I have some applications where on our winders if you get within 24 inches of the material and plant conditions are right and operator have the static control system turned off you will get a blue arc to your skin that will take you to your knees.

I remember that at a company I did some work for. Blown film extrusion for plastic bags, Used to look like a lighting show when the treaters were on and static control failed.