I am from a commercial background (15 years), and have moved to industrial controls. Many questions I never had to previously consider, I am now faced with on a daily basis. One of them which has recently come up, I cannot come to a solid conclusion on yet. If you could please reference relevant code sections with your answer it would be greatly appreciated. Here is my question:
In an industrial control panel we have a class one power source supplying 24VDC source. The 24V source is then used to power a three wire level probe. The level probe is enclosed in a metal enclosure that is supplied with the device. There is a grounding terminal in the device, but for some reason the contractor has only run 3 wire cable with shield. I asked why he didn't ground the case and he said it isn't required for 24VDC devices. I asked for a reference, and he told me when he got some fee time he would send it over. I am a bit confused, and have spent quite a bit of time looking for an answer. One place I found another forum where a person suggested (without a code reference) is that with DC sources at 24V you have the option to attach the negative DC terminal to ground, or leave it floating. They said if you attach it to ground then all your devices must have an equipment grounding conductor. This kind of lines up with what our contractor said, but I can't find a definite answer in the code yet, so I was hoping someone more experienced with this topic could point me in the right direction. Thanks in advace!