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Test Stand wiring #91371
01/12/05 02:16 PM
01/12/05 02:16 PM
Bill39  Offline OP
Joined: Nov 2001
Posts: 75
Indianapolis, IN, USA
OK guys, I need ideas on how to provide a safe & NEC compliant installation for the following:

Customer makes water faucets and has several test stands that are actually sinks with electro/pneumatic actuators that hook up to the knobs and levers on faucets. The solenoids are 24VDC and the motors are 90-100VDC. Everything is within sight of the main control panel, about 10 ft. away. There is a main disconnect on the panel and separate fuse blocks inside for the individual motors, etc.

Water will be flowing out of the faucets into the sinks while the actuators are moving and energized. Cords from a wireway connect to the test stand to feed power to these units. Each of these cords has a female cord cap on it to connect to the test stand.

What really concerns me is that the 90-100VDC cords from the wireway are long enough to fall into the sink when they are disconnected. Due to the test stand design, the cords cannot be shortened. The area is only accessible to qualified personnel. Shutting off the main disconnect to connect or disconnect one cord is not feasible because it will interrupt testing on other units. I’m thinking separate disconnects will need to be added and the customer should provide employees with a written procedure for working on this equipment. What else????????

Thanks in advance for your ideas.

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Re: Test Stand wiring #91372
01/25/05 03:47 PM
01/25/05 03:47 PM
Cobtronics  Offline
Joined: Jul 2003
Posts: 18
In my plant, this would be considered a "piece of in-house built (test) equipment". Some of this equipment can be the size of a large workshop. It's all one piece of utilization equipment. Then, we would not necessarily build to NEC. We always build to comply with OSHA standards. We have internal corporate safety standards that we follow in some cases. In others, we follow NFPA79, with local modifications, under the direction of our Electrical Safety Engineer. The wiring to the disconnecting means is the responsibility of the Plant Electrical Inspector (plant AHJ/NEC). Downstream, it is the Safety guy (equipment AHJ/NEC only as applies to utilization equipment). We often use NEC wiring methods, but it requires engineering judgement and careful risk assessment. Since the equipment is only accessible to qualified personnel and the control panel controls all the "stuff" then we would call the whole test stand the utilization equipment. The place it gets interesting is the qualifications of the folks working on the equipment and their status WRT OSHA for LOTO and with the written procedures on how to operate the test equipment, including procedures on how to change the Object Under Test. Remember, pressurized water can be a form of hazardous energy, not just the electricity. IMHO, this is where you get into what we call Equipment Engineering in my industry.
When I have to engineer something like this, I like to put GF sensors and use isolated LV for the actuators. I have actually found 24VAC to be safer than DC because of the ease with which one can sense a ground fault. Plus, you can get better actuation with less power and corrosion. I would throw in a low force cable retractor hooked to a Kellums grip on each cord to yank it up out of the way when disconnected for an added safety bonus. If its just the falling in the sink hazard, then maybe that's all you need? Just my 7.5 cents...


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