I have this 480V 3ph load center and I am using a transformer along with it to get my 120V which will operate my exhaust fans and alarms. The 480V is used for my oil heater and centrifugal fan. I need to place an E-Stop in this circuit. My question is where would I place this E-Stop and how would I show it on a wiring diagram.

 

Just how an estop has to be wired depends on many factors that none of us can know. one of the big factors is the result of the risk assessment that has to be conducted first to determine just why you need an estop, how many you need, potentially if you need one at all, and just what the estop has to do.

Until the risk assessment is performed, it is not going to be possible to answer this question.

--
Bob

 

Approach the problem in a pragmatically.

First quantify the problem to be solved.

What do you want the E-stop to control?

All power,only the 120vac, or just a specific function. Once the problem has been identified go about formulating solutions. A common guideline is to have devices fail in a de-energised state. An example would be to cut the 120 power by routing the output of your transformer to a fuse or circuit breaker, then through a relay. The coil of the relay would be in series with the physical e-stop button. If any problems occur like a loose wire, or defective device then the whole circuit drops out, and presto no 120vac to anything. I hope this helps, and I know that my spelling is very poor.

 

As long as you are using the 120V off the secondary of the transformer for the control voltage on everything you listed, you can simply put the E-stop in line just after the point where your alarms get their power on the secondary of the transformer. This will drop out your control voltage thus dropping out all your contactors.

 

Your spelling is perfect.

 

Bob is correct. With all the new OSHA and ANSI safety rules a risk assessment should be conducted to determine the safety requirements of the system. Today the E-stop monitor module can be purchased with a forced guided relay. This module does nothing but monitor your estop button in your system. The forced guided relay can be sized to be installed before the motor starter on your fan and your heater after the 480VAC fuses. Disconnect---fuses-----force guided relay---fan motor starter---heaters. I can send a drawing in PDF format if need be.

 

Ron... For a well thought out answer to the infamous question "To E-Stop or not to E-Stop", I suggest you refer to Tim Park's article in the Feb-2000 issue of "PTdesign Magazine."

He has an excellent grasp of the intent of the E-stop function. For additional information see:

http://www.control.com/thread/950636217

Regards, Phil Corso