Protection

Depends on the device, depends on the circuit, depends on the application, depends on the jurisdiction, depends on the situation... I could go on, but hopefully you see the point.

If you have a specific situation you are curious about, post details; ALL THE DETAILS. Someone here can likely help.

To be specific, its a conveyor belts interlocks. i designed a circuit which can allow one to overide the interlocks if they fails, ie, u can only overide one conveyor at the time, certain individuals will be appointed for that and a password will be used to restrain anyone from doing it. the will be procedure drafted, reason kept up with production while stanby is called out to minimise downtime. is it possible?

And one thing, are interlocks safety circuits?

Smoke, fire, melting, sparks, electric shock and fatalities are some of the usual references, Matey. How d'yer think I got where I am today? <Wheeze, splutter>

But there is at least one case where the protection is not allowed by the code (NEC): it is the overload protection of the fire pump.

- MS

The main code is "make sure you can't be blamed" if things go wrong.

Hi Dan,

The Electrical Code already specifies the minimum installation requirement for protection.

Now, if the installation experiences problem like tripping of a circuit breaker, then it indicates a problem in the system. Bypassing protection is not recommended as it may result in further problems like fire.

And we do not want that.

Sometimes it is necessary to override a protective device for test purposes, such as a quick check of pressure switch operation versus oil pressure gauge reading. But you have to understand the risks! For example, you would start only the oil pump NOT the machine after over-riding the trip. Overiding trips to keep plant in service is bad practice. Sometimes, if there are other protective measures, it may be done because the faulty device is identified, but spare is not immediately available e.g output press switch on pump when there is an independent shut-down switch at bearing.

This is usually the case as technicians want to keep a production line running. But overriding protection and controls is a sign of bad planning. Spares must be made available as soon as possible. Overriding should be more of an exception and immediately reported and replaced.

Every effort must be made for spare.

Violation of NEC and its consequences are disastrous in the long run.

This sounds like if one conveyor belt stops due to some problem, they all stop. This is usually done to keep from spilling stuff all over. To get the system going again, an over-ride would have to be used to get the system going again. As each belt starts back up the one feeding it would start too, as soon as it sensed proper operation.

Many systems have off-manual-auto controls. How is your system different?