Motor Control Schematic

[sjwelter]

I work under a Phd Electrical Engineer who is the project manager on a project. I received a schematic for the motor controls running a blower. To me, it presents a huge safety issue for the operations/maintenance employees. I have pointed out the problem to the engineer i work under who is telling me that it is not a problem, the operator will be assumed to be made familiar with the controls. I cannot, in good faith, put something out there that creates an electrical/mechanical hazard for the people operating and working on this equipment, and he wont budge unless i can find something in the code that prohibits this. Please someone take a look and tell me what you think.

The specifications state: Blower unit controls also shall include local start and local stop, an HOA (Hand / Off / Auto) switch to select local or remote operation, and run status indicator (see Figure 5)
Figure 5 does not even match the wording of the specs, the HOA does not select local or remote operation. When an operator sets it to local operation (in my opinion, assuming it is now set to isolated control), it can still be remotely started.
I provided him this drawing of how i wanted to wire it, he wont even ask them if this will be ok, unless i can come up with something out of the code that prohibits this (which i cannot find anything)

Thanks in advance for your help.

 

[petersonra]

It is not a safety issue IMO.

Might be an operations issue.

I have seen this kind of thing in the past where they want to be able to stop it remotely but be able to start it either locally or remote.

His arrangement also allows the local stop PB to work all the time which might be arguably safer.

 

[sjwelter]

The local stop is a momentary button, as soon as it is released the remote start is re-enabled. You can push the stop all you want, but if the remote start is calling for "run" its going to run. This can happen at any time, the operator switches it to "Local" control and hits stop, begins to work on the equipment, then the remote start kicks in and chops his fingers off or electrocutes him. just sayin

 

[Jraef]

The local stop is a momentary button, as soon as it is released the remote start is re-enabled. You can push the stop all you want, but if the remote start is calling for "run" its going to run. This can happen at any time, the operator switches it to "Local" control and hits stop, begins to work on the equipment, then the remote start kicks in and chops his fingers off or electrocutes him. just sayin

I think your assessment of the control scheme is astute, I would prefer to see it your way.

But...

Control of a Start/Stop circuit is NEVER safe enough to work on equipment to where someone can get their fingers chopped off. NEVER. It must ALWAYS be locked out with the motor power circuit open on all ungrounded conductors. Period.

So, I'll advised? Yes. Unsafe? Maybe, but irrelevant from a service standpoint. It's just like any other 2 wire control circuit. All that is necessary by safety codes for a controller like this is a sign that says, "Warning, machine may start automatically".

 

[GoldDigger]

All that is necessary by safety codes for a controller like this is a sign that says, "Warning, machine may start automatically".

Notice that if the switch is put in the Off rather than the Hand position, the remote start is locked out. Still not adequate compared to a disconnect for actual service on the machinery, but a signage and interpretation issue of the switch label.
In the case of a fan, the important operational issue may be to force it on without the possibility of remote shutdown to get positive ventilation, and still allow a remote start if conditions called for it.
If the switch said "Local" instead of "Hand", I would see a better argument that the labeling was misleading.
The part of the specification that mentions Local Control seems to be the really misleading part, since that apparently is NOT what the customer wants.

 

[sjwelter]

Thank you everyone for your input. Getting other points of view is really helping me. I can be hard headed at times, well most times. The problem for me boils down to what a maintenance person expects/assumes. I have been around this stuff a fairly long time. In my mind, when a maintenance person (who works on a ton of equipment, not just these blowers) comes up to the starter and sets it to Hand, he assumes it is now set to isolated control from the starter. I may be wrong, but this is my experience. I always try to err on the side of caution, and i really don't believe that a maintenance employee is going to go through the control schematic to see how the controls work before he begins to perform his tasks.

 

[GoldDigger]

Thank you everyone for your input. Getting other points of view is really helping me. I can be hard headed at times, well most times. The problem for me boils down to what a maintenance person expects/assumes. I have been around this stuff a fairly long time. In my mind, when a maintenance person (who works on a ton of equipment, not just these blowers) comes up to the starter and sets it to Hand, he assumes it is now set to isolated control from the starter. I may be wrong, but this is my experience. I always try to err on the side of caution, and i really don't believe that a maintenance employee is going to go through the control schematic to see how the controls work before he begins to perform his tasks.

Not necessarily practical, but if the label said something like "Remote Stop Disable" instead of "Hand" or "Local" would you feel better about it?

 

[petersonra]

Thank you everyone for your input. Getting other points of view is really helping me. I can be hard headed at times, well most times. The problem for me boils down to what a maintenance person expects/assumes. I have been around this stuff a fairly long time. In my mind, when a maintenance person (who works on a ton of equipment, not just these blowers) comes up to the starter and sets it to Hand, he assumes it is now set to isolated control from the starter. I may be wrong, but this is my experience. I always try to err on the side of caution, and i really don't believe that a maintenance employee is going to go through the control schematic to see how the controls work before he begins to perform his tasks.

he should not be working on it unless it is locked out. PERIOD. how the thing functions is an operations issue. I don't especially like the control scheme the engineer selected but it is possible that he intended it to work exactly as shown.

 

[sjwelter]

he should not be working on it unless it is locked out. PERIOD. how the thing functions is an operations issue. I don't especially like the control scheme the engineer selected but it is possible that he intended it to work exactly as shown.

This will be an installation in a remote location, no other humans around for miles. I doubt that lockout/tagout procedures will be followed. I cannot come up with any functionality benefit for deviating from what i consider to be industry standard wiring practices. I just don't see why the engineer wouldn't want to select either 100% Auto or 100% Local operation.

 

[GoldDigger]

I just don't see why the engineer wouldn't want to select either 100% Auto or 100% Local operation.

As mentioned earlier, so that either the operator OR the remote device can cause the fan to run unless it is explicitly switched off. Whether that is a good enough reason depends on just what the purpose of the fan is.
For example, suppose its purpose is to vent toxic or combustible gasses. The operator may want to manually start the fan for more ventilation without allowing the remote control (sensor based?) to stop it. But if he presses the stop button while in Hand mode, for safety the remote sensor should still be able to start the fan.

 

[sjwelter]

As mentioned earlier, so that either the operator OR the remote device can cause the fan to run unless it is explicitly switched off. Whether that is a good enough reason depends on just what the purpose of the fan is.
For example, suppose its purpose is to vent toxic or combustible gasses. The operator may want to manually start the fan for more ventilation without allowing the remote control (sensor based?) to stop it. But if he presses the stop button while in Hand mode, for safety the remote sensor should still be able to start the fan.

No toxic gasses here, the blowers will be inside of an antennae enclosure (radome). The ones that look like a big golf ball. The blowers are used solely to control temperature inside the dome.

 

[kwired]

This will be an installation in a remote location, no other humans around for miles. I doubt that lockout/tagout procedures will be followed.

Apparently somebody is around when lockout/tagout is followed (or not followed) for maintenance.

If there is ever a serious injury or death, right or wrong, you don't think the topic will ever come up when they try to figure out why things happened the way they did.

 

[sjwelter]

You have all eased my mind. I put in a RFI for the conflict of the wording of the specs and the drawing. I am going to wait until they come back to us with which way to go. It really isn't the liability that i am worried about, I truly am just worried about the possibility of anyone getting hurt in the field because of my decision to follow engineered drawings without question. Again, thank you all.