motor hand-auto selector switche 1

[dpoppeli]

Application is central air-handlers in a university building. Apparently some here want to specify that hand-off-auto selector switches be installed for fractional horsepower motors such as freeze-protection pumps (hot water air-handler coils) and electrical closet exhaust fans. My argument is that it's unecessary and the switch can be left in the off position accidentally and then freeze protection or exhausting of heat is defeated with possible repurcussions (I have experienced this actually). In general I strive to keep things simple and so I will argue against the extra "button" when not really needed. The arguement for it is that it eases maintenance troubleshooting and the added cost is minimal.

Anyone have any opionion on this?

 

[DRWeig]

dpoppeli,

I'm going to side with your techs. While it's true that a control can be left in an "off" condition, my experience is that it's far more common to need to manually force something "on" or "off" to correct a problem. Without an H-O-A, you either wire up a jumper (dangerous) or manually push a contactor button in (dangerous) or get a helper to make the start/stop happen from a remote control position (time consuming and frustrating).

If inadvertent disabling of freeze protection is an issue, they are available with locking provisions. I say spend the extra couple of bucks.

Good on ya,

Old Dave

 

[walkes]

My thoughts would be that the fractional hp motors can be monitored and controlled more easily via DDC systems. The way things are going these days more and more operators seem to want to be able to check things out while they are sitting at their desk, giving them the ability to cover more of the campus during their working days. Thereby spending more time actually fixing problems. The additional monitoring can be helpful for troubleshooting by getting an idea prior to getting to the scene of the problem.

 

[MintJulep]

It is possible to configure a switch for auto or on without off being a possibility.

It would also be possible to configure an alarm for "off and getting pretty cold", but seems more trouble than it's worth.

 

[DRWeig]

MintJulep,

Good point. I have a client hospital with 80 air handling units but only one guy in the building on evening and night shifts. We did one of those "off and getting pretty cold" alarms with a flow switch and low-limit in series for every one of the AHU's just so the lone fix-it-up-chappy could get a page from the DDC system if he were busy plunging a toilet or something when a freeze-protect pump died.

Most often, though, it's not worth the extra cost...

Old Dave

 

[ChasBean1]

I side w/DRWeig also. There would be 'soft' start/stop for the freeze pumps and electrical closet cooling anyway (based on outdoor temperature or room temperature). These would work with the switch in auto. However, if a sensor fails or reads incorrectly, you can have the option to run the system in hand, which would bypass the temperature input. -CB

 

[cme]

What I would do is specify some blurb-age to shut the OSA damper when the current switch on the pump lead trips (pump fails) and alarm to the DDC head end.

Same for the electrical closet, alarm to the DDC say when room temp rises above 90F or so.

 

[lilliput1]

I would be less confusing if all motors w/ automatic control to have HOA. No matter what the season is if it has HOA, it should be on Auto unless there is a problem

 

[dpoppeli]

Thanks for opinions. Looks like I'm outvoted by coworkers and we will be installing the switched starters.