Low voltage BMS questions

[Wruderman79]

I have a couple of questions and after checking out this site for the past few hours I feel that this is the perfect place to try to receive educated answers.

1) when supporting low voltage cables used exclusively for an hvac system is said system an acceptable plane to affix to?

2) I have seen an accepted practice of using a small changeover piece of flexible metallic conduit when running conduit on to an air handler (for the feeding of the fan or control devices) is this always required even if the fan itself is on isolating springs?

3) On my current job I am working on the BMS a different contractor is doing the fire alarms. The way they want this system set up is in a fire condition the fire alarm is sending a shutdown signal to the variable frequency drives for several air handlers, the air handlers are in control of the fire smoke dampers and are wired to open and close whenever the vfd is on or off. The endswicth off the fire smoke dampers are wired in series back to let the fan start my question is this legit or does the drive now have to be considered a fire alarm device because it is soley controlling the fire smoke dampers?

Thanks this is a great site and I look forward to reading your thoughts

 

[nhfire77]

I have a couple of questions and after checking out this site for the past few hours I feel that this is the perfect place to try to receive educated answers.

1) when supporting low voltage cables used exclusively for an hvac system is said system an acceptable plane to affix to?

2) I have seen an accepted practice of using a small changeover piece of flexible metallic conduit when running conduit on to an air handler (for the feeding of the fan or control devices) is this always required even if the fan itself is on isolating springs?

3) On my current job I am working on the BMS a different contractor is doing the fire alarms. The way they want this system set up is in a fire condition the fire alarm is sending a shutdown signal to the variable frequency drives for several air handlers, the air handlers are in control of the fire smoke dampers and are wired to open and close whenever the vfd is on or off. The endswicth off the fire smoke dampers are wired in series back to let the fan start my question is this legit or does the drive now have to be considered a fire alarm device because it is soley controlling the fire smoke dampers?

Thanks this is a great site and I look forward to reading your thoughts

3- so the end switch allows the VFD to be bypassed and allow the AHU to run? If Im hearing you correctly that wouldn't be permissible, the AHU must stay off until the alarm is reset, unless local rules over ride that.

Now I'm a bit confused because you said dampers. Do the dampers only shut when then VFD is off? They should be closed by a fire alarm input, if that input is via the VFD, that might be ok, depending on if it can be overridden and/or AHJ ok.