I was informed by a colleague today that an AHU needs to be shut down by an in-line contactor and that a signal from a control system does not satisfy code due to the fact that it can be by-passed by a hand-off-auto switch. Can anyone provide a code reference or experience in this matter?
AHU Shut Down
- Thread starter Artemis
- Start date
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quogueelectric
Senior Member
- Location
- new york
An ahu needs to be shut down by an aproved fire alarm relay. You can break the control feed right at the origin therefore preventing bypass by hoa switches.
RJohnsonMasterElectrician
Senior Member
- Location
- Right now ??, previously VT
over 2000cfm
izak
Senior Member
- Location
- Springfield, MO
ive never installed anything that could shut down an AHU from fire alarm that HAD an HOA
the large air handlers ive been around had a set of dedicated contacts to connect the F/A signal to
but there was never any Hand/Off/Auto anywhere in the system
the large air handlers ive been around had a set of dedicated contacts to connect the F/A signal to
but there was never any Hand/Off/Auto anywhere in the system
weressl
Esteemed Member
I think that he may be mixing requirements with LOTO where interruption of the control circuit does not satisfy the requirement of power removal. The same is not aplicable to AHU. AHU control circuit supervisory action over the FA system is an acceptable method of stopping the air suply in case of fire. It should override any other controls.
Mr. Wizard
Senior Member
- Location
- Texas
Fire alarm shutdown trumps all other control safeties on any AHU. Regardless of the position of the HOA (except off), the FA system will dictate the shutdown in the event of a fire. The FA isn't actually tied into the building automation system, but on it's own system. If it's a duct detector, just tie into the N.C. dry contacts on it, and you should be alright. Depending on the size of the AHU, there may be a supply and return duct detector that you may have to tie into. The idea behind it is whether the unit is in auto or in hand, it will be subject to FA shutdown in the event of a fire.
weressl
Esteemed Member
LOTO stands for OSHA's Lock-Out-Tag-Out.
steelersman
Senior Member
- Location
- Lake Ridge, VA
no, it stands for lock out tag out.
I think the OP is referring to the use of a control circuit instead of an actual disconnect switch as the service disconnecting means for a Roof Top Unit. 430.103 and 430.109 I believe would be the code sections that prohibit this. 430.103 states that a disconnect for a motor must "open all ungrounded supply conductors". Clearly a de-energized control circuit does not accomplish this. 430.109 lists the different types of disconnects that can be utilized to accomplish the 430.103 requirement. "De-energized control coil" is NOT one of them.
steelersman
Senior Member
- Location
- Lake Ridge, VA
Aha. I think you are right. I am with you on this. I think that is what he was getting at as well.
Safety Circuit
Safety Circuit
How about 2008 NEC 725.31 & exhibit 725.3
Where do those saftey device wire into the AHU motor starter.... I belive it is code required that they are in series with the motor starter & the overload.
Thus an AHU shuts down on a safety weather its a duct detector or a High pressusre switch.
Can anyone agree or disagree with this....?
FYI: Good VFD's come with a 120v safety circuit to string all of the N/C contact in series with...
Safety Circuit
How about 2008 NEC 725.31 & exhibit 725.3
Where do those saftey device wire into the AHU motor starter.... I belive it is code required that they are in series with the motor starter & the overload.
Thus an AHU shuts down on a safety weather its a duct detector or a High pressusre switch.
Can anyone agree or disagree with this....?
FYI: Good VFD's come with a 120v safety circuit to string all of the N/C contact in series with...
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