Wiring number to local control panel for AHU

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Leo Li

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Hi Sir, normally how many wirings will be pulled from panel board to 3P, 208V AHU control panel (VFD, relay ,contact ec,. control device will be inside this control panel), locally (China) we will pull five wirings( A,B,C,N and G, control circuit normally is A-N ) I am not sure how will be in US project in this case? I saw some US project drawings it was only four wirings(A,B,C and G) but no wiring for nutral, if so I would like to check how is control circuit if no Neutral wiring? the control circuit will be A-B?Thanks!
 
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For a 3 phase control panel it could just be 3 hots, maybe an EGC. No neutral as most panels will have a control transformer. Deepens on voltage and customer preference
 
As the other poster said it kind of depends on what the customer wants and what he bought. With 208 three phase if you run a neutral man any line to neutral is 120 volts and could be used for control circuit wiring, or a control transformer might be supplied, or a 208 volt input power supply might be supplied if the control circuits are all 24 volts DC.

Normally you would run at least three phase lines and an equipment grounding conductor, although if you use metal raceways you can skip the equipment ground and conductor if you want and use the raceway for that purpose. It won't hurt you to run the neutral out there even if it's not used.

Air handling units sometimes have a convenience receptacle included for powering up lights and tools which would need the neutral.
 
Most manufacturers here will use a small step down transformer for controls. Having to pull a neutral for a small circuit is not that big of a deal, but if you have, say a 200 amp feed to a cabinet, it is not at all practical to pull a neutral just for the controls.
 
hillbilly1 said:
Most manufacturers here will use a small step down transformer for controls. Having to pull a neutral for a small circuit is not that big of a deal, but if you have, say a 200 amp feed to a cabinet, it is not at all practical to pull a neutral just for the controls.
Click to expand...
Thanks！
 
petersonra said:
As the other poster said it kind of depends on what the customer wants and what he bought. With 208 three phase if you run a neutral man any line to neutral is 120 volts and could be used for control circuit wiring, or a control transformer might be supplied, or a 208 volt input power supply might be supplied if the control circuits are all 24 volts DC.

Normally you would run at least three phase lines and an equipment grounding conductor, although if you use metal raceways you can skip the equipment ground and conductor if you want and use the raceway for that purpose. It won't hurt you to run the neutral out there even if it's not used.

Air handling units sometimes have a convenience receptacle included for powering up lights and tools which would need the neutral.
Click to expand...
Thanks!
 
The secondary of the control transformer will typically either be ungrounded or have one side bonded to the EGC, doubling as a GEC (Ground Electrode Conductor), or to building steel, as a Seperately Derived System (SDS). If a neutral is present, the low side of the secondary can be connected to that neutral as a non-SDS.
 
Control components likely to be 24 volt or in some cases maybe 120 volt.

I could still see it to be common to have a control voltage transformer at said control panel and it's primary connected to the incoming line to line volts and no need for a neutral with the supply conductors. This control transformer likely even has multiple input taps so you can use same control transformer on units with other input voltages.
 
kwired said:
Control components likely to be 24 volt or in some cases maybe 120 volt.

I could still see it to be common to have a control voltage transformer at said control panel and it's primary connected to the incoming line to line volts and no need for a neutral with the supply conductors. This control transformer likely even has multiple input taps so you can use same control transformer on units with other input voltages.
Click to expand...
Thanks！Yes， I did see some control ciruits is line to line volts 120volt.
 
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