VAV Box/ 240 3-phase feed

[ZACHARY]

Heating and Air guys installed a VAV box with a heating element and a damper. On the front of the door to the controls box, it calls for 3-phase 240V. Pulls 39 amps on each phase = #8's w/ #8 ground. The schematic on the front shows:

L1 - 39A
L2 - 39A(N)
L3 - 39A

Inside the box on the line diagram it calls for 3-phase(black, red, blue)as the power feed. I have only a single phase 240V panel from which to bring power to this unit. Here's my question....

Why does L2 have (N) next to it like it's calling the second phase a neutral?

Can I double up on a phase(be it black or red) and feed the unit? The heating element doesn't care about phase rotation, so will this toast the unit?
It only takes 2 phases and transforms it down to low voltage once in the line diagram.....

 

[peter d]

What you described makes no sense, but reading between the lines I'll give it a shot.

First of all, it's unlikely that this unit is "240 volt, 3 phase." More likely it's 208 volt 3 phase.

It's possible that the unit can be configured for both 3 phase or single phase operation, but keep in mind that the ampere rating will increase if you can rewire it for single phase operation. If you cannot change the connection in the field, you are out of luck.

You can tell if it requires a neutral by checking the connection block. Just look for a connection labeled "N." I just finished a few of these units myself (3 phase, 480 volts), and they required a neutral.

 

[infinity]

Could you post the make and model number of this unit?

 

[loren]

This unit is a 240 volt 3 phase unit. The N next to the L2 represents that you can use a grounded B phase system. Not common but I have seen them.

 

[Smart $]

I have only a single phase 240V panel from which to bring power to this unit.

Unless the VAV has reconfiguring instructions for single phase use, I suggest you make the HVAC guys aware that the unit will need to be replaced with a 120/240V 1? unit. Taking it upon yourself to reconfigure the unit will violate its listing.

 

[ZACHARY]

Manufacturer(York) Reply

Manufacturer(York) Reply

They said it was satisfactory to wire it 3-phase 208v. It does not give this option anywhere on the equipment.

Thanks everybody for your input.

 

[necnotevenclose]

Is this a heat only VAV with no fan? VAV's usually inlcude heat & fan but I have also seen VAV's spec'd with heat and no fan or fan and no heat. It's my understanding that the neutral is provided either for the single phase fan motor or for the internal low voltage controls.

 

[Smart $]

They said it was satisfactory to wire it 3-phase 208v. It does not give this option anywhere on the equipment.

It doesn't matter. You don't have a 3? power source.

 

[George Stolz]

With that in mind, how did they say to wire it?

 

[infinity]

Somethings seems odd about this unit. The manufacturer is saying that it can be wired @ 208 volts but this will give the heating element a reduced output.

Either way, as Smart pointed out, you'll need three phase to run this unit. My guess is that the (N) is to indicate that on a three phase, 3W, corner grounded delta system, the grounded phase would connect to the L2 leg on the unit.

 

[ZACHARY]

There ARE existing 3-phase 208v power sources in our facility, just no 3-phase 240v. This is where my problems stemmed from because the unit is solely listed to be fed with 3-phase 240v. Nowhere on the unit is it labeled marked as being reconfigured or allowable to be fed with 208v 3-phase.

The unit is a continuous forced air, no fan. To cool, the damper opens up. To heat the damper closes slightly and the heating element kicks on. I would guess that the unit most definitely has a lower heating element output due to the lower voltage feed(208 versus 240), but apparently it does not affect it's performance to any noticeable degree as it has been running for a couple weeks now.

Maybe it would make a difference in a larger unit or one with a fan that had a motor...... I dunno........

 

[Pierre C Belarge]

Get in touch with the manufacturer. They can give you an answer that we would just be taking a stab at. If you call the manufacturer, don't forget to take the model number with you when you call.