Multiple VAVs on one circuit

[Platinum2012]

Hey guys,

A contractor wants to group (4) VAVs (heat only, 5kW each) together and feed it from one circuit breaker 208V, 3phase.
Total load would be 20 kW which i calculate to be around 56A load.
He wants to use a 70A circuit breaker which would require #4AWG.

My concern is he would have to run #4AWG's to each of the 4 VAV boxes correct? He would not be allowed to tap down to a smaller guage wire to feed one of the VAVs, right? The VAV's come with an integral disconnect which is non-fused.

All of these 5kW VAV's are 208V, 3phase. Is it wise to group these together and feed from one larger breaker? It seems like it would be more expensive this way?? Bigger breaker, bigger wire. But on the other hand you are saving panel space....

 

[iwire]

OK,

First off the VAVs likely have a maximum over current device rating.

If they do, to move ahead with the plan you would need to install fused disconnects or breakers at each VAV so each could be properly protected.


As far as coming out with 4 AWG and then down sizing ... maybe. It will depend on the distances between VAVs

This feeder tap rule might be able to be applied.

240.21(B)

(2) Taps Not over 7.5 m (25 ft) Long. Where the length of
the tap conductors does not exceed 7.5 m (25 ft) and the tap
conductors comply with all the following:

(1) The ampacity of the tap conductors is not less than
one-third of the rating of the overcurrent device protecting
the feeder conductors.

(2) The tap conductors terminate in a single circuit breaker
or a single set of fuses that limit the load to the ampacity
of the tap conductors. This device shall be permitted
to supply any number of additional overcurrent devices
on its load side.

(3) The tap conductors are protected from physical damage
by being enclosed in an approved raceway or by other
approved means.

So if the VAVS are all within a 50' circle and if you ran 4 AWG to the middle of the group and if you ran a raceway to each VAV and if each VAV had a fussed disconnect you could reduce the wire size down to 1/3 that of the feeder conductors.


I would keep them separate.

 

[Platinum2012]

Thanks Iwire.

So it seems like there are 3 options -

1. Circuit each VAV individually.

2. Circuit them as a group by running #4AWG to each VAV.

3. Circuit them as a group and using the feeder tap option (which has certain requirements).

 

[iwire]

2. Circuit them as a group by running #4AWG to each VAV.

If you were to do this you would have to keep an eye on the units labeling for maximum over current protection rating.

You would likely need to add an OCPD at each VAV.

 

[jumper]

multiple vav boxes off one circuit and then individual ocpd/discos is quite common. have done many.

 

[petersonra]

I don't have a huge problem with the idea in general. Like a lot of things, the devil is in the details. Many times things like this are proposed as a cost saving measure but end up not saving all that much and being a hassle for people down the road.

 

[iwire]

multiple vav boxes off one circuit and then individual ocpd/discos is quite common. have done many.

I agree, it is quite common in office buildings around me.

 

[david luchini]

He wants to use a 70A circuit breaker which would require #4AWG.

It there is not an MOCP requirement for each VAV as Bob pointed out, then the proposed arrangement would violate 424.3(A) and 424.22(B).

 

[Platinum2012]

It there is not an MOCP requirement for each VAV as Bob pointed out, then the proposed arrangement would violate 424.3(A) and 424.22(B).

Interesting i was not aware of that article. So it looks like i can't go above a 60A breaker...