Changing circuit from 120V to 240V - how to trace?

[busman]

Got asked by an HVAC contractor to change a 120V circuit for a home air handler to 240V, the voltage of the new handler. Obviously not hard to change in the panel, but how would you be able to be sure that this is an Individual Branch Circuit. Obviously, BAD things will happen if there are other loads on this circuit. I so far have done the following:

1) Visually traced the Romex from the basement panel, outside the house where it follows the refrigerant lines and into a sealed attic space (cape code house) above the finished attic where the AH is located.

2) Put an ammeter on the line with the AH shut off to verify no load.

3) Shut off circuit and checked everything in the house that I could find to make sure they were still energized.

4) Put a wire tracer on the circuit to try to find any branches above the attic ceiling; didn't detect any.

Is there anything I'm missing?

As always, thanks in advance; you are a great source of information.

Mark

 

[hillbilly1]

Curious why the new airhandler is 240? There may be more to it than that, if it is a heat pump, there may be strip heat that the old 15 or 20 amp circuit will not handle anyway. Or they are just using an airhandler that's in stock at their warehouse. It would be unusual for gas backup or gas main heat to be 240, but not out of the realm of possibilities.

 

[busman]

Curious why the new airhandler is 240? There may be more to it than that, if it is a heat pump, there may be strip heat that the old 15 or 20 amp circuit will not handle anyway. Or they are just using an airhandler that's in stock at their warehouse. It would be unusual for gas backup or gas main heat to be 240, but not out of the realm of possibilities.

I was quite surprised myself. Planning to ask the HVAC guy tomorrow and will let you know. Yes, I've only ever seen 240V when they have backup heat for a heat-pump.

Thanks,

Mark

 

[hillbilly1]

I was quite surprised myself. Planning to ask the HVAC guy tomorrow and will let you know. Yes, I've only ever seen 240V when they have backup heat for a heat-pump.

Thanks,

Mark

He probably neglected to tell you "Oh, by the way, it needs to be 50 amp!" LOL!

 

[busman]

He probably neglected to tell you "Oh, by the way, it needs to be 50 amp!" LOL!

Actually made sure the put the 15A, 240V in writing, as I thought it was odd. Why would they go to 240V for just the fan motor?

 

[Little Bill]

I was about to post the same thing. I didn't hear a mention of size/amps. I have to laugh everytime I get a call/request saying "I need a 220 line run". Me: Ok, what size/amps? Them: "IDK, just a 220"

 

[LarryFine]

1) Visually traced the Romex from the basement panel, outside the house where it follows the refrigerant lines and into a sealed attic space (cape code house) above the finished attic where the AH is located.

If it follows the refrigerant lines, it was added when the central HVAC was added to the house, so it's dedicated. Anything else it powers would be at the air handler.

Is there anything I'm missing?

Only that Romex should not have been used for the outside portion of the run (or at all to avoid junctions..

 

[LarryFine]

Actually made sure the put the 15A, 240V in writing, as I thought it was odd. Why would they go to 240V for just the fan motor?

I've seen it more commonly used recently; perhaps to reduce motor inventory.

Given the option, I've always preferred the higher-voltage versions of motors.

 

[Eddie702]

240 volt has been use for AHUs for years around here. Mine is 34 years old and is 240v. Most ahus have a blank off installed where an electric heat strip can be added. Of course the circuit has to be sized properly. I think they do it just to standardize the AHUs if electric heat is added. Otherwise they would have to stock AHUs with the same capacity with 120 or 240 volt motors

 

[OldSparks]

It COULD be that the new AH has a 3-phase motor being fed by a VFD in order to vary the speed according to demand. Just a hunch.

 

[kwired]

240 volt has been use for AHUs for years around here. Mine is 34 years old and is 240v. Most ahus have a blank off installed where an electric heat strip can be added. Of course the circuit has to be sized properly. I think they do it just to standardize the AHUs if electric heat is added. Otherwise they would have to stock AHUs with the same capacity with 120 or 240 volt motors

That is my observation. only 120 volt blower only units I have seen were made prior to ~1980 and were not designed to install optional heat strips.

Past 40 years or so you just order a unit without any heat strips, and in more recent years even if you want heat strips you usually have to order the AHU and field install the heat strips.

Are there 120 volt units available, maybe, but they will not be stocked and therefore are seldom ordered.

 

[busman]

All went well with the change-over. It was an Individual Branch Circuit, as expected. My real concern had been maybe an attic fan that wasn't accessible.

Anyway, just wanted to thank you all for the time.

Mark