Facility maintenance upgrade

[bonded&grounded]

Okay, so we're looking at upgrading an older building. The power feed is 208V, but this new air handler needs 480V at 60A. Wondering if I can just grab power from the existing 100A disconnect using a transformer? What do you think?

 

[lightbender]

Okay, so we're looking at upgrading an older building. The power feed is 208V, but this new air handler needs 480V at 60A. Wondering if I can just grab power from the existing 100A disconnect using a transformer? What do you think?

You'll need more than that 100A disconnect, the transformer for 480V/60A would overload it. Either upsize the feed or run a proper 480V supply

 

[General_Valeria]

Yes, you can run a step-up transformer from 208 to 480, but size it correctly.... at least 50 kVA for that air handler, and you'll want a dedicated disconnect on the secondary side. Don't even think about piggybacking off the old 100A one without checking available capacity.

 

[Elderb3rry]

Okay, so we're looking at upgrading an older building. The power feed is 208V, but this new air handler needs 480V at 60A. Wondering if I can just grab power from the existing 100A disconnect using a transformer? What do you think?

just want to add some quick tips for a safe installation. first, you're going to need a completely new, dedicated circuit run from your main panel, because that 100 amp disconnect won't be enough. The transformer will actually be pulling around 139 amps on the 208 volt side, so you need a new circuit sized to handle that load.
Before you even get started on that, you should definitely have a contractor do a full load analysis of the entire building to make sure your main service has the capacity to handle the new air handler.
And yeah, this is for sure a job for a licensed electrician to make sure everything is up to code.

 

[theWirewiz]

You're spot on about the load calculations. That 139A draw on 208V is quite substantial, and most panels simply can't manage that extra load without some upgrades. The load analysis is crucial as well, many older buildings are already close to their capacity, and adding this load might necessitate a service upgrade to 400A or more. This isn't something they should try to tackle on their own, especially given the current requirements and issues with code compliance.

 

[hiddenarena]

Make sure you select a proper distribution transformer rated for your kVA and 60 Hz. And also the size of the protection and conductors per code and motor starting needs.

 

[franilly78]

just want to add some quick tips for a safe installation. first, you're going to need a completely new, dedicated circuit run from your main panel, because that 100 amp disconnect won't be enough. The transformer will actually be pulling around 139 amps on the 208 volt side, so you need a new circuit sized to handle that load.
Before you even get started on that, you should definitely have a contractor do a full load analysis of the entire building to make sure your main service has the capacity to handle the new air handler.
And yeah, this is for sure a job for a licensed electrician to make sure everything is up to code.

Appreciate the heads-up. Is the 139 amps continuous or peak draw? Also, do you know if the transformer has any inrush protection or soft-start features built in? Trying to figure out how much margin I need on the breaker sizing.

 

[PGB1]

Hi Bonded & Grounded,

Does the Air Handler also supply cooling, heating or is it simply a make-up air? Knowing this will help you size the new transformer properly.

Example: Something with a compressor starting at the same time as indoor and outdoor fans will have considerable inrush current. Something with a. small blower motor and resistance heaters will have very little inrush.

Higher inrush will require a larger transformer. They don't have "cushion". (There are other, very costly, ways to handle inrush load on the transformer that we use in industry and distribution.)

The 139 that was provided others above is the exact no-decimal amperage of a 480 volt, three-phase 60 amp device IF the secondary voltage is exactly 480 volts, the primary voltage is exactly 208 volts. If your figures are different, you have to adjust the calculations.

Hope This Helps,
Paul
PS: I suggest an engineer instead of an electrician to view and size your equipment. Many electricians aren't knowledgeable in such matters.