Step Up Transformer

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charlie b

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Location
Lockport, IL
Occupation
Retired Electrical Engineer
My mechanical colleague is selecting an insta-hot water heater to serve an eye wash / shower for a small building in which aircraft engines will be tested. The shower (and thus the water heater) are most likely to sit idle for decades. In order to get the temperature and flow rate he needs, he is looking at 80 KVA and higher. His manufacturer's data sheets only give him the option of 480V or 600V. The building has only 208V. I would like opinions (and concerns) over using a transformer to step up the voltage to 480.

  1. If this system is needed in an emergency, it will go from idle to full power immediately. The transformer's 208V primary will be live at all times, so I don't expect an issue with transformer inrush current. But are there other concerns?
  2. Will the project be better off if I ask the ME to look for other manufacturers who can work with a 208V source? Please note that we would be dealing with a 230+ amp branch circuit that will run 100 feet or longer.
  3. Any other ideas?

TIA
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
My mechanical colleague is selecting an insta-hot water heater to serve an eye wash / shower for a small building in which aircraft engines will be tested. The shower (and thus the water heater) are most likely to sit idle for decades. In order to get the temperature and flow rate he needs, he is looking at 80 KVA and higher. His manufacturer's data sheets only give him the option of 480V or 600V. The building has only 208V. I would like opinions (and concerns) over using a transformer to step up the voltage to 480.

  1. If this system is needed in an emergency, it will go from idle to full power immediately. The transformer's 208V primary will be live at all times, so I don't expect an issue with transformer inrush current. But are there other concerns?
  2. Will the project be better off if I ask the ME to look for other manufacturers who can work with a 208V source? Please note that we would be dealing with a 230+ amp branch circuit that will run 100 feet or longer.
  3. Any other ideas?

TIA

I don't see any issue except you will have to live with the xformer no load losses forever. The green police may have an issue with that. Of course locate the xformer at the source end so you can have a smaller (and less voltage drop) long run to the heater. Also be sure to use a 208 delta primary X 480 Y secondary to make things simpler and a little safer.
Maybe consider 2 or 3 smaller heaters in parallel that might be available @ 208 V to avoid the transformer and avoid the perpetual no load losses?
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I would not surprise me if the shower is required to be tested on a regular basis, so the system won't be entirely idle.

With that said, it is likely to be used infrequently, and can likely tolerate large voltage drop.

My preference would be for something that can use 208V rather than eating the transformer losses and the cost of the transformer.

-Jon
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Thanks, Texie. I had planned on putting the transformer in the electric room, with a local secondary OCPD, and running 480V across the building. It is a water heater, not a space heater, so I don't think using multiple smaller heaters is an option. The component will not require a neutral. But I agree with the delta-wye, as it provides additional options. The building is not eligible for LEED certification, so they would have to live with the no load losses.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
If you use an instantaneous heater at 480V, you have standby losses from the transformer and the transformer space requirements.

If you use a tank type heater, you have standby losses from the tank and the tank space requirements.

Maybe compare the two options and see which is cheaper/uses less space. Also, you could use both: a lower temperature tank water heater (less standby losses) with a smaller 208V instantaneous heater (no transformer losses).

Cheers, Wayne
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I would think that, for emergency use, a small storage-tank water heater near the point of use would be the way to go.

Is there no bathroom nearby?
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Maybe a storage water heater would work for an eye-wash, but safety showers have huge flow requirements, have to run for perhaps 15 minutes, and need 'tepid' water. You are not talking a small storage tank.

https://www.grainger.com/content/qt-emergency-shower-eye-wash-stn-req-120

20 gallons per minute for 15 minutes!

This will be an expensive install no matter how you slice it. A 300 gallon storage tank won't be cheap and will have considerable standby losses. Since you only need 'tepid' water, you could use a smaller tank at higher temperature and a mixing valve...but the tank is still pretty large. I think that Charlie's ME has already settled on using an electric 'demand' heater for this application; and the question is limited to 'what is the best electrical install'.

At 230A and 208V, the conductors required are large enough that voltage drop is not a significant issue at 100 feet. Remember that the larger the conductor the lower the 'amps per circular mil'.

For this application the heater can also reasonably tolerate quite a bit of voltage drop; you are not worried about energy efficiency for such infrequent use. Say you get 10% voltage drop, that corresponds to a 20% loss in heater output; so you simply design using a slightly larger heater rating.

So in addition to my suggestions above about sticking with 208V (to save on the cost of the transformer and the ongoing costs of running the transformer) I suggest that the expected voltage drop be sent back to the ME so that heater size can be adjusted.

-Jon
 
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