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Old 09-23-2018, 04:53 PM   #1
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Default Buck boost transformer

I need your guys help to see if this setup is code compliant.

Service is 120/208 three phase. I'm using a buck boost transformer to supply single phase 120/240 to a panel in an X-ray room. My PM told me to just pull the neutral trough the buck boost and terminate in the panel because there is no xo tap. Is this correct?

I am also concerned about the voltages at this panel. I am getting 148v on L1 and 120v on L2. Is it compliant to simply feed all my 120 loads off B phase? There is only one 240 volt load coming from this panel and it does not require a neutral.

Thanks for your help. This is my first time dealing with a buck boost transformer.
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Old 09-23-2018, 05:22 PM   #2
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Quote:
Originally Posted by eric626 View Post
I need your guys help to see if this setup is code compliant.

Service is 120/208 three phase. I'm using a buck boost transformer to supply single phase 120/240 to a panel in an X-ray room. My PM told me to just pull the neutral trough the buck boost and terminate in the panel because there is no xo tap. Is this correct?

I am also concerned about the voltages at this panel. I am getting 148v on L1 and 120v on L2. Is it compliant to simply feed all my 120 loads off B phase? There is only one 240 volt load coming from this panel and it does not require a neutral.

Thanks for your help. This is my first time dealing with a buck boost transformer.
I dont know how you make the connection on the BB ( buck and boost ) transfomer and is that load on 240 volts have be on 240 volt range or it can work on 208 volts ?

It sure dont sound right the way you make the connection at all.
I would stop right there and get someone who know the BB system better to help you before you destory a Xray and related equiment.

I would move that BB transfomer connection to strictly on 208 side and boost it up and nothing on 120 volts then it will read correct.
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Old 09-23-2018, 05:56 PM   #3
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If I remember correctly that is normal for a buck boost transformer to be getting around 148 volts on one of the phases. I would use the buck boost transformer to feed the x-ray machine directly and nothing else. Make sure the transformer is large enough for the x-ray machine
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Old 09-23-2018, 06:00 PM   #4
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You using a single BBB to Boost voltage?

Post the model number.
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Old 09-23-2018, 06:24 PM   #5
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Thanks for the replies.

Frenchelectrician the equipment defiantly needs 240v. The manufacture states it will not operate on anything less than 230v. I did have my project manager come in and check everything. He says everything is fine but I wanted to get a second opinion. I defiantly don't want to destroy anything because this stuff costs more than I make in a year.

Julius I agree that it would be better to feed the equipment directly from the BB but the prints call for it to be set up like this. They want a couple 120v dedicated receptacles fed from this panel.

Brian John yes I am using a single BB. Model number is K1XLF16-5 Federal Pacific buck boost auto transformer 5kva single phase.
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Old 09-23-2018, 06:41 PM   #6
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Thanks for the replies.



Brian John yes I am using a single BB. Model number is K1XLF16-5 Federal Pacific buck boost auto transformer 5kva single phase.

The output voltage at 208 is 236 and The neutral NOT used in the transformer one phase passes through and would remain at 120 VAC normally we would not use the secondary of a boost transformer for 120 VAC loads. If this feeds one piece of equipment we would use a Fused Safety Switch.
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Old 09-23-2018, 06:50 PM   #7
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The prints seem very poorly engineered.

One must go from L1 to L2 to feed the BB if you want to lift 208V up to 240VAC.

It's a law of physics.
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Old 09-23-2018, 07:07 PM   #8
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Brian John is it ok to just have the neutral pass through the BB uninterrupted? Also what kind of problems will I have supplying 120 from the secondary side of the BB? I'm just trying to be more informed before I raise any issues with the GC because they specialize in imaging rooms. They also designed this setup and supplied all the equipment.
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Old 09-23-2018, 07:27 PM   #9
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I do not like this set up one bit. I can't imagine feeding an unknown load with a BB.
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Old 09-23-2018, 08:12 PM   #10
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Quote:
Originally Posted by eric626 View Post
Thanks for the replies.

Frenchelectrician the equipment defiantly needs 240v. The manufacture states it will not operate on anything less than 230v. I did have my project manager come in and check everything. He says everything is fine but I wanted to get a second opinion. I defiantly don't want to destroy anything because this stuff costs more than I make in a year.

Julius I agree that it would be better to feed the equipment directly from the BB but the prints call for it to be set up like this. They want a couple 120v dedicated receptacles fed from this panel.

Brian John yes I am using a single BB. Model number is K1XLF16-5 Federal Pacific buck boost auto transformer 5kva single phase.
Let me read this right the Xray machine is strictly 240 volts and nothing on that run on 120 volts ? ya running full 4 conductor in or 3 conductors in ? that will clear up some details on this set up.
for 120 volts dedicated receptacles I would tie that before the BB tranfomer and never after that due the voltage will be wonky it will hit about 143 to 147 volt range and can destory some items if they are not designed to run more than 125 to 130 volts tops.

Ask the GC for RFI on the connection diagram to verify it.
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Old 09-23-2018, 08:28 PM   #11
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You are straight up using the wrong transformer for what you need.
If you just want to provide the machine 240 volts, that's good.
Forget anything about the "neutral" you don't have one and you can't use the line side neutral.
The 120 volt circuits in the X-ray room can come from the 120/208 house panel.
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Old 09-23-2018, 09:09 PM   #12
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Thanks for the replies everyone. I'm going to let my office and the architect who drew the plans figure this one out. It seems we should be feeding the X-ray room panel with 120/208 then from there feed the 240 equipment using the buck boost.
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