buck/boost transformers

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alfiesauce

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Situation-
A tanning bed fed via a 3pole 80amp breaker off a 120/208 service
Above the t-bar is a 12X12 with three transformers hanging off of it -http://ecatalog.squared.com/pubs/Electrical%20Distribution/Low%20Voltage%20Transformers/Buck%20and%20Boost/3616.pdf
They have 246 Volts at the bed but they want 236 Volts ideally.
It seems to me that the service feeders went straight through the 12x12 and then three wires came back up to to boost transformer set up.

Not having seen this kind of set up for a very long time and then when I did, in a school setting, could someone point to some stuff I could read up about this stuff on?
From what I can gather this is considered a closed delta system as there is no neutral point in it whatsoever. It seems like this is the least favorite wiring method of them so would it be prudent to rewire down to a two transformer system?
 
If you have a 120/208 system you have a Wye with a neutral point. If you are using three transformers they are also in a Wye, I would hope. If you had two then it would be an open delta. You should be able to raise the voltage to 235 volts with the correct ones. I am surprised that the beds require 236 as the ones I have worked on were rated for 208. Get the load of the fixture in Kva or watts and call tech assistance. http://www.jeffersonelectric.com/cgi-bin/site.pl?3208&dwContent_contentID=17 or look at the choices on page 9.7 in the Product List link. Also, make sure your 208 volts is actually 208 volts.
 
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ZZZ said:
If you have a 120/208 system you have a Wye with a neutral point. If you are using three transformers they are also in a Wye, I would hope. If you had two then it would be an open delta. You should be able to raise the voltage to 235 volts with the correct ones. I am surprised that the beds require 236 as the ones I have worked on were rated for 208. Get the load of the fixture in Kva or watts and call tech assistance. http://www.jeffersonelectric.com/cgi-bin/site.pl?3208&dwContent_contentID=17 or look at the choices on page 9.7 in the Product List link. Also, make sure your 208 volts is actually 208 volts.
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They are definatly rated for 236.
This is an installed system.
I'm pretty positive it's 208 - not 120/208 there is no neutral being carried through to the bed at all.
And when you do searches they talk about a closed delta system that you shouldn't use because it's inefficient but it looks like that's what was done.

So then are you telling me you would scrap what the past electricians did and start from scratch and ensure the xmers are properly sized, disconnect one of them and just go with the standardized method of a two xmer delta boost setup?
 
236-245?

Are there any issues?
A 4% differences is minimal and not all that unusual in distribution systems.
Why were you contacted? Usually the end user has no clue what the voltage at their equipment is.
 
Apparently, according to the manufacturer, that 4% difference is enough to burn out the lamps out more quickly. Those said lamps cost over 1500 dollars to replace- this makes them queasy apparently.
The end user doesn't really know, but his cousin is a "handy" man and does know but is not brave enough to attempt to change the xmer wiring himself.
 
Okay, the transformer datasheet that you linked shows a 120 or 240V primary, and a 16 or 32V secondary. You have a bunch of choices as to how these transformers could be connected.

If you have the neutral available, then you can use the transformers, connected 120V primary and 16V secondary, primary connected to secondary in a boost configuration to give 136V line to neutral. This is 236V line to line, exactly what you are asking for.

If you don't have the neutral available, then you can use the transformers, connected 240V primary (but operated at 208V) and get a boost in your line-line voltages, but you only have a choice of 228V or 250V.

I'd suggest you determine exactly how the feeder is connected, and if you have a neutral available at the transformer location.

-Jon
 
alfiesauce said:
They are definatly rated for 236.
This is an installed system.
I'm pretty positive it's 208 - not 120/208 there is no neutral being carried through to the bed at all.
And when you do searches they talk about a closed delta system that you shouldn't use because it's inefficient but it looks like that's what was done.

So then are you telling me you would scrap what the past electricians did and start from scratch and ensure the xmers are properly sized, disconnect one of them and just go with the standardized method of a two xmer delta boost setup?
Click to expand...

I only mentioned you have a wye supply with a neutral because your post stated you had 120/208 power. It is unimportant for selecting transformers and the beds don't need a neutral as you said. The correct connection for the transformers is determined by the application and the tables will have the diagram number to use. You may be able to use the the B&B transformers you have, but you need to select the correct ones for the application in order to see if they are correct. You must know the exact supply voltage, it must be measured. You need the load voltage from the nameplate. You need the KVA of the bed. Then you go to the 3 ph. selection table. Find the input and output voltages that closest match what you desire. If your numbers are accurate it will be 120x240v pri, 16/32v sec. models. Follow the row to the right to the correct KVA for your application. When you reach this point the choice will be made for how many (2 or 3) transformers and how they will be connected. See page 7 on the Sola link: http://www.sola-hevi-duty.com/products/transformers/pdfs/bboost/3phselec.pdf
 
An 80 amp breaker is interesting, I never saw a bed use over 40 amps on 3 phase. Maybe they're just smaller around here.
 
glene77is said:
Alfie,

Surely this is not a Service & Feeder in the same trough?
Click to expand...

Yeah, positive. There is a 1" conduit that comes across the ceiling down to a 12x12 that has the three xmers attached to it. Then a piece of flex off of the 12x12 that goes down to a disconnect behind the tanner that then attaches to the tanner.
Then the three wires coming in from the panel through the conduit that splice in the 12x12 straight through down to the disconnect. Then there are three wires that that come back up through the conduit that connect to the xmers.

Definitely 80A three phase.
I think at this point I'm going to assume that someone has been messing around with the system - perhaps they upgraded the bed at some point and didn't check above the ceiling. So if I assume that, it will mean assuming it's wrong, recheck sizing of the xmers and then connect with the recommended 2 xmer connection and look brilliant!

The bed is some crazy bed that apparently you get pretty much a full tan in like 15 minutes if you can actually handle being in it for that long....
 
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