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Discussion Starter · #1 ·
Howdy y'all :jester:

Went to take a look at an issue earlier this week and I'm scratching my head about it a bit.

At a 911 call center in a nearby town, they have a UPS supplying a bunch of their communication and server equipment. It is an Eaton Powerware unit (don't recall the exact model). They had a tech come out to do maintenance on it, and he reported some voltage issues, so they called us up and I was sent out to take a look.

I'll try to keep this concise: The building service is 208/120 3 phase, but apparently the UPS is only rated to take a 240/120 single phase input. I didn't see the nameplate or literature to verify that. So whoever wired it installed a boost transformer to bump the voltage up to the supposed required input for the UPS. Now here is the issue as I see it: measuring from L1 to N and L2 to N from the boosting transformer, I get something like 150V and 23V, respectively. About 240V L1-L2. That's the voltage going into the UPS.

The report from the tech said that the issue is the bypass switch. I don't know exactly what the deal is there, but he says that it's due to the voltage discrepancies.

I suspect that because the supply to the transformer is 208/120 single phase, but only the L1 and L2 wires are going to the transformer, that the 240 output doesn't have a proper reference to neutral. If this is the case, what can I do about it?

I would love to just eliminate the transformer entirely but supposedly the UPS won't accept 208. I couldn't find the nameplate on the unit (might be inside of it) and the documentation is long gone. Any ideas?
 

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Bilge Rat
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The bypass is looking at the output vs. the input.

The output is 120 - 120 / 240 and the input is 150 - 120 / 240. The leg with 150 is the problem.

The true solution is to get a transformer that has a 208 primary and a 120/240 secondary.

Another possibility is to reconnect the B/B so it boosts both legs 12 volts rather than one leg 24 volts. This isn't a textbook solution, but it could possibly allow the bypass to operate sort of properly.
 

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cog
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Doesn't the UPS take a look at the supply in order to decide whether or not to bypass?

edit: nevermind, see above
 

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Discussion Starter · #4 ·
The bypass is looking at the output vs. the input.

The output is 120 - 120 / 240 and the input is 150 - 120 / 240. The leg with 150 is the problem.

The true solution is to get a transformer that has a 208 primary and a 120/240 secondary.

Another possibility is to reconnect the B/B so it boosts both legs 12 volts rather than one leg 24 volts. This isn't a textbook solution, but it could possibly allow the bypass to operate sort of properly.
I don't know what the margin of voltage is on the UPS, but do you think it would accept 220 volts on each leg?

Anyway, that'd be a pretty decent size transformer for this particular unit. I'll look into it.
 

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Bilge Rat
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It's hard to say; all UPSs have a range of voltages they will accept, and from what I've seen, it's pretty tight.

I thing the main thing will be the fact that the two L-Ns don't add up to the L-L.

It'd be fairly easy to reconnect the B/B, I'd try that first. It might accept 132/240. Maybe not though.....

I've done the 208-120/240 before, but it was a new installation. 15KVA; that transformer was PICKIN HEAVY going up the stairs!!
 

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The bypass is looking at the output vs. the input.

The output is 120 - 120 / 240 and the input is 150 - 120 / 240. The leg with 150 is the problem.

The true solution is to get a transformer that has a 208 primary and a 120/240 secondary.

Another possibility is to reconnect the B/B so it boosts both legs 12 volts rather than one leg 24 volts. This isn't a textbook solution, but it could possibly allow the bypass to operate sort of properly.
What Micromind said. If the voltage is out of range the static bypass switch will 'fail to sync" if there is an internal failure.
 

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Howdy y'all :jester:

Went to take a look at an issue earlier this week and I'm scratching my head about it a bit.

At a 911 call center in a nearby town, they have a UPS supplying a bunch of their communication and server equipment. It is an Eaton Powerware unit (don't recall the exact model). They had a tech come out to do maintenance on it, and he reported some voltage issues, so they called us up and I was sent out to take a look.

I'll try to keep this concise: The building service is 208/120 3 phase, but apparently the UPS is only rated to take a 240/120 single phase input. I didn't see the nameplate or literature to verify that. So whoever wired it installed a boost transformer to bump the voltage up to the supposed required input for the UPS. Now here is the issue as I see it: measuring from L1 to N and L2 to N from the boosting transformer, I get something like 150V and 23V, respectively. About 240V L1-L2. That's the voltage going into the UPS.

The report from the tech said that the issue is the bypass switch. I don't know exactly what the deal is there, but he says that it's due to the voltage discrepancies.

I suspect that because the supply to the transformer is 208/120 single phase, but only the L1 and L2 wires are going to the transformer, that the 240 output doesn't have a proper reference to neutral. If this is the case, what can I do about it?

I would love to just eliminate the transformer entirely but supposedly the UPS won't accept 208. I couldn't find the nameplate on the unit (might be inside of it) and the documentation is long gone. Any ideas?
Can you find a model number that you could look up directions on the Internet? That's what I do for technical issues that I need answers to.
 

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Salty Member
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Eric in my opinion it will never work correctly unless they get the right UPS or scrap the BBs for a standard seperatly derived system transformer.

A UPSs entire reason for exsistance is to monitor the incoming power and switch to battery when that incoming power is out of whack. There are trying to fool it into working with the BBs.

This is one application I would say BBs are not going to work.
 

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Discussion Starter · #12 ·
I'm more than a little curious where they're getting the "neutral." From those voltage readings it almost seems like they tried to pick up a tap on the BB itself.
There is a bypass switch enclosure on the wall near the UPS and the transformer.

The incoming 208/120 single phase comes into the bypass enclosure. The neutral lands directly on the line input neutral terminal. The phase legs go through the bypass enclosure directly to the BB transformer, get transformed, and come back and terminate on the line input terminals along with the neutral.

Eric in my opinion it will never work correctly unless they get the right UPS or scrap the BBs for a standard seperatly derived system transformer.

A UPSs entire reason for exsistance is to monitor the incoming power and switch to battery when that incoming power is out of whack. There are trying to fool it into working with the BBs.

This is one application I would say BBs are not going to work.
Gotcha, that seems to be the consensus.

In looking into this job, apparently it was one of my company's guys that wired it a long time ago before I showed up :laughing: That'll be fun to explain to the customer :rolleyes:
 

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Discussion Starter · #14 ·
Maybe I'm missing something obvious, but I just don't see how single phase 208 would produce those voltages when connected to a buck-boost.

I would expect to see L1-N=120V and L2-N=150V and L1-L2=240V.
When I go back there I'll measure it again and see if I read my meter right and take pictures.
 

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Is there a polarity issue with the winding on L2 - N ?


OP said "reference to neutral" ?
Does he even need a neutral ?
If its a 240v load ?
 

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To me that suggests it requires 2 hots and a neutral just like a 240/120 labeled electric dryer.
Interesting thread.

I just wired up a BB, 240 1 phase in to 120/240 out to UPS.

Eventually, I have to change it over to a 1 phase 208 feed.

I was kinda surprised it used a neutral feed on Erics situation.

Im curious to find out what he found.
 

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It seems to me if the unit could run on straight 120 they would not have installed BBs to get 240.

And if the unit could run on straight 240 we would not even be talking about it as the BBs would work.
 
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