US 208V L1-L2 to UK 220V L-N

E

electrabishi

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Location
Alaska
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EE
I have seen this issue infrequently over the years. Never got any definitive solutions. But I have a need to drive this one to ground so to speak.
Short problem description is:
I am in a US facility where we have 208Y/120V panels for serving Telecom equipment.
For me that means a 208V branch circuit has an L1-L2-G.
I have a European company that is locating a server rack in my facility and it is totally wired for European 220V L-N-G.
For me to feed L1-L2 I need to have dual pole breakers.
In their cabinet, because they only have 1 hot lead and a neutral, all their breakers and switches are single pole.

In the past I have required clients to upgrade their circuitry to include dual pole breakers.
But this is a little more complex. I need a way to put an isolation transformer in and separately derive a new neutral so I can feed them 208V L-N.

All of the popular companies offer isolation transformers that are step down. I want a straight 1:1 unity transformer for 208V that I can separately derive the neutral bond on the output. Nobody makes such an animal. How can that be. I've done a little diligence on this forum to see if there were any other similar postings. If there is could someone direct me to them? This could be a Grounding issue (Neutral Bonding), its certainly a safety issue with hot leads in a cabinet not switched or protected, Meeting UL listings in that if I just build it from a dry transformer then have no listing.

There is another issue that also arises when some of the end equipment is not isolated. There are still companies in my field that still use the chassis of their equipment as a ground return. This non-isolated equipment shows itself when you try to feed a cabinet wired for 220 L-N with 208V L1-L2. But it makes it easy to identify, because in this situation it will automatically trip the first dual pole breaker in the line. Fortunately I don't have this problem in this installation. But the isolation transformer with a separately derived neutral bond should fix that too.

Any comments or ideas. Hard for me to believe this is something new.
 

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electrabishi said:
There is another issue that also arises when some of the end equipment is not isolated. There are still companies in my field that still use the chassis of their equipment as a ground return.
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Are you saying that the neutral is bonded in the equipment? If so I cannot see how this can actually be used in the US.
 
electrabishi said:
I want a straight 1:1 unity transformer for...
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You can use any transformer to do this.
For single phase, just configure the primary as 240V and connect it to your 208V lines, wire the secondary as 240V and connect one wire to ground. Unless you mess with the taps you will have a 1:1 ratio transformer.
 
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Yes. Thats what I'm saying. It still happens and out of habit I will always check continuity of new equipment from Line-Ground and Neutral to Ground. Most things are fully isolated these days especially equipment with plastic cases. But there still are some that are not. In this situation its not my problem. The problem is that there are wires in the cabinet that are Blue (Neutral) in the UK/EU that will be always hot if I try to hook them to my 208V L1-L2 branch.
 
No they do not. I would provide the neutral L1-L1-N-G in the event there were any circuits that required 120V. Its just a straight 208V L1-L2-G feed.

Now on the cabinet side, what they really need is 220V (208 is what I have) L-N-G. Because over there they use 220V single phase.

The specs on the UPS in my circuit indicate it will operate either on the input.
The supply is listed as 208/220V L1-N(L2)-G. Which is OK for the UPS input, but all the line side stuff downstream references Hot to neutral as 208V. But what comes out of the UPS is L-G=110V and N-G=110V. All their so called neutral wiring is hot 110V to real ground.
 
This is what I need to do. This unit outputs a split phase 120V and brings both 120V phases out. I need them to delete the 120V phases, just come off the two Line taps, and ground reference one of the Lines. But Eaton does now have and will not modify this to be what I need.
 

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I personally might try stepping up a 120V circuit to 240V with an autotransformer to neutral rather than 208V phase to phase and creating a neutral in a transformer.

Though you will have to worry about it taking more power. Hopefully it would even out with the 3ph for the feeder. But the neutral current might be high.
 
electrabishi said:
No they do not. I would provide the neutral L1-L1-N-G in the event there were any circuits that required 120V. Its just a straight 208V L1-L2-G feed.

Now on the cabinet side, what they really need is 220V (208 is what I have) L-N-G. Because over there they use 220V single phase.

The specs on the UPS in my circuit indicate it will operate either on the input.
The supply is listed as 208/220V L1-N(L2)-G. Which is OK for the UPS input, but all the line side stuff downstream references Hot to neutral as 208V. But what comes out of the UPS is L-G=110V and N-G=110V. All their so called neutral wiring is hot 110V to real ground.
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Well, actually, they do not need a 120V L1 or L2 connection to Neutral.
What they need is a 208V Line to Neutral. Which is exactly the problem.
 
electrabishi said:
Well, actually, they do not need a 120V L1 or L2 connection to Neutral.
What they need is a 208V Line to Neutral. Which is exactly the problem.
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You don't need to reinvent the wheel here. They make 110V to 220V power converters for when you travel. You should just use a similar principle with a autotransformer. Single pole 120V breaker to a autotransformer to bump to 220V line to neutral.
 
That gets me somewhere. I don't want to re-invent the wheel.
But its a 6KVA UPS meant to run 30A@208V.
So if I feed it 120V I would need a 60A 120V branch circuit.
Do they make those "travel" converters that big?
 
For electrabishi:
If you want to move your kit from EU to USA:
(a) EU is 230Vac, not 220V
(b) EU is 50Hz, not 60Hz
 
Here is the isolation transformer version:


www.ato.com

30 kVA Isolation Transformer, Single Phase, 110V to 220V

30 kVA isolation transformer, single-phase distribution power transformer foe sale, step up 110V primary to 220V secondary voltage or step down 220V input to 110V output, LCD display voltage, aluminum wire or copper wire, low temperature rise.
www.ato.com www.ato.com

Here is a power converter for plug connections. Might not be a reliable product though.

 
Not quite sure about what you mean when you say nobody makes an isolation transformer. Lots of companies do.

You have not indicated what kind of load you are looking at. You mention a Telecomm Server Rack - but how much power does it need? Is it only the UPS you are looking to power?

Here is a10 second look at what Hammond Power has in their catalog - and assuming single phase. Square D, Eaton, Acme, etc should all have similar things.

These start at 15 kVA. Not sure if that's too big...

1742329198544.png

The first group in the screenshot above could be fed from your facility 208 VAC mains and give you 240 on the secondary. Leave the center tap floating, ground one end, and that gets you 240 L-N as an SDS. If that's too "hot", you can likely adjust a primary tap to get ~ 230 easily.


The second group above can be wired - exactly like Jim mentioned in post #3 - as a true isolation transformer. Just like your image in post #9. Connect the 2 primaries in parallel for "240" and the 2 secondaries in series will give you "240". And again, ground one end of the secondary. If you feed this setup with 208, you simply get 208 on the output L-N.

Hope this helps.
 
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electrabishi said:
Short problem description is:
I am in a US facility where we have 208Y/120V panels for serving Telecom equipment.
For me that means a 208V branch circuit has an L1-L2-G.
I have a European company that is locating a server rack in my facility and it is totally wired for European 220V L-N-G.
For me to feed L1-L2 I need to have dual pole breakers.
In their cabinet, because they only have 1 hot lead and a neutral, all their breakers and switches are single pole.
Click to expand...
Are you 100% sure about this?
My understanding of the regulations over there is they always have to use a double pole switch, because while they standardized on 230V because its simpler :) they allow many different grounding schemes (earthing systems) so blue is not guaranteed to be a 0 volts to ground and should never be treated that way, for example a IT earthing system in countries like Norway would have both blue and brown 'hot' with respect to equipment ground.
I have seen lots of 220V - 230V 50/60 hz labeled EU equipment work great off 208 - 240 (Line to Line) but it wont tolerate 277 don't ask how I know.
A 208 to 240 isolation transformer would be a waste of money and 24/7 vampire load.
Where does your responsibility end? A receptacle ? A disconnect?
If they don't have a 2 pole switch on their rack, just throw a standard disconnect within sight and call it a day.
 
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Thanks for all the responses. I have see that (funny name brand) Up/Down transformer on Amazon. But its rated at 6KW and appears to have only a 110V 15A plug on it. I'm skeptical. @MD Automation, the total load of the cabinet is 6KVA. Technically my responsibility is at the input terminals to the UPS. They only have 1 double pole circuit breaker on the input to the UPS. All the other 12 breakers are single pole. So there are a number of blue wires inside the cabinet that are not neutral (110V to ground) and not switched. If I have any of my guys in there working on stuff and they grab onto what the client drawing says is neutral, that could be bad. So not only is there a coloring mismatch, there are hot wires not fed through a breaker. In the past I've had clients upgrade to dual pole beakers. And that would work in this case and probably clears up any NEC problems. I was trying to come up with the solution that was minimally intrusive to the customer equipment. My main concern with just putting in a 1:1 and grounding one side of the secondary is if it violates any UL listing requirements. I know it would work.

​

 
infinity said:
Are you saying that the neutral is bonded in the equipment? If so I cannot see how this can actually be used in the US.
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That would be a TN-C system like our older 10-50 range and 10-30 dryer receptacles where neutral and equipment ground are Combined and is also a big no-no just about anywhere that uses IEC standards.
 
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