What's wrong with the step down transformer?

[DonsDaMan]

Most inverters are "ungrounded" on purpose. He should go with the two prong approach. If one of his loads has a problem with shock (as he states), then he has multiple problems.

This is an unsafe condition, and needs a full analysis by a competent electrician or engineer. I'm not going to try to diagnose this "long distance."

Don't drill holes, add grounds, or otherwise modify a circuit without checking the diagrams first. This is insanity. I'm glad no one got hurt (so far), but that's about the only good thing I can say about this situation.

 

[ckchew666]

Hi,

Thanks for all the replies & hints. It's Friday 11.40pm here, tomorrow I'll go back to my office early morning and measure the connectivity among all the pins with multimeter.

If possible, I'll post a pic of the transformer and the APC UPS as well.

I'm sorry if some of you feel disturb on this topic, I do not post it here purposely for you guys to guess, wasting your valuable time and mine as well. As I'm not good in electrical problem diagnostic, so I'm posting here to get some help. I'll provide as much info as possible to get this issue solve, yeah for some of you might be as easy as ABC, but not for me

This UPS is used to power a PC and some vision devices, which cost around USD 100-150K, that's why I must handle with care

Yes, I got electricity shock! We have 2 identical system with same hardware and field devices, we have two UPS, 2x transformer as well.

I do not know that 110VAC has a polarity (for the UPS), so far I taught the 110VAC and 0VAC can be interchanage. In malaysia not much of machine using 110VAC, only machine comes from US. 240VAC, 24VDC are more common here.....anywhere thanks for everyone...I'll be back soon.

 

[MarkTTU]

All single phase AC voltages SHOULD have 'polarity' regardless of 110 (120), 240, etc...

One wire is HOT or LIVE and the other is NEUTRAL (also called grounded neutral, or earthed neutral). Its called grounded neutral because it is tied to ground.

From the secondary of a transformer if you do not tie either leg to ground then there is no reference for the transformer to ground; you will have 110AVC between the legs but could have ANYTHING from either leg to ground; this is a VERY dangerous situation and should be avoided unless you have a very specific reason for not grounding your secondary.

From a practical standpoint a device operating on 110VAC has only two wires that are used for power consumption; these wires are hot and neutral; it does not matter which is hot and which is neutral as long as there is 110VAC measured from leg to leg.

Where I think you have a problem is that somewhere (maybe inside the transformer itself if the transformer has a built in plug socket) you have hot tied to ground... Your UPS's ground prong (the round one in the middle) should be tied to the metal case of the UPS. If you have the ground prong tied to hot instead of neutral then the outside of your UPS will be energized (HOT) and it WILL shock you.

Please post a picture and wiring diagram of the transformer. A wiring diagram of how you want this setup would also be helpful.

 

[ckchew666]

Due to space limitation, i've uploaded my files to :

http://s29.yousendit.com/d.aspx?id=1F5PNL280040K0Z622BOGU6XW4

The file will be on the server for 7 days. If you have problem downloading the file, please give me your email at [email protected]

A white paper from APC discuss the myth of neutral wiring available at:

ftp://www.apcmedia.com/salestools/SADE-5TNQYQ_R0_EN.pdf

Referring to page 3 of the white paper, the 0VAC or Neutral is grounded. We also tried shorting the Neutral(110VAC) to the Earth(240VAC), but no luck.


The Earth prong does not have any contact with the coil/HOT/LIVE when I plug it into the transformer output (110VAC).

I've check the connectivity, the result as below:

240VAC
Live & Neutral = YES
Live & Earth = NO
Neutral & Earth= NO

110VAC
110VAC & 0VAC = YES
110VAC & (110VAC)Earth = NO
0VAC & (110VAC)Earth = NO

110VAC & 240VAC(Live) = YES
110VAC & 240VAC(Neutral) = YES
110VAC & 240VAC(Earth) = NO
0VAC & 240VAC(Live) = YES
0VAC & 240VAC(Neutral) = YES
0VAC & 240VAC(Earth) = NO
110VAC(Earth) & 240VAC(Live) = NO
110VAC(Earth) & 240VAC(Nuetral) = NO
110VAC(Earth) & 240VAC(Earth) = YES

The above is checked with the UPS socket plug into the transformer & also unplug from the transformer. The result is the same. The transformer is not plug into the wall socket (240VAC).

I do not have the wiring for the transformer and the UPS.

 

[Eric Nelson]

Thanks for the pictures, though I couldn't decipher much on the secondary side. I guess you don't have a 'macro' setting on your camera?...

I don't like the fact that you have continuity between the primary and secondary windings (110VAC & 240VAC(Live) = YES and 110VAC & 240VAC(Neutral) = YES). Of course, if you read continuity on one, you will have it on the other because of the coil. Could this be an autotransformer?...

Aha! It is an autotransformer! I can (barely) make out the words "AUTO TRANSFORMER" in the 4^th picture... :nodi:

Right now, I should probably shut up and just tell you to hire an electrician to clear up this mess, but for some reason I'm thinking you're not gonna do that. Therefore, I'll continue with advice.

Since it's an autotransformer, you DON'T want to ground either of the secondary leads to crerate a neutral. The secondary neutral comes from the primary. Assuming the transformer is wired properly, the fuse will be in the 'hot' lead of the secondary. From what I can tell from the pictures, this appears to be the slot closest to the fuse. If that's the case, then you did indeed drill you 'magic' hole on the wrong side. If you're not gonna replace the receptacle with a 'proper' 3-pole (I wish you would), then pop the receptacle out and turn it around. Don't drill any more holes... You've already drilled one too many!...

This STILL doesn't explain the "We also tried connecting an extension (no load) into the transformer, it also tripped our CB." scenario, unless the extension cord was defective. There still might be an inrush issue...

Please be safe!... :nodi:



-Eric

 

[rsdoran]

The easiest solution is to decide on which standard you plan to use when purchasing devices...ie US or Euro. The UPS has a standard US style 3 prong plug, the transformer has "something else"...I cant say what country/standard because I do not know.

Since you are having problems with preconfigured devices (I just do not understand that) then go back to the old way, use a transformer and wire your own plug to match whatever device you have.

These DIN mount receptacles are easy to wire: http://www.leviton.com/sections/prodinfo/surge/sheets/dinrailsurge.htm
and work well with transformers like these:
http://www.solaheviduty.com/products/transformers/LVGP/general.html
OR these:
http://www.solaheviduty.com/products/transformers/LVGP/general.html

Another source for transformers that offers more details on wiring:
http://www.acmepowerdist.com/products.asp?PAGE=prod_landing.html

If this project is too complicated then you should hire an electrician....after 2 transformers etc I would say it is too complicated for you and your associates.

 

[ckchew666]

Eric,

Thx for ur prompt reply. I'm sorry for the poor quality of the pics, I just grab my PDA this morning and take a few snap shots in my office and post it quickly.

Based on ur comment "then you did indeed drill you 'magic' hole on the wrong side" this means that the HOT & Neutral prong are accidentally interchanged? The 'magic' Earth (110VAC) hole should be drilled at the bottom, instead at the top?

Yes there is a fuse connected to the HOT (110VAC). The extension also has a 3 prongs socket like the UPS. But when we connect the extension to the transformer we did not connect any load to the extension.

rsdoran,

The UPS comes with the machine from US. They do not supply the transformer for us because US is using 110VAC only. Anywhere, thx for ur info, in the mean time i'll try to source out for a new transformer as well

 

[rsdoran]

The UPS comes with the machine from US. They do not supply the transformer for us because US is using 110VAC only. Anywhere, thx for ur info, in the mean time i'll try to source out for a new transformer as well

I dont understand why anyone says 110vac...its not something we have for a power source in the US, our standard low AC voltage is 120.

The fact that you drilled a hole AT ALL was WRONG...Adapters (with grounds) are available for converting a US plug to a EURO plug. TECHNICALLY fused adapters are available to plug a 120vac US device into a EURO 230vac receptacle...ie you could have just used a EURO receptacle and adapter that is rated for 500VA or more.

I do not know how that plug is denoted but in the US the larger or silver "pin" will be neutral.

Here is a situation where a person is in an ENGINEERING position that "IMPROPERLY MODIFIES" ELECTRICAL equipment and all of you experts have made no comment. THE simple fact that HE DID DRILL anything but the panel to mount it should have been jumped on...but nothing.

Experts...safety...yeah right...it never changes.

 

[Eric Nelson]

THIS page (from Peter Nachtwey's favorite website) might be helpful...



-Eric

 

[John Gaunt]

Ups Supply Neutral Must Be Earthed

UPS SUPPLY NEUTRAL MUST BE EARTHED
I have had this same problem with UPS's in Asia where it is
common to run Active and Neutral but no proper Earth.
I have recently installed some 10 S7-400 PLC systems in India
and another in Korea. I have had to threaten to get on the next
plane to get a proper Earth.
Most UPS's are designed to work with a supply where the Neutral
is bonded to Earth.
Make sure this is the case and that the Earth is a real Earth.
I have been given a nice big green wire but followed it out of the
control room to find it ends un-terminated after about 20 metres.
In one case an un-earthed supply caused a new UPS to fail needing
to be replaced.

If you want to talk to somebody in Malaysia contact my friend
[email protected]
kk will confirm that UPS supply Neutral must be Earthed

Good luck with it...........John Gaunt

P.S. Regarding use of a Step Down Transformer with a UPS
after it. In this case you MUST Earth the Transformer
secondary that you assign as being your Neutral otherwise
most commercially available UPS's will "go up in smoke"

 

[boxhead]

Transformer

So why did it trip the breaker? Was it because the neutral inside the ups was tied to earth? And once plugged in the wrong way grounded the 110vac hot wire?


Cheers

Corey

 

[MarkTTU]

Based on ur comment "then you did indeed drill you 'magic' hole on the wrong side" this means that the HOT & Neutral prong are accidentally interchanged? The 'magic' Earth (110VAC) hole should be drilled at the bottom, instead at the top?

rsdoran,

The UPS comes with the machine from US. They do not supply the transformer for us because US is using 110VAC only. Anywhere, thx for ur info, in the mean time i'll try to source out for a new transformer as well

Based on what you've said I'll offer this advice.

Contact the original manufacturer of the machine in the US. Ask them to supply you with a pre-configured pre-wired step down control transformer for this machine.

If they won't do this then first off do not buy ANYTHING from them ever again as they obviously do not intend to support their overseas customers. Second get yourself a proper control transformer and a proper three prong US prog socket. It should be wired like this:

Please note that the ground/earth must actually be a ground. Use a real ground rod banged into the ground and make sure its a good ground. If you do not have a good ground you will fry the UPS; it may work ok at first, but when the power goes off and the UPS inverter kicks on to generate 110VAC power you'll smoke it.

As a side note 110VAC is what we are nominally supposed to have in the US. Back in the 50's and 60's it was usually about 110-115 depending on location, but now its usually 120-125 depending on location. Over the years the transmission line voltage has been bumped up because of higher power demands; higher power demands at the same voltage leads to higher currents which leads to melted conductors. The easy way for the power companies to not melt their very expensive transmission lines was to raise the voltage thereby lowering the current for the same power demands. The thing they have not done is go back and replace all the transformers to maintain 110VAC at the plug socket.

 

[Eric Nelson]

....get yourself a proper control transformer and a proper three prong US prog socket...

Just to emphasize the point that Mark's drawing shows the proper hookup for an ISOLATION transformer. Do NOT try this with your existing 'box with an extra hole'. You have an autotransformer. Using Mark's picture as a basis, an autotransformer looks like this:

-Eric

 

[MarkTTU]

Good point Eric. Now that I've seen your drawing I feel a bit like an idiot for not pointing that out.

 

[Terry Woods]

Just to clarify the clarification... it's a visual thing...

If the supply side is grounded (H1 = Ground = X1), H2 is the high-side of the 240VAC and X2 is the high-side of the 120VAC source.

If the supply side is NOT grounded, then don't ground either H1 or X1... leave them floating.

If H2 is grounded, and X1 is grounded... well,... that's called a dead-short.

Your continuity readings are somewhat confusing.

You didn't indicate what scale you were using to read resistance between the various points. Is one side of your supply voltage grounded or not?