Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 08-16-2007, 03:06 PM   #1
BCK
Newbie
 
Join Date: Aug 2007
Posts: 4
Rewards Points: 10
Question

electrical isolation


I need a 1:1 isolation transformer installed in my lab. I've seen transformers with and without ground leads for the input and output of the transformers. I need to connect the output to some sensitive equipment.

What is the appropriate way of grounding the isolated circuit and why do many isolation transformers have ground leads as if the ground were passed through? Doesn't this defeat the purpose of isolation?

BCK is offline   Reply With Quote
Old 08-16-2007, 04:48 PM   #2
Agent 000
 
SecretSquirrel's Avatar
 
Join Date: Jun 2007
Posts: 334
Rewards Points: 250
Default

electrical isolation


The ground is passed through. All grounds are sourced from one place... mother earth. The actual purpose is to allow a safe path for any short circuit that should occur. The ground has no potential (voltage), except during a momentary short circuit, so it will not affect your sensitive equipment. You cannot "float" the ground via isolation windings and have it perform its job correctly. There may be wiring considerations such as isolating the ground in the sense that it not come in contact with any metal or another ground except at the delivery point and the main panel where the ground source resides.

In my previous occupation I specified isolation transformers for our lab and had them appropriately installed.

Here's some selection information if you need any.

http://ecatalog.squared.com/pubs/Ele...7400CT9601.pdf

If you need any assistance beyond the chat forum then feel free to private message me and I'll do what I can.


Last edited by SecretSquirrel; 08-16-2007 at 04:49 PM. Reason: spelling
SecretSquirrel is offline   Reply With Quote
Old 08-17-2007, 09:26 AM   #3
BCK
Newbie
 
Join Date: Aug 2007
Posts: 4
Rewards Points: 10
Default

electrical isolation


So do the 'hot' and 'neutral' wires in the secondary then 'float' from the ground? How does this effect equipment? Is there a possibility of a hazardous voltage between ground and 'neutral'?
BCK is offline   Reply With Quote
Old 08-17-2007, 09:35 AM   #4
Agent 000
 
SecretSquirrel's Avatar
 
Join Date: Jun 2007
Posts: 334
Rewards Points: 250
Default

electrical isolation


Quote:
Originally Posted by BCK View Post
So do the 'hot' and 'neutral' wires in the secondary then 'float' from the ground? How does this effect equipment? Is there a possibility of a hazardous voltage between ground and 'neutral'?
I'm a little rusty in citing code examples but I believe the NEC prohibits the isolation of the neutral and it must remain "common" between systems when using an isolation transformer. I'll see if I can dig up a transformer wiring schematic. It would be helpful if you can tell me the voltage and KVA of your proposed transformer.

And yes the hot(s) are distinctly separate from the primary and the secondary.

Last edited by SecretSquirrel; 08-17-2007 at 09:39 AM. Reason: additional info
SecretSquirrel is offline   Reply With Quote
Old 08-17-2007, 09:53 AM   #5
BCK
Newbie
 
Join Date: Aug 2007
Posts: 4
Rewards Points: 10
Default

electrical isolation


I need just a 120 to 120. I don't need much power and a coworker is willing to let me have his 600VA transformer. So are you saying that both the neutral and ground should be passed through?
BCK is offline   Reply With Quote
Old 08-17-2007, 10:07 AM   #6
Agent 000
 
SecretSquirrel's Avatar
 
Join Date: Jun 2007
Posts: 334
Rewards Points: 250
Default

electrical isolation


Quote:
Originally Posted by BCK View Post
I need just a 120 to 120. I don't need much power and a coworker is willing to let me have his 600VA transformer. So are you saying that both the neutral and ground should be passed through?
Hang on a few minutes and I'll have a definitive answer for you.
SecretSquirrel is offline   Reply With Quote
Old 08-17-2007, 11:00 AM   #7
Agent 000
 
SecretSquirrel's Avatar
 
Join Date: Jun 2007
Posts: 334
Rewards Points: 250
Default

electrical isolation


I don't have an NEC codebook within my grasp but I'm attempting to get clarification on article 250.30 Grounding and Bonding of Separately Derived
AC Systems.

I think where this is leading is you will have to bond your neutral to the transformer. This isn't any different than a conventional transformer hookup.

Looking at the attached diagram;


Source hot to H1 & H3
Source neutral to H2 & H4

Secondary hot X1 & X3
Secondary neutral X2 & X4 bonded to the transformer frame

The source ground will also be connected to the transformer frame.

Please pardon my previous comment about the neutral remaining common between systems as I was relying on stale memory. I do have a call into one of my contacts at Acme Transformer and I will have him validate this connection scheme. As soon as I hear back from him I will post the results.

Source: Acme Transformer Wiring Diagrams
Attached Images
 

Last edited by SecretSquirrel; 08-17-2007 at 11:56 AM.
SecretSquirrel is offline   Reply With Quote
Old 08-17-2007, 11:11 AM   #8
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,041
Rewards Points: 2,052
Default

electrical isolation


Quote:
I need just a 120 to 120. I don't need much power and a coworker is willing to let me have his 600VA transformer. So are you saying that both the neutral and ground should be passed through?

An isolation transformer is only allowed to isolate the hot and neutral wires. The grounding wire is the only wire passed straight through. A design consideration for computer circuits including data communication circuits is that they are connected to the grounding wire and not the neutral wire, the isolation transformer or any power conditioner or UPS with an isolation transformer has absolutely no affect on computer grounding problems. An isolation transformer is not permitted by safety regulations to interrupt the grounding wire. Consider dedicated lines and isolation transformers to reduce inter-system noise and interference problems and neutral to ground wire noise. An isolation transformer cannot provide any reduction in Inter-System Ground Noise, which a dedicated line can provide.
An isolation transformer does provide surge protection, which a dedicated line does not provide. An isolation transformer does eliminate any noise between the neutral wire and the grounding wire on a dedicated line. Circuits having multiple loads are not allowed to interrupt the ground wire so an isolation transformer is no help. Since I'm not sure what exactly your protecting it is hard to specify and I'm not sure I would be the one who could make that decision as I am not a design expert for sensitive equipment. Anything that emits radiation causes unwanted magnetic coupling of power wires and isolation transformers are sometimes specified.

I really would advise consulting a power management person with your needs as you may not get what you want without professional help.

Stubbie
Stubbie is offline   Reply With Quote
Old 08-17-2007, 11:18 AM   #9
Agent 000
 
SecretSquirrel's Avatar
 
Join Date: Jun 2007
Posts: 334
Rewards Points: 250
Default

electrical isolation


We always used Sola Power Conditioners. This concept of using a standard transformer as an isolater provides only basic "isolation".
SecretSquirrel is offline   Reply With Quote
Old 08-17-2007, 11:24 AM   #10
BCK
Newbie
 
Join Date: Aug 2007
Posts: 4
Rewards Points: 10
Default

electrical isolation


Quote:
Originally Posted by Stubbie View Post
A design consideration for computer circuits including data communication circuits is that they are connected to the grounding wire and not the neutral wire,
The grounding wire is only supposed to carry current under fault conditions, so how could the neutral not be connected?
BCK is offline   Reply With Quote
Old 08-17-2007, 11:44 AM   #11
Agent 000
 
SecretSquirrel's Avatar
 
Join Date: Jun 2007
Posts: 334
Rewards Points: 250
Default

electrical isolation


Quote:
A design consideration for computer circuits including data communication circuits is that they are connected to the grounding wire and not the neutral wire, the isolation transformer or any power conditioner or UPS with an isolation transformer has absolutely no affect on computer grounding problems. An isolation transformer is not permitted by safety regulations to interrupt the grounding wire. Consider dedicated lines and isolation transformers to reduce inter-system noise and interference problems and neutral to ground wire noise. An isolation transformer cannot provide any reduction in Inter-System Ground Noise, which a dedicated line can provide.
Stubbie, If you are going to cut and paste information off the internet it would be in proper form to give a link to your reference and credit to the author.

See; http://www.powermanagementdesignline.com/howto/51201145
SecretSquirrel is offline   Reply With Quote
Old 08-17-2007, 12:05 PM   #12
Agent 000
 
SecretSquirrel's Avatar
 
Join Date: Jun 2007
Posts: 334
Rewards Points: 250
Default

electrical isolation


Quote:
Originally Posted by BCK View Post
The grounding wire is only supposed to carry current under fault conditions, so how could the neutral not be connected?
BCK, this is a paradox and looks like it contradicts what I said initially about the grounding conductor. If you didn't bond the neutral at the transformer it would be "floating" but still would find a return path via the transformer. Before I offer any more comment I need to get to that NEC article. I'm hoping someone with a codebook will pop in and clarify this.
SecretSquirrel is offline   Reply With Quote
Old 08-17-2007, 09:33 PM   #13
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,041
Rewards Points: 2,052
Default

electrical isolation


Quote:
Originally Posted by SecretSquirrel View Post
Stubbie, If you are going to cut and paste information off the internet it would be in proper form to give a link to your reference and credit to the author.

See; http://www.powermanagementdesignline.com/howto/51201145
Secret:

The reply is an obvious cut and paste. I believe anyone who reads it can tell it is a copy. The reply simply clarifies the purpose of isolation transformers and the questions being asked. Without knowing what he is doing I don't see how you or I or anybody else can give design advice. I can't I'm not an authority in that area of design, I believe I made that statement earlier a couple times. He needs to consult a power management specialist as it would appear to me neither you nor I can give advice that is based on experience. In this day and age it is rather foolish to try to steal info off the internet and project it as your own, someone else who is searching for helpful information (because they don't know the answer either) will always catch you. However, I agree reference to the site should have been given, alas I'm not perfect. I wonder though why you are taking the lead in this thread and you are searching the internet for the answers to BCK's questions. He can do that himself and probably has already. He needs someone who is sure of his advice based on having designed systems utilizing isolation tranformers of the size he specified.

BTW your blue text is giving us headaches

Did you notice we are talking about a 5 amp isolation transformer? Something we can buy at radio shack? For all we know he may need nothing more than a small noise suppressor/filter.

Stubbie

Last edited by Stubbie; 08-18-2007 at 07:11 AM. Reason: added text
Stubbie is offline   Reply With Quote
Old 08-17-2007, 10:40 PM   #14
UAW SKILLED TRADES
 
Stubbie's Avatar
 
Join Date: Jan 2007
Location: Kansas
Posts: 5,041
Rewards Points: 2,052
Default

electrical isolation


Quote:
The grounding wire is only supposed to carry current under fault conditions, so how could the neutral not be connected?
It is on the line side of the transformer or at the service equipment. But never on the load side of the grounded conductor after the service disconnect. This creates objectionable current on the ground fault path.

Stubbie

Last edited by Stubbie; 08-18-2007 at 12:40 AM. Reason: incorrect wording
Stubbie is offline   Reply With Quote
Old 08-18-2007, 07:45 AM   #15
Agent 000
 
SecretSquirrel's Avatar
 
Join Date: Jun 2007
Posts: 334
Rewards Points: 250
Default

electrical isolation


Stubbie,

I'm not sure why you insist that I am not qualified to give advice in this matter. Until the point that BCK said he was acquiring this transformer from a friend it should have been a no brainer in terms of picking out the correct solution for his application. As I stated in the beginning of this thread I have had experience in the application of isolation transformers. I have used a number of Sola constant voltage regulators, Square D Topaz conditioners, VSD (variable speed drive) isolation transformers, line reactors, and so on... some suited for laboratory grade equipment, some not. It is a matter of lining up the the correct solution with the requirements of the equipment, which btw we don't currently happen to have. I am not going to make apologies for using the internet as a research tool. If I didn't have the internet I would be fumbling through a bunch of catalogs and making phone calls. Either way, it's research. My success in the electrical project engineering field is largely due to having good people around me; good vendors and good factory technical resources. That's how we accomplished our goals. I'm applying BCK's needs in the same fashion. However, when one chooses a public forum for specific technical needs it is a crap shoot as to the quality of response that he will receive. I believe BCK is astutely aware of that as he seems to be fielding the responses with appropriate questions.

Assuming that you and I can get over our disagreement can you help further this effort by looking up the code article: 250.30 Grounding and Bonding of Separately Derived AC Systems and see if it has any meaning in regards to BCK's request?

BCK here's what you can do if you're still interested in pursuing this;

It would be helpful to know the specific instrument that the isolation transformer is needed for. What are the electrical requirements? Secondly can you tell us more about this transformer that your buddy has? Depending on what it is, it may only provide basic isolation, no shielding, no voltage regulation, and nothing for harmonic distortion.


Last edited by SecretSquirrel; 08-18-2007 at 07:51 AM. Reason: content
SecretSquirrel is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What's the ICC Electrical Code? Chuck Electrical 7 02-20-2013 10:19 AM
Home Electrical / Car Stereo Question pjpjpjpj Electrical 4 08-12-2012 06:59 PM
Furnace Electrical Supply.... caseywa HVAC 2 12-28-2006 10:37 AM
Electrical continuity Tool Rze Electrical 11 10-01-2006 04:10 PM
Finishing basement - electrical code ??? normwannabe Electrical 1 01-23-2006 07:48 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.