Isolation transformer

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siver295

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Specs call for an isolation transformer in an elevator modernization project. Company is asking me to confirm that the line voltage is symmetrical with respect to ground. Can you clarifiy the meaning of symmetry with respect to ground?
Thank you,
Steve
First post - long time reader.
 
Several questions:
  • What company?
  • Is that in the specs, or is the owner asking for this separately, or is this a request from your own boss?
  • Is this a request for a post-installation test, or a request for something you have to include with your procurement submittals?
  • Is the transformer a delta-delta or a delta-wye?
What this phrase (an awkward one, at best) is telling me is that the voltages from Phase A to ground, and from Phase B to ground, and from Phase C to ground are all the same.

Welcome to the forum.
 
And to add to Charlie's questions:
It reasonable to assume that you mean a three-phase system?
Are the primary and secondary voltages the same? The term "isolation transformer" rather infers that. If not, what are they?
Why is an isolation transformer specified? What is it intended achieve?
 
The question originated from company suppling motion controllers for elevator company.
The existing service is 3 phase, 120/208V. I have not received any specs for isolation transformer.
I am the EC asked to bid on project but was not firmiliar with the term symmetry in reference to ground. In other words, are the phases balanced.
Thanks for the insight.
 
siver295 said:
The question originated from company suppling motion controllers for elevator company.
The existing service is 3 phase, 120/208V. I have not received any specs for isolation transformer.
I am the EC asked to bid on project but was not firmiliar with the term symmetry in reference to ground. In other words, are the phases balanced.
Thanks for the insight.
Click to expand...
Because you are dealing with a "motion supplier", I believe the term is asking for a isolation transformer with a grounded wye connected secondary. I am sure all you need to supply is a standard "drive isolation" transformer.
 
jim dungar said:
Because you are dealing with a "motion supplier", I believe the term is asking for a isolation transformer with a grounded wye connected secondary. I am sure all you need to supply is a standard "drive isolation" transformer.
Click to expand...
If the existing service is 3 phase, 120/208V why would an isolation transformer be required?
Just asking.
 
Besoeker said:
Wouldn't an input line reactor be cheaper, smaller and achieve the same result?
Click to expand...

Yes, maybe, yes. But, to each their own design.

In many installations a step down transformer (i.e. 480-208) may be required so the 208V equipment manufacturer says to "include an isolation transformer" as a generic installation requirement rather than including additional options.
 
Ya, did a lot of that, elevator companies want that kind of thing. The big national company?s seem to be O.K. with spending the more $ for the isolation transformer. And that?s good work. Modernization codes that come into affect in the next few years will require more of that work. IMHO most of the building?s that need updating are in densely populated area?s. Wherefour you?ll need the iso trans. From what I understood the cheep fix like surge arrestor or what ever just don?t cut it with the new hardware the elevator company?s install. Second of all the national company don?t want the trial and error of the cheep stuff, ya it could work but???and there goes the good name of the elevator company. Condo boards are so weird anyway. And lets not forget about building engineers. Spend the extra money do it right.
 
duplexoutlet said:
Ya, did a lot of that, elevator companies want that kind of thing. The big national company?s seem to be O.K. with spending the more $ for the isolation transformer. And that?s good work. Modernization codes that come into affect in the next few years will require more of that work. IMHO most of the building?s that need updating are in densely populated area?s. Wherefour you?ll need the iso trans. From what I understood the cheep fix like surge arrestor or what ever just don?t cut it with the new hardware the elevator company?s install. Second of all the national company don?t want the trial and error of the cheep stuff, ya it could work but???and there goes the good name of the elevator company. Condo boards are so weird anyway. And lets not forget about building engineers. Spend the extra money do it right.
Click to expand...
The use of line reactors is not "cheap work" and would be my suggestion if a voltage change was not required. Generic instructions are rarely intended to address every possible installation.
 
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