Teardown and modification of Noratel IMED e 150 isolation transformer

[electr_peter]

I recently acquired a medical isolation transformer Noratel IMED_e 150 for isolated power purposes in the lab. Medical isolation transformers are used in medical facilities to reduce leakage currents and as an extra safety measure. This unit will be used as a lab isolation transformer after small internal modification.

DISCLAIMER - equipment modifications shown in this thread are considered dangerous. Isolation transformers are not safe by default to touch or leave unattended and can cause hard to spot dangers. Do not remove earth from grounded equipment. Lab isolation transformers should only be modified by experts and used in controlled environment. I do not take any responsibility for your actions.

Unit arrived in original box from manufacturer. Box contained isolation transformer, IEC mains cable, 2 spare 1A 250V fuses, 2 mounting brackets and instruction. Unit is like new from outside and inside - no dust or scratches. There are 4 rubber feet on the bottom, so unit stays put on flat surfaces. Transformer box is made from 2 metal pieces screwed together at 4 places with hex screws.

To my pleasant surprise, unit has dual input fuses on both L/N lines. This is an extra safety measure in case L/N wires are switched. In continental EU schuko mains plugs/sockets are not polarised.
Transformer also has MOV, NTC resistor and internal thermal fuse for protection. All the wiring is superb, everything is neatly soldered/heat-shrunk/crimped. Earth is connected to both metal parts of case with crimped connectors and welded metal studs. Toroidal transformer is screwed in place and filled with epoxy for shock absorption.

Internal wiring in this unit is such that input and output L/N connections are completely isolated from each other. Input goes to primary winding, output is taken from secondary winding. Input earth is connected to:

• transformer shield between primary and secondary
• bottom and top parts of metal case
• output earth

Output L/N connections are not tied to earth in any way.

However, earth is directly carried through from input to output. Output earth may be a problem in sustaining isolation from mains in lab environment so I decided to disconnect output earth in this unit. Output earth crimp terminal was removed. Clear heat shrink provides insulation. This modification ensures that output L/N/E socket is in no way connected to input L/N/E socket and full isolation is provided. Modification is non-permanent and can be easily reversed.
To ensure that modification is obvious, additional markings were added to the case.

Transformer is very well constructed, safe and build to last. Unit will serve as an isolated AC source in a lab.

See added photos for reference.

[HighVoltage]

Internal wiring in this unit is such that input and output L/N connections are completely isolated from each other. Input goes to primary winding, output is taken from secondary winding. Input earth is connected to:

• transformer shield between primary and secondary
• bottom and top parts of metal case
• output earth

Output L/N connections are not tied to earth in any way.

Great to see that this makes sense.
Thanks for the teardown

[Falkra]

Thank you for the teardown, analysis and explanations, very kind from you. 

[roli_bark]

Nice !- Why did you choose a Toroidal based ?
And what is the shop link ?

[Falkra]

It was a seller on eBay, he had 5 or 6 in total, I posted the link and some member of the forum got them.
Now he is out of stock.

I didn't check the prices, but here is the manufacturer :
http://www.noratel.com/products/

(down, isolation transformers, medical IMED series)