208V Transformer for CT/MRI AREA

N

NathanH

Member
Location
California
Occupation
Electrician
Hello all can someone explain this to me im confused why a panel that is 208/120 is feeding a transformer to output 208/120. information on the panel is that it feeds convenience outlets around the MRI/ CT area of a veterinary clinic. Is there any type of transformer that protects these circuits around these areas? IMG_0439.png
 
To provide additional isolation from the main power supply. Note that the 40 amp primary breaker is less than the primary full load current.
 
don_resqcapt19 said:
To provide additional isolation from the main power supply. Note that the 40 amp primary breaker is less than the primary full load current.
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I agree for isolation but not really what that will accomplish other than maybe lower available fault current beyond the transformer?

You still need to bond your secondary neutral to the GES which will basically put it at same potential as the service grounded conductor and EGC's are also common both sides of things even if you had an ungrounded system - which you can't do with a wye system.
 
kwired said:
I agree for isolation but not really what that will accomplish other than maybe lower available fault current beyond the transformer?

You still need to bond your secondary neutral to the GES which will basically put it at same potential as the service grounded conductor and EGC's are also common both sides of things even if you had an ungrounded system - which you can't do with a wye system.
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There are still a lot of engineers that want a "clean" EGC and they think this installation provides that.
 
IEEE 142 IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems (Green Book) states that it is useful to provide power source grounding (neutral-to-ground bond) close to the loads, which is recommended for electronic loads.
It reduces the effects of a long grounded conductor and potential N-G voltages.
 
ron said:
IEEE 142 IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems (Green Book) states that it is useful to provide power source grounding (neutral-to-ground bond) close to the loads, which is recommended for electronic loads.
It reduces the effects of a long grounded conductor and potential N-G voltages.
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The Funny part about this installation is that the panel isn’t even next to the transformer. The transformer is about 100-150 feet away from the panel right next to the switch gear.
 
Out of curiosity, who is the equipment manufacturer?
 
Eaton is good to work with in my experience so you could ask their engineering if this level of isolation is really necessary.
As an aside, all radiology, MRI's, CT scan, etc ... that I have done does have it.
 
don_resqcapt19 said:
there is not, but a lot of engineers seem to thing there is
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Isolation transformers are shielded which reduces the capacitance between the input and output coils which is how much of the higher frequency noise is transmitted from primary to secondary. Whether this is of any real value or not is something else. I am not convinced it is especially useful.
 
NathanH said:
I was just wondering the reason they have the transformer there if it’s not converting to a different voltage but staying the same.
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For the aforementioned isolation.
 
NathanH said:
I was just wondering the reason they have the transformer there if it’s not converting to a different voltage but staying the same.
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I think it was common practice for years whether needed or not. I never worked in bigger hospitals, but used to do the electrical in a small community hospital until they finally closed it. They had installed new x-ray and CT in the last couple years of it's existence. The x ray replaced older x ray, the ct was entirely new. When they remodeled the room I discovered two isolation transformers above the ceiling that supplied two different panels that supplied items in that area. Never knew they had isolation transformers on those old panels before then. That would have all been new construction in early 1970's. in that portion of the facility.
 
kwired said:
I think it was common practice for years whether needed or not. I never worked in bigger hospitals, but used to do the electrical in a small community hospital until they finally closed it. They had installed new x-ray and CT in the last couple years of it's existence. The x ray replaced older x ray, the ct was entirely new. When they remodeled the room I discovered two isolation transformers above the ceiling that supplied two different panels that supplied items in that area. Never knew they had isolation transformers on those old panels before then. That would have all been new construction in early 1970's. in that portion of the facility.
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There are a lot of things that are done in the name of reducing noise, or getting better grounds, or reducing noise with a better ground, etc. I am pretty much convinced they are all hokum.

Now, you can filter out noise with RFI filters. They are pretty good at that. But they are not real good at reducing voltage spikes. They may actually make the waveform "worse".
 
petersonra said:
There are a lot of things that are done in the name of reducing noise, or getting better grounds, or reducing noise with a better ground, etc. I am pretty much convinced they are all hokum.

Now, you can filter out noise with RFI filters. They are pretty good at that. But they are not real good at reducing voltage spikes. They may actually make the waveform "worse".
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Was that much of a problem in early 1970's with what they had for medical equipment then? I could see it being bigger issue maybe about mid 1980's with the more advances in computer chips and such by then. early 70's was when that addition to the facility I mentioned would have been built.
 
Let's not mistake this conversation with 517.160 systems.
 
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