Line Impedance

[john37]

I would like to get some opinions on an issue I'm coming across right now.
I'm working on a women's health clinic that has two Digital Mammo x-ray machines in the space. Currently I have a 480/277V 3 phase with a 45KVA
step down transformer feeding a 208/120V 3 phase panel.
Currently there is a 2.4KW 1 phase a/c unit on the same 208/120V 3 phase panel. The mammo x-ray equipment vendor is insisting that a power conditioner be put on the dedicated branch circuit feeder each of the mammo x-ray machines. The mammo x-ray equipment manufacturers requirements call for a maximum line impedance not to exceed 0.20 ohms for a 208V line.
Does anyone think that by having the a/c unit on the same panel will affect the mammo x-ray equipment and do you think it would exceed the 0.20 ohms requirement just by having the a/c unit feeding off the same panelboard?
Any input or suggestions would be greatly appreciated. Thanks.

 

[glene77is]

Chris,
At first thought, it seems like TWO questions.

It seems like the Line Impedance of .2 Ohms is a separate issue from
the possible interference between the A/C and the X-ray equipment.

I had to provide power conditioner transformer to isolate an elevator from the lab equipment in a hospital.

The .2 Ohms line impedance could affect
(1) the ability of the X-ray equipment to startup (ie, start surge),
or
(2) the X-ray equipment might require surges (spikes) of power for its pulse generator.

:smile:

 

[john37]

Sorry if I was not clear. On the manufacturer shop drawings it states for a maximum line imedance not to exceed 0.20 ohms on the 208V 1 phase breaker feeding the mammo x-ray equipment.

Bottom line question is if having a small a/c unit on the same panel as the 35A x-ray equipment does anyone think it will affect the x-ray equipment? The a/c nameplate calls for a 2P40A breaker and the mammo x-ray equipment calls for a 2P35A breaker. There are two mammo x-ray equipment machines on the same 208/120V panel as the a/c unit. Since everything is installed, what would be my best option to provide a "clean" line to the x-ray equipment should we have to proceed in that direction? Thanks

 

[glene77is]

John,

I think you have re-phrased the original question.

"It seems like the Line Impedance of .2 Ohms is a separate issue from the possible interference
between the A/C and the X-ray equipment."

In fact, there may be little / or no inteference between the two.

(1) Both units are on a 2 pole 208V OCPD,
so I expect that each load will be well isolated
from the other 2 pole 208V load.

(2) They may never startup at the same time,
so little concern for a tug-o-war over source power.
The A/C unit is 2.4KVA, and the X-ray is what? maybe 5 KVA peak?
This is maybe 10% of the available 45KVA.

:smile: