Hi All!
I was doing some wiring for a change-over switch for a UPS that powers a server rack. The incoming power is 277/480 vac 60 Hz 32 amps.
I saw some what I think (guessing) are toroidal coils in the unit and am curious about their purpose.

They look similar to metering Current Transformers that I install on buildings' mains, but there are no taps for metering wires. I guessed that they are toroidal coils, but don't know what they are used for in this installation. Much studying on line taught me quite a bit about such coils, but I didn't take away anything that helped me figure out the purpose in this installation.

Two of the coils have the phase and neutral (but not ground) wires that go to and from the UPS looped through. There is a smaller coil that has the wires which are used on a control or monitoring circuit. I don't know anything about the control circuit's voltage or function.

It's kind of hard to explain the power flow to illustrate where in the circuit the coils are placed, but I'll try:
In "normal" mode, the building branch circuit power goes to the change-over switch and out to the UPS device. It leaves the UPS device and heads to the server rack, via the switch enclosure. In this case, the left coil in the photo will have power from an inverter.
In "bypass" mode, the power skips the UPS and is shunted directly to the server rack. The wires for the left toroidal coils are not energized in this loop.

I've wired circuits for many UPS systems, as well as emergency power change-over devices, and never saw coils around the load wires until now. Me being me, I am quite curious why they're here!

So I am wondering a) are these toroidal coils? and b) what is their function in this installation? Is it to prevent eddy currents from causing inducted power to transfer between the sets of wires?

Thanks For The Education!
Paul

 

The toroidal cores are wound as inductive chokes to reduce EMI conduction (high frequency interference from the switching circuits) through them, likely from the equipment to the power lines or to the control unit.
All such equipment needs to meet FCC interference limits on conducted and radiated EMI and such chokes help with that.

 

The toroidal cores are wound as inductive chokes to reduce EMI conduction (high frequency interference from the switching circuits) through them, likely from the equipment to the power lines or to the control unit.
All such equipment needs to meet FCC interference limits on conducted and radiated EMI and such chokes help with that.

Correct, those are painted / epoxy coated ferrite toroids. Many formulations available. Here's one manufacturer:
https://www.mag-inc.com/products/ferrite-cores/ferrite-toroids

 

Toroids used in that way, for controlling EMI/RFI, are usually called "beads", even when they are really big. Shapes vary - there are ones with holes for flat ribbon cable and ones that are much longer than they are in diameter. Sometimes they are called "suppression cores".

Most beads for EMI/RFI suppression are made of ferrite formulations specifically for that application. Typically a manufacturer will offer at least two material types and sometimes more for suppression. Some are better for lower frequencies some are better for higher frequencies.

The beads do contribute a bit of inductance, but primarily they work as if there were frequency-dependent resistors put in series in the wire. The formulations for suppression are made to be "lossy" in their useful frequency range so that the unwanted high frequency energy is actually converted to heat. It is rare to have more than 2 or 3 turns on a suppression core. In your photo two cores have been used on each wire group. This more or less doubles the effectiveness of a single core. They could have use a single longer core. Suppression cores may or may not be painted. Unpainted ferrite is dark grey.

Such suppressors are usually placed near where cables exit or enter the box. That way they are useful both for conducted interference originating inside the box and interference that may radiate from elsewhere inside the box to the wires and potentially become interference conducted to the outside.

Materials other than ferrite are sometimes used, but they tend to be quite expensive and generally only used for small beads. Toshiba used to (may still, I haven't looked for many years) produce beads from an amorphous metal mixture. They sold small ones called "Ammobeads," I don't remember what the larger ones were called.

You often see cylindrical lumps on cables connected to computers, typically video cables and USB cables. The cable vendors and others will try to tell you this is to keep noise out of the signals through the cables. The actual function, if there is any that is worthwhile, is to keep noise that is inside a box from getting out. Mostly they are useless annoyances because the rules for EMI/RFI certification require the crud to be controlled without some lump of stuff on a cable on pluggable cable supplied by a third party. Older video monitors often had a core on the video cable just outside the case on a permanently attached cable. In that case the core would almost certainly be doing something useful to assure compliance of the whole assembly.

 

Thank You All for your excellent explanations & the resultant education. And, of course, I'll now go off to learn more since the subject just became very interesting to me.

After reading your post, crutschow, I looked at a paper that was with the unit and noticed the FCC statement. I never paid attention before.

Thanks for the link, Bd6Xray. They have good, educational information on the site.

Thanks ebp for the great tutorial.
Those coils are, indeed, right where the cables exit/enter the enclosure. It is kind of curious, though, that the size of this enclosure is far less than what I would be required to use under the Conductor Fill rules of NFPA 70 for that number & size of conductors if I were site building this device. The rules for premisses wiring are, of course, quite different from those for 'utilization equipment'. (i.e. Stuff)
I can't help but wonder how hot it gets in that box.

In your last paragraph, ebp, you mentioned the lumps on video cables. I always wondered what their purpose was and never pursued it.
By coincidence, today I was installing a 120/208 volt 45 kVA isolation transformer and I was dealing with the site's video engineer. I messed with him a bit, telling him I was a genius because I knew what the lumps on his monitor cords' function was.
He said exactly the same thing you did, ebp,- Useless Annoyances.

I've learned more on this forum than you guys can imagine and I appreciate it!
Thanks Again All & Enjoy This Day!
Paul

 

Try to watch this video about ferrite beads

 

Thank You Jony130 for the link!
That is a very informative video. The author's introduction to ferrite beads certainly explains quite a bit and does it in a way that amateurs, like me, can understand.
Enjoy Today!
Paul