Isolating transformers from chassis and star grounding them

Has anyone used regular rubber well nuts to isolate a transformer from the chassis? They seal the chassis hole on both sides and isolate the mount screw electrically from the chassis. They also provide vibration damping because they are rubber. I'm thinking of star grounding my transformers to a common point rather than depending on just having the mount screws in contact with the chassis for the ground, which violates star grounding considering there are 12 bolts holding down three transformers. I know someone makes transformer mounting isolators but they are kind of pricey and not rubber. They are used often for attaching things to a boat for a seal, or attaching glass.

25 Rubber Well Nuts M5-.8 .554 Length 3/8" Hole: Amazon.com: Industrial & Scientific

Well nuts, EPDM rubber with brass insert, #6-32 thread, 1/4" body - Bolt Depot
 
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What benefits do you think will accrue, and how?

Star grounding is typically related to signal paths, whereas the ground path for an exposed transformer core is there principally for earthing protection if a fault occurs, and otherwise is a current path caused by parasitic capacitance and dV/dt (which if it is an important concern is usually managed by electrostatic screening where one can define the point of screen connection(s)).
 
There is no benefit to "isolating" power/output transformers electrically from the chassis. And they need no "shock mounting" either. So with that said, going to all the fuss with rubber grommets is a waste of time. Transformers should be bolted directly on a chassis. It's been done that way for decades, and there's never been any issue with it.
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
> What kind of currents do you expect from transformer bells?

Just what I was wondering.

1) There's stray capacitive coupling. This is "garbage". We usually use the chassis as our garbage-shield. It seems quite proper to bold the tranny solid to chassis.

2) There is transformer break-down. Shocking but it happens. A proper defense is to dump the fault current through a *low* resistance path back to power-circuit "PE" so it will blow a basement fuse quickly. While this could be wires, chassis is simpler thus safer.

Not a problem for today: I have restored a lot of old gear where all the rubber was rotten. Also stinky and throwing tarnish-fumes around. I am not a fan of rubber in electronics.
 
There is no benefit to "isolating" power/output transformers electrically from the chassis. And they need no "shock mounting" either.
Actually you might reduce mains hum/vibration that way, especially if the chassis is resonant at a harmonic of the mains. Mains transformers vibrate slightly at twice the mains frequency due to the magnetostriction effect in the core, decoupling that from the chassis might be beneficial.
 
In conclusion, there is any difference keeping transformer core phisical isolated from chassis ? Or do any diference if is electrical conected by one scew bolt and the rest of three bolts isolated ? Does it any chance to minimise the flux leak to be induced into a iron chassis just managing how the transformer core is isolated or not from chassis for a determined transformer position, please ? Thanks.
 
In conclusion, there is any difference keeping transformer core phisical isolated from chassis


No difference.
Since the beginning of time, transformers were simply bolted to the chassis.
And there was no issues.


A lot of what you may read on the internet is pure paranoia and obsessions, along with dreamt-up myths, and has nothing to do with the actual reality of things.
 
A lot of what you may read on the internet is pure paranoia and obsessions, along with dreamt-up myths, and has nothing to do with the actual reality of things.
Beware of those comments :p
Some people take them as personal insults :cool: :rolleyes:

Under those misdirected ideas, the worst insults book, chock full of them ... is a Physics Book :eek:
 
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