Isolation transformer - does it offer protection


Say I have an isolation transformer "isolating" a sub panel and then a few dedicated circuits from that sub panel to a listening room where all audio equipment is connected to these curcuits.

Does the isolation transformer help protect equipment from power surge/spikes. If so, why. If not, why not.

Thanks to all with the technical background to help with this question.
dangelod
The Isolation transformer will protect against spikes but not surges or sags. It isolates but does not regulate. It is just a transformer.
Nope it doesn't and I can't I can't tell you why but I can tell you about what happened to me. I had an amp plugged into an industrial 1.8 KVA Topaz Isolation transformer and there was a spike/surge that occurred over this past weekend. Now the left channel of the amp is out and the left speaker is blown. I was breaking in speaker cables and was using an Ipod as a source directly to the amp. It could have been worse had I just not had that specific set-up for the speaker cable break-in.

The good news is that with Isolation transformers in place I did hear an improvement in my sound systems. A lot more clarity and detail.
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It may attenuate a spike but won't eliminate it.

An ideal transformer will pass any changes in the primary to the secondary so any spikes, surges, sags, or distortions in the incoming signal theoretically get passed through. In reality transformers have limits in frequency response and will saturate at some point so they do offer some protection, but don't count on them to protect your equipment.

For protection you need a unit with an isolation transformer and some other circuitry for surge protection. Even then, if the spike is too big (think lightning strike) their is no device in the world that will protect against it.

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what good does an iso do, then?
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Most of what is sold as an isolation transformer like these come in a box that contains more than just the transformer so you get RF filtering along with surge and spike protection. The transformer itself does some things that might benefit your system including the ability to break a ground loop and offer balanced power. It will also filter out some noise.

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Once found some retail site that claimed 8:1 spike reduction. Even had a picture of an oscilloscope for evidence. Never seen that confirmed by a manufacturer and doubt they would even test for something that was not it's intent. Seems logical that they just aren't fast enough.
FYI, the discontinued PS audio ultimate outlet used a balanced (balun) isolation transformer plus filtering that works well to reduce noise-- it also claims to stop spikes, but I have no way to test. Keces also makes a high end iso sold through ebay-- looks well made.
07-12-11: Jedinite24
Nope it doesn't and I can't I can't tell you why

07-12-11: Herman
It may attenuate a spike but won't eliminate it.

An ideal transformer will pass any changes in the primary to the secondary so any spikes, surges, sags, or distortions in the incoming signal theoretically get passed through.
I think shielded isolation transformers can effectively attenuate (filter) voltage transients (voltage spikes) through two mechanisms, if their rating is sufficient to handle the level of spike;
1) The Faraday Shield shunts energy to ground(& common mode noise)
2) Lenz's Law (see animation at link) which loosely translates to "The Induced current is such as to OPPOSE the CHANGE in applied field."

Electricity and controls for HVAC/R By Stephen L. Herman, Bennie L. Sparkman
The reason a transformer can greatly reduce any voltage spikes before they reach the secondary is because of rise time of current through an inductor. The current in an inductor rises at an exponential rate, Figure 18-3. As the current rises in value, the expanding magnetic field cuts through the conductors of the coil and induces a voltage that is opposed to the applied voltage. The amount of induced voltage is proportional to the rate of change of current. This simply means that the faster the current attempts to increase, the greater the opposition to that increase will be. Spike voltages and currents are generally very short in duration, which means they increase in value very rapidly, Figure 18-4. This rapid change of value causes the opposition to the change to increase just as rapidly. By the time the spike has been transferred to the secondary winding of the transformer, it has been eliminated or greatly reduced, Figure 18-5.
i have no technical experience or reference.

OTOH i do use an Equi=tech 10WQ Wall Panel System which uses a 10kw balanced isolation transformer for my audio circuits in a dedicated room. i have all the lights, HVAC and non audio electical on a separate panel. forgetting the performance advantages across the board, which are considerable, since i installed the Equi=tech last summer, when the lights flicker my system is not affected, it plays along unaffected. and twice when i had power outages my system continues playing for 4-8 seconds after the lights go out. my amp blows a fuse if the power is turned on and off quickly, as that triggers the protection circuit. so now i have a buffer of time to get up, walk over and turn it off.

does my experience indicate that spikes are reduced or eliminated. i don't know. but it seems like i have considerable protection from the bad stuff.
BTW, the shield shunting to ground obviously requires that an outlet, it's corresponding fused circuit/panel, and the entire house are properly grounded in the first place - which a frightening number are not.
07-12-11: Jedinite24
Nope it doesn't...I had an amp plugged into an industrial 1.8 KVA Topaz Isolation transformer
While that might seem like a large isolation transformer by weight, it really isn't that large when it comes to electrical spikes. 1.8KVA=120V x 15A.

I bought six Topaz 2.4KVA Ultra-Isolators from a guy who was using three in series per channel, which is called "cascading"(?). He was doing so for common noise reduction, but the effect also works for filtering of spikes(I think). Each succeeding transformer knocks down the remaining spike until none, or very little, is passed.

Or, you can just do it right from square one and get a big daddy at your panel like Mike.
Depends on the frequency response characterisitcs of the transformer and its construction.

For mid frequency transients, it may work very well. But some solation transformers capacitively couple very high frequency spikes from input to output without significant attenuation. So you cannot use them by themselves without additional surge protection.

I prefer using a good transient surge protection like Furman's products better than an isolation transformer.
07-20-11: Dhl93449
...But some solation transformers capacitively couple very high frequency spikes from input to output without significant attenuation. So you cannot use them by themselves without additional surge protection.
I was not aware of this, thanks for the tip.
Seek some thorough advice. http://http://en.wikipedia.org/wiki/Surge_protector

My house was once hit by lightening a mere 6 feet from my on stereo. The system was plugged into a Sound Application unit. While most of the electronic on one side of my house was fried, neither the SA or my system were harmed.
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your link doesn't work.. too many http://

http://en.wikipedia.org/wiki/Surge_protector

Perhaps the SA wasn't harmed...

Many surge protectors have components that absorb the spike but by design they get fried in the process. It is possible that your unit protected your stereo but can't do it again.

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Herman, I just clicked on it and got right to the surge section.
In an isolation transformer the output winding will be isolated, or floating from earth ground unless bonded at the time of installation. Secondary neutral to ground bonding virtually eliminates common mode noise, providing an isolated neutral-ground reference for sensitive equipment and an inexpensive alternative to the installation of dedicated circuits.

An isolation transformer allows an AC signal or power to be taken from one device and fed into another without electrically connecting the two circuits. Isolation transformers block transmission of DC signals from one circuit to the other, but allow AC signals to pass. They also block interference caused by ground loops. Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment.