Hi guys, maybe you can clear something up for me. I use a 230-230v isolation transformer between the mains socket and some sound equipment as the supply is on a different ring most of the time from the equipment on the stage. (amps etc.) I don't suffer from earth loop and also feel it makes things safer. A few people on a sound group have suggested this is illegal and dangerous as it disconnects the PE. Could somebody explain the isolation transformer thing and tell me if I am in deed causing safety problems.
I can't speak to the legality, as I'm not familiar with UK laws. Safety I can speak on. You don't mention what you do the safety ground connection in the electrical supply. The ground must be connected to the building electrical ground system, preferably the same ground system as the rest of the equipment. If you have disconnected the safety ground connection, then you have set yourself up to have a dandy electrocution hazard. The purpose of the safety ground is to provide a lower resistance path to earth for fault currents than the one provided by your sweaty body. This diverts most of the electrical shock away from you, and hopefully allows enough current to flow to allow protective breakers or fuses to open up, stopping the electrical flow before they set your gear on fire. Power isolation transformers are a good solution to a few rather uncommon problems. But what it sounds like you are doing is breaking the safety ground connection and adding an isolation transformer. Rather dangerous, and probably a waste of time and resources. You would have better results by putting those resources into fixing the pin one problem (see AES paper #48, I think) that your gear has, and don't screw around with the power supply side of things. Work on the signal lines where the fault currents are measured in milliamps, and audio level isolation transformers only weigh an ounce or so.
Thanks for your thoughts Dale. The transformer I use is a off the shelf unit and there is no disconnection of the earth in the plug top or any of the outlets. I think I am asking is if this gives me better safer protection. Rather like a building site isolation transformer.
Protection from what? The main thing an isolation transformer as I understand your usage, would protect you from power factor problems in your electrical supply, or if you are in a particulary grotty area for electrical power. So if you are next to a welding factory or something like that it is worthwhile. Read the AES paper on the pin one problem. Learn about ground loops and how to troubleshoot them. Better information can be found on the rec.audio.pro news group.
Andy, in days of old TVs and radios were often built with "hot"chassies. it was intended that these chassied be connected to neutral but it was possible to get the hot/neutral reversed. the chasseis were "safely" protected by an insulated cabinet however an unwary serviceman could be killed hence the use of isolation transformers in the shop.
in addition in modern equipment some switching power supplys omit the use of an isolation transformer thus the use of an isolation transformer is recomended when servicing.
the whole purpose for this is so that if the tech is somehow grounded to earth he can safely touch either AC wire (but not both) and not be shocked.
in your case, you are using a (small) line transformer at FOH (front of house or the mixer position) to help break a ground loop to the power amps and thus reduce or eliminate an unwanted "buzz". i would not think that there was anything illegal about this (your local laws may vary) as long ts the transformer is not overloaded or modified. it not much different (IMO) then plugging in a battery charger.
if personal safety is an issue (remember even big transformers can short) just add a GFI (GFCI) breaker after the transformer.
personally i avoid the issue by habitually running power from the amp rack to FOH. i have a quad box of 1:1 audio isolation transformers for contingencies. the move away from unbalanced amplifier sends helps too.
In the US, PE stands for "professional engineer." You would not want to wire one into the circuit. :=) You made me guess but my guess is your PE stands for "power earth" which to us would be the "system ground." You certainly would want to maintain such a connection presumably to protect against equipment failures that could make exposed metal parts and cabinets a danger. A transformer failure could do that if exposed metal were not ground .. er earthed. If there is only one grounded conductor, there should be now loop problem.
I remember that well. In more than one instance, the metal screw holding the chassis to the "insulated" cabinet was easily contacted. That was real fun when the radio was put on a grounded radiator.
These days, most equipment comes with polarized plugs to insure proper insertion into the socket. Nevertheless, there are more wiring code violations around that I like to contemplate.
I'm a little confused here, and maybe it is just terminology. Ordinarily, an isolation transformer has a connection to the green grounding wire on the primary side. On the secondary side, there is no direct connection to primary hot, neutral, or ground.
There should be essentially zero voltage between the secondary hot or neutral (if they are so designated) and the primary ground (hence the earth). Carrying the grounding wire from the primary to the secondary provides no safety benefit at the secondary. A short from the primary to the case or the core will trip the primary's fault protection as usual.
In many cases, if one wishes to have a ground connection to the secondary, the neutral (if so designated) of the secondary is used as an earth ground.
I see no safety hazard here that is alleviated by carrying the grounding wire from the transformer input to its output.
"Protection by Electrical Separation" is recognised / permitted in BS7671 (UK Wiring Regs.) provided that the protective conductors of all equipment supplied by the transformer are connected together and the cords/ cables are open to view. This would be satisfied, for example, by just plugging the equipment into a "normal" multi-way trailing socket. on the transformer's output. (The equipment would, of course, have passed its routine PAT and therefore not have its protective ("earth") leads chopped off!) The isolating transformer output must have no connection whatsoever inside to the protective contact in its output socket. This is safe.
Consider fault 1; One side of supply shorts to case. Still safe. Fault 2: Same side of supply shorts to case in another piece of equipment.No change.All works and still safe. Fault 3: Other side of supply shorts to case in yet another piece of equipment.This shorts the supply out and a fuse blows, in the transformer or a plug and something stops working, showing there are at least 2 faults to correct.
Consider faults 1 and 2 and all protective conductors damaged. Still safe.
Consider faults 1 and 3 with one of the relevant protective conductors damaged. You get a shock between the case of that equipment and any of the others, but not through your feet to a concrete floor, nor to any of your other equipment connected directly, and earthed to, the mains.
I can't see how this can be less safe than having equipment fed directly from the same phase of the mains, let alone from different phases, but I'm happy to have any fallacies in my understanding pointed out.
An isolating transformer to the old BS3535 and whatever the new corresponding EN is, is, by definition, designed and constructed not to fail in that manner.
So much for the UK changing our terminology to harmonised IEC versions, which I'd expect to be understood in an international newsgroup. Why did we bother? Oh, well... Yes, CPC; that name superseded PE, and is more appropriate in the OP's case, when using "electrical separation." I wonder if the rest of the world has heard of that? Is there a FAQ or website anywhere with translations between the various "English-speaking" countries' terminologies?
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