I have a question which was inspired by another thread which i don’t want to hijack; it was awakened in me by Fuji Kitakyusho’s post. I’m going to set up some 110v American style plug outlets in my 220volt house in Spain using a step-down transformer. I’m already using various american 110v appliances with this transformer (1000 watts)
fuji had written:
“Oh, one more thing: BLACK = LINE (hot), WHITE = NEUTRAL, GREEN = SAFETY GROUND (chassis) - this is the standard, but be prudent and don’t count on it… your electrician could have been smoking something. Play it safe and test with a voltmeter or circuit tester. Also, make sure the breaker is opened (OFF) prior to messing around with the wiring”.
In respect to this comment, being that I do not have these colour wires, I have black, blue (these are really interchangeable here)and a green/yellow ground cable, how should I determine with a voltmeter which wire is HOT and which is NEUTRAL?
Measured from the hot to ground should read full line voltage, from neutral to ground should be zero, from neutral to hot should be full voltage. Make sure meter is set to AC volts and is set higher than max possible voltage, be carefull.
In Europe, blue is normally neutral. Be aware that you are only transforming voltage and that you will still be subject to the 50 Hz power generation, which can affect appliance motors over the long haul. Most electronic gear is not cycle sensitive any more (except turntables), but may be. Check the data plate.
Also, most transformers used by Americans overseas are sensitive to polarity. I won’t go into the whole explanation here, but if the polarity is reversed, you can develop a dangerous potential to the case of the transformer and to your appliances (we fried a lot of computer motherboards in our embassy offices before I got the problem corrected). Have an electrician check to make sure not only the plug is wired correctly, but also the outlet you are plugging in to, and that you are matching the neutral prong on the plug to the neutral slot on the outlet. I don’t know Spain’s plug configuration, but many Euro outlets and plugs are completely reversible, unlike the American plug which has a larger blade for the neutral connection. If this is the case in Spain, make sure that if you have to unplug the transformer for any reason that you plug it back in the same way.
No, this is wrong. Transformers are designed and built with isolation from the mains in mind (autotransformers are an exception, but you never encounter these in consumer products). There is never any connection from the primary to the chassis, and almost never is there one from the secondary, and then only when the chassis is grounded so it has zero volts potential regardless of the polarity of the mains plug. If you had a a transformer damaging equipment due to reversed polarity, it was an extremely poor design, and not at all typical.
I’ve got some bad news for you. The design mentioned is not counted as a bad design here. It is one of the standard designs for a step-down transformer. I’d have to dig it up again, but it has standards definition and is accepted practice. The standards do acknowledge, though, that it is not an especially safe design and reccommends other designs for residential use.
Just to qualify the transfomer. It is not " most transformers used by Americans overseas" but a normal step-up step-down transformer made in China. 100v -220V and 220v-110v. Does this change anything.
Disconnect the transformer from all power sources and loads. Check the resistance between the black on the primary side and the black from the secondary side. Do the same for the blue (blue primary to blue scondary.) Both of these should be open circuits - extremely high resistance of at least several hundred thousand ohms. If this is so, then you should be pretty safe.
I am not sure what would be best with the green wire. I tend to think you will want it connected straight through so that a short to the chassis on your connected equipment would be lead back to the household ground and trip your ground fault interruptor.
The difficulty with that leads us back to the reason for “polarized mains plugs.” Some equipment doesn’t have a ground wire, so chassis ground is connected to the neutral line from the mains. Since the equipment is insulated anyway, this doesn’t usually matter.
Unless you try to connect two pieces of equipment together. If both are connected properly, then the chassis on both are at the same potential and everything is fine. If, however, one of them is connected backwards, you will connect the neutral chassis of one to the “hot” chassis of the other and fry something. This can happen when a signal (audio or video or printer cable or whatever) has a ground wire connected to the chassis. for this reason, US equipment has the polarized plug - it is cheaper than putting a ground wire into the mains cable of the equipment and using a chassis ground that is really grounded.
For the most part, neutral IS grounded at the main junction box in a house. Not always, though, especially if the electrician was doped (or had a couple of beers too many at work that day as happens with Germans,) or if some yo-yo was trying to save a couple of bucks again. I know for a fact that many houses in Germany are wired with only two wires to each outlet - hot and neutral - and the ground pin on the outlet is tied to neutral right on the outlet. If neutral is properly bonded to a real earth ground at the junction box, and if the neutral wire isn’t damaged or broken along the run to the outlet, then you are fine. If anything happens to the neutral connection to the outlet, however, then you are screwed.
I don’t know what appliances you are running on a one thousand watt transformer, but if you are using equipment that electrically connects to the 220V system (say, and American CD player with a polarized mains plug to a European amplifier) then I would be very careful. There is the possiblity of current flowing in the ground lines connecting the two pieces of equipment - with the potential to fry you or the equipment or both.
I see someone beat me to an answer, but in fact MOST of the transformers we had overseas were indeed autotransformers, most of them are still out there, hence the warning.
None of the ones we can get here in the States are, at least none of thoes I’ve ever seen. All things being equal, autotransformers are slightly cheaper to make, since no additional insulation is needed between primary and secondary, and because it can be wound in a single pass. So, maybe economics plays a factor…but yikes. Still. I don’t see how a computer mainboard could be destroyed by a reverse-poloarized autotransformer, since the PC power supply itself provides isolation. Unless the safety ground was defeated and something bad happened inside the case…
I have never run across an instance where neutral was tied to chassis, even on equipment with polarized/non-grounded plugs. Such would be very dangerous, IMO (if a plug is used).
I’m not saying it’s never happened, and perhaps it was common many decades ago. I’m just saying that I do not believe neutral is ever tied to chassis on modern equipment when an AC plug is used…
Yikes is right. Most of the transformers that we had were purchased in the U.S. from Beltway Bandits in DC. The things were mass produced in China and other places, and were obtained pretty cheaply by wholesalers. The problem with computer motherboards seemed to crop up only when the computer was wired for 220v (plugged into the wall) and the printer was a 120v only, and plugged into a transformer. Best I could figure was that somehow voltage was bleeding over to the printer parallel cable, energizing the computer frame, and frying the boards. All I know for sure is that when the polarity was made consistent throughout the circuit, the problems stopped. The other problem we had was with UPS units that people tried to plug into transformers. They kept alarming because (apparently) of the 50Hz. But perhaps that problem has been cleared up by now. I can also tell you that surge supressors didn’t take kindly to reversed polarity.