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I've an old Bosch German made automotive charger transformer with ratings 14V/9V, 220-250V @ 50/60Hz 132VA. Can I use it on the 220 to 240V outlet here in the US which uses a split - phase system as the transformer was intent to be used on Europe style 240V with a Live and Neutral system? Will there be any difference in its performance?

Note: I'd initially asked this question in the comments section of "How is the 220V line in US different from other parts of world? Does a US 220V line need two switches for each wire?". But has been removed by moderators and was asked to make separate thread so this info is seen by everyone.Thanks.

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  • \$\begingroup\$ European transformers are designed for 230 V, not for 240 V. \$\endgroup\$
    – Uwe
    Oct 24, 2022 at 19:28

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Yes, you can connect that to a US 220-240 V outlet. Just connect to the two hot lines and connect nothing to the neutral. However, there are normally only 30 to 60 amp 240 volt outlets available in US residences. They are dedicated to clothes dryer cooktop and oven use. To add a 240 volt circuit requires two adjacent 120 volt circuit breaker spaces in the distribution box. You will need a 15 or 20 amp double breaker whichever is the smallest available. You can connect additional 120 volt circuits to the same breaker, but they must not be circuits like bathroom and kitchen outlets that can not be mixed with outlets elsewhere.

It is not a good idea to connect to a higher current circuit because the higher rated circuit breaker might not prevent a fire if you have a short-circuit in the charger or in the charger cord. If you want to do that you should have smaller fuses near the outlet. I don't know if that is permitted by code.

You should use a US receptacle and plug rated for 240 volts and the fuse or circuit breaker current rating. You probably will not find a suitable converter for a 240 volt US receptacle.

There could be a difference in performance related to the actual voltage in the previous vs. present locations. However the transformer will be operating within the specified voltage and frequency range, so that is nothing to be concerned about. If the new voltage is higher, the charging current may be a little higher and the charging time a little quicker and the opposite if the voltage is lower. I assume an old charger may not have any voltage regulation. The operating temperature may be lower or higher.

A 15 or 20 amp 240 volt receptacle installed for a window air conditioner is an excellent choice for this application.

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    \$\begingroup\$ That would be a good thing to do. \$\endgroup\$
    – user80875
    Oct 30, 2017 at 19:09
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    \$\begingroup\$ @RahulSalin, you can use that A/C outlet for anything that meets the electrical requirements. People in the US refer to them as the A/C unit outlet and think that's the only thing you can use it for because that's pretty much the only commonly available 240v appliance sold in the US (in the 15-20A range). \$\endgroup\$
    – JPhi1618
    Oct 30, 2017 at 20:22
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    \$\begingroup\$ Note that this is only okay because the appliance is rated for 50-60Hz. \$\endgroup\$ Oct 31, 2017 at 4:28
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    \$\begingroup\$ @chrylis Yep. Its written on the transformer label that it can run on both 50/60Hz. So, it seems to be fine in this case. But isn't it okay to run a 50Hz only transformer on 60Hz supply? Because the other way the transformer get heated up due to bigger current draw if I'm correct. \$\endgroup\$ Oct 31, 2017 at 5:34
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    \$\begingroup\$ Just to note: Schuko to NEMA 20 converters are easy to find (contrary to what the answer says? Not sure I understood it correctly). Example: bhphotovideo.com/c/product/1225290-REG/… (the photo seems to be wrong). \$\endgroup\$
    – chx
    Oct 31, 2017 at 10:06
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If the device has a Schuko plug or an Europlug, you should be able to use it on a split-phase system. The plug is unpolarized anyway, so the device has to be able to accept live voltage on any of the two pins. The mains power switches in Schuko devices always switch both live and neutral for this reason.

You should just make sure to use an adapter with an earthing pin if the charger uses a Schuko plug. Operating a Schuko device without earthing might be quite dangerous.

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  • \$\begingroup\$ The body of the charger is plastic. So, the earth wire isn't connected on it when I looked inside. \$\endgroup\$ Oct 30, 2017 at 19:05
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Sure, there's no problem. You see common 120V receptacles all over houses in North America. You can do exactly the same thing with 240V circuits.

The normal 120V plugs are called NEMA 5-15 plugs, and they go into either NEMA 5-15 or 5-20 sockets. The Electrical Code says the breaker must be 15A or 20A, and the socket ampacity must match the breaker, except 5-15 sockets are OK on a 20A circuit if there's more than one socket.

The same exact rules apply to 240V circuits (no neutral) except you use NEMA 6-15 and 6-20. The sockets are almost identical but are keyed not to fit NEMA 5.

NEMA 6-20

You could take a 120V circuit and just convert it to 240V by changing all the sockets to NEMA 6 and landing its 2 conductors on a 240V breaker. However, Code requires certain mandatory sockets in homes, and those mandatory ones must be 120V. Other than that, fit all the NEMA 6-15 or 6-20 sockets you desire. It's no more difficult than installing a 120V circuit. You cable it with the normal /2 cable (twin and earth) and you tape the white wire to indicate it is a hot.

Now, one person talked about making a 240V circuit that serves both 120V and 240V loads. That's allowed but is a little awkward. It needs the more special /3 cable with two hots and a neutral. From the 120v circuit's perspective, it is a multi-wire branch circuit with some funny rules. GFCI/AFCI, if needed, wont be any harder than on a straight 240V circuit, but will probably end up needing to be in the breaker panel.

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  • \$\begingroup\$ "Now, one person talked about making a 240V circuit that serves both 120V and 240V loads. That's allowed but is a little awkward. It needs the more special /3 cable with two hots and a neutral. From the 120v circuit's perspective, it is a multi-wire branch circuit with some funny rules. GFCI/AFCI, if needed, wont be any harder than on a straight 240V circuit, but will probably end up needing to be in the breaker panel." Did you mean the 4 pin connector type outlet here? Like L14-30R/50R etc. \$\endgroup\$ Oct 31, 2017 at 7:08
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    \$\begingroup\$ @RahulSalin NEMA 14 provides the neutral and both hots which makes it a "universal donor", but it is an expensive and very balky connector. I would just fit a 2-gang junction box and put NEMA 5 and 6 right next to each other. Keep in mind the receptacle rules, the receptacle rating must match the breaker rating, so L14-20 on a 20A circuit. There is also a rule that if the load draws less than 1500W, must be the 15A style plug. NEMA 14-15P is hard to find. 20A receptacles are keyed to accept 15A plugs. \$\endgroup\$ Oct 31, 2017 at 15:26
  • \$\begingroup\$ Currently I'm using the NEMA 5-20 & 6-20 next to each other on my garage repair bench where I'm using the charger now. Even most of the Window A/C outlets are also of these type i.e., the perpendicular type 20A. \$\endgroup\$ Oct 31, 2017 at 19:32
  • \$\begingroup\$ Using /3 cable and "multiple circuits" begins lots of nuanced rules with NEC "code". Most discussions about code are IMHO irrelevant chest thumping save for one aspect: if there is "discussion", just consider it not to code as far as an inspector goes. Further, without using a voltmeter, the concept of the "220" outlet is almost meaningless. It can be 208, 220, 230, etc etc depending on how the power company supplies it. Most of the time, this won't matter... but engineering is in the details of how nuances cause problems and failures. \$\endgroup\$
    – Krista K
    Aug 16, 2019 at 6:45
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    \$\begingroup\$ @ChrisK that's my habit from diy.se, where we pretty much live in the Codebook (deviations must be justified). Once you get to know NEC you find every rule has a reason. \$\endgroup\$ Aug 16, 2019 at 16:25
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A transformer designed for the european grid with 50 Hz will work with 60 Hz too. For a higher frequency the transformer may be a little lighter. A transformer designed for 60 Hz only may be a little too small to work with 50 Hz. So the 60 Hz transformer should be 20 to 25 % larger than necessary to be used with 50 Hz too.

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