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I'm currently in Peru and have a three-pronged travel adapter. This was fine in Colombia but the plug sockets here mostly have inputs for two prongs.

I want to plug my UK Macbook charger (which fits Peru voltages) into my three-pronged adapter and then that into a two-pronged adapter. Is this safe? I can't find a UK-to-two pronged adapter where I am in Peru.

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    Picture's might help understand what kind of adapters you have. – Joren Vandamme Oct 15 at 13:16
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    Yes, that is not that the word "adapter" stand for? – JuanCa Oct 15 at 14:39
  • It would be useful to know if your travel adapters are branded and purchased from a reputable retailer or purchased from a market or online importer. I understand that the quality and safety of these devices can vary wildly. – Martin Oct 16 at 10:28
  • Just don't do it this way youtube.com/watch?v=X5SkW7K0e3Y – Sam Dean Oct 16 at 14:26
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    Safe with care. Main issues are 1. What others said - lack of ground MAY matter. 2. Unstable stack may expose contacts with shock risk. Easy to do accidentally. 3. Substantial currents through poor contacts could create a fire risk. Unlikely with laptop level loads. – Russell McMahon Oct 17 at 11:59
47

Yes, it's generally safe. Adapters don't have any active components, so assuming they're all rated for the voltage/amps you're putting through, there's little risk of overload etc like there is with transformers.

The main catch is that if you plug a three-pin plug into a series of adapters that "loses" the third pin, your device will no longer be grounded. (Then again, this can happen with a single "wrong" adapter as well.) Also, while more annoying than dangerous, stacks of adapters tend to be fiddly and come loose easily.

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    With a macbook adapter, you're probably fine, but some devices are definitley not safe if not properly grounded. – CMaster Oct 15 at 15:00
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    There is also the danger that the resistance of (cheap) connectors add up to an amount that a short on the device side doesn't trip the fuse anymore, creating a fire hazard. – etarion Oct 16 at 9:53
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    and some adapters are sold as "sets" which are intended to be used in this way – Mick Oct 16 at 11:38
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    @etarion: While in principle that's true, if you have devices that accept a range of input voltages making it suitable to use a simple travel adapter, it's unlikely they pull more than 2A (and most significantly less than that), so it's not going to be an issue. That would only matter if you were plugging in something like a hairdryer or electric heater. – R.. Oct 16 at 12:22
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    @R.. If the device is faulty and creates a short, it doesn't matter how much current it's designed to draw, it only matters how much current is required to trip the fuse. If you plug it into a socket on a 16 A circuit, you're going to need more than 16 A to trip the fuse. – wrtlprnft Oct 18 at 6:10
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In the specific case of a MacBook, it's safe: the MacBook power supply is non-grounded. The grounding pin on your UK "type G" plug is probably a plastic dummy pin, so going from a UK "type G" to a Colombian three-pin "type B" to a Peruvian two-pin "type A" or "type C" doesn't lose the ground connection.

If, on the other hand, you're using a device that requires grounding, it's only safe if the "Peruvian two-pin" plug is a "type F" (Schuko) plug. "Type A" and "type C" plugs don't have ground connections, and you risk getting electrocuted if, for example, a wire inside the device breaks and comes in contact with a metal case.

  • Regarding grounding, this may be version dependent, in that at least some of the magsafe macbook chargers do have a ground connection via the metal stud the lead connects to (and thus a metal earth pin). – origimbo Oct 16 at 13:05
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    Apple is weird on grounding, with my macbook charger it gets grounded if you use the cord, but not if you use the wall-wart style head! The charger has a "double insulated" symbol but it's inside a section labeled "apple japan", so does it only apply in japan?! – Peter Green Oct 16 at 14:21
  • @PeterGreen It definitely is grounded in the US when you use the extension cable. The metal on the laptop (next to the trackpad) feels different when you use the extension cable with three prongs–which I believe is an indication of grounding. – Ezekiel Elin Oct 16 at 16:34
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    @PeterGreen for whatever reason, ground pins/sockets are rather rare in japan (at least from what I saw). So possibly in Japan, the charger ships with a two-prong cord, and the symbol lets people know its compliant with safety standards even though its a bit like the ground pin has been "defeated"? – mbrig Oct 16 at 18:44
  • Yeah, the bit I don't get is that even in the UK apple shipped two different ways of connecting the adapter to the mains, one of which (the cord) was grounded, the other of which (the wall-wart head) was not. – Peter Green Oct 16 at 18:45
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It really depends on the travel adapter(s)

Stacking two of them isn't really the issue. It's that an awful lot of that stock is made in the far east, and lacks any certification by any competent testing lab. (in fact the CE mark can be counted on to be counterfeit unless an EU bricks-and-mortar manufacturer made or imported it).

So look for ones with the stamp of a reputable testing lab. These shops don't bury the lede: If they have a hard-won UL Listing, ETL, BSI, CSA, TUV etc. -- they'll put it front and center. However if the most prominent mark is CE or CCC, that means they couldn't get a proper listing; it's a self-admission of junkness.

It also depends on the load, in two axes.

Is the load double insulated?

If you see a "Square on Square" symbol (literally a square inside a square), that means your load is double-insulated. That will help compensate for adapter problems; not least that these adapters love to exchange hot and neutral. [not least, British BS1363 (Type G) puts hot on the left (ground down), US NEMA 5 (Type B) puts it on the right.]

Is the load small?

Adapters are notorious for very flimsy connections. You can get away with murder if your load is only a 10 watt iPad charger. But trying a 1500 watt hair dryer is asking for trouble. The issue is "series arcing faults", where the power jumps (arcs) across a flimsy connection in order to get through your device. The more current, the more arcing; shut off the load and arcing stops. An arc-fault detecting circuit breaker will help protect you, but those are rare.

Is the outlet GFCI/RCD protected?

A GFCI aka RCD/RCBO device will help keep you from getting shocked by a loose or broken adapter. It won't do anything to prevent arc-caused fires, the aforementioned arc-fault breaker (AFCI) would do that.

Either protection could be located anywhere in the building; the proof of the pudding is if you hit its TEST button, the outlet loses power. It's generally at the receptacle itself, or at a nearby receptacle, or at the circuit breaker; all are equally acceptable.

  • Testing RCDs/GFCIs is fine if it's your own property, but not really very practical for travellers. – Peter Green Oct 16 at 16:58
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    @PeterGreen presuming you have physical access to the TEST button, then it's rather unlikely that it will affect any occupancy but your own. – Harper - Reinstate Monica Oct 16 at 21:06
  • @PeterGreen what Harper said; besides, if you have access to the TEST button and it does affect another occupant... that building has 💩 wiring and I wouldn't plug anything expensive or high-current in there in the first place! – Doktor J Oct 17 at 15:02
  • "So look for ones with the stamp of a reputable testing lab" Eh, this is nonsense. There are lots of fully accredited test houses that aren't world-wide famous. You can have 3rd party validation just fine without attaching some test house label on the product. Futhermore, the CE mark is only relevant in Europe (+ some countries) and the UL mark is only being relevant in the US (+ some countries). So getting a CE mark for a product only to be used in USA etc, is pretty senseless. – Lundin Oct 18 at 10:54
  • @Lundin all due respect, you don't understand how these certifications work, and you're mocking things that are established. Popularity is not an issue, national recognition as a testing lab is. You also equate the CE mark with the UL mark; UL is a nationally rcognized third party testing lab; CE is a voluntary self-certification. They are not similar things. A recognized-lab file number reflects that real design review and testing happened, regardless of which country the product is in. You also disregard how companies evade these standards, but that's too big for a comment. – Harper - Reinstate Monica Oct 18 at 15:31
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Earthing (grounding) is covered in the other answers but the other thing you should make sure of is that there isn't too much mechanical stress on the adapters or on the socket that you're using, as that could lead to a poor contact which could overheat.

If the socket is trailing (e.g. on the end of an extension lead) you can lie it down so the MacBook adapter is on the floor. If it's a wall socket I would probably try and support the MacBook adapter from underneath with some object so as to take the weight off the socket. Remember the MacBook adapter gets warm, so don't cover it up.

I'd also suggest not leaving this arrangement unattended while plugged in.

3

Travel adapters are problematic in several ways.

  1. They often lose the ground. Sometimes sadly you have little choice but to accept the additional risk from operating an appliance that should be grounded without a ground, because the available sockets don't provide one but other times you end up losing the ground even if both the appliance and the socket have a ground connection.
  2. They often try to generalise to multiple plug and socket types resulting in a loose fit, which can lead to arcing and numerous large holes, which can lead to mis-plugging.
  3. They are often poorly constructed in general. I have seen reports of adapters where the only thing connecting the pins to the sockets was them being pressed together by the adapter body! I have seen reports of adapters that apparently had grounds on both the plug and the socket side, but they weren't actually connected together.
  4. Any adapter adds weight and leverage which means more stress on the socket than there would be with a normal plug.

Stacking adapters, and/or stacking wall-warts on top of adapters can compound the issues, there are more (often-questionable) contacts to fail, more chance of losing the ground, and more mechanical stress on the flimsy, poorly fitting connections from the extra weight/leverage.

Having said that I would take a stack of two good-quality well-fitting adapters over a single low quality poorly fitting one any day. Indeed Swiss brand Skross actually sells some of their adapters in the form of a stack, to accomodate the "Schuko" side-contact earthing system.

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    Also, once you start stacking them, they can be connected in all sorts of fun ways. For example, you could plug the earth pin into the live connection, thus sending mains voltage directly to the casing of the device. Point is, keep these out of reach of kids, and don't plug them in in the dark. – user3757614 Oct 16 at 22:38
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Safe with care.

Main issues are

  • What others said - lack of ground MAY matter.
    Check on a case by case basis.

  • Unstable stack may expose contacts with shock risk.
    Easy to do accidentally.
    This will not be "too" common but definitely should be something you are aware of.

  • Substantial currents through poor contacts could create a fire risk.
    Unlikely with laptop level loads.

0

Such daisy chaining will work fine in practice for reasonable loads, but it's not recommended, because you worsen the short circuit protection. Be aware that the short circuit protection equipment is designed to trip at a rather high current (e.g. a typical 16 A fuse is allowed not to trip until you reach 30 A).

If you plug your notebook charger in a chain of adapters and that charger fails with an internal short circuit, the total resistance of the contacts of several adapters may be enough to keep the current limited. If the current stays below 30 A, the protection may never trip, and the total dissipated power of 230V*30A = 6.9kW will quickly set your adapters and the charger on fire.

Note that it doesn't matter how low the nominal load is in this case, the only thing that matters is the maximum power the mains outlet is able to deliver. Indeed, if the load is high enough, a stack of daisy chained adapters can overheat and catch fire at a nominal current without any fault in the load, but that's a separate issue which doesn't affect laptop chargers.

Also, most laptop chargers (MacBook included) are double-insulated and don't need protective earthing to be safe. But if you have non-insulated equipment you plan to plug into the adapter, like a toaster or a hair drier, don't use any adapters which would break the protective earthing connection. Any adapter with only two prongs is guaranteed to break it, with 3-pronged adapters you have to verify that all three contacts actually match. The protective earthing will allow the protection to trip the moment your equipment starts leaking current into the earth terminal, not the moment you touch it and it starts leaking current into you.

So, be careful, only use adapters which make good contact (if you hear noise while powered it's a bad sign) and don't leave the contraption unattended. Or better yet, buy a single adapter.

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