I'll start a new topic, although the subject ties in with the previous discussions concerning plugs and sockets.
There are about a dozen different plugs in use in the world, not counting different manufacturing tolerances in different countries. Even if a new standard plug is introduced, old sockets will remain in place and in use for at least half a century. People and goods are becoming increasingly mobile, although we shouldn't expect an explosion.
This means that the already extensive use of travel adapters will increase further. Unfortunately, travel adapters is the last field where rules for electrical safety are lacking. Either the authorities look the other way if it says travel adapter, or they ban them altogether, creating a "grey" market.
Both manufacturers and users of these adapters seem to accept the unsafe products sold today. These adapters also reinforce the image of poor electrical safety outside your own country.
If we accept that the traveller is not going to buy a suitcase of adapters, which features should a general purpose travel adapter have?
I can think of the following:
Protection from electric shock
The input side of the adapter should be designed to prevent the user from receiving dangerous electric shocks from live parts, such as the prongs. As it has to be compatible with existing sockets, the only options are sleeved pins and a design of the adapter that makes touching of live pins difficult.
The output side also needs to protect the user from electric shock, something which can be achieved by:
- User operated switch, switched on when the plug is inserted
OR
- Residual current device, cutting power in case of fault
OR
- Collar around the holes. This is incompatible with many plug types.
The adapter should also prevent the user from shock hazard arising from the bypassing of earth, which is a common feature of many adapters. This can be achieved by
- Having both input and output sides protective earth, but this rules out a general purpose design. (There are more earthed plugs than unearthed)
OR
- Preventing the insertion of earthed plugs on the output side. This limits the usefulness of the adapter.
OR
- Featuring a residual current device.
Protection from electric fire
On the input side, the risk of fire arises mainly from overloading of the socket and/or poor fit between current carrying pins and socket. With different manufacturing tolerances and socket ratings in different countries, the possible methods of protection are:
- Overcurrent protection from fuse or thermal breaker
OR
- Overheat protection, acting on overheating of the pins. (60-70°C)
The adapter in itself must be safe from fire, which can be achieved by:
- Sizing of current carrying parts to match highest likely current, 20A.
OR
- Fire resistant material
OR
- Overload or overheat protection and depending on the design, possibly also short-circuit protection.
The output side must prevent the attached plug, cord and appliance from short-circuit. This can be achived by fuse or electromagnetic breaker.
Futhermore, preventing the use of appliance on incorrect voltage or frequency reduces the risk of both fire and damage to equipment. As plug designs do not match voltages or frequency, the only ways of achieving this are:
- Indicating the voltage and/or frequency coming out of the socket, having the user determine the suitability for the appliance.
OR
- Having a setting on the adapter, which only allows current to flow when the voltage and frequency is within the permissible range.
[This message has been edited by C-H (edited 03-25-2003).]
