Two vs three pronged plugs

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RustyViewer

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#295669 13-Apr-2022 09:56

Not sure if this is the correct forum for this or not but this seemed like the closest fit at a glance.

What is the difference between two and three pronged plugs and how important is the distinction?

I am concerned that I may have inadvertently swapped a two with a three for a couple of devices. Will this harm them? Are they interchangeable? I have had a device from a normally reliable brand have a complete meltdown after also wrecking other devices it was attached to. It appears it was having power surges. After disconnecting the device, my power bill dropped $20 for the month. Could something like swapping a 2 with a 3 prong plug be enough to cause this?

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#2901776 13-Apr-2022 10:04

The third prong is the Earth pin.

If your device doesn't have an earth wire, it won't be doing anything.

If you have swapped a two pin plug for a three pin, it won't make any difference to the device, or your power usage.

RustyViewer

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#2901780 13-Apr-2022 10:09

If a device has an earth wire, but you only put in a two prong plug, could that cause problems?

billgates

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#2901781 13-Apr-2022 10:12

RustyViewer:

If a device has an earth wire, but you only put in a two prong plug, could that cause problems?

Yes. Buy a 3 prong plug if the device has an earth wire.

Do whatever you want to do man.

richms

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#2901783 13-Apr-2022 10:15

RustyViewer:

If a device has an earth wire, but you only put in a two prong plug, could that cause problems?

You cant buy 2 pin plugs for that exact reason. It would leave the item un earthed which would be 1. unsafe and 2. possibly cause excess leakage to the chassis making you get a tingle from it. That is why apple secretly added the earth on their chargers thru the stud that holds their cable to the charger on some models. People complained about tingles but they didn't want to have to admit it was a problem.

Richard rich.ms

decibel

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#2901862 13-Apr-2022 12:08

RustyViewer:

If a device has an earth wire, but you only put in a two prong plug, could that cause problems?

Whatever you do, DON'T wire up any plugs yourself.

shk292

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#2901999 13-Apr-2022 15:16

Slightly OT, but in the UK up to 1992, no appliance that you bought from a shop was fitted with a plug. You had to buy a plug separately, then fit it yourself along with the correct fuse (UK plugs have a separate, changeable fuse). I think plugs were supplied with a 13A fuse, so if you were lazy, you just left that one in.

I can't remember why this was done - maybe because there had previously been different types of plug in use - but it makes me wonder what proportion of home-fitted plugs were safe and how many accidents were caused. Fitting a plug has never been a challenged to me but I'd agree that if you don't understand what the third wire is for, maybe get an expert in to do it for you

lxsw20

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#2902008 13-Apr-2022 15:27

If the device has a picture of a square in a square on it then it doesn't need an earth as it's double insulated. But yeah if a device has an earth wire it should 100% be connected, for safety reasons.

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Senecio

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#2902010 13-Apr-2022 15:33

I grew up in Australia where it was illegal to change plugs yourself. I moved to Ireland in my mid 30s and found out that changing a plug is just one of those things that a young boy learns from his father.

What I saw over there would make you shudder! A friend of mine bought 4 sets of Christmas lights one year. He only had one power point where he wanted to install them and was too tight to buy a power board. He simply cut the plugs off them, twisted the wires together and wired all 4 sets of lights into one plug! he just shrugged it off, Its what his Dad would have done.

mkissin

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#2902017 13-Apr-2022 16:03

shk292:

Slightly OT, but in the UK up to 1992, no appliance that you bought from a shop was fitted with a plug. You had to buy a plug separately, then fit it yourself along with the correct fuse (UK plugs have a separate, changeable fuse). I think plugs were supplied with a 13A fuse, so if you were lazy, you just left that one in.

I can't remember why this was done - maybe because there had previously been different types of plug in use - but it makes me wonder what proportion of home-fitted plugs were safe and how many accidents were caused. Fitting a plug has never been a challenged to me but I'd agree that if you don't understand what the third wire is for, maybe get an expert in to do it for you

Here in NZ there's a slightly unfortunate hole in the safety provided by our fusing.

You have the MCB breakers to protect the in-wall wiring, and an appliance will generally contain a fuse to protect the cable from a fault within the appliance. But if the cable itself develops a fault, there's no protection. A fuse within the plug would stop this and you would have no unprotected parts, assuming an appropriate fuse was selected.

johno1234

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#2902038 13-Apr-2022 16:36

RustyViewer:

If a device has an earth wire, but you only put in a two prong plug, could that cause problems?

Potentially lethal. The earth wire is connected to the touchable metal exterior of the appliance, so that any short circuit is diverted to earth through the third pin.

Double insulated appliances don't need the third pin as they are designed to ensure that the exterior is insulated from any possible internal fault.

rogercruse

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#2902045 13-Apr-2022 16:58

shk292:

Slightly OT, but in the UK up to 1992, no appliance that you bought from a shop was fitted with a plug. You had to buy a plug separately, then fit it yourself along with the correct fuse (UK plugs have a separate, changeable fuse). I think plugs were supplied with a 13A fuse, so if you were lazy, you just left that one in.

I can't remember why this was done - maybe because there had previously been different types of plug in use - but it makes me wonder what proportion of home-fitted plugs were safe and how many accidents were caused. Fitting a plug has never been a challenged to me but I'd agree that if you don't understand what the third wire is for, maybe get an expert in to do it for you

I worked for a major electrical retailer at the time (in the IT dept and had the job of find their sales history), the margin for plugs was often much greater than the plug-less item. And the profit in selling a TV was buried in the sale of the plug. Later when the retailer I worked for brought the major competition their policy was to give the plugs away. And they had a 6 million pound hole in their accounts!

When we asked why the sale wasn't being recorded as a sale the answer was always "that what the business wanted" and not that it was fundamentally wrong as every customer exchange should be treated as a sale with a calculated profit or loss margin .

We picked their system apart, rebuild the sales history, extracted any good bits and finally got rid of most of their IT people inside two years!... happy days!

mclean

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#2902076 13-Apr-2022 18:34

mkissin: Here in NZ there's a slightly unfortunate hole in the safety provided by our fusing.

You have the MCB breakers to protect the in-wall wiring, and an appliance will generally contain a fuse to protect the cable from a fault within the appliance. But if the cable itself develops a fault, there's no protection. A fuse within the plug would stop this and you would have no unprotected parts, assuming an appropriate fuse was selected.

I don't think it's completely unprotected - the upstream MCB probably still provides short circuit protection for most flexible appliance leads, and that's the nature of most cable faults. And as long as the flexible is correctly matched to the appliance (which it should be) then the flexible shouldn't overload (cheap multi-boxes aside).

Apart from being safer, the nice thing about the UK/Singapore plugs/sockets is that when an appliance fault happens it doesn't take out the whole circuit.

mkissin

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#2902096 13-Apr-2022 19:10

mclean:
I don't think it's completely unprotected - the upstream MCB probably still provides short circuit protection for most flexible appliance leads, and that's the nature of most cable faults. And as long as the flexible is correctly matched to the appliance (which it should be) then the flexible shouldn't overload (cheap multi-boxes aside).

Apart from being safer, the nice thing about the UK/Singapore plugs/sockets is that when an appliance fault happens it doesn't take out the whole circuit.

In general, I agree, but there’s lots of corner cases. What about the tiny cord for my alarm clock? It’s probably 1mm2, and being protected by the upstream 20a MCB? It’s very possible for the cord to become damaged and by the time the MCB trips it could be very hot.

It’s obviously not a huge problem, but one that is protected against by shifting the fuse into the plug rather than the alarm clock.

Bung

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#2902140 13-Apr-2022 20:36

The UK could be the only country that requires a fuse in the cord plug. Apparently this could follow on from their ring mains that have comparatively high fuse values.

roobarb

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#2902168 13-Apr-2022 22:29

decibel:

Whatever you do, DON'T wire up any plugs yourself.

It used to be very common for mains powered consumer devices to be sold without a plug and you had to attach it yourself.

https://www.worksafe.govt.nz/managing-health-and-safety/consumers/safe-living-with-electricity/getting-electrical-work-done/doing-your-own-electrical-work/

Before you do any work, make sure that:

you have the necessary knowledge and skills
the power is turned off
you are not working where conductors or terminals are live or could become live.

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