Sparkies: Why did this 2-into-1 and socket burn?

Forums › Home Workshop DIY › Sparkies: Why did this 2-into-1 and socket burn?

kiwigander

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#147331 16-Jun-2014 14:47

A puzzle for the sparkies and electrical engineers here.

A powerpoint in our kitchen had a 2-into-1 adapter plugged into it. When my wife tried to plug her stick mixer into the right hand socket of the 2-into-1 she couldn't insert the plug. Taking the 2-into-1 out we found the damage you see in the pictures.

Interesting, the burnt blade on the 2-into-1 and the burnt receiver on the powerpoint are those of the neutral conductor. I've probed a bit and confirmed that phase and neutral are not reversed in the powerpoint.

Background: The powerpoint was installed a few years ago by the electrical firm who originally wired the house and who've done other work for us. The 2-into-1 had a stand mixer (325 w) plugged into its left hand receptacle; its right hand receptacle was generally empty and occasionally accommodated the stick mixer (100 w or thereabouts). The right hand receptacle of the powerpoint accommodated the microwave.

I am assuming that the 2-into-1 failed somehow, overheated and burnt the half-sleeve off its neutral blade and conducted the heat into the powerpoint, thus burning the neutral receiver on that side. But am I likely correct and is this a common occurrence with these 2-into-1's (when they've never been overloaded)? And why should it be the neutral blade that failed?

(I am going to replace the powerpoint as who knows whether it's safe now. As far as I know all the home powerpoints are PDL.)

Any comments are welcome.

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#1066707 16-Jun-2014 15:11

Cheap crappy double-plug manufacture... saving a dollar has cost you a hundred, though of course you were not necessarily to know until too late.

The burn pattern to me suggests the heat was coming from the double adapter. Perhaps crack it open to have a look inside. Power goes in one pin and out the other, with the earth used in the event of a problem. Either pin can heat up with a bad (high resistance) connection.

A motor has significant startup current. The blender would draw more than 325w for a brief period of time as the motor starts and a poor connection will arc.

This is one reason the NZ electrical regulations are being tightened up as there is too much Chinese electrical rubbish coming into the country. All electrical items will have to ship with some sort of certification that they meet a standard (I can't remember what the paperwork is called.) Partly driven by the insurance companies who will wiggle out of paying where they can these days, but partly because some of the electrical equipment coming into the country is legitimately dangerous because of poor design / build quality.

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solival

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#1066780 16-Jun-2014 16:22

Bad electrical contact on burnt pin. May be pin is shorter/thinner than needed, or socket contacts deformed due age/extensive use.

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graemeh

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#1066786 16-Jun-2014 16:30

Consider this an opportunity :)

Now you can get the dual socket replaced with a 4 way socket.

kiwigander

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#1066787 16-Jun-2014 16:31

Thanks for the quick replies (and apology for duplicating this posting if it's indeed duplicated - I seem to have been kicked off the forum while composing this follow-up message)

I didn't fancy my chances at doing a post-mortem on the 2-into-1 as it was held together by two one-way security screws. Just took a bit of firm pressure with the screwdriver, though.

Each blade receiver in the left hand socket is connected by a wee jumper to the corresponding blade receiver in the right hand socket. Phase and neutral are red, earth is blue. Outer diameter of those jumpers (including insulation) is about 2 mm, so I assume the conductors are 1.0 mm^2. Is that OK because it's over such a short distance? I'd have thought those conductors should be at least 1.5 mm^2 as the 2-into-1 claims to be rated at 10 A.

With my faithful old DSE multimeter I check resistance of each conductor from left-hand receiver to right hand blade. Results:

Phase-phase: 0.2 ohms
Earth-earth: 0.2 ohms
Neutral-neutral: all over the place, like from 0.2 up to hundreds of ohms, and a bit of vibration opens the circuit completely. Of course this is after it's been damaged by heat.

The neutral jumper has been routed below the right hand earth receiver. Where the jumper hooks around the square plastic profile that houses the earth receiver, insulation has been lost (some has been deposited on the housing of the 2-into-1). I assume that's secondary to overheating.

I can post more pictures if anyone reckons it's worthwhile.

But in response to your comment about saving a buck on the adapter, losing a hundred on the powerpoint: I'd much rather pay the extra buck or two for a quality adapter, but how do you tell nowadays? I just put a new powerpoint into the workshop - HPM. Decent Aussie brand. Made in the PRC. Should I be worried? (I wasn't trying to save money but the only PDL stockist I knew of in the area refused to deal with a non-sparkie.)

Some years back some of my staff were getting fed up with the wonky old toaster in the tea room so I sent one of them out for a new toaster. I told her I didn't care what it cost - just get something not made in the PRC.

She came back empty handed an hour later.

Dynamic

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#1066789 16-Jun-2014 16:32

We paid for 4 socket outlets in my office, but they are significantly more expensive than 2 dual sockets.

You could certainly had a second dual socket added or the quad-socket outlet. Great idea.

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Dynamic

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#1066794 16-Jun-2014 16:40

kiwigander: But in response to your comment about saving a buck on the adapter, losing a hundred on the powerpoint: I'd much rather pay the extra buck or two for a quality adapter, but how do you tell nowadays? I just put a new powerpoint into the workshop - HPM. Decent Aussie brand. Made in the PRC. Should I be worried? (I wasn't trying to save money but the only PDL stockist I knew of in the area refused to deal with a non-sparkie.)

Some years back some of my staff were getting fed up with the wonky old toaster in the tea room so I sent one of them out for a new toaster. I told her I didn't care what it cost - just get something not made in the PRC. She came back empty handed an hour later.

It can certainly be near impossible for a layman to know what has been manufactured in China to decent specifications, and what has been manufactured too cheaply. I rely on the brand name in many cases and have some faith that a name brand has significant quality control processes.

I can absolutely believe the toaster story - even if you had given her a whole day!

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skewt

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#1066802 16-Jun-2014 16:50

Dynamic:

This is one reason the NZ electrical regulations are being tightened up as there is too much Chinese electrical rubbish coming into the country. All electrical items will have to ship with some sort of certification that they meet a standard (I can't remember what the paperwork is called.) Partly driven by the insurance companies who will wiggle out of paying where they can these days, but partly because some of the electrical equipment coming into the country is legitimately dangerous because of poor design / build quality.

Last time I did my refresher, the inspector told me the law changes have already happened where If you are electrically qualified and use a non-certified appliance (no certificate) then you lose insurance as you should know better

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#1066829 16-Jun-2014 17:22

because it's the kitchen, does that circuit for the plugs need to be on an RCD at the board?

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#1066830 16-Jun-2014 17:25

Most all of the PDL range is made in China now, including the PDL 600 series outlet shown in the OP's post. This isn't necessarily a bad thing as PDL's quality control is very good.

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andrewNZ

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#1066835 16-Jun-2014 17:34

Goosey: because it's the kitchen, does that circuit for the plugs need to be on an RCD at the board

If you modify it, yes, if you repair something and replace like for like, no.

kiwigander

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#1066838 16-Jun-2014 17:40

1. We wanted a 4-socket powerpoint, as we have elsewhere in the kitchen and around the house, but when the installation took place it was not possible. I can't recall why - may have been that the sparkie didn't have one in his van. Not a trivial problem when travel time was 2 1/4 hours each way. To change it now would involve cutting ceramic tile - can be done but we'd rather not. There is actually a quad powerpoint nearby, just out of reach of the microwave's lead. A short extension lead clipped tidily in place should suffice.

2. All the circuits are protected by MCBs that in turn are protected by RCDs at the switchboard. I understand that's the new regulation - all circuits must be protected by RCDs.

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#1066856 16-Jun-2014 17:50

Goosey: because it's the kitchen, does that circuit for the plugs need to be on an RCD at the board?

Depends on the age of the house. An RCD wouldn't have changed anything as it is designed to trip if there is any difference in the current in phase and neutral indicating another circuit (possibly you) has been found.

High resistance contacts can overheat without blowing circuit breakers. I understand that some electricians use thermal imaging to check for hotspots.

richms

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#1066876 16-Jun-2014 18:18

kiwigander: 1. We wanted a 4-socket powerpoint, as we have elsewhere in the kitchen and around the house, but when the installation took place it was not possible. I can't recall why - may have been that the sparkie didn't have one in his van. Not a trivial problem when travel time was 2 1/4 hours each way. To change it now would involve cutting ceramic tile - can be done but we'd rather not. There is actually a quad powerpoint nearby, just out of reach of the microwave's lead. A short extension lead clipped tidily in place should suffice.

Shouldnt have to cut tile as the quad outlets just go over a single flushbox.

Chances are the adapter wasnt making good contact with whatever was plugged into it, or else its one of the crap designs that passes current thru rivets rather than a single stampped piece. the need to have the insulation on the pins has made the riviting much more common as its the easiest way to get the insulating piece on the pin and then attach it to something else. Large stresses on those joins as people oafishly plug in things at angles etc which makes it worse, and the fact that people will plug large loads like kettles and toasters into them and run both and nothing happens because they lack any overcurrent protection.

Richard rich.ms

kiwigander

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#1066943 16-Jun-2014 19:13

richms: Shouldnt have to cut tile as the quad outlets just go over a single flushbox.

Chances are the adapter wasnt making good contact with whatever was plugged into it, or else its one of the crap designs that passes current thru rivets rather than a single stampped piece.

1. I'll check that out - would save us future annoyance.

2. The 2-into-1 blades were indeed riveted.

Just for fun I disassembled another 2-into-1 I had lying around, an old black unit called "IMPACT" by D.R. Britton Ltd. It's a vertical 2-into-1 so it may have been easier to engineer, but each pair of blade receivers and its connection (P-P, N-N and E-E) is a pair of brass bars. No jumpers, no rivets that I can see.

DarthKermit

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#1066953 16-Jun-2014 19:23

richms: Shouldnt have to cut tile as the quad outlets just go over a single flushbox.

If we're talking about the PDL 644 quad horizontal outlet, then yes that's true. However, these come with four extra (optional) mounting screw holes as the two outer sockets are quite far from the two screws that go into the flush box.

The OP might want to drill holes to mount a quad outlet in a more sturdy manner.

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