Thread: The Damage Arcing can do to a Plug and Socket

Dean thanks for posting that.
If it's OK with you I'd like to post that in our Mens Shed newsletter to remind our members to lock in their 3Phase power cords.

Hmmm. Guess what I will be doing from now on.

Phil

Originally Posted by Steamwhisperer

Hmmm. Guess what I will be doing from now on.

Phil

I second that

Originally Posted by BobL

Dean thanks for posting that.If it's OK with you I'd like to post that in our Mens Shed newsletter to remind our members to lock in their 3Phase power cords.

By all means Bob. My intention was to point out the possible risks. Our Cellar Manager has another one in his office from a few years ago, but it is minor in comparison. Both are 32A plugs. This one ran a smallish motor turning a rotary screen and a pump connected to a level switch. The pump operates intermittently, but can be on a fair percentage of the time. Maybe this has something to do with the result? Phil. Good idea. I suppose most members who use 3ph sockets/plugs are aware how much they cost to replace? If not you might get a surprise. My lathe VFD is fitted with the 240v version although only 10A. Tonight was supposed to be my last 12hr shift for the year, but alas I have to do another week of nights yet. We were also told recently that the company is cutting the amount of grapes to our site for the future to about a third. There is a chance of losing my job.Dean

Yep, the proper 3ph plugs and sockets are damn expensive! I never bothered with them because of that. A junction box, connectors and a quality switch will run under $80. You can get it under $40 if you go the cheaper switches.. I can't say I have had any problems with them but they are not cycled every day.

Having said that, I'm not up to scratch with the rules and regs for industrial sites...they change pretty regularly and are very strict.

Gosh, that's quite impressive to say the least!
I'm guilty of being lax at times at work, that's definitely going to change now!
I trust you'll be happy for me to pass this on to our safety guy so he can use it as a safety educational tool

Originally Posted by LordBug

Gosh, that's quite impressive to say the least!I'm guilty of being lax at times at work, that's definitely going to change now!I trust you'll be happy for me to pass this on to our safety guy so he can use it as a safety educational tool

Yes. Go for. Surprising that work sites have not already got this covered. I presume Phil was referring to work. We have 2 resident sparkies tho and most of our equipment is on wheels or designed to be moved by forklift and also most areas out in the weather. We don't stop because it is raining and neither does the equipment. Anyone who wants to use tthis information just go for it. Nice to know I can be of assistance and who knows, maybe save an expensive repair. Dean

You see the same sort of damage in plugs that are correctly locked, but haven't been terminated properly, one thing we always do when commissioning a new switchboard is to go around every terminal with an infrared thermometer after running at full load for a while... surprising how many terminals need to be re-torqued after being bounced around in transport.

Not uncommon to get another half turn on terminals after transport.

Ray

Originally Posted by RayG

You see the same sort of damage in plugs that are correctly locked, but haven't been terminated properly, one thing we always do when commissioning a new switchboard is to go around every terminal with an infrared thermometer after running at full load for a while... surprising how many terminals need to be re-torqued after being bounced around in transport.Not uncommon to get another half turn on terminals after transport.Ray

Another thing to look out for, providing you are in a position to do so that is. The sparkies at Work Jamie check everything before putting things into service and most plugs have been replaced by them because someone drove off with a fork without disconnecting etc etc. Never done anything like that myself tho Dean

Originally Posted by Oldneweng

I thought some might be interested in seeing this picture.

20150416_060407-2.jpg

Caused by not having the plug locked into the socket properly (or at all), although the operator(s) said it was. The machine it was connected to was undamaged. At least one of the guys does not do up the plug locking ring at all. Been caught a couple of times when taking over a job from him and having to call the sparky for another matter.

Dean

Dean, I personally find it hard to believe this sort of damage can be caused simply by not having the locking ring tightened. If this was the case, then this type of plug would indeed be a very bad, flawed design. Particularly if one takes into account the extremely high price asked for these exclusive Australian Standard plugs and sockets. But as far as I recall, the contact pins engage for quite some length even before the threaded locking ring is done up - far enough to safely carry the nominal current even before the ring is done up.

I much more believe that the reason for this damage is poor installation. I have seen many (AU licensed) electricians not using ferrules on the wires. But instead just lightly twisting the wire strands, then inserting and half-heartedly doing up the fixing screws. Also, I have seen many (licensed) electricians not paying due attention to properly strain reliefing the cable with the cable clamp and gland on the plug.

Or there could have been some water ingress into the socket, suggesting the wrong IP rating plug/socket was used.

Originally Posted by cba_melbourne

Dean, I personally find it hard to believe this sort of damage can be caused simply by not having the locking ring tightened. If this was the case, then this type of plug would indeed be a very bad, flawed design. Particularly if one takes into account the extremely high price asked for these exclusive Australian Standard plugs and sockets. But as far as I recall, the contact pins engage for quite some length even before the threaded locking ring is done up - far enough to safely carry the nominal current even before the ring is done up.

I much more believe that the reason for this damage is poor installation. I have seen many (AU licensed) electricians not using ferrules on the wires. But instead just lightly twisting the wire strands, then inserting and half-heartedly doing up the fixing screws. Also, I have seen many (licensed) electricians not paying due attention to properly strain reliefing the cable with the cable clamp and gland on the plug.

Or there could have been some water ingress into the socket, suggesting the wrong IP rating plug/socket was used.

Who knows how well the plug was inserted? The equipment was being moved regularly. 32A plugs are quite hard to push into the socket. Using the locking ring would of course alleviate this risk which goes back to the original point. Use of the locking ring is a subject that is often pointed out to us as a reminder. It has been mentioned that these plugs can extract themselves due to arcing.

Ferrules are not used, but we are talking about some very serious cable here. I know from watching them that the sparkies do up the fixing screws very very tight. This is not an issue, believe me. Same with cable clamps and glands. I am just stating what I have observed. Our maintenance department also do up plumbing fittings to the point of stupidity, in my opinion lol.

Water? Possible. I don't know the location of the socket when this occurred. I know it was outside. There are 4 locations it could have been located. I don't know which one. It may have had some shelter above or maybe not. Shelter above would just be structural stuff that just happened to be in the right spot. I don't think water caused it tho because we have not had any serious rain. Only a bit of light drizzle. Anyway the proper use of the locking ring would have prevented water ingress. If water was the culprit, this would have happened many times in the past, believe me. I know what some people are like at ignoring the proper precautions at work. We have many machines and pumps that get used outside in the rain regardless of how heavy it gets. This particular type of machine generally spends its entire life outside.

Looking at the picture shows that the damage is restricted to the outside of the plug so internal connections are not involved.

I am not claiming I know exactly what caused this as even the experts would not have been able to say for sure what was the cause due to the extensive damage. The locking ring appears to be relatively intact, tho it used to be orange. What I can say is that all the evidence points towards the fact that it was caused by something that should have been prevented if the ring was tight.

One other thing I will point out is that this exact plug type is very difficult to first push in and even harder to do the ring up tight. There is no room for anything but fingertips except for a small space visible in the picture. Look at the bottom edge of the socket as it appears in the pic. This is also no help at all. I usually start the ring, rock the plug up/down which pulls it in a bit, rinse and repeat until the plug feels firm.

I understand what you are thinking Cba, but although our electricians may be deficient in "other areas", when it comes to their work they cannot be faulted. I have never heard of issues from their work and believe me it would have been spread around. Factions! lol The manager of the maint department is an electrician as well. Regarding the "other areas", the number 1 sparky came out to my house to install a new breaker box when I converted to modern gear. He spent about 2hrs mucking about then told me he thought the RCD I had supplied (from Clipsal S.A.) was faulty. Then he read the instructions. lol That had me beat because they are the same ones used at work. He does like to drink a bit. Ok a lot. Maybe that was the problem then.

Dean

Regarding the use or not of ferrules, this is my personal opinion:

- I do not know of any industrial quality installation not using ferrules. As far as I am aware, only residential installations are done without.
- Ferrules prevent the copper from flowing under the clamping pressure, thus preventing the connection getting loose over time.
- Ferrules prevent single strands of the wire being broken by the screw tips.
- Ferrules also prevent the wire strands to flex directly where they are clamped, preventing fatigue wire breaks.
- Many switch gear is designed to be used with or without ferrules. The wires are not directly clamped by the tip of the fastening screw. There is a clamping plate or strip between the screw tip and the wire. But in the case of the connector on your picture, I lnow that this is not the case. Each contact has two small brass screws that contact directly the wire. And this is why I always use ferrules with these connectors. If I am at a customer site insisting that the house electrician hooks my machine's power lead up to such a connector, I take it apart again after he leaves and redo the job with proper ferrules.
- if it is a solid wire, no need to use ferrules. But if it is stranded wire, as it clearly is on your picture, ferrules should be used.

By the way, the reason I insist on these expensive captive type connectors being used, is that before working on the machine I like to unplug the power cord personally and leave it on the floor where I can see it. I will not trust wall mounted switches, as some electrician may have wired them improperly. Nor will I trust a contactor in a distant fuse box being turned off, as some idiot may tun it on again anytime without me noticing.

Originally Posted by cba_melbourne

Regarding the use or not of ferrules, this is my personal opinion:

- I do not know of any industrial quality installation not using ferrules. As far as I am aware, only residential installations are done without.
- Ferrules prevent the copper from flowing under the clamping pressure, thus preventing the connection getting loose over time.
- Ferrules prevent single strands of the wire being broken by the screw tips.
- Ferrules also prevent the wire strands to flex directly where they are clamped, preventing fatigue wire breaks.
- Many switch gear is designed to be used with or without ferrules. The wires are not directly clamped by the tip of the fastening screw. There is a clamping plate or strip between the screw tip and the wire. But in the case of the connector on your picture, I lnow that this is not the case. Each contact has two small brass screws that contact directly the wire. And this is why I always use ferrules with these connectors. If I am at a customer site insisting that the house electrician hooks my machine's power lead up to such a connector, I take it apart again after he leaves and redo the job with proper ferrules.
- if it is a solid wire, no need to use ferrules. But if it is stranded wire, as it clearly is on your picture, ferrules should be used.

By the way, the reason I insist on these expensive captive type connectors being used, is that before working on the machine I like to unplug the power cord personally and leave it on the floor where I can see it. I will not trust wall mounted switches, as some electrician may have wired them improperly. Nor will I trust a contactor in a distant fuse box being turned off, as some idiot may tun it on again anytime without me noticing.

I don't disagree with you with regards to the use of ferrules. I now use Bootlace Ferrules on all connections since being advised to do so on the forum.

It is indeed obvious that ferrules are not being used as seen in the picture.

Regarding the use of connectors so you can see that it is disconnected, I am with you on this one. These connectors also have holes to fit a padlock so that they can be locked in the off position. The sparky etc keeps the key in their pocket. This hole (2 actually) cannot be seen because the switch is not in the picture. I guess it wasn't damaged. I am not aiming this at you Chris. I know this is old hat to you.

These lockouts are used extensively in industry as everything has to be securely deactivated before performing any operation that could put the operator in harms way. This includes even casual workers as they often do cleaning operations in/around equipment/tanks. You don't think permanents would do that sort of work do you? Thats what casuals are employed for! Lock it out, Tag it so other people know who set the lock, test the equipment to make sure it does not work anymore and put the key in your pocket. If multiple workers then each has their own lock and key. Lock, Tag, Try. We have found isolation switches that have been in place for years that don't isolate. The reason for the try! To remove a lock that has been left on by someone who has left work it is necessary to have a manager look at the situation and determine whether it ok to remove it. The plan is to use backup keys stored in a secure location. I have only ever seen the boltcutters come out tho.

I could suggest that the sparkies use ferrules in future but for some reason I don't think this would work.

Dean

With or without lockrings, I find the biggest contributor to poor contact is the fact that most 3 phase plugs in good condition have a very firm friction fit between pins and receptacles. This requires the average worker to take a firm two handed grip on the plug and wiggle it from side to side to remove it. In the process the pins, having a split down their length to spread them ensuring contact, are compressed till they lose effective contact on one or more. Then, perhaps under heavy starting current an arc will occur and some carbon will track across between phases resulting in a fairly spectacular meltdown.
As I have a few portable devices that are regularly plugged and unplugged, I find my best defence is to occasionally slightly spread the pin tips with a small blade or similar, and then apply a shot of Switch Cleaner/Lubricant, (not a dewatering fluid or other snake oil), to plug and socket and allow a little drying time. Choose a product that claims on the label to "Improve Electrical Properties". Have kept some quite old electrical gear going for years with some physical cleaning and some spraycan therapy. And my plugs slip in and out without having to wrestle them. It's a bit of simple maintenance that seems to work for me.
Combustor.