Behavior of Joule Heating in few contact points terminals and arcing

[tersh]

The leading cause of fire in the Philippines is faulty electrical wiring. We have 2000 fires each year in the capital alone. For example our substandard outlets made for at most 15A were protected by 30A breakers so the breaker can't protect the wires.

https://www.gmanetwork.com/news/new...trical-wiring-cause-most-ncr-fires-bfp/story/


Also it came to my attention that many contractors and electricians use inferior unlisted lugs where there are only few contacts points between the surface of it and the bus bar (that is, either the locally made bus bar or lugs were not flat). For example they drill additional hole and didn't sandpaper the bottom resulting in inducted few contact points. My electrician has bought 5 pcs of such himself. So let me take the opportunity to thoroughly understand its behavior. Supposed the bus bar and lugs have few contact points only like the following:

​

Consider the red bits as only 0.5 millimeter contact points between bus bar and chair lugs where there are only very few (say 0.8% compared to the surface area). At a small amperage, the few contact points would heat up. Let's say it crosses certain ampere and heating threshold where the contact points are on the merge of melting. Would it just melt? If it does, would the bus bar and chair lugs reposition themselves so there is more even contacts? (assuming the chair lugs goes down by gravity). Or would arc form between the gap and destroying other parts of the surface?

I couldn't find details of this in google and I've wanted to understand the details lately. So what happens in joule heating and melting (and arcing?) in microscopic contact points between bus bar and chair lugs when the surfaces are not evenly in contact? What's the exact step by step progression when they get destroyed (or is there readjustment to equilibrium where there is eventually more contacts as they melt into each other surface)?

This also applied to few contact points between wires in terminals or other loose connection scenario.
​

 

[romex jockey]

Bad connections , often with some sort of evident 'joule effect' are the lions share of my service calls Tersh

I'll even wager they're they constitute the lions share of electrical fires

Mostly it's some termination , which the NEC has had a lot of focus on in recent cycles

Which of course begs specifics , are the 'terminals' rated & listed for their use correctly? Did the electrician properly install them?

Coincidentallly , we've a new ahj who took it upon himself to quiz his contingent on his rounds , as to if we should properly 'prep' any given terminal surface

which ended up with >>>

250.12 Clean Surfaces. Nonconductive coatings (such as
paint, lacquer, and enamel) on equipment to be grounded
shall be removed from threads and other contact surfaces to
ensure good electrical continuity or be connected by means of
fittings designed so as to make such removal unnecessary.

hopefully others will chime in...


~RJ~

 

[hbiss]

My electrician has bought 5 pcs of such himself.

Pictures? I think your biggest problem is that your so called "electricians" wouldn't know how to screw in a light bulb. An apprentice here would know that a bent or burred improperly finished lug is defective and shouldn't be used. We don't need 10 pages of trivia about the possible heating effects of a conductor or lug that doesn't make proper contact.

-Hal

 

[mbrooke]

Pictures? I think your biggest problem is that your so called "electricians" wouldn't know how to screw in a light bulb. An apprentice here would know that a bent or burred improperly finished lug is defective and shouldn't be used. We don't need 10 pages of trivia about the possible heating effects of a conductor or lug that doesn't make proper contact.

-Hal

Be nice, education is the solution to screwing in a light bulb correctly

 

[tersh]

Pictures? I think your biggest problem is that your so called "electricians" wouldn't know how to screw in a light bulb. An apprentice here would know that a bent or burred improperly finished lug is defective and shouldn't be used. We don't need 10 pages of trivia about the possible heating effects of a conductor or lug that doesn't make proper contact.

-Hal

This is a sample.

A major electrical distributor sold him 5 pcs of these which has extra drilled holes. When I looked at the bottom. It's not polished (imagine drill ends with protruding sides). He has installed this in my commercial building last year. Only a few contact points exist so I wonder what is the step by step progression to breakdown. Like whether arcing can occur between the close but nontouched surfaces. I already let him sandpaper the bottom of the above but I have another one installed that is not polished. I'll share a picture of the bottom when he can replace it first this weekend.

However, even when the bottom is sandpaper. It is not yet flat, and there is few contact points too. Notice the lugs has no marking of any kind. Not even the wire sizes. It is made in china poor quality and they can't even engrave specs to it.

How does one compute how close the spacing between two metals when arcing can occur and the current that can initiate it?

Anyone has idea so I can share the physics of it to the electrician and local engineers who are just ignoring it?

 

[tersh]

Bad connections , often with some sort of evident 'joule effect' are the lions share of my service calls Tersh

I'll even wager they're they constitute the lions share of electrical fires

How does it contribute to fires? It's the arcing the contributes to fire? But I'd like to understand the behavior of the few contact points. Do they melt first before arc forms or do arc forms before they the few contact points melt?

Mostly it's some termination , which the NEC has had a lot of focus on in recent cycles

Which of course begs specifics , are the 'terminals' rated & listed for their use correctly? Did the electrician properly install them?

Coincidentallly , we've a new ahj who took it upon himself to quiz his contingent on his rounds , as to if we should properly 'prep' any given terminal surface

which ended up with >>>



hopefully others will chime in...


~RJ~

 

[hbiss]

This is a sample.

I don't see a problem with it though I would call it Chinese crap. What difference does it make if the bolt hole is oval? Is that what you are talking about?? The washer and bolt will tighten down just fine.

You have an overactive imagination!

-Hal

 

[tersh]

I don't see a problem with it though I would call it Chinese crap. What difference does it make if the bolt hole is oval? Is that what you are talking about?? The washer and bolt will tighten down just fine.

You have an overactive imagination!

-Hal

No. I wasn't concerned about the shape of it, but the bottom of it has drilling sides not cleaned. Imagine when you drill through a metal, the bottom would have uneven surfaces (I wonder what is the exact term for this). They didn't even sandpaper it. And they distributed it to hundreds of customers.

 

[hbiss]

No. I wasn't concerned about the shape of it, but the bottom of it has drilling sides not cleaned. Imagine when you drill through a metal, the bottom would have uneven surfaces (I wonder what is the exact term for this). They didn't even sandpaper it. And they distributed it to hundreds of customers.

Yeah, it wasn't deburred. So it's a substandard product just like thousands of other items sent to us from there- from car parts to sneakers. Surprise, surprise. I'm not going to analyze what can happen and why when the soles separate from cheap Chinese boots because I really don't care and I know the manufacturers don't either. They are just looking to sell cheap products to unsuspecting buyers. This goes back to what I said earlier, if your "electricians" had any knowledge they would have noticed something like that right away and not used them. So don't blame the manufacturer or distributor if they "distributed it to hundreds of customers" because those customers should be professionals and know what they are using, or at least be able to evaluate the suitability for the intended use.

-Hal

 

[ptonsparky]

The mfg was probably using some of the same materials they used in Sheetrock prior to making lugs.

I have to agree with Hal. You have junk being installed by totally untrained people into a substandard electrical system. You’re lucky it’s only 2000 fires.

 

[romex jockey]

This is a sample.

How does one compute how close the spacing between two metals when arcing can occur and the current that can initiate it?

Anyone has idea so I can share the physics of it to the electrician and local engineers who are just ignoring it?

Good Q, i wish i knew the answer.

What i do know is almost every termination has tourqe specifications , an issue the NEC has also focused on , along with one ahj i have actually asking to see our tollage pursuant to this

It's assumed that somewhere, be it in some NRTL and/or manufacturers laboratories ,an engineer has calculated the ohmic value juxtaposed to specified tourqe

How does it contribute to fires? It's the arcing the contributes to fire? But I'd like to understand the behavior of the few contact points. Do they melt first before arc forms or do arc forms before they the few contact points melt?

Another good Q, it's usually considered that any given contact point will endure expansion and contraction. Of course we all know that different metals ,etc , will have different rates , which is why the NEC also addresses 'dissimilar metals' where applicable.

With that said, the usual degrade is first seen as a 'hot spot' , note this has evolved to be a 'niche industry' w/in the electrical trade assessing existing equipment as a maintenance routine.

Here's one study>

https://youtu.be/_2HyTRxzwXs


~RJ~

 

[tersh]

Good Q, i wish i knew the answer.

What i do know is almost every termination has tourqe specifications , an issue the NEC has also focused on , along with one ahj i have actually asking to see our tollage pursuant to this

Do you actually use torgue wrench to tighten screws in breakers or panels? Here we never use it. 0% use it. They just tighten it manually. We never even have any torgue wrench for sale anywhere in the country. If I get one for the electrician and contractors to use. I'd be the first one to do so.

It's assumed that somewhere, be it in some NRTL and/or manufacturers laboratories ,an engineer has calculated the ohmic value juxtaposed to specified tourqe








Another good Q, it's usually considered that any given contact point will endure expansion and contraction. Of course we all know that different metals ,etc , will have different rates , which is why the NEC also addresses 'dissimilar metals' where applicable.

With that said, the usual degrade is first seen as a 'hot spot' , note this has evolved to be a 'niche industry' w/in the electrical trade assessing existing equipment as a maintenance routine.

Here's one study>

https://youtu.be/_2HyTRxzwXs


~RJ~

 

[romex jockey]

Do you actually use torgue wrench to tighten screws in breakers or panels? Here we never use it. 0% use it. They just tighten it manually. We never even have any torgue wrench for sale anywhere in the country. If I get one for the electrician and contractors to use. I'd be the first one to do so.

We're supposed to tourqe everything to manufacturers spec's , an old issue recently brought to the forefront of the NEC>>>>

110.14....

N(D) Installation. Where a tightening torque is indicated as a
numeric value on equipment or in installation instructions
provided by the manufacturer, a calibrated torque tool shall be
used to achieve the indicated torque value, unless the equip‐
ment manufacturer has provided installation instructions for
an alternative method of achieving the required torque.

The truth being that the larger equipment is usually addressed before smaller terminations.

Our (at least my turf) AHJ's normally ask to see toolage, and leave it at that....

As an aside to this, much larger equipment instructs an annual retourqe , wich is seldom (if ever) done...


~RJ~

 

[tersh]

The mfg was probably using some of the same materials they used in Sheetrock prior to making lugs.

I have to agree with Hal. You have junk being installed by totally untrained people into a substandard electrical system. You’re lucky it’s only 2000 fires.

But if you will check out this original Siemens load center lugs. The bottom isn't deburred too. So when put in the bus bar, there is not 100% even surface contacts.

I bought 2 sets just to see how original US made lugs look like. I was thinking it was Milspec flat at bottom. It's made in Mexico so maybe the workers just didn't deburr it thoroughly.

I am wondering what current and few contact points percentage ratio before arcing can form.

 

[romex jockey]

QUOTE=tersh;1978683]

But if you will check out this original Siemens load center lugs. The bottom isn't deburred too. So when put in the bus bar, there is not 100% even surface contacts.

one woud imagine any savvy sparky wanting to 'prep' such a terminal for more and/or better contact. The introduction of no-lox comes to mind, it's even incorporated via manufacture into many different terminals

I am wondering what current and few contact points percentage ratio before arcing can form

I'm thinking that depends on a number of factors ,paschens law being one that comes to mind

~RJ~

 

[ptonsparky]

But if you will check out this original Siemens load center lugs. The bottom isn't deburred too. So when put in the bus bar, there is not 100% even surface contacts.

I bought 2 sets just to see how original US made lugs look like. I was thinking it was Milspec flat at bottom. It's made in Mexico so maybe the workers just didn't deburr it thoroughly.

I am wondering what current and few contact points percentage ratio before arcing can form.

...Installation Instructions...

I don't see any of them as being optional.

Follow the directions.

After that you still have torqueing and sizing requirements for the wire.

'Glowing connections' can occur at very low current levels and are different from arcs. AFCIs would be more popular if they were, and they worked.

 

[kwired]

How does it contribute to fires? It's the arcing the contributes to fire? But I'd like to understand the behavior of the few contact points. Do they melt first before arc forms or do arc forms before they the few contact points melt?

No. I wasn't concerned about the shape of it, but the bottom of it has drilling sides not cleaned. Imagine when you drill through a metal, the bottom would have uneven surfaces (I wonder what is the exact term for this). They didn't even sandpaper it. And they distributed it to hundreds of customers.

Those "burrs" are likely to flatten out to some extent when you compress them with the mounting fastener, plus you have additional contact surface area on the nut/washer you secure it with.

But even if you have too little contact points for the load being carried, it is going to heat up those contact points, eventually to the point it likely increases oxidation of the material which further complicates things. Then thermal expansion and contraction because of loads that do cycle on/off makes things even worse.

 

[hbiss]

How does it contribute to fires? It's the arcing the contributes to fire? But I'd like to understand the behavior of the few contact points. Do they melt first before arc forms or do arc forms before they the few contact points melt?

The failure mode is through the termination generating heat due to the resistance, and that is directly proportional to the current. There is no arcing, no arc fault fireball that will engulf the building and destroy every living thing within 100 feet. If the connection gets hot enough, the insulation on the conductor can melt and burn, but usually by that time somebody should have noticed. If not, it's then when you can have faulted conductors because the insulation has burned off. But that greatly depends on what wire is used, how the conductors were run and their proximity to each other. Commonly used THHN, for instance, is resistant to the spread of flame.

-Hal

 

[kwired]

The failure mode is through the termination generating heat due to the resistance, and that is directly proportional to the current. There is no arcing, no arc fault fireball that will engulf the building and destroy every living thing within 100 feet. If the connection gets hot enough, the insulation on the conductor can melt and burn, but usually by that time somebody should have noticed. If not, it's then when you can have faulted conductors because the insulation has burned off. But that greatly depends on what wire is used, how the conductors were run and their proximity to each other. Commonly used THHN, for instance, is resistant to the spread of flame.

-Hal

Environmental conditions can contribute to problems though. A little dust, moisture or combinations of both can cause more dramatic failures at times. Doesn't always need to have an already hot spot to occur either, but that heat can be a catalyst for something bigger at times. The more conductive the dust is the easier it may contribute to faulting conditions. Maybe it isn't all that conductive, until it gets a little moisture on it for some reason.

 

[tersh]

Loose connections can cause arcing..why cant loose bus bar and chair lugs contacts (with only few contact points)?