# Belleville (Spring) Washers For Electrical Connections



## CMP (Oct 30, 2019)

I thought I would add some information and links for further learning about Belleville Washers to the forum for education about them, as they are not that common in residential or light commercial applications, but are often used in industrial applications.

Their main use in our trade is to keep electrical joints tight when they are exposed to expansion and contraction from thermal cycling and vibrations. 

There are several types and materials, types with nuts incorporated. They can come in different thicknesses for different clamping forces, they are available in in several materials, platings, and finishes. They are used in many applications besides electrical. In the electrical trade they are often used on heavier bus and cable connections to keep the clamping forces tight when the materials expand and contract due to thermal cycling.

When current is flowing the metal expands and puts extra pressure on the fasteners and the base metals. When the current subsides and the joints cool, the connections can become loose from the metals being compressed or stretched. After several cycles the loss of the correct joint tension, the looseness will lead to high resistance, and joint failure and burnout.



Mbit said:


> Lol yeah I think they forgot the little washers on the terminal posts. It only lasted like 5 days before I had to go out and change it. I put the new washers on and cranked those m6 nuts haha
> View attachment 168000





Almost Retired said:


> im not familiar with the term "bellville"
> so to put it another way .... are they cupped?
> if so they need a proper torque, or at least dont crush them completely
> other wise they wont be able to acommodate the expansion and contraction from the heating





Mbit said:


> I call them bellville but I'm sure there are other names that's just what i know them by.
> Yeah I know that's the theory but I checked with a guy who's been doing this a long time and he said yeah, no crank em. So that's what I did.
> 
> Honestly these little guys don't have enough spring force to rely on IMHO. But that's why I checked first with someone that's done a ton of these motors. They do t last long as is.


The serrated type shown above are normally in the metric sizes, and made of stainless steel, such as these.








Belleville Washer Stainless Small OD NFE 25-511


Bel-Metric sells metric hardware & specialty automotive supplies nationwide. Visit our website to purchase metric fasteners, nuts, bolts, Time-Sert kits & more.




belmetric.com





I can remember years ago the first time I encountered them, putting up some reconditioned plug in busway. The vendor supplied them, along with new carriage bolts and hex nuts, but I was unsure on how tight to make up the joints.

The smooth American types are tightened just till the Belleville washer is drawn down flat, not torqued down tight like you would do for a standard bolted connection.

If the equipment came with instructions and hardware, follow the manufacturers instructions. Here is some additional study information from other sources and manufacturers.



https://en.m.wikipedia.org/wiki/Belleville_washer



ECM- How to use Belleville washers. 






Belleville Disc Washer Springs - Learn About | Lee Spring


Learn more about Lee Spring Belleville Washer Disc Springs. Belleville washers available in stock or custom.




www.leespring.com










Search for Belleville Washers | Lee Spring


Search Lee Spring's inventory of Belleville Washers by part number or by specifications. Browse by Imperial or Metric units for your convenience.




www.leespring.com







https://www.leespring.com/sites/default/files/2019-01/Belleville_Washers_LeeSpring_US_Eng.pdf





https://www.solonmfg.com/documents/Installation%20Techniques%20using%20Belleville%20Springs%20-%20NECA.pdf








High-Performance Belleville Spring Washers | Conical Washers







www.solonmfg.com










Resource Library







www.solonmfg.com













Downloads - Belleville International


Downloads PRODUCTS AND SERVICES BELLEVILLE SPRING FLANGE WASHERS: HIGH TEMPERATURE & CRYOGENIC Offered in H13, Inconel and 17-7 PH SS. Reduce leaks, Fugitive Emissions & Costs by installing Belleville International’s Flange Washers. In a well designed joint system, belleville washers will...




www.bellevilleintl.com


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## CAUSA (Apr 3, 2013)

I am familiar with this design. I have never known it in be called Belleville. I have known it to be called convex washers.
Thanks for the links.


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## MikeFL (Apr 16, 2016)

CMP said:


> I thought I would add some information and links for further learning about Belleville Washers to the forum for education about them, as they are not that common in residential or light commercial applications, but are often used in industrial applications.
> 
> Their main use in our trade is to keep electrical joints tight when they are exposed to expansion and contraction from thermal cycling and vibrations.
> 
> ...



Nice post. Thanks for the heads up. That's information that many of us have used but never quite understood until taking the time to see and hear it out as to what we're doing, why and how it works.

Here's a nice short article on the subject:








What are Belleville washers? - Fastener Engineering


Fastener Engineering covers the technology of fasteners, adhesives, springs and all aspects of fastener technology.




fastenerengineering.com


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## Wirenuting (Sep 12, 2010)

It is an interesting topic. 
Are the screws (M) that hold the bi-metallic o/l’s in the Square D block come with those types of washers?

The reason I ask is that I had several 10hp motors go out, age related. After replacing them one pump started tripping after about 30 minutes. 
Current was low and pump ran fine, but it was the same o/l phase that would trip. 
With a heat spy I found the hot spot and a DoP test showed a bad connection, but not by much.

I saw that the washer had been crushed flat on that one screw. I changed it out and now it works fine.

Are those screws (M) belville washers?


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## paulengr (Oct 8, 2017)

Wirenuting said:


> It is an interesting topic.
> Are the screws (M) that hold the bi-metallic o/l’s in the Square D block come with those types of washers?
> 
> The reason I ask is that I had several 10hp motors go out, age related. After replacing them one pump started tripping after about 30 minutes.
> ...


No. They are brass or a similar alloy.


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## Navyguy (Mar 15, 2010)

It is actually a code in the CEC...

Rule 12-118 5) a) and b)



> 5) Field-assembled connections between aluminum lugs and aluminum or copper busbars or lugs, involving bolts or studs 9.5 mm in diameter or larger, shall include as part of the joint any of the
> following means of allowing for expansion of the parts:
> a) a conical spring washer;
> b) a helical spring washer of the heavy series, provided that a flat steel washer of a thickness not less than one-sixth of the nominal diameter of the bolt or stud is interposed between the
> ...


Cheers
John


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## MikeFL (Apr 16, 2016)

This topic would be good material for an apprenticeship curriculum.
It gives one respect for proper torque and an understanding of why it matters.


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## paulengr (Oct 8, 2017)

I’ve been down this road but I’ve soured on them. The most common washers we run into (ignoring say reducing washers) are flat washers and helical spring washers. Wait you say…I did NOT mention lock washers, for good reason.

First let’s cover bolt theory. The web site boltscience.com has a huge amount of both theoretical and practical information. The idea that fasteners can self loosen from vibration if they are properly sized and tightened is basically debunked tribal knowledge.



Self-Loosening of Bolts and Nuts



Summary: It CAN happen but it has to be super loose in the first place, too small for the hole, and subject to such hard vibration that basically the nut bounces off long enough to allow a sideways motion to turn it when it flips around in the hole.

Now I’m going to add an asterisk here. I have seen many damaged mechanical lugs after they fail. The copper is melted and stretched and so is the bolt/stud. Any gaps between strands are gone. If you cut the cable in half it’s highly corroded and solid, no air gaps. It has visibly “shrank” compared to the rest of the wire. So this is NOT evidence for loosening. Every burned up mechanical lug no matter how it fails always looks like this. Quite often I’ve seen burned up lugs on BOTH ends of the same cable, often with a nearby phase with no damage. Clearly this is a case of very high current on the conductor damaging both lugs, not the same installer messing up tightening just one lug on both ends of the same cable (highly unlikely)

Second from the same site we get into helical spring washers. If you enter (lock washer” into McMaster-Carr you get nothing. That’s because those little split washers don’t prevent looseness. Their intended purpose as the name suggests is to act as a spring for maintaining proper joint tension. But when you tighten a fastener properly they completely collapse flat and don’t provide any spring tension at all. This is the selling point of Belleville washers. In fact in actual testing helical spring washers actually increase self loosening!



Helical Spring Washers



Washers with serrated teeth also don’t do any good. NASA Fastener Design Manual says that at best they do nothing. But they can gouge the mating surface which creates a stress riser and can promote cracking and other failures making them also worse.



https://ntrs.nasa.gov/api/citations/19900009424/downloads/19900009424.pdf



Flat washers are definitely a plus. The purpose is to spread out the pressure, definitely a positive with soft metals like copper and aluminum. It’s not recommended of course but they also help bridge the gap when you are stuck with situations like say 3/8” hole lugs mating to 1/2” holes. It’s not perfect but it happens.

With electrical contacts, we have to consider several other things. This very deep technical paper from the Copper Development Association gives lots of details:



https://electrical-engineering-portal.com/res/Copper-for-busbars.pdf



Look at figure 60 and 61. This shows the recommended way to do bus bar joints. Bus bars are subject to very high forces and high currents and heating yet what is missing? Yep just flat washers.

Look at section 6.3.2, especially figure 69. This shows that as you apply pressure, you reach a point of diminishing returns where increased pressure doesn’t decrease resistance. In fact you can never equal the resistance of a non-jointed bus bar. We will come back to this in a moment.

Now look at table 20 and the equation below it. This is the sales pitch for Belleville washers. If you use steel bolts and nuts the tension increases 5.5 x10^-6. This is pretty much a worst case. So on say 1/4” bus bars with 1/2” bolts if temperature reaches 150 C starting from 40 C is not nearly enough to exceed the yield stress. Shortly after that table 22 gives typical bolting arrangements with no Belleville washers required.

What I’m reading from this is that if you do what you are supposed to do, Belleville washers aren’t needed because there is enough flex in the bolt and bus bar that it can easily stretch without deforming the fastener. You can argue for the extra protection in the event of overheating but you’ve already lost the insulation and the temper in everything. Belleville washers will not fix this.

Now as far as looseness goes, this is where we get back into figure 69. In an electrical joint we never make 100% contact. All electrical materials (copper, aluminum) have oxide coatings. When we tighten the fastener we crack the oxide and the high spots form aloha spots which are mechanical cold welds. Increased pressure smears the existing alpha spots and forms more of them. As we loosen the joint though we get hysteresis. The aloha spots stick around right up to the point of total failure of the joint as the charts in the article below explain,



https://zero.sci-hub.se/2479/08df0ec8e0764d75f40420d7b892ced7/electrical-contact-resistance-properties-of-stationary-interface.pdf?download=true



Belleville washers are pretty cool but they simply aren’t necessary if you don’t try to do crazy things like bolt multiple bus bars together in a huge stack. Even then you can avoid it by using stainless steel or bronze fasteners which have vastly lower differences in expansion rates. (over 10 times less). It doesn’t require special washers and special stacking methods. Of those I’m partial to bronze. Stainless galls bad and isn’t as strong as steel. There is a lot less risk of something going wrong with either aluminum or silicon bronze, and the strength is similar to steel. They are just expensive,

So summarizing:
1. No such thing as “lock washers”. Throw these away.
2 Belleville washers work. Star, serrated, helical spring washers don’t. Throw those away. Use Bellevilles if the design calls for it. If not don’t do things that require them. Stagger joints or use better bolts.


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## paulengr (Oct 8, 2017)

Navyguy said:


> It is actually a code in the CEC...
> 
> Rule 12-118 5) a) and b)
> 
> ...


Aluminum bronze (6061 aluminum is not a good bolt material) is nearly an identical expansion rate to copper and a tensile strength of mild construction grade steel. Not my first choice.

I mixed them up earlier when I said silicon bronze was strong. Silicon bronze is pretty much all copper and much weaker than aluminum bronze. It just has much lower electrical resistance.


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## Wirenuting (Sep 12, 2010)

paulengr said:


> No. They are brass or a similar alloy.


I understand that, but the B sized ones seem to have a slight concave to the washers. 
Comparing the bad one with other known good ones, the one that heated seemed to be flattened.

I don’t know, but it was the first time I’ve ever seen that issue before. I have new screws coming for a dozen o/l blocks as these are all the same age and I don’t want to loose the heating or cooling pumps again.


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## CMP (Oct 30, 2019)

Wirenuting said:


> I understand that, but the B sized ones seem to have a slight concave to the washers.
> Comparing the bad one with other known good ones, the one that heated seemed to be flattened.
> 
> I don’t know, but it was the first time I’ve ever seen that issue before. I have new screws coming for a dozen o/l blocks as these are all the same age and I don’t want to loose the heating or cooling pumps again.


Your correct to trust your eyes and observations. That’s why your mom gave them to you. The SqD heater screws do contain a steel belleville washer, albeit a special one along with the screw. The screw has a reduced shank underneath the head, so that the internal serrated belleville washer, will be permanently retained.
















To prove to yourself that the washer is spring steel, instead of a brass alloy, all you need is a small magnet. If it has lost its concave shape it has been overheated or mistreated. They are manufactured that way for a reason, heaters are designed to tolerate thermal cycling.

Some factory spare screws are a wise investment to prevent future damage and downtime. Just as your observations have shown you. Just because you seen it on the net, doesn’t mean it’s always gospel. Especially if they don’t proofread what they write.


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## joe-nwt (Mar 28, 2019)

Who knew washers could be so complicated!


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## Wirenuting (Sep 12, 2010)

CMP said:


> Your correct to trust your eyes and observations. That’s why your mom gave them to you. The SqD heater screws do contain a steel belleville washer, albeit a special one along with the screw. The screw has a reduced shank underneath the head, so that the internal serrated belleville washer, will be permanently retained.
> 
> To prove to yourself that the washer is spring steel, instead of a brass alloy, all you need is a small magnet. If it has lost its concave shape it has been overheated or mistreated. They are manufactured that way for a reason, heaters are designed to tolerate thermal cycling.
> 
> Some factory spare screws are a wise investment to prevent future damage and downtime. Just as your observations have shown you. Just because you seen it on the net, doesn’t mean it’s always gospel. Especially if they don’t proofread what they write.


Thank you. 
When the new ones arrive I’ll take a side by side comparison picture.


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## wiz1997 (Mar 30, 2021)

I first came across the Bellville washer back in the early 90's.

I was working in the Exxon Refinery in Baytown, Texas as a contractor.

Our project was to troubleshoot a 10" pipeline, which carried sulfur from the sulfur unit to the loading docks, about 5 miles of pipeline.

Why is an electrician involved with a sulfur pipeline?

This pipeline had been out of service for several years, now we had to get it going again.

To pump sulfur through a pipe it has to be in a molten state, anything below 350 degrees F, it became rock solid.

The pipeline used impedance heating to keep the pipe hot.

Craziest thing I have ever seen, the pipe itself is part of the circuit, the pipe actually has an electrical current flowing through it.

Transformers were installed every 400 feet, with three cables from each transformers attached center and then 200 feet each way.

The problem was, they had used lock washers on the bolts used to terminate the cables to the pipe.

As mentioned above the expansion and contraction from the heating and cooling cycles would loosen the bolts.

Eventually the lock washers would split, and fall out.

This created a loose connection, but that wasn't the big concern.

When the lock washer fell out it was very hot.

The hot lock washer set the grass on fire, which is not what you want in an oil refinery.

We had to replace every lock washer with a Bellville washer, replaced all the nuts and bolts also.

Repaired anything we found that needed it. 

Leaned how to pin point ground faults on the sections.

Actually had a question on a Master's exam review about how to calculate where a ground was.

NEC Article 427


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## Mbit (Feb 28, 2020)

wiz1997 said:


> I first came across the Bellville washer back in the early 90's.
> 
> I was working in the Exxon Refinery in Baytown, Texas as a contractor.
> 
> ...


I just learned something new and it's only 5 o'clock haha!


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## Djea3 (Mar 8, 2019)

CAUSA said:


> I am familiar with this design. I have never known it in be called Belleville. I have known it to be called convex washers.
> Thanks for the links.


Belleville is the correct US specific term used in all industries for this kind of washer. At least it has been in Aerospace, precision fabrications and structures, as well as electronics assemblies for the last 50 plus years I know of.


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## Almost Retired (Sep 14, 2021)

Thanks but i will just keep saying "bell washer"


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## CAUSA (Apr 3, 2013)

CMP said:


> I thought I would add some information and links for further learning about Belleville Washers to the forum for education about them, as they are not that common in residential or light commercial applications, but are often used in industrial applications.
> 
> Their main use in our trade is to keep electrical joints tight when they are exposed to expansion and contraction from thermal cycling and vibrations.
> 
> ...


Is there a NEC code reference for this type of washer for use in a Bus assembly.

In the CSA there is one. Just trying to compare code similar aspects.?


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## CMP (Oct 30, 2019)

CAUSA said:


> Is there a NEC code reference for this type of washer for use in a Bus assembly.
> 
> In the CSA there is one. Just trying to compare code similar aspects.?


Off of the top of my head, I don’t recall one. I think it depends on how the product is UL listed. I will use them on used or refurbished equipment, even if not provided, if I feel or see there could be an issue. This applies especially to aluminum bus products where you know there will be a lot of expansion and contraction.

Besides overhead plug in busway, I rarely see them on bus connections in switchboards and service riser buss. I have a job in a old switchboard now to repair the bus to finger tap connection is burned to repair. It’s aluminum and could have used the belleville washers in the beginning, I got a box of them to add to all of the internal connections once we take the board down.
I will try to remember to look in the NEC for you when back at the office.


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## Almost Retired (Sep 14, 2021)

i am pretty sure i have seen spring washers in 200A breaker panels where the main is bolted to the buss bars


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## joe-nwt (Mar 28, 2019)

Almost Retired said:


> i am pretty sure i have seen spring washers in 200A breaker panels where the main is bolted to the buss bars


Lots of panels use nuts with spring washers built in for the main breaker/bus connection.


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## CMP (Oct 30, 2019)

CAUSA said:


> Is there a NEC code reference for this type of washer for use in a Bus assembly.
> 
> In the CSA there is one. Just trying to compare code similar aspects.?


I took a look in the 2017 and 2020 NEC for you. Not one search result returned in the entire book for belleview washer or spring washer. I read the busway article to be sure, nada.


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## CAUSA (Apr 3, 2013)

CMP said:


> I took a look in the 2017 and 2020 NEC for you. Not one search result returned in the entire book for belleview washer or spring washer. I read the busway article to be sure, nada.


That is interesting. Thanks for the search.

The closest I could find in the ANSI C37.23 code as a summery, with out purchasing the code. is this.

Bolted bus bar connections shall be made with the bolts passing through the bus bars in a way that they can be properly torqued and locked in place to maintain full and uniform pressure under all operating conditions. Torque requirements in N.m.


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