Failure of Brass Bolts

I was watching a video posted on YouTube last evening by an electrician who runs his own business. One topic was earthing rods, specifically ones made from brass, and his advice was to discard the brass nut and bolt supplied with the rod, which is used to secure the circuit protection conductor after installation and replace it with a stainless steel nut and bolt. The reason he gave for this advice was that on several occasions he'd gone back to a job done several months earlier and discovered the head of the brass bolt broken away from the shank, and the CPC trailing uselessly on the ground. Can anyone tell me, please, why brass should exhibit this behaviour, and if they've had experience of this? Thank you.

The main trouble is that brass being and alloy, mainly of copper & zinc, can display the weakness of both those metals. It's imperative for any engineered parts to be made to a careful specification when they have to be brass,...e.g. for non-magnetic purposes etc. Brass exists in an infinite range of alloys and often even the manufacuturer or stock holder does not really know what's in it! In addition, brass is very prone to 'work hardening' during any manipulative process in making the brass into a component...this in turn, makes for brittleness under load. Quite possibly the said screws were made of a well specified brass but during their production they became brittle enough to fail easily in service. If you research online you can easily find the various constituents of all the main brasses.

Even in my clock-making exploits I never make any screws or small 'active' components out of brass if at all possible. All of my screws and bits are always from steels....and clocks are about as low dymanic as it gets!

The use of stainless is interesting as SS is yet another alloy that exists in a limitless range of content and strengths,....however, it IS steel and unlikely to corrode or fail easily in such an application

I think you will find that the military spec for these installations will be bronze nuts/bolts.

Earth rods over here in France are copper sheathed steel rods or galvanised steel with either a Brass/bronze or galvanised clamp ie: no through bolt and swaged eyelet on the earth wire.

I wonder how tight said" electrician" was doing his nuts up ?

Also I thought that earthing in the UK was often done by the PME sheath of the incoming supply.

Yes in many cases PME is used but also the lead sheath of supply cables can in some cases be used. The electrical installation has to conform with certain regulations before it can be connected with a PME supply, where it doesn't comply a RCCB is used to provide protection to the installation.

The earth stakes I installed when at work all had bronze nuts and bolts to secure the conductor to the stake.

Emgee.

Dead on the money re practical aspects. The earthing rod is there mainly to protect any metal plumbing remaining live if a fault condition exists - thereby blowing a fuse rather than remaining live and potentially killing anyone who touches the metal plumbing anywhere in the building.

Brass is a swine for that.

Once had to recover loads of 'slide in units' full of dtype plugs. Every one of the dtype screw heads sheared off even with only light index finger and thumb pressure.

Brass is chosen here for electrical reasons, not because it's strong.

Substituting stainless on an earth rod isn't a good idea because two different metals in contact form a battery and corrode, fastest when the joint is damp. While a stainless fastener will remain physically strong, corrosion between it and the earth rod will become a very poor conductor - the 'earth' is likely to go high-resistance, useless for safety purposes.

How quickly a stainless bolt reacts with Brass depends on what sort of Stainless it's made of, which is unknown. Some are better than others. But it's worth remembering that electricity is powerful enough to break water apart. When two metals are in contact best to ensure they are close together in the electrochemical series. Unknown engineering is bad engineering.

While brass isn't as physically strong as steel, it's certainly fit for purpose in this application, ie connecting a copper earth wire to a brass rod, or a copper-plated steel rod. The most likely cause of failure is stress cracking due to over-enthusiastic tightening. Another possibility is acid damp dezincifying the brass, but the characteristic pink colour is hard to miss.

As Brass is about 80% as strong as mild-steel, the tightening torque should be reduced accordingly. A stainless or high-strength bolt could be 3 times stronger than mild-steel; in comparison a brass nut and bolt is easily damaged.

Failed to find a table of recommended tightening torque for Brass Fasteners, but did find a suggestion that a sample brass bolt should be deliberately broken with a torque wrench, and real ones tightened to no more than 60% of that value.

Dave

Have you seen the way some electricians use hand tools? Probably way overtightened the brass nuts and bolts on installation. Stainless will put up with a lot more abuse and still hang together.

There is a new regulation that car charging points are to have separate earth rods

**LINK**

Just thought that this is useful to this post.

David

It just so happened that, last evening, I also watched the video concerned. To be sure of what I'm about to post, I've just watched the opening minutes again.

The actual earth rod is clearly copper-coloured so it's either solid copper (unlikely) or copper-clad steel. The actual clamp looks to be tinned, only the securing bolt & nut look to be brass.

As already stated, there's stainless steel and then there's stainless steel! Some varieties of stainless are actually weaker than mild steel. Also, stainless steel can be either anodic or cathodic (but, of course, not both at the same time ), depending on the local environment, including the oxygen availability.

I like the suggestion to use bronze fittings in lieu of brass but I've no idea where one would obtain them in small quantities!

One of the books on my shelf is 'Earthing', published by the Copper Development Association, it may be available on-line nowadays. It shows earth rods being driven by an early form of Kango hammer. BICC (whatever happened to them? ) used to sell an earth rod of copper or, maybe, cadmium-copper, that came in sections with driving points, driving heads and couplings as accessories. The rods were star-shaped in cross section to maximise contact area vs length. The driving head protected the coupling thread from damage so the next section could be attached without difficulty when required.

Best regards,

Swarf, Mostly!

Tightening electrical connections is essential to stop sparking, overheating and a loose live wire. Therefore all good electricians ensure all connections are properly tight. As that is their way of working they are going to overtighten some fasteners occasionally.

Thanks for that David, it's very useful, especially as I own a Nissan Leaf.

More generally, looking at all the previous posts, (and thanks to all who responded), my guess is that the electrician was a bit heavy-handed when he tightened the brass screw. Also, he did admit in his video that there was the risk of inter-metallic corrosion if a stainless fastener was used.

David, seems it only applies when the power source is from a PME installation, no mention of TN-S systems but the same loss of cpc could occur in extreme circumstances.
Another business opportunity to test the power supply to and operation of any RCCB EV charging points at fairly frequent intervals.

Emgee

I was trained to tighten brass screws in electrical equipment till the brass squeaked, but in those days the brass was annealed after being headed, and you soon found out the screws that had not been annealed properly when one half of the slotted head popped off. We installed many hundreds of the old ELCB's, and used a length of 3/4 conduit knocked in as far as possible (often it came out to be replaced by a longer length) and then a Tenby earth clamp attached the wire to the conduit. We rarely used the brass or copper earth spikes, mainly because of cost, and also because of the above problem! The BICC system was good, but very expensive. Todays electrical equipment uses mainly steel screws, with plating of one sort or another, sometimes brass, which the more cynical of us (IE me) think is to make you think that they are brass, the clamp style terminations on mcb's and the like are also often plated steel so they have abviously decided to ignore the effects of galvanic corrosion, or figure that "It all makes work for the working man to do" Really glad I have retired from the industry!

Phil

Will electric cars have to have an earth array draped behind them in the future ? Or perhaps electrically conductive rubber tyres ?

Will electric cars have to have an earth array draped behind them in the future ? Or perhaps electrically conductive rubber tyres ?

Ive fitted quite a few earth rods during my working years and I have never had a 'nut' break off in fact I can't recall going back to one that I had fitted. When I fitted one I was in the habit of smearing petroleum jelly round the connection.

H