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Posted By Topic: Earth Clamp

elecnz
Aug 27 2019 14:19

Hi guys

today my apprentice crossthreaded a cheap transnet brass earth clamp, se he proceeded to get another one , was then told by 2x inspectors that it doesn't matter if the earth clamp twists on the earth electrode and to not tighten soo much, i find this against all our electrical principals. Also coming from 2x inspectors

Whats everyones opinion on this ??...


   

KeithWig
Aug 27 2019 16:30

Logic says the clamp must be tight on the electrode to minimise resistance / earth loop impedance. Not sure where your two inspectors are coming from ??
   

AlecK
Aug 27 2019 17:04

Perhaps the same cornflake packet they found their "Inspector" licence in.

The connection of MEC to electrode is required to be firm, same as all other connections in conductors [3.7.2.3.1]
   

SaintAlan
Aug 29 2019 10:06

Some earth clamps are made of crappy material, like a lot of stuff nowadays. The threads strip easily, but can be fixed with a nut on the back or a new bolt right through if the original was a strange thread.
I have seen stainless hose clamps used, two of them holding the MEC against the E-rod. Seemed like a good idea.
   

DougP
Aug 29 2019 10:36

And if you do them up too tight, some of the pressed brass clamps break.
   

oldspark
Aug 29 2019 13:55

Copper clamped to galv with s/s clamps??? When I was an apprentice It was never allowed to have Pyro (copper) cabling touching galv wire ties attaching wooden bearers to concrete piles. Chemical reaction between the two metals would cause the copper sheath to corrode. True or fairytale???If we add s/s to the mix ??BOOM???? Any thoughts out there.
   

OwenK
Aug 29 2019 23:30

Good old galvanic reaction. Take two different metals and add water. The further apart on the periodic table, the more reaction. Bronze is an alloy but like other alloys fits in the list. I was taught when I was but a green apprentice (so last century) to not put Aluminum and Galvanized steel together outside but Aluminum and stainless steel was fine. Others may beg to differ
   

AlecK
Aug 30 2019 10:29

For marine work, the norm is to use Cu "talurit" splices for s/s wire., and Al ones for galv wire. If you crimp Cu splicing sleeves onto galv wire, the zinc corrodes away in short order.

For our earth electode / MEC connections, we have (typically) galv electrode and CU MEC, and it's NOT a good idea to have then in direct contact. The norm is to use either a brass clamp (being alloy of copper & zinc) or a s/s strap clamp. Either way the cu wire isn't in direct contact with the zinc galvanising. That reduces - but doesn't eliminate - the corrosion.

Should always use an anti-corrosion treatment in order to comply with 5.5.1.2(d).