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NOD113 (Electrical)
27 Mar 08 0:02
We are having several different opinions regarding Bolts used for Busbar connections of MV Cables as well as motor terminations in drawer compartments. Since we are working in Europe. Client maintains we should use 8.8 which is a metric medium carbon steel type bolts 120000psi  along with recommended torque values. My company has purchased A2 & A4 gr 70 stainlees Steel bolts and we have used them extensively throughout our project. There is now a discussion as  to replacing these bolts. I have stated that there is nothing wrong with the Stainless Steel bolts being used as long as the correct torque value is used, and that the Short Circuit Withstand values will not be compromised by these bolts.  I have quote the fact that ABB Siemens and other Engineering companies use these satainless steel bolts for terminations on Generators and switchgear. However we are working under some Russian PUE, Gost & SNIP  codes
Can anyone substantiate my conconclusions
Helpful Member!  prc (Electrical)
27 Mar 08 0:50
If there is no chance for corrosion,mild steel bolts are oK.ie there is no chance of eddy heating on such  MS bolt connections.But if current flows through bolts,stainless steel bolts will heat more due to higher resistivity.
waross (Electrical)
27 Mar 08 4:43
And, because of the higher resistivity, the stainless bolts tend to carry less of the total current.

Bill
--------------------
"Why not the best?"
Jimmy Carter

NOD113 (Electrical)
27 Mar 08 5:20
The Amperage is not a question in our case. The question is are Stainless Steel bolts an approved method for making such terminations. Since for the past 10 years we have had all types of bolts come up for terminations, (Phosphor Bronze, Cadmium Plated, Sherizied Mild steel, Brass etc even Gavinized Steel)
Apart from the Resistivity is there any knowledge of non approval of the A2 or A4 bolts for electrical terminations providing as with any bolts,correct washers and nuts along with specific torque values.
Helpful Member!  desertfox (Mechanical)
27 Mar 08 8:49
Hi NOD113

Another issue in changing bolt material is the switchgear testing on short circuit etc if the gear was tested with Stainless bolts then it should not be changed irrespective of whether or not plain or stainless steel bolts will withstand the forces you invaladate the test certificate.
In addition it may also impact on the temperature rise tests carried out on the gear.

Regards

desertfox
Helpful Member!(2)  stevenal (Electrical)
27 Mar 08 12:11
We use stainless exclusively. Make sure you use Belleville washers.
TestBeforeTouch (Electrical)
27 Mar 08 16:46
The Copper Development Association has a very good write up on this.
See http://www.cda.org.uk/megab2/elecapps/pub22/sec7.htm


"Galvanised steel bolts are normally used but brass or bronze bolts have been used because their coefficients of expansion closely match the copper conductor and hence the contact pressure does not vary widely with operating temperature. Copper alloy bolts also have the advantage that the possibility of dissimilar metal corrosion is avoided. Because these alloys do not have an easily discernible yield stress, however, care has to be taken not to exceed the correct tightening torque.

Because of their non-magnetic properties, copper alloys may also be preferred to mild or high-tensile steel where high magnetic fields are expected. Alternatively, a non-magnetic stainless steel may be used. In most cases however, high-tensile steel is used for its very high yield stress."

oldfieldguy (Electrical)
27 Mar 08 20:12
stevenal--

A star!  You pushed a button.  
I wish I had a dollar for every time I was told that the specification was for 'bevel' washers.

old field guy

NOD113 (Electrical)
27 Mar 08 21:58
Hi TestBeforeTouch,Oldfieldguy,
I have found that most clients now dissapprove of the use of Galvanised Bolts on switchgear and that the use of Stainless steel bolts is more acceptablein the USA. The probvlem is that when working with IEC standards they have different preferences, this leads to the questions regarding the suitability.
We do use Bellville washers on BUSBAR Fishplate connections with flat washers and lock washers on cable terminations.
My conclusion from all the quality answers I have received comes down to preferential engineering by the client and so far and both types of bolts are acceptable providing all the parameters mentioned in these threads are taken into consideration.
I thank you all for the answers you have given and thatis waht makes this site an excellent reference location.
Thank you all
prc (Electrical)
28 Mar 08 0:05
Probably the IEC  allergy to stainless steel bolts may be due to the "not having discernible yield stress and hence care has to be taken not to exceed the correct tightening torque."In certain electronic products stainless steel is not allowed due to higher resistivity and consequent heating.

Copper development group's suggestion of using non-magnetic material at high magnetic fields seems not correct.Even at currents of 10 KA bus bars, mild steel bolts are not getting heated up.So high tensile mild steel bolts are used in oil filled high current connections eg transformers.In out door  applications non corrosive property of stainless steel is a plus point.
LionelHutz (Electrical)
28 Mar 08 9:04
I'd like to add that just using Belleville washers isn't really useful. The Belleville needs to be able to exert the required tensile force that the bolted joint makes. Basically, if the bolt is to work slightly loose the Belleville still needs to keep the clamping force on the joint the same. I've seen Belleville washers that were too small being used on more than one occasion.



stevenal (Electrical)
28 Mar 08 20:01
Agreed. We've disassembled bars to find flat washers where the Bellevilles used to be. Now we use thick ones that maintain their spring.

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