Best way to bond metal framed building?

[HappyHippyDad]

Evening..

I have been trying to think of the best way to attach a bonding clamp to a steel structure and could do with some opinions please.

At present I am thinking of a bolt through one of the steel columns and attach the clamp to this, but I'd rather get the clamp on a smooth surface (rather than the thread of the bolt) so that it makes a greater surface area connection.

Any ideas?

 

[Leesparkykent]

Evening..

I have been trying to think of the best way to attach a bonding clamp to a steel structure and could do with some opinions please.

At present I am thinking of a bolt through one of the steel columns and attach the clamp to this, but I'd rather get the clamp on a smooth surface (rather than the thread of the bolt) so that it makes a greater surface area connection.

Any ideas?

http://www.kingsmillearthing.co.uk/files/ww/Product Catalogue - Edition 6.pdf

 

[HappyHippyDad]

Cheers Lee... top chap!

 

[Hellmooth]

I think everyone should just pm Lee with any queries, would be a quiet forum mind you........!

 

[davesparks]

Why not just put a lug onto the bolt rather than try to fit a clamp designed for a pipe onto a bolt?

 

[Leesparkykent]

I think everyone should just pm Lee with any queries, would be a quiet forum mind you........!

Lol

 

[Marvo]

Does nobody use thermite welding any more? I used to enjoy thermite welding but haven't done any for years. Maybe it's not so easy to get hold of nowadays over the counter at wholesalers and I could imaging buying it could get you on some kinda terrorist watchlist.

 

[davesparks]

It is used extensively in some parts of the industry, particularly for underground earthing connections.
Furse do a range of stuff for it, including one-shot kits I think

 

[Robson689]

Does nobody use thermite welding any more? I used to enjoy thermite welding but haven't done any for years. Maybe it's not so easy to get hold of nowadays over the counter at wholesalers and I could imaging buying it could get you on some kinda terrorist watchlist.

Did a fair bit of thermite welding a couple weeks ago on a substation!

 

[Lucien Nunes]

I'd rather get the clamp on a smooth surface (rather than the thread of the bolt) so that it makes a greater surface area connection.

Like Davesparks, I've no idea why you would want to put a strap clamp onto a bolt, as the bolt and lug is a standard way of making a sound heavy connection for any purpose. I would simply crimp on a lug and bolt it to the structure, suitably treated to prevent corrosion etc. But your comment raises an interesting point.

When two smooth metal surfaces appear to be in contact under moderate pressure, due to microscopic roughness and contamination only tiny high-spots (asperities) actually make metallic contact that will pass current. These total a very small fraction, sometimes as little as one millionth, of the apparent surface area. As the pressure is increased, more and more of these asperities are crushed and spread out, increasing their area and allowing lower spots to start making contact too. Pressure = force / area, so when you have a certain maximum clamping force available e.g. from a particular size of screw tightened as hard as it will stand, within limits you will get better and more reliable contact with smaller area and it will be more gas-tight and corrosion resistant.

The best contact that a strap clamp makes with a pipe is mainly where the pips on the saddle touch, the rest of the clamp merely holding it in place and providing backup contact. I would expect as low or lower contact resistance on the thread compared to a smooth pipe of the same material, as the bits that dig in will dig in at least as well. I'd agree that it's a bad idea to clamp a thread, however, because the long thin line of (good) contact is very exposed to the atmosphere by the groove of the thread and prone to corrosion.

 

[HappyHippyDad]

Why not just put a lug onto the bolt rather than try to fit a clamp designed for a pipe onto a bolt?

Like Davesparks, I've no idea why you would want to put a strap clamp onto a bolt, as the bolt and lug is a standard way of making a sound heavy connection for any purpose. I would simply crimp on a lug and bolt it to the structure, suitably treated to prevent corrosion etc. But your comment raises an interesting point.

When two smooth metal surfaces appear to be in contact under moderate pressure, due to microscopic roughness and contamination only tiny high-spots (asperities) actually make metallic contact that will pass current. These total a very small fraction, sometimes as little as one millionth, of the apparent surface area. As the pressure is increased, more and more of these asperities are crushed and spread out, increasing their area and allowing lower spots to start making contact too. Pressure = force / area, so when you have a certain maximum clamping force available e.g. from a particular size of screw tightened as hard as it will stand, within limits you will get better and more reliable contact with smaller area and it will be more gas-tight and corrosion resistant.

The best contact that a strap clamp makes with a pipe is mainly where the pips on the saddle touch, the rest of the clamp merely holding it in place and providing backup contact. I would expect as low or lower contact resistance on the thread compared to a smooth pipe of the same material, as the bits that dig in will dig in at least as well. I'd agree that it's a bad idea to clamp a thread, however, because the long thin line of (good) contact is very exposed to the atmosphere by the groove of the thread and prone to corrosion.

À lug! I've just been doing that for the SWA, why didn't I think of that! Probably because my brain just thought 'must be a bonding clamp as used in domestic situations'.

Thankyou both.

 

[davesparks]

I'm very concerned that someone claiming to be an electrician is unaware of the basic methods of connecting conductors.

I think we're all doomed

Just don't forget to clean the metal surface and then treat the expose steel with red-oxide once the connection is made.
And obviously make sure it's safe to drill a hole in the structural steel in the first place!

 

[GMES]

It may be me but I just can't see it catching on!!!!!

 

[Richard Burns]

Would anyone consider the use of beam clamps instead of drilling the beam?
I tend to think it may be structurally better to avoid penetrating load bearing structures, however the general idea always seems to be to drill into the beam.
Whilst I can see that the electrical connection may be more durable over time, it probably would not matter if the building had collapsed!

 

[Dave OCD]

I doubt very much that a 10mm max hole through a huge RSJ will result in catastrophic failure at any time.