Structural steel bonding clamps

[Antdoran]

Hello All,

I am working on a kitchen extension which has 3 Universal Beams bolted together which sit on block-work. There is no direct connection to earth. However when tested it has a path to MET of 2kOhm.

As a result I plan to bond this steelwork.

The design of the room means these beams will be exposed. Getting a Furse1 style clamp on the beam will be pretty clunky. One of the bolted connections will be hidden so I am currently planning on getting a Earth Tag onto the end of the M22 bolt.
Is there any product that isn't an M25 or M20 style earth tag available? Or is my plan to use a 25mm SWA earth tag sandwiched between two M22 washers a reasonable solution?
I could perhaps get a BS951 clamp on the thread of the bolt but the surface area of the thread might not be a great contact.

I'm not too keen to drill a hole in the steel for a smaller connection.

The structural steel is also getting a thick coating of a Fire Retardant paint inline with Part B.

Any thoughts?

Ant

1 https://www.electrika.com/catalogue...S350/-METALWORK-BD-FOR-8MM-COPPER/part/127596

 

[cliffed]

I personally don’t think it should be bonded,it’s gonna be painted,it’s actually on blockwork so no direct contact with Earth.
How are you getting the ohm reading.
[automerge]1590223616[/automerge]
A reading below 22,000 ohms will mean the metallic item is an extraneous-conductive-part which does require bonding.

 

[Ian1981]

I doubt that the beams require bonding plus are they not covered within the building fabric so are not accessible to touch?

 

[snowhead]

How high are these beams and have they recently been installed on freshly laid blockwork?

 

[Antdoran]

Thats

I personally don’t think it should be bonded,it’s gonna be painted,it’s actually on blockwork so no direct contact with Earth.
How are you getting the ohm reading.
[automerge]1590223616[/automerge]
A reading below 22,000 ohms will mean the metallic item is an extraneous-conductive-part which does require bonding.

I'm getting the reading with a Megger1730 and Zero'ed wander lead.

This is why I am planning on making the bond. Even if you considered the Ib value to be 0.03A you'd need the resistance to be at least 6667ohms.

I'm not sure why I am getting a relatively low resistance path to earth. I'll double check my readings next week.
One of the steels will have an aluminium framed bifold door underneath so wonder if its worth bonding anyway as this will probably decrease this resistance reading further. Depending on fixings etc.

I wondered if I could get away with saying its not exposed so unlikely to introduce a potential. Will double check the exact wording in the Blue book when I can drag myself to the vehicle.
[automerge]1590225845[/automerge]

I doubt that the beams require bonding plus are they not covered within the building fabric so are not accessible to touch?

They are exposed but will be coated in a fire retardant paint which I imagine to be fairly thick.
[automerge]1590226090[/automerge]

How high are these beams and have they recently been installed on freshly laid blockwork?

They are standard door height approximately, for arguments sake lets say 2m.
One of the steels spans new brick peirs but been in situ for a few weeks. There are three ends that are on old brickwork.

But either way, the resistance to MET is still less than 22,000 Ohms.

 

[pc1966]

Using a banjo and washers seems like a goo idea, or maybe a U-bolt sort of clamp that you could use a M8 ring terminal on such as this:

Standard M8 Thread Exhaust U Bolt Clamps

Standard 8mm Thread (M8) U Bolt Clamps • U bolt exhaust clamps complete with nuts. • Variety of uses for exhausts, TV aerials, Satellite Dishes, framing fasteners and anchors. • All ID (internal diameter) sizes are available from 29mm to 130mm. • Measurement is the inside diameter (For example...

www.clampcouk.co.uk

You can get proper earth clamps for beams (big versions of the radiator earth clamps) will look...
[automerge]1590230164[/automerge]
Something like this, but ideally with a pointed-tip bolt is what I was thinking of:

HFL2-M10 Heavy Duty Beam Clamp for 10mm Threaded Rod (Sold in 1's)

Heavy duty screw clamp for horizontal flanges up to 23mm thick

www.cef.co.uk

 

[Antdoran]

Using a banjo and washers seems like a goo idea, or maybe a U-bolt sort of clamp that you could use a M8 ring terminal on such as this:

Standard M8 Thread Exhaust U Bolt Clamps

Standard 8mm Thread (M8) U Bolt Clamps • U bolt exhaust clamps complete with nuts. • Variety of uses for exhausts, TV aerials, Satellite Dishes, framing fasteners and anchors. • All ID (internal diameter) sizes are available from 29mm to 130mm. • Measurement is the inside diameter (For example...

www.clampcouk.co.uk

You can get proper earth clamps for beams (big versions of the radiator earth clamps) will look...
[automerge]1590230164[/automerge]
Something like this, but ideally with a pointed-tip bolt is what I was thinking of:

HFL2-M10 Heavy Duty Beam Clamp for 10mm Threaded Rod (Sold in 1's)

Heavy duty screw clamp for horizontal flanges up to 23mm thick

www.cef.co.uk

I had looked at the furse style clamp in the original post. Unfortunately as these need to clamp onto the edge of the flange it will be tricky to hide as all flanges are either totally visible or they will be behind a finished plastered surface so any flange clamp will protrude into the room. At least going on to the bolts on the web they are a little more hidden from view.

 

[westward10]

If you are going to bond them the connections cannot be rendered inaccessible.

 

[pc1966]

Do you need more than one bond, or are the beams all electrically connected as a structure?

 

[Antdoran]

If you are going to bond them the connections cannot be rendered inaccessible.

Gotya, but hidden on a web which is out of view is fine.
[automerge]1590230971[/automerge]

Do you need more than one bond, or are the beams all electrically connected as a structure?

They are all bolted together with M22 bolts. I'd need to check for sure but I'd hope the fixings give a decent enough connection.

 

[radiohead]

If the blockwork is relatively new it's likely that the 2k reading is simply from moisture in the building structure. If it can be visually verified that there is no direct contact with anything earthy I see no reason to bond.

 

[pc1966]

Another possibility is to check it is OK to drill one of the webs, then drill and countersink to allow a M8 or whatever countersunk bolt & nut to be fitted to provide you with a stud for earthing out of view. If the beams are being coated anyway the flush head will probably disappear from view completely (or at least look like part of an engineered structure).

The stud and nut part would need to be protected during coating so you can later remove the protection and have a clean contact point for a ring terminal, etc.
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It is a pity they used M22, as for M20 you can get small-ish ring terminals such as these:

14-20 | JST, R Uninsulated Ring Terminal, 20mm Stud Size, 10.5mm² to 16.78mm² Wire Size | RS

uk.rs-online.com

 

[davesparks]

Another possibility is to check it is OK to drill one of the webs, then drill and countersink to allow a M8 or whatever countersunk bolt & nut to be fitted to provide you with a stud for earthing out of view.

I normally drill and tap for earth connections to steel whenever possible, I feel it gives a solid connection to bare metal via the threads that doesn't rely so much on the surface of the steel being in perfect condition.