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Supplementary bonding question

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Supplementary bonding question

Posted by TomLonsborough on Jan 16, 2020 1:29 pm

Alright folks,

Looking for a bit of advice with supplementary bonding. Bit of background - I'm in the process of repairing some metal bollards: I decided the best option was to rip out the old guts which comprised of some old fluorescents complete with all the control gear and no IP rating, and replace it with an IP rated LED flood. Supply is via SWA into a fused block; I've terminated the included LED flex into this block.

Question is this: do the bollards require bonding?

Initially I thought no, because they are simply a housing for the self-contained flood and the block. However upon taking a continuity reading between certain parts of some of the bollards and the MET, I was getting around 3 Ohms. R < 50A/100 (C 10A MCB, no RCD protection) is therefore not satisfied. I decided to add fly-leads connected to the block via bolts screwed into the bollard housing. Problem is the because of the condition of the bollards, i.e. rusty, painted in parts, continuity readings now vary from 0.2 Ohms to no reading at all. An insulation resistance test between MET and various parts of the bollards are also coming back as not satisfactory, i.e. <22000 Ohms. Am I potentially introducing a potential here under fault conditions with these fly leads which would not be present otherwise? Save for replacing the bollards with shiny new ones altogether, I'm not sure what I could do!

Any advice would be gratefully received!

Tom.

TL;DR Supplementary bonding of rusty metal bollards! Necessary or not?

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Re: Supplementary bonding question

Posted by Chris Pearson on Jan 19, 2020 9:10 pm

AJJewsbury:

there is no proper clamp for pipe which is smaller than 15 mm.

There are some (if non BS 951) - I've used these in the past for supplementary bonding in a bathroom with microbore heating pipes - https://uk.rs-online.com/web/p/earthing-straps/2365264/
(admittedly not much use for a 10mm² conductor for main bonding a oil pipe say but there may be other variants out there).
Andy, thank you. My one gripe with RS is having to buy things in quantity. I lost a 6 mm (or was it 1/4"?) ball bearing recently. Anybody want to buy 19 of them? 😁

Re: Supplementary bonding question

Posted by AJJewsbury on Jan 19, 2020 11:08 pm

How much? Ouch!

Eh, about £1.80+VAT each?
 

My one gripe with RS is having to buy things in quantity.

True.
   - Andy.

Re: Supplementary bonding question

Posted by Sparkingchip on Jan 19, 2020 11:36 pm

Can you buy a single clamp from Screwfix or any other similar place?

 Andy B.

Re: Supplementary bonding question

Posted by Zoomup on Jan 20, 2020 10:06 am

 I lost a 6 mm (or was it 1/4"?) ball bearing recently. Anybody want to buy 19 of them? 😁

 

The local cycle shop perhaps. But what if they only buy in 20s?

Z.

Re: Supplementary bonding question

Posted by Zoomup on Jan 20, 2020 10:10 am

AJJewsbury:

How much? Ouch!

Eh, about £1.80+VAT each

 

Ouch, that's more than double the cost of a common EC15 earth clamp.

Z.

Re: Supplementary bonding question

Posted by AJJewsbury on Jan 20, 2020 10:24 am

Ouch, that's more than double the cost of a common EC15 earth clamp.

That's not a bad increase for something that's a bit unusual (less economy of scale for the supply chain) - try looking at some plumbing fittings - go just one size above what's "usual" and you can easily see a 5x or 10x price hike.

   - Andy.

Re: Supplementary bonding question

Posted by Chris Pearson on Jan 20, 2020 12:17 pm

Zoomup:

 I lost a 6 mm (or was it 1/4"?) ball bearing recently. Anybody want to buy 19 of them? 😁

The local cycle shop perhaps. But what if they only buy in 20s?
Oh no, they went long ago like the banks, newsagents, fishmonger, etc.

Leaving aside all those packs of nuts, bolts, screws, etc. isn't the whole idea that the shop buys in bulk and then sells small quantities at a profit. Isn't that what you do with customers?

Re: Supplementary bonding question

Posted by Zoomup on Jan 20, 2020 4:39 pm

 

Oh no, they went long ago like the banks, newsagents, fishmonger, etc.

 

I think that we have one family run cycle shop locally. Of course there is always Halfords. The problem is that to sell just one ball bearing, the profit on it is instantly eaten up with the cost of the bag provided to prevent the customer losing it on the way home. Anyway, isn't  it better engineering practice to change the whole set of balls rather than just one, if the races are in good condition? Or is it for your air gun?

Z.

Re: Supplementary bonding question

Posted by Sparkingchip on Jan 20, 2020 7:20 pm

Henly supply armour bonding kits though looking at the photos it may not be possible to retrofit a kit.

Andy B.

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