Main bondage

[Chr!s]

So as Geoffsd and Serpico said:

for a 100A domestic supply, the Ia value would be either 1200 at 0.4s or 630 at 5s

To which the higher would make the maximum permittable resistance of the main bonding conductor is 0.041 ohms if R< 50/1200

The cable measured was directly from the conductor at the MET to the bonding clamp using croc clips?

So would a resistance of 0.25 Ohms mean that the bonding conductor is unsafe as the resistance is too high in the event of a fault?

Forget about resistance, select the right size job done. If the bonding conductor is in place and the right size, just test its resistance so that it relates to length and csa.

 

[Geoffsd]

Forget about resistance,

How can you do that?

select the right size job done

Someone has done that.

If the bonding conductor is in place and the right size, just test its resistance

Oh.

so that it relates to length and csa.

But it doesn't - that's the problem.

 

[Chr!s]

How can you do that?


Someone has done that.


Oh.


But it doesn't - that's the problem.

Well, it may or may not be correct, we don't know it's route, or how it was tested.

Regardless of the above a resistance of 0.05 or 0.5 is not going make much difference.

 

[Geoffsd]

Of course it is.

 

[Guitarist]

I think the point several people are trying to make here is that if it's a reasonable length of cable, correctly sized, then the reistance WILL NOT BE that high and there is an issue somewhere which needs looking into.
It may be 0.25 ohms now (still not acceptable), but what will it be in the future if the connection is poor or there is some form of corrosion at work?

 

[Chr!s]

Of course it is.

Of course it is?

Geoff, do you want to expand further and explain you touch voltage concept. It's very different to how I've been taught.

 

[DJ Ovengloves]

Some of the comments in this thread are absolutely frightening!

 

[Geordie Spark]

This thread is much duller than I was hoping. Anyone got the phone number of trading standards?

Aye ........... the thread title got me all excited for a couple of minutes too.

 

[Heisenberg]

Damn! I opened up this post with 'Bondage' in the title hoping for something else How dissapointed I am.

You should be reading '50 Shades of T&E' :ihih:

 

[telectrix]

i generally find 1.5mm singles are best for bondage.

 

[Guitarist]

i generally find 1.5mm singles are best for bondage.

Silicone insulation?

 

[telectrix]

fur...

 

[ultinator]

from MET @ CU, (front of house) removed 10mm cable, then where the stopcock is for water (rear of extension of house) removed the 10mm cable there. The resistance of this between one end and the other is 0.25. ohms.

As i cannot see the run, nor is there easy access to where it may be, and the fact that there are 3 x 10mm cables at the MET I would like to think that it is one length of cable, but the resistance readings simply doesnt state that.

But the bonding continuity has been verified.

 

[Gavin A]

Is this not pretty simple?

the 0.25 ohms reading is not even in the ballpark of being vaguely acceptable for the multiple reasons given in this thread. Given that the incoming water pipe has been moved this would be a strong indication that when they moved it they jointed and extended the bonding cable to move the bonding point to the new incoming mains point, and the chances are that this joint is the cause of your high resistance reading for one reason or another.

If you were working for me I'd be seriously unimpressed right now tbh, stop dithering and get it sorted then move on to the next job, bonding of water and gas pipes is about as basic as it gets isn't it?

apologies if you're a trainee.

 

[Guest55]

if the actual resistance value of the protective bonding conductors was of such great importance you'd think that IET electrical certificates of any format would require you to record these readings ?

but they dont........?
in fact they ask no more than to confirm connection with a simple tick box......
which for the most part can can be done visually and a poke around with a screwdriver.

one could then reasonably assume that by selecting the correct conductor size as per the relevent tables in bs7671 fulfils these obligations whether the actual resistance reading is 0.05 or 0.25 ohms.

just a thought........

 

[Elmer BeFuddled]

Even to this inexperienced oik, if I got a reading as you are, my 2nd step would've been to get the wander lead out and check the cable end to end, then, seeing as I was under the sink, between MET and pipe ~ MET and clamp.

 

[tidyboiler]

Aye ........... the thread title got me all excited for a couple of minutes too.

Jeez that's a novelty!!!............

 

[MDJ]

When I saw the thread title I too wondered what it was about and wondered if the Mods were up to no good having a laugh at us lol, I love these mis-printed threads, posted by a Iphone I bet lol.

 

[Jonny66]

from MET @ CU, (front of house) removed 10mm cable, then where the stopcock is for water (rear of extension of house) removed the 10mm cable there. The resistance of this between one end and the other is 0.25. ohms.

As i cannot see the run, nor is there easy access to where it may be, and the fact that there are 3 x 10mm cables at the MET I would like to think that it is one length of cable, but the resistance readings simply doesnt state that.

But the bonding continuity has been verified.

Hi Ultinator....bet you wish you'd not bothered with the test now and I bet you regret asking for advise on here......but you did and good on ya mate........10mm at 1.83 milli ohms per meter (measured end to end) suggests around 136m of 10mm cable (I know already stated)....now as this measurement was an end to end measurement then I'm sure you can see that there is something amiss here, unless of course the cable length is 136m long.......By the way I quite like Geoffsd touch voltage concept.....would love to hear anybody else's reasons why 0.05ohms is used as a recommendation...

And just out of interest, why is it every time I post, I have to copy it, because if it takes longer than say 2mins to post, I get logged out and lose what I've posted...confused? cos I'am

 

[VoltzElectrical]

This is my take on it after a phone call to a much more knowledgeable friend.

The 0.05 value is BETWEEN simultaneously accessible extraneous parts, i.e. a gas pipe and a water pipe next to each other. Take for example this was the case, but each pipe was bonded separately back to the MET. Then the two would have to cross bonded.

The figure of 0.05 is not the value that needs to be achieved from the MET to the bonded extraneous part.