Ring end to end results not text book for cu change.. do we need to ensure 1.67 times

[bleach]

Hi,

Cu change pre tests (TT) indicate non text book results: r1=072, rn=0.92, r2=1.58 another ring: r1=0.67 n=0.67 r2=1.60

As can be seen the r2 values are more than 1.67 times r1 or rn possibly due to loose connections. Are we responsible to try and bring these values in line for a cu change only? or just record?

Many thanks people

 

[Andy78]

Are you sure the 1.67 factor is applicable to the cable being tested ?

 

[drzsta]

Re: Ring end to end results not text book for cu change.. do we need to ensure 1.67 t

It could be 1.00mm cpc depending on the age of the cable.

 

[Taylortwocities]

Re: Ring end to end results not text book for cu change.. do we need to ensure 1.67 t

Even so, r1 should be about the same as rn. The r2 figure does look high. I too would suspect loose connection either in one (or many) sockets or a hidden underfloor JB:thumbs_down:

 

[HappyHippyDad]

Re: Ring end to end results not text book for cu change.. do we need to ensure 1.67 t

Hi,

Cu change pre tests (TT) indicate non text book results: r1=072, rn=0.92, r2=1.58 another ring: r1=0.67 n=0.67 r2=1.60

As can be seen the r2 values are more than 1.67 times r1 or rn possibly due to loose connections. Are we responsible to try and bring these values in line for a cu change only? or just record?

Many thanks people

The second set of results look spot on for a ring with a 1mm CPC, so as long as Zs requirements are met then it's fine. (i.e r1(0.67)x2.5=1.67))

The first set of results are a bit out. Assuming the r1 is correct then the rn is a bit high, as Taylor said a loose connection somewhere perhaps.

As for the responsibilty, 'yes' I'm afraid. You would need to investigate as to why the resistance for the neutral is almost 30% greater than the r1. It's not just a case of testing the installation for the sake of writing the figures down, any faults found need to be rectified. I (now - didn't when I first started to my detriment!) always add in my quote that if any complications arise then their may be additional costs.

 

[Richard Burns]

Re: Ring end to end results not text book for cu change.. do we need to ensure 1.67 t

If you are doing a CU change then you are assessing whether the circuits you are reconnecting are safe to reconnect not whether they are complaint with the regulations, although this is a very good guideline to work to.

In your case I would be tempted to measure the resistance again and make sure your probes are in good contact with the cores to eliminate any contact resistance errors.
If the results are still out then you can either decide that they are not too far out and so you can safely reconnect them as the Zs would still be complaint or you can provide in your quote for the CU change the additional cost of investigating and resolving the higher resistance values.

 

[Richo77]

Re: Ring end to end results not text book for cu change.. do we need to ensure 1.67 t

I think r1 and rn should only have a difference of 0.05 ohms. That is the max acceptable difference in the measured values. That's what I got in my brain anyway!

 

[Englishman]

Re: Ring end to end results not text book for cu change.. do we need to ensure 1.67 t

The second set of results look spot on for a ring with a 1mm CPC, so as long as Zs requirements are met then it's fine. (i.e r1(0.67)x2.5=1.67))

The first set of results are a bit out. Assuming the r1 is correct then the rn is a bit high, as Taylor said a loose connection somewhere perhaps.

As for the responsibilty, 'yes' I'm afraid. You would need to investigate as to why the resistance for the neutral is almost 30% greater than the r1. It's not just a case of testing the installation for the sake of writing the figures down, any faults found need to be rectified. I (now - didn't when I first started to my detriment!) always add in my quote that if any complications arise then their may be additional costs.

Doesn't warrant the installation as unsafe in my eyes, and other than noting/mentioning, I see nothing wrong with reconnecting on a board change and there is no way I would consider it my "responsibility" to piddle about tightening all connections to bring rN down such a small amount. If it's miles out then fair enough, but 0.2 of an ohm?!

Also, I don't class that as a fault, and I don't see how you could even justify telling a customer that it is a fault that needs rectifying.

 

[HappyHippyDad]

Re: Ring end to end results not text book for cu change.. do we need to ensure 1.67 t

Doesn't warrant the installation as unsafe in my eyes, and other than noting/mentioning, I see nothing wrong with reconnecting on a board change and there is no way I would consider it my "responsibility" to piddle about tightening all connections to bring rN down such a small amount. If it's miles out then fair enough, but 0.2 of an ohm?!

Also, I don't class that as a fault, and I don't see how you could even justify telling a customer that it is a fault that needs rectifying.

Thats fair enough chap.

Perhaps I did word it a bit too strongly. I'd still spend 30mins tightening up a few sockets though and get the figure down a little.

 

[Englishman]

Re: Ring end to end results not text book for cu change.. do we need to ensure 1.67 t

Thats fair enough chap.

Perhaps I did word it a bit too strongly. I'd still spend 30mins tightening up a few sockets though and get the figure down a little.

I tend to do that in my day job, but I'm paid a wage and it's completely irrelevant how long I spend on each job, they're also voids, but those figures aren't anything to hugely worry about and are something we continually come across. I just think that when it comes to charging for that work, it's a bit of a grey area because There's not enough discrepancy in the reading.

Bonding/earthing and IR issues are probably the only things I'd refuse a board upgrade over, anything else can just be left unconnected if the client objects, wrote it down, get a signature, and then they can do as they please.