Board Change

[uksparks]

Hi,

Went to look at a board change this morning, all seems fine, nothing untoward, only thing was on the downstairs ring the CPC continuity was higher than I would have liked.

r1 = 0.39
rn = 0.41
r2 = 1.44

I was half expecting around 0.75 ish, how far over the expected do you accept without investigation? I would imagine its probably just a poor connection in a socket somewhere. Usually I would look and see if i tighten them all up a bit, but would it be acceptable to change the board would you say without doing anything and just making a note of it?

The Zs on all sockets were fine, just the continuity on the ring that's all. So really just wondering if you have an upper limit as to saying "yeah that will do" before you look into it.

Where do you draw the line of acceptable?
Cheers,

 

[Plonker 3]

I wouldn't be too concerned, you have proven it's RFC, as long as you don't have spurs off spurs which may cause this and your happy with the R1+R2 readings then crack on. Like you,say it's probably a loose connection which you can remedy when you install DB.

 

[uksparks]

Well that's what I thought, it's not like it's 200 ohms.

 

[Plonker 3]

Exactly, yes there's a issue. Your R1+R2 will prove its ring then just a case of hopefully finding the connection.

 

[telectrix]

check the cable. back in the 70's a lot of 2.5mm T/E had only a 1.0mm cpc. that would account for the higher than expected resistance.

 

[flowlec1]

Could be a 1.0 mm earth so the reading would be 2.24 times. So not necessary that loose

 

[uksparks]

I did have one a while ago where the cpc was 3. Something, it's a question I've been meaning to ask for a while. I suppose strictly speaking anything other than expected should ideally be investigated but it's interesting to know where people draw the line of acceptable.

 

[uksparks]

Could be a 1.0 mm earth so the reading would be 2.24 times. So not necessary that loose

It was 2.5/1.5

 

[Richard Burns]

If your calculated R1+R2 plus Ze meets the regulatory requirements for disconnection then you should be OK, however a slightly loose connection can develop to a very loos connection, so it may be worth checking R2 to find the resistance rise, but I would probably not worry about that too much.
0.6 * 1.44 should give r1 of 0.8 so not really within the 0.05 Ω, but not terrible.

 

[uksparks]

The house was built in 1990, definately 1.5 as its bigger than the lights which is 1.0

Whst is it 2.3 ohms on a 32A type B x 0.8, so yes it will be under so not concerned.

Richard, where are you getting the 0.6 from?

 

[telectrix]

no, your max Zs for a 32A type B is 1.44. 1.08 if you use the 0.8 correction.

 

[telectrix]

i've seen RFCs installed with the cpc's wired to the back boxes and fly leads taken to the sockets. this could leads to high resistance.

 

[uksparks]

i've seen RFCs installed with the cpc's wired to the back boxes and fly leads taken to the sockets. this could leads to high resistance.

My house was done like that until I changed it, it's only when I thought I'd replace all the faceplates then thought, damn who did this, it's a bit cowboy ish IMHO.

 

[uksparks]

no, your max Zs for a 32A type B is 1.44. 1.08 if you use the 0.8 correction.

I must be thinking of a 20A, I'm doing this job in a week 10 days ish, so I'll see what the readings are, what was nice, I said to the customer, please can you make sure everything is unplugged Nd switched off and all light bulbs removed and all light switches on, and they did, couldn't believe it, the iR on all ircuits to my amazement was greater than 500M ohms

 

[Richard Burns]

The house was built in 1990, definately 1.5 as its bigger than the lights which is 1.0

Whst is it 2.3 ohms on a 32A type B x 0.8, so yes it will be under so not concerned.

Richard, where are you getting the 0.6 from?

Sorry that is just my method of calculation, backward from recommended. If the cpc is 1.67 x the resistance of the line for 2.5/1.5 then the line is (1/1.67) = 0.6 x the resistance of the cpc. I just find it easier to multiply by six and divide by ten in my head than try and multiply by 1.67.